Manual Aplicatii Grupuri T030body

8/2/2019 Manual Aplicatii Grupuri T030body

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Application Manual

Liquid Cooled Generator Sets

3/04 T–030f



Application Manual – Liquid Cooled Generator Sets

2TABLE OF CONTENTS

TABLE OF CONTENTS

WARRANTY 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 INTRODUCTION 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Overview 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .About this Manual 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Related Application Manuals 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Safety 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 PRELIMINARY DESIGN 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Overview 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Power Requirements 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General Requirements 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Specific Requirements 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

System Types and Ratings 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The One–Line Diagram 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Guidelines for Generator Set Power Ratings 13. . . . . . . . . . . . . . . . . . . . . . . . . . . .Standby Power Rating 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Prime Power Rating 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Base Load Power Rating (Continuous Power Rating) 15. . . . . . . . . . . . . . . . .

Sizing 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Location Considerations 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Outdoor Location Considerations 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Indoor Location Considerations 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fuel Selection Considerations 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Diesel Fuel 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Biodiesel Fuel 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Natural Gas 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LPG (Liquefied Petroleum Gas) 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Gasoline 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Substitute Fuels 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Environmental Considerations 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Noise and Noise Treatment 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Noise Laws and Regulations 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Engine Exhaust Emissions Regulations 20. . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fuel Storage Regulations 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fire Protection 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Preliminary Design Checklist 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 ELECTRICAL LOAD IMPACT ON GENERATOR SIZING 23. . . . .

Overview 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Applications and Duty Ratings 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Generator Set Duty Ratings 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mandated and Optional Applications 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Understanding Loads 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Load Running and Starting Requirements 24. . . . . . . . . . . . . . . . . . . . . . . . . .

Load Step Sequencing 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Load Types 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




3TABLE OF CONTENTS

Load Characteristics 32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 EQUIPMENT SELECTION 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Overview 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AC Alternators 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voltage 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Insulation and Ratings 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Windings and Connections 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fundamentals and Excitation 36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Engines 45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Governors 45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Engine Starting Systems 46. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Controls 49. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Relay–Based 49. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Electronic (Microprocessor) Based 49. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

“Full Authority” Electronics 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Control Options 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Accessories and Options 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Control Safeties and Annunciators 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Main–Line Circuit Breakers 51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Batteries and Battery Chargers 51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Exhaust Systems and Mufflers 52. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Housings (Canopies) 53. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Alternative Cooling and Ventilating Configurations 53. . . . . . . . . . . . . . . . . . .

Lubricating Oil Level Maintenance Systems: 54. . . . . . . . . . . . . . . . . . . . . . . .

Standby Heating Devices for Generator Sets 54. . . . . . . . . . . . . . . . . . . . . . . .

Fuel Tanks (Diesels) 56. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mounting Vibration Isolators 56. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Power Switching Equipment 57. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Additional Equipment Needs 57. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 ELECTRICAL DESIGN 58. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Overview 58. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Design Considerations 58. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Electrical Connections 58. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General 58. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AC Power Connections at Generator 59. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AC Power Conductors 61. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Leading Power Factor Load 64. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

System and Equipment Grounding 64. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Selective Coordination 67. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fault and Overcurrent Protection with Generator Sets 70. . . . . . . . . . . . . . . . . . .

Sizing a Main–Line Generator CircuitBreaker 70. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Generator Set Sources 71. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Overload Protection of Generators 72. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Medium Voltage, All Applications 76. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 MECHANICAL DESIGN 78. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Foundation and Mounting 78. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




4TABLE OF CONTENTS

Generator Set Mounting and Vibration Isolation 78. . . . . . . . . . . . . . . . . . . . .

Foundation Provisions 79. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Vibration Isolating Foundation 79. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Vibration Isolators 81. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Earthquake Resistance 83. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Power and Control Wiring Strain Relief 84. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Exhaust System 84. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Exhaust System General Guidelines 84. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Exhaust System Calculations 89. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Engine Cooling 93. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Skid–Mounted Radiator 93. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Remote Radiator 95. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Deaeration Type Remote Radiator System 97. . . . . . . . . . . . . . . . . . . . . . . . .

Remote Radiator with Auxiliary Coolant Pump 97. . . . . . . . . . . . . . . . . . . . . . .

Remote Radiator With Hot Well 99. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Multi–Loop Engine Cooling–Remote Radiators 101. . . . . . . . . . . . . . . . . . . . . .

Radiators for Remote Radiator Applications 101. . . . . . . . . . . . . . . . . . . . . . . . .

Fuel Cooling with Remote Radiators 105. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cooling Pipe Sizing Calculations 106. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Ventilation 108. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General Guidelines 108. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Air Flow Calculations 111. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Field Testing of Ventilation Systems 111. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Skid–Mounted Radiator Ventilation 111. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ventilating Heat Exchanger or Remote Radiator Applications 114. . . . . . . . . .

Example Ventilating Air Flow Calculation 114. . . . . . . . . . . . . . . . . . . . . . . . . . .

Fuel Supply 115. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Diesel Fuel Supply 115. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Diesel Fuel Piping 120. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sub–Base Fuel Tank 121. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Day Tanks 121. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Gaseous Fuel Supply 121. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Gaseous Fuel Quality 122. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Generator Set Fuel System Design 124. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Site Fuel System Design 124. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Gaseous Fuel System Calculations Fuel Pressure 126. . . . . . . . . . . . . . . . . . .

Reducing Noise in Generator Set Applications 132. . . . . . . . . . . . . . . . . . . . . . . . . .

The Science of Noise 132. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Generator Set Noise 135. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reducing Structure–Transmitted Noise 136. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reducing Airborne Noise 136. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sound Attenuated Enclosures (Canopies) 137. . . . . . . . . . . . . . . . . . . . . . . . . .

Exhaust Silencer Performance 137. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fire Protection 137. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Equipment Room Design 138. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General Considerations 138. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 APPENDIX 140. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A. Sizing Generator Sets With GenSizet 140. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Overview 140. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




5TABLE OF CONTENTS

Project Parameters 141. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Entering Loads 143. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Definition of Terms 145. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Detailed Load Calculations 145. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Entering Loads Into Steps 152. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Load Step Considerations 152. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Step Sequence Guidelines 152. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Recommendations and Reports 153. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reports 157. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B. Reduced Voltage Motor Starting 159. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A Comparison of Motor Starting Methods 159. . . . . . . . . . . . . . . . . . . . . . . . . . .

Full Voltage Motor Starting 160. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Autotransformer Motor Starting, Open Transition 160. . . . . . . . . . . . . . . . . . . .

Autotransformer Motor Starting, Closed Transition 161. . . . . . . . . . . . . . . . . . .

Reactor Motor Starting, Closed Transition 161. . . . . . . . . . . . . . . . . . . . . . . . . .

Resistor Motor Starting, Closed Transition 162. . . . . . . . . . . . . . . . . . . . . . . . . .

Star–Delta Motor Starting, Open Transition 162. . . . . . . . . . . . . . . . . . . . . . . . .

Part Winding Motor Starting, Closed Transition 163. . . . . . . . . . . . . . . . . . . . . .

Wound Rotor Motor Starting 163. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Synchronous Motor Starting 164. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General Application Note 164. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C. World Voltages and Supplies 165. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

D. Useful Formulas 167. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E. Maintenance and Service 168. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

F. Codes & Standards 170. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Related Product Standards 170. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Modification Of Products 170. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

G. Glossary 171. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Index of Formulas 179. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Index of Tables 179. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Index of Figures 180. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




6WARRANTY

WARRANTY

Warranty: This manual is published solely for information purposes and should not be con-sidered all inclusive. If further information is required, consult Cummins Power Generation.Sale of product shown or described in this literature is subject to terms and conditions out-lined in appropriate Cummins Power Generation selling policies or other contractual agree-ment between the parties. This literature is not intended to and does not enlarge or add toany such contract. The sole source governing the rights and remedies of any purchaser ofthis equipment is the contract between the purchaser and Cummins Power Generation.

NO WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING WARRANTIES OF FITNESSFOR A PARTICULAR PURPOSE OR MERCHANTABILITY, OR WARRANTIES ARISINGFROM COURSE OF DEALING OR USAGE OF TRADE, ARE MADE REGARDING THE

INFORMATION, RECOMMENDATIONS AND DESCRIPTIONS CONTAINED HEREIN.Each customer is responsible for the design and functioning of its building systems. We can-not ensure that the specifications of Cummins Power Generation products are the properand sufficient ones for your purposes. You must satisfy yourself on that point.

In no event will Cummins Power Generation be responsible to the purchaser or user in con-tract, in tort (including negligence), strict liability or otherwise for any special, indirect, inci-dental or consequential damage or loss whatsoever, including but not limited to damage orloss of use of equipment, plant or power system, cost of capital, loss of power, additionalexpenses in the use of existing power facilities, or claims against the purchaser or user byits customers resulting from the use of the information, recommendations and descriptionscontained herein.




71 INTRODUCTION

1 INTRODUCTION

Overview

The world is becoming more and more electricity– dependent. Electric power supplies are critical toalmost any facility, and a reliable electric supply isvital to an increasing number of facilities. Facili-ties such as large office buildings and factories,as well as telecommunications installations, datacenters, and Internet service providers aredependent on electric power that is available 24hours a day, seven days a week with essentiallyno interruptions. This need is also fueled by thecontinuing proliferation of electronic computers indata processing, process control, life support sys-

tems, and global communications –– all of whichrequire a continuous, uninterrupted flow of electri-cal energy. Beyond reliability concerns, there aregrowing economic incentives favoring the instal-lation of on–site engine–generator sets. As aresult, engine–generator sets are routinely beingspecified for new building construction as well asfor retrofits. They provide emergency power in theevent of utility power failure and can be used toreduce the cost of electricity where the local utilityrate structure and policy make that a viableoption. Because of their important role, generator

sets must be specified and applied in such a wayas to provide reliable electrical power of the quali-ty and capacity required.

Prime power electrical supplies, to both remotecommunities that are not served by a commercialelectric power grid, and to those sites where thecommercial power grid is for some reason notavailable for extended periods of time, are alsobecoming a requirement, rather than a luxury, tomany users.

Whatever the use of the on–site power isintended to be, reliability of service from the on– site equipment, performance, and cost–effective-ness are primary concerns of users. The purposeof this manual is to provide guidance to system

and facility designers in the selection of appropri-ate equipment for a specific facility, and the

design of the facility, so that these common sys-tem needs are fulfilled.

About this Manual

This manual describes the specification andapplication of stationary, liquid–cooled, dieseland spark ignited engine–generator sets – referred to as “generator sets” in this manual.This manual consists of seven major sections:Preliminary Design, Electrical Load Impact onGenerator Sizing, Equipment Selection, Electri-

cal Design, Mechanical Design and Appendix.

Preliminary Design describes preliminary consid-erations for a generator set project. Equipmentand installation requirements vary depending onthe reasons for having the generator set and itsintended use. When designing a generator setinstallation, Reviewing and understanding thesereasons is useful as a starting point for the systemdesign and equipment choices.

Electrical Load Impact on Generator Sizing

explains various load types, their characteristicsand their impact on the generator set size, opera-tion and equipment choices. Also covered is thetopic of sequence of load connection.

Equipment Selection explains the fundamentalparts of a generator set and related equipment,their functions and interrelationships, and criteriafor choices. Functional characteristics, criteria forchoices and optional equipment needed are dis-cussed.

Electrical Design covers installation design of the

generator and related electrical systems, theirinterface with the facility along with load and gen-erator protection topics. The electrical designand planning of the on–site generation system iscritical for proper system operation and reliability.




81 INTRODUCTION

Mechanical Design covers installation design forthe generator set and related mechanical sys-tems along with their interface with the facility.The mechanical design and planning of the on– site generation system is critical for proper sys-tem operation and reliability. Topics include

foundation and mounting, exhaust systems, cool-ing systems, ventilation, fuel systems, noisereduction, fire protection and equipment room.

The Appendix contains numerous useful topicsincluding an overview of GenSizetsizing soft-ware and the Power Suite contents. Alsoincluded are a discussion of reduced voltagemotor starting and useful references to worldvoltages, maintenance concerns, formulas, Codeand Standards references and a glossary ofterms.

This manual describes the application of station-ary gensets. This manual does not cover theapplication of stationary–designed commercialgensets into mobile applications, which are gen-erally considered to be an unintended applica-tion. Cummins Power Generation (CPG) doesnot approve any mobile application of its commer-cial gensets except for those applications specifi-cally designed and tested by CPG. If CPG’s dis-tributors or customers desire to applystationary–designed commercial gensets into

other mobile applications, then they should do soonly after extensive analysis, testing, and clearcommunication with the end–use customerregarding possible limitations on the use ordesign life of the genset. CPG cannot ensure thatthe attributes of the product are the proper andsufficient ones for customers’ mobile applica-tions, therefore each customer must satisfy itselfon that point. Each customer is responsible forthe design and function of its own applicationsand installation.

A black bar placed to the left of a paragraph is asignal that the text in that paragraph haschanged, or the paragraph is new since the lastrevision.

Related Application Manuals

Every generator set installation will require powertransfer equipment, either transfer switch(es) orparalleling switchgear. The proper system for

the job and its proper application are crucial toreliable and safe operation. The following Cum-mins Power Generation application manualsaddress related aspects of standby and emer-gency power systems. Because these manualscover aspects requiring decisions that must be

taken early in the design process, they should bereviewed along with this manual.

Application Manual T–011–Automatic PowerTransfer Systems. Many applications utilize mul-tiple power sources to enhance electric powersystem reliability. These often include both utility(mains) service and generator set service to criti-cal loads. T–011 covers the various types of pow-er transfer systems available, and considerationsfor their use and application. Careful consider-ation of power switching system at the start of a

project will enable a designer to offer the mosteconomically viable and most reliable service tothe facility user.

Application Manual T–016–Paralleling and Paral-leling Switch Gear. Paralleling equipment makestwo or more generator sets perform as one largeset. This can be economically advantageous,especially when the total load is greater than1000 kW. The decision whether to parallel setsmust be made in the early stages of design, espe-cially if space and the need for future expansion

are critical factors.

Safety

Safety should be a primary concern of the facilitydesign engineer. Safety involves two aspects:safe operation of the generator set itself (and itsaccessories) and reliable operation of the sys-tem. Reliable operation of the system is related tosafety because equipment affecting life andhealth is often dependent on the generator set – such as hospital life–support systems, emergen-cy egress lighting, building ventilators, elevators,

fire pumps, security and communications.

Refer to the Technical Reference section for infor-mation on applicable electrical and fire codes forNorth America, Central America and Europe.Standards, and the codes that reference them,are periodically updated, requiring continualreview. Compliance with all applicable codes isthe responsibility of the facility design engineer.




91 INTRODUCTION

For example, some areas may require a certifi-cate–of–need, zoning permit, building permit orother site–specific certificate. Be sure to checkwith all local governmental authorities early in theplanning process.

NOTE: While the information in this and related manuals is intended to be accurate and useful, there is no substitute for the judgment of a skilled, experienced facility design professional. Each end user must determine whether the selected generator set and emergency/standby system is proper for the application.




102 PRELIMINARY DESIGN


Overview

Designing a generator set installation requiresconsideration of equipment and installationrequirements. These vary depending on the rea-sons for having the generator set and its intendeduse. Reviewing and understanding these rea-sons is an appropriate starting point for the sys-tem design and equipment choices.

Power Requirements

General Requirements

The need for on–site generation of emergency

and standby electricity is usually driven by man-datory installations to meet building code require-ments, and/or risk of economic loss due to loss ofelectric power.

Mandatory installations for emergency andstandby power follow, from building code require-ments referenced by the regulations of federal,state, local, or any other governmental authority.These installations are justified on the basis ofsafety to human life, where loss of the normalpower supply would introduce life safety or health

hazards. Voluntary installations of standby powerfor economic reasons are typically justified by amitigation of the risk of loss of services, data, orother valuable assets. Mandatory and voluntaryinstallations of on–site generation may be justi-fied on the basis of favorable load curtailmentrates offered by the electric utility. The same on– site generation system may be used for both ofthese general needs, provided that life safetyneeds have priority, e.g. generator capacity andload transfer arrangements.

Specific RequirementsA wide range of specific requirements will result inthe need for on–site electric generation systems.Some common needs are outlined below.

Lighting: Egress lighting for evacuation, illumi-nated exit signs, security lighting, warning lights,

operating room lighting, elevator car lighting, gen-erator room lighting, etc.

Control Power: Control power for boilers, aircompressors, and other equipment with criticalfunctions.

Transportation: Elevators for fire departmentuse.

Mechanical Systems: Smoke control and pres-surization fans, waste water treatment, etc.

Heating: Critical process heat.

Refrigeration: Blood banks, food storage, etc.

Production: Critical process power for laborato-

ries, pharmaceutical production processes, etc.Space Conditioning: Cooling for computer equip-ment rooms, cooling and heating for vulnerablepeople, ventilation of hazardous atmospheres,ventilation of pollutants or biological contamina-tion, etc.

Fire Protection: Fire pumps, jockey pumps, alarmand annunciation.

Data Processing: UPS systems and cooling toprevent data loss, memory loss, program corrup-tion.

Life Support: Hospitals, nursing homes, and oth-er health care facilities.

Communications Systems: 911 service, policeand fire stations, hi–rise building public addresssystems, etc.

Signal Systems: Railroad, ship, and air trafficcontrol.

System Types and Ratings

On–site power generation systems can be classi-fied by type and generating equipment rating.

The generating equipment is rated using standby,prime, and continuous ratings. The ratings defini-tions are important to understand when applyingthe equipment. Please refer to the ratings guide-lines that follow. The type of on–site generationsystem and the appropriate rating to use is basedon the application. See Table 2–1 and descrip-tions of the following.





Emergency Systems: Emergency systems aregenerally installed as required for public safetyand mandated by law. They are typically intendedto provide power and lighting for short periods oftime for three purposes: to permit safe evacua-tion of buildings, for life support and critical equip-

ment for vulnerable people, or for critical commu-nications systems and facilities used for publicsafety. Code requirements typically specify theminimum load equipment to be served.

Legally–Required Standby : Legally–requiredstandby systems are generally installed as man-dated by legal requirements for public safety.These systems are typically intended to providepower and lighting for short periods of time wherenecessary to prevent hazards or to facilitate fire– fighting operations. Code requirements typically

specify the minimum load equipment to beserved.

Optional Standby: Optional Standby systems aregenerally installed where safety is not at stake,but loss of power could cause an economic loss ofbusiness or revenue, interrupt a critical process,or cause an inconvenience or discomfort. Thesesystems are typically installed in data centers,farms, commercial and industrial buildings, andresidences. The owner of the system is permittedto select the loads connected to the system.

In addition to providing a standby source of powerin case of loss of a normal power supply, on–sitegeneration systems are also used for the follow-ing purposes.

Prime Power: Prime power installations use on– site generation in lieu of a utility electricity supply,typically where utility power is not available. Asimple prime power system uses at least two gen-erator sets and a transfer switch to transfer supplyto the loads between them. One or the other ofthe generator sets runs continuously with a vari-able load, and the second generator set serves asbackup in case of a failure, and to allow downtimefor required maintenance. A changeover clockwithin the transfer switch alternates the lead gen-erator set on a predetermined interval.

Peak Shaving: Peak shaving installations useon–site generation to reduce or flatten peak elec-tricity use for the purpose of saving money onenergy demand charges. Peak shaving systemsrequire a controller that starts and runs the on– site generator at the appropriate times to flatten

the user’s peak demands. Generation installedfor standby purposes may also be used for peakshaving.

Rate Curtailment : Rate curtailment installationsuse on–site generation in accordance with elec-tric energy rate agreements with the serving elec-tric utility. In exchange for favorable energy ratesthe user agrees to run the generators andassume a specified amount of load (kW) at timesdetermined by the utility, typically not to exceed aspecified number of hours per year. Generation

installed for standby purposes may also be usedfor rate curtailment.

Continuous Base Load : Continuous base loadinstallations use on–site generation to supply aconstant power (kW) typically through intercon-nection equipment into a utility grid. These instal-lations are usually owned by electric utilities orunder their control.

Co–Generation: Often, continuous base loadgeneration is used in Co–Gen application. Sim-ply put, Co–Gen is utilizing both the direct elec-tricity generation and waste exhaust heat to sub-stitute for utility supplied energy. The waste heatis captured and either used directly or convertedto electricity.

Generator Set Rating

Standby Prime Continuous

Emergency PrimePower

Base Load

Peak

Shaving

RateCurtailment

OptionalStandby

Legally–required

Standby

S y s t e

m T y p e

Co–Gen

Table 2–1. Rating and System Types





TO NON-EMERGENCY LOADS

TO EMERGENCY LOADS

UTILITYTRANSFORMER

SERVICEOVERCURRENT DEVICE

FEEDEROVERCURRENT DEVICES

NORMALDISTRIBUTION PANEL

EMERGENCYDISTRIBUTION PANEL

TRANSFER SWITCHES

EMERGENCYGENERATOR

SET

CIRCUIT BREAKER(IF REQUIRED)

Figure 2–1. Typical One-Line Diagram of an Electrical Distribution System

The One–Line Diagram

A one–line electrical system diagram is an impor-tant element for understanding the system andconnection arrangement. It can be especially crit-ical for communicating that information duringplanning, installation, startup and/or servicing thesystem. These diagrams depict the major com-

ponents such as generator(s), power transferequipment, protective relaying, overcurrentprotection and the overall connection scheme. Aone–line diagram should be developed as earlyas possible during the project planning to aid thesystem design. Figure 2–1 is a typical one–linediagram of a basic generation system.





Guidelines for Generator Set Pow-er Ratings

Power ratings for generator sets are published bythe manufacturers1. These ratings describe max-imum allowable loading conditions on a generator

set. The generator set will provide acceptableperformance and life (time between overhauls)when applied according to the published ratings.It is also important to operate generator sets at asufficient minimum load to achieve normal tem-peratures and properly burn fuel. Cummins Pow-er Generation recommends that a generator setbe operated at a minimum of 30% of its nameplaterating.

The following explanations describe the ratingstypes used by Cummins Power Generation. The

associated Figures, 2–2 thru 2–5, depict theload levels (P1, P2, P3, etc.) and time at that loadlevel (T1, T2, T3, etc.) allowed under the variousratings.

Standby Power Rating

The standby power rating is applicable to emer-gency power applications where power is sup-plied for the duration of normal power interrup-tion. No sustained overload capability is availablefor this rating (Equivalent to Fuel Stop Power inaccordance with ISO3046, AS2789, DIN6271

and BS5514). This rating is applicable to installa-tions served by a reliable normal utility source.This rating is only applicable to variable loads withan average load factor of 80 percent of the stand-by rating for a maximum of 200 hours of operationper year and a maximum of 25 hours per year at100% of its standby rating. In installations whereoperation will likely exceed 200 hours per year atvariable load or 25 hours per year at 100% of rat-ing, the prime power rating should be applied.The standby rating is only applicable to emergen-cy and standby applications where the generator

1 Ratings for generator sets from Cummins Power Generation

are published in the Power Suite software package.

set serves as the back up to the normal utilitysource. No sustained utility parallel operation ispermitted with this rating. For applications requir-ing sustained utility parallel operation, the primepower or base load rating must be utilized.

Prime Power RatingThe prime power rating is applicable when sup-plying electric power in lieu of commercially pur-chased power. The number of allowable operat-ing hours per year is unlimited for variable loadapplications but is limited for constant loadapplications as described below. (Equivalent toPrime Power in accordance with ISO8528 andOver Load Power in accordance with ISO3046,AS2789, DIN6271 and BS5514.)

Unlimited Running Time Prime Power: Prime

power is available for an unlimited number ofannual operating hours in variable load applica-tions. Applications requiring any utility paralleloperation at constant load are subject to runningtime limitations. In variable load applications, theaverage load factor should not exceed 70 percentof the Prime Power Rating. A 10 percent overloadcapability is available for a period of 1 hour withina 12–hour period of operation, but not to exceed25 hours per year. The total operating time at thePrime Power Rating must not exceed 500 hoursper year.

Limited Running Time Prime Power: Prime poweris available for a limited number of annual operat-ing hours in constant load applications such asinterruptible, load curtailment, peak shaving andother applications that normally involve utility par-allel operation. Generator sets may operate inparallel with the utility source up to 750 hours peryear at power levels not to exceed the Prime Pow-er Rating. It should be noted that engine life will bereduced by constant high load operation. Anyapplication requiring more than 750 hours of

operation per year at the Prime Power Ratingshould use the Base Load Power Rating.





STANDBY POWER RATING 100%

MAXIMUM PERMISSIBLEAVERAGE POWER 80%

P1 P2 P3 P4 P5 P6

AVERAGE POWER =T1 + T2 + T3 + T4 + T5 + T6 + ... + Tn

(P1 x T1) + (P2 x T2) + (P3 x T3) + (P4 x T4) + (P5 x T5) + (P6 x T6) + ... + (Pn x Tn)

NOTES:I Total running time (T1 + T2 + T3 + T4 + T5 + T6 + ... + Tn) must not exceed 200 hours.

II The total number of hours at 100% of standby rating (P3) must not exceed 25 hours per year.

III Do not count periods of shutdown (Ts).

IV There is no overload capability.

TIME

T1 T2 T3 T4 T5 T6Ts Ts Ts

Figure 2–2. Standby Power Rating.

MAXIMUM OVERLOAD RATING 110%

PRIME POWER RATING 100%

MAXIMUM PERMISSIBLEAVERAGE POWER 70%

RECOMMENDED MINI-MUM POWER 30%

P1 P2 P3 P4 P5 P6

I Count loadings of less than 30 percent as 30 percent (P5).

II Do not count periods of shutdown (Ts).

III A 10 % overload (P3) is available for 1 hour in 12 for a total annual not to exceed 25 hours.

IV The total number of hours per year at or above the Prime Power Rating (P2 and P3) must not exceed 500 hours.

TIME

AVERAGE POWER =T1 + T2 + T3 + T4 + T5 + T6 + ... + Tn

T1 T2 T4 T5 T6T3Ts Ts

(P1 x T1) + (P2 x T2) + (P3 x T3) + (P4 x T4) + (P5 x T5) + (P6 x T6) + ... + (Pn x Tn)

NOTES:

Figure 2–3. Unlimited Running Time Prime Power





PRIME POWERRATING 100%

NOTES:

I Total running time (T1 + T2 + T3 + T4 + ... + Tn) must not exceed 750 hours.

II Do not count periods of shutdown (Ts).

III Maximum overload capacity is not allowed fro limited running time prime rating

TIME

T1 T2 T3 T4Ts Ts Ts Ts

P P P P1 2 3 4

Figure 2–4. Limited Running Time Prime Power

TIMENOTES:

I Time Ts denotes regularly scheduled shutdown for maintenance.

II No overload capacity allowed for base load rating.

Ts

BASE LOADPOWER RATING 100%

Ts

PP P

TT T

Figure 2–5. Base Load Power

Base Load Power Rating (Continuous PowerRating)

The base load power rating is applicable for sup-

plying power continuously to a load up to 100 per-cent of the base rating for unlimited hours. Nosustained overload capability is available at thisrating (Equivalent to Continuous Power in accor-dance with ISO8528, ISO3046, AS2789,DIN6271 and BS5514). This rating is applicablefor utility base load operation. In these applica-tions, generator sets are operated in parallel witha utility source and run under constant loads forextended periods of time.

Sizing

It is important to assemble a reasonably accurate

load schedule as soon as possible for budgetingproject costs. If all the load equipment informa-tion is not available early in the project, estimatesand assumptions will have to be made for the firstsizing calculations These calculations should beiterated as more accurate information becomesavailable. Large motor loads, uninterruptiblepower supplies (UPS), variable frequency drives(VFD), fire pumps, and medical diagnostic imag-ing equipment have considerable effect on gener-





ator set sizing and should be looked at closely.Tight specifications on transient performance,voltage and frequency dip and recovery times,during motor starting and block load acceptancealso have considerable effect on sizing. See sec-tion 3, Electrical Load Impact on Generator Sizing

in this manual regarding sizing calculation andthe kinds of information needed for different typesof load equipment.

For preliminary estimation purposes some con-servative rules of thumb may be used:

• Motors – ½HP per kW.• UPS – 40% oversize for 1∅ and 6 pulse, or

15% oversize for 6 pulse with input filters and12 pulse UPS.

• VFD – 100% oversize unless pulse–width–

modulated, then 40% oversize.

When loading the generator set, division of theloads into discrete steps or blocks of load mayhave a favorable effect on the size of generatorset required. Use of multiple transfer switches orsome other means (time delay relays, PLC, etc.)would be necessary to allow the generator setvoltage and frequency to stabilize between steps.

Depending on the total load (generally above 500kW), it may be advantageous to parallel genera-tor sets. Although technically feasible, it is usually

not economically feasible to parallel generatorsets when the total load is 300 kW or less.

Location Considerations

One of the first design decisions will be to deter-mine whether the location of the generator set willbe inside a building or outside in a shelter or hous-ing. The overall cost and ease of installation of thepower system depend upon the layout and physi-cal location of all elements of the system –– gen-erator set, fuel tanks, ventilation ducts and lou-

vers, accessories, etc. For both indoor andoutdoor locations, consider these issues:

• Generator set mounting• Location of distribution switchboard and

transfer switches• Branch circuits for coolant heaters, battery

charger, etc.• Security from flooding, fire, icing, and vandal-

ism

• Containment of accidentally spilled or leakedfuel and coolant

• Possible simultaneous damage to normaland emergency services

• Service access for general maintenance andinspections.

• Access and working space for major worksuch as overhauls or component removal/re-placement.

• Access for load bank testing when requiredfor maintenance, proper excersize, or code.

Outdoor Location Considerations

• Airborne noise and treatment. Sound barri-ers may be required. In addition, increaseddistance between the generator set and thenoise sensitive area will decrease the per-ceived noise. Acoustic housings are often

available and may be required to meet cus-tomer expectations or local noise ordi-nances.

• Weather protective housing may berequired, as their name suggests, for protec-tion from weather but also may provide a cer-tain level of security as well as aesthetic con-tainment of the generator set.

• Starting and accepting load, and doing sowithin specific time constraints, in cold ambi-ent temperatures may be an issue. Emer-gency systems as defined by codes require

the ambient temperature around the gensetto be maintained at minimum levels. Exam-ples are NFPA110 which requires the mini-mum ambient temperature around the gen-erator set to be 40° F (4° C), and CSA 282which requires this minimum temperature tobe 10° C (50° F). Maintaining these minimumtempeature requirements in a “skin–tight” orother similar housing may be difficult orimpossible. An insulated and perhapsheated housing may be required. A housingthat is designed strictly for acoustic treatment

will contain insulation material but may notprovide sufficient heat containment. Singleunit “drop over” housings or walk in enclo-sures are usually available with insulation,motorized or gravity louvers, and heaters ifnecessary.

• Several auxiliary heating devices may berequired for starting or improved load accep-tance, even if the application is not an emer-gency system. Heaters for coolant, bat-





teries, even oil may be necessary. Refer tothe section in this manual titled StandbyHeating Devices for Generator Sets undersection 4, Equipment Selection for moredetailed information.

• Fuel conditioning and heating. At cold ambi-

ent temperatures diesel fuel will becomecloudy, clog filters and pumps, or not flow suf-ficiently. Blended fuels are often used toaddress this issue however, fuel heating maybe required for reliable operation.

• The salt air in coastal regions may cause cor-rosion issues on outdoor–installed steel gen-set enclosures, skid bases, and fuel tanks.The use of an optional aluminum gensetenclosure and skirt, whenever offered byCPG, is considered to be proper installationpractice due to the additionial corrosion

resistance and is thus required for outdoorapplications in coastal regions, defined aslocations 60 miles and closer to bodies ofsaltwater.

• Service access for major repairs, componentreplacement (such as radiator or alternator),or overhaul, should be considered in thedesign of housings and placement of genera-tor sets near other equipment or structures.If major work is required due to high hours ofoperation or major component damage/fail-ure, access allowances will be critical. These

allowances include access covers, remov-able housing walls, adequate spaces tonearby structures, and access of requiredsupport equipment.

• Security fences and sight barriers• Property line distances• Engine exhaust must be directed away from

vents and building openings.• Grounding – Electrodes or grounding rings

may be required for separately–derived sys-tem and/or equipment grounding.

• Lightning protection

Indoor Location Considerations

• Dedicated generator room – For emergencypower systems, certain codes may requirethat the generator room be dedicated for thatpurpose only. Also consider the effect thatlarge ventilating airflow would have on otherequipment in the same room, such as build-ing heating equipment.

• Fire rating of room construction – Codes typi-cally specify a 1 or 2–hour minimum fireresistance rating. Consult local authoritiesfor applicable requirements.

• Working space – Working space aroundelectrical equipment is usually specified by

code. In practice, there should be at leastthree feet (1 M) of clearance around eachgenerator set. The alternator should bereplaceable without removing the entire setor any accessories. Also, access for majorwork (such as overhaul or componentreplacement such as a radiator) should beallowed for in the installation design.

• Type of cooling system – A factory–mountedradiator is recommended, however, theradiator fan can create a significant negativepressure in the room. Access doors should

therefore swing into the room – or be lou-vered –– so that they can be opened whenthe set is running. See Generator Cooling inthe Mechanical Design section for additionalcooling options.

• Ventilation involves large volumes of air. Anoptimum room design draws intake air direct-ly from outdoors and discharges the airdirectly outdoors through the opposite wall.Room ventilation fans will be required foroptional generator set cooling configurationsthat involve heat exchanger or remote radia-

tors.• Engine exhaust – The engine exhaust outletshould be as high as practical on the prevail-ing down–wind side of the building anddirected away from building intake vents andopenings.

• Fuel storage and piping – Local codes mayspecify fuel storage methods inside buildingsand restrict fuel storage amounts. Early con-sultation with the local Cummins Power Gen-eration dealer or the local fire marshal is rec-ommended. Access will be required forrefilling storage tanks. See Fuel Selectionbelow.

• It is recommended that provisions beincluded in the electrical distribution systemfor connection of a temporary genset loadbank.

• Location within a building must allow foraccess both for initial product delivery andinstallation, and later for servicing and main-





tenance. The logical preferred location for agenerator set in a building based on this is onthe ground floor, near a parking lot or accessdriveway, or in an open parking ramp.Understanding that this is the premium build-ing space, if forced to an alternative location,

keep in mind that heavy equipment may beneeded for placement or major service of theunit. Also, deliveries of fuel, coolant, oil, etc.are needed at various intervals. A fuel sys-tem will most likely be designed with supplytanks, pumps, lines, day tanks, etc. but lubri-cating oil and coolant changes can be difficultif the materials have to be hand carried inbarrels or buckets.

• Rooftop installations, while common, requirefurther planning and structural design con-sideration. Vibration and fuel storage/deliv-

ery may be problematic with rooftop installa-tions.• Indoor locations generally require a dedi-

cated room with fire resistive construction.Providing the required airflow to an interiorroom may be difficult. Fire dampers in duct-work to interior rooms are generally not per-mitted. Ideally the room will have two exteriorwalls opposite each other so that intake airflows over the generator set and is dis-charged out the opposite wall on the radiatorend of the unit.

Fuel Selection Considerations

The selection of natural gas, diesel, or LPG fuelwill affect generator set availability and sizing.Consider the following:

Diesel Fuel

• Diesel fuel is recommended for emergencyand standby applications. ASTM D975 No.2–D Grade diesel fuel is recommended forgood starting performance and maximum

engine life. Consult the engine manufacturerdistributor regarding the use of alternativegrades of diesel fuel for various engines.

• On–site fuel storage must be provided, how-ever the tank should not be too large. Dieselfuel lasts up to two years in storage, so thesupply tank should be sized to allow for fuelturnover based on scheduled exercise andtesting in that time period. A microbicide mayneed to be added if fuel turnover is low, or ifhigh–moisture conditions promote the

growth of fuel microbes. Microbes in the fuelcan clog fuel filters and disable or damagethe engine.

• Cold climates –– Premium No. 1–D Gradefuel should be used when ambient tempera-tures are below freezing. Fuel heating may

be required to prevent fuel filters from clog-ging when temperatures fall below the cloudpoint of the fuel –– approximately 20° F (–6°C) for No. 2–D and –15° F (–26° C) for No.1–D.

• Emissions requirements may be applicable.See Environmental Considerations.

Biodiesel Fuel

Biodiesel fuels are derived from a broad variety ofrenewable sources such as vegetable oils, ani-mal fats, and cooking oils. Collectively, these

fuels are known as Fatty Acid Methyl Esters(FAME). When used in diesel engines, typicallysmoke, power, and fuel economy are all reduced.While smoke is reduced, the effect on other emis-sions varies, with some pollutants being reducedwhile others are increased. Biodiesel fuel is asubstitute fuel, meaning the performance andemissions of the engine cannot be warrantedwhen operated on this fuel2.

A blend of up to 5% volume concentration biodie-sel fuel with quality diesel fuel should not cause

serious problems. Above 5% concentration seri-ous operational problems should be expected.Cummins neither approves nor disapproves ofthe use of biodiesel blends. Consult Cummins foradditional information.

Natural Gas

• No on–site fuel storage is required for mostsites.

• Natural gas may be an economical fuelchoice where available, at required flow ratesand pressure.

• An on–site backup LPG fuel supply may berequired for emergency power supply sys-tems.

• Field natural gas can be used with certaingenerator sets. However, fuel analysis andconsultation with the engine manufacturerare required to determine potential power

2 Cummins Power Generation assumes no warranty responsibil-

ity for repairs or increased costs of operation with biodiesel fuel.





derating and whether fuel composition willlead to engine damage due to poor combus-tion, detonation, or corrosion.

• Detonation and engine damage may resultwhen some utilities occasionally add butaneto maintain line pressure. Natural gas

engines require clean, dry, pipeline–qualitygas to generate rated power and ensure opti-mal engine life.

• Frequency stability of spark–ignited enginegenerator sets may not be as good as dieselengine generator sets. Good frequency sta-bility is important when supplying UPS loads.

• Cold climates –– In ambient temperaturesbelow 20° F (–7° C) spark–ignited enginesgenerally start easier and accept load soonerthan diesel engines.

NOTE: Cummins Power Generation does not recommend piping high–pressure natural gas (5 psig [34 kPa] or more) into buildings.

LPG (Liquefied Petroleum Gas)

• The local availability of LPG should be inves-tigated and confirmed prior to selecting anLPG–powered generator set.

• On–site fuel storage must be provided. LPGcan be stored indefinitely.

• Frequency stability of spark–ignited enginegenerator sets may not be as good as diesel

engine generator sets. This is an importantconsideration when supplying UPS loads.• Cold climates –– Either the LPG storage tank

must be sized to provide the required rate ofvaporization at the lowest ambient tempera-ture expected, or liquid withdrawal with avaporizing heater must be provided.

NOTE: Cummins Power Generation does not recommend piping high–pressure LPG (20 psig [138 kPa] or more), liquid or vapor, into buildings.

Gasoline

Gasoline is not a suitable fuel for stationary stand-by generator sets due to volatility and shelf life ofgasoline fuel.

Substitute Fuels

In general, diesel engines may be run on substi-tute fuels with acceptable lubricity during peri-ods when the supply of No. 2–D diesel fuel is tem-porarily limited. Use of substitute fuels may affectwarranty coverage, engine performance, andemissions. The following substitute fuels aregenerally within prescribed limits:

• 1–D and 3–D diesel fuel• Grade No. 2 fuel oil (heating fuel)• Grade Jet A and Jet A–1 aviation turbine fuel

(commercial jet fuel)• Grade No. 1 GT and No. 2 GT non–aviation

gas turbine fuel• Grade No. 1–K and No. 2–K kerosene

Environmental Considerations

The following is a brief approach to evaluatingenvironmental issues related to noise, exhaustemissions, and fuel storage. Refer to theMechanical Design chapter for more completeinformation.

Noise and Noise Treatment

Noise treatment, if required, needs to be consid-ered early in the preliminary design. Generally,noise treatment methods will add a considerablecost and increase the physical area required for

the installation. A generator set is a complexnoise source that includes the cooling fan noise,the engine noise, and the exhaust noise. Effec-tive noise treatment has to address all of thesesources of noise. For the most part, the recom-mended noise treatment methods modify or redi-rect the path for the noise from the generator setsource to people hearing it. Simply using a criticalgrade muffler may or may not do anything toreduce the noise level at a specific location.Because noise is directional, careful consider-ation needs to be given to the location, orienta-

tion, and distance of the generator set withrespect to property lines or places where thenoise may be objectionable.





NOISE ZONES PEAKDAYTIME

dB(A)

PEAKNIGHTTIME

dB(A)

CONTINUOUSDAYTIME

dB(A)

CONTINUOUSNIGHTTIME

dB(A)

Urban—Residential 62 52 57 47

Suburban—Residential 57 47 52 42

Very Quiet Suburban

or Rural Residential

52 42 47 37

Urban—Nearby Industry 67 57 62 52

Heavy Industry 72 62 67 57

Table 2–2. Representative Outside Noise Levels

Noise Laws and Regulations

In North America, state and local codes establishmaximum noise levels for given areas. Mostcommunity noise regulations specify the maxi-mum allowable noise level at the property line.Table 2–2 shows some representative outdoor

noise level regulations. Compliance with noiseregulations requires an understanding of theambient noise level and the resultant noise levelwith the generator set running at full load in thatambient.

Noise regulations also exist to protect worker’shearing. Persons working in generator roomsshould always wear ear protection while a gener-ator set is running.

Engine Exhaust Emissions Regulations

Generator sets, regardless of application, may besubject to engine exhaust emissions regulationson a local or national level or both. Compliancewith emissions regulations usually requires spe-cial permits. Certain localities may have specificdesignations requiring gaseous–fueled enginesand/or exhaust after–treatment strategies for die-sels. Check with the local air quality agency earlyin the design phase of any project for permittingrequirements.

Table 2–3 includes typical diesel exhaust emis-

sions for 40–2000 kW generator sets withuntreated exhausts which can be used for esti-mating purposes. Consult the engine manufac-turer for detailed information on specific products.

In North America, mobile generator sets (that aremoved more than once a year) are subject to EPACertification which essentially limits NOx Federalemissions to 6.9 g/bhp • hr. See a Cummins Pow-er Generation distributor for available models.

Fuel Storage RegulationsFuel supply tank design and installation in manyareas is controlled by regulations that are gener-ally written for two separate purposes: environ-mental protection and fire protection. Becausethe regulations, their enforcement and exemp-tions from regulation vary by location, it is neces-sary to research and understand local require-ments.

In North America, environmental protection regu-lations generally exist at both federal and state

levels. Different sets of regulations apply tounderground vs. aboveground fuel storage tanks.These regulations cover design and constructionstandards, registration, tank testing, and leak

CRITERIA POLLUTANTS GRAMS /BHPwHR

HC (Total Unburned Hydrocar-bons)

0.1–0.7

NOx (Oxides of Nitrogen as NO2) 6.0–13.0

CO (Carbon Monoxide) 0.5–2.0

PM (Particulate Matter) 0.25–0.5

SO2 (Sulfur Dioxide) 0.5–0.7

Table 2–3. Typical Diesel Exhaust Emissions





detection. They also cover closure requirements,preparation of spill prevention plans, provisionsfor financial responsibility, and trust fund cover-age. As a general statement subject to local veri-fication, exemptions from regulation are grantedfor underground and above–ground diesel stor-

age tanks serving on–site emergency generatorsets where 1) the capacity of the facility storagetanks is 1,320 gallons (500 L) or less, 2) no singletank has a capacity in excess of 660 gallons (250L), and 3) the fuel is consumed at the facility (notdispensed).

Even when an installation is exempt from regula-tion it must be recognized that cleanup expensesmay be very high for even small amounts of fuelspill resulting from leaks, overfilling, etc. Thetrend in diesel fuel storage for on–site generator

sets both indoors and outdoors, has been

towards third party certified above ground dual– wall sub–base tanks with leak detection and over-fill protection. See Section 6, Mechanical Design ,for more information on fuel system design.

Fire Protection

In North America, fire protection regulations typi-cally adopt or reference one or more of theNational Fire Protection Association (NFPA)standards. These standards cover such require-ments for indoor fuel storage capacity, fuel pipingsystems, the design and construction of fueltanks, fuel tank locations, diking, and/or safedrainage provisions. Refer to NFPA Standard No.37, Installation of Stationary Engines. Local fireauthorities may have more restrictive require-ments or interpretations of requirements thanthose in the national standards.





Preliminary Design Checklist

System Type

EmergencyLegally–Required StandbyOptional StandbyPrime PowerPeak ShavingLoad CurtailmentBase Load

Generator Set Rating

Standby RatingPrime RatingContinuous Rating

Generator Set Size

Single Unit ___ kW ___ kVA ___ PFParallel Units ___# ___ kW ___kVA ___PF

Generator Set Voltage andFrequency

___ Voltage ___ HZSingle–phaseThree–phase

Location

Indoor

Ground LevelUpper LevelBelow GroundOutdoorGround LevelRooftop

Direct Access for Instal/ServiceYes ___ No ___

Fuel

DieselNatural Gas

LPG

Fuel Supply – Diesel

Day TankSub–Base TankOutdoor Tank

Fuel Supply – LP

Vapor WithdrawalLiquid Withdrawal

Housing

Weather ProtectiveAcousticWalk–In EnclosureDrop OverCoastal Region

Accessories

Paralleling SwitchgearAutomatic Transfer SwitchBattery ChargersNetwork InterfaceRemote Alarms/MonitoringCircuit Breakers(s)Paralleling Control ModulesMufflerVibration Isolators

Special Alternator Requirements

Reduced Temperature Rating, 105C 80CRTDs or Thermistors

Cooling System

Unit Mounted RadiatorRemote Radiator




233 ELECTRICAL LOAD IMPACT ON GENERATOR SIZING


Overview

This section focuses on the impact of loads ongenerator set sizing. It is important to assemble areasonably accurate load schedule early in thedesign phase of power generation projectsbecause the load is the single most important fac-tor in generator sizing. If all the load equipmentinformation needed for sizing is not available ear-ly in the project, the first sizing calculations willhave to be based on estimates and assumptions.This should be followed by recalculations whenactual, more accurate information becomes avail-able. Different load types – motors, uninterrupt-

ible power supplies (UPS), variable frequencydrives (VFD), medical diagnostic imaging equip-ment and fire pumps, have considerable and dif-ferent influences on generator set sizing.

Applications and Duty Ratings

Generator Set Duty Ratings

Determining the loads required to be supportedby a generator set is a function of the type ofapplication and required duty. Generally, thereare three duty classifications for generator set

applications, Standby, Prime or Continuous.These classifications are defined in Section 2,Preliminary Design . Available ratings for genera-tor sets vary according to these classifications. Agenerator set used in Standby applications isused as a backup to the primary (utility) powersource and is expected to be used infrequently, sothe Standby rating is the highest available for theset. Prime rated sets are expected to operateunlimited hours and the generator set is consid-ered the primary source of power for varyingloads, so the Prime rating is typically about 90% of

the Standby rating. In Continuous duty applica-tions, the set is expected to produce rated outputfor unlimited hours at constant load (applicationswhere the set may be operated in parallel with autility source and base loaded), so the Continu-ous rating is typically about 70% of the Standbyrating. Load carrying capability of the generatorset is a function of the expected life or intervalbetween overhauls.

Mandated and Optional Applications

Fundamentally, generator set applications can belumped into two basic categories, those that aremandated by codes (legally required) and thosethat are desired for economics (generally associ-ated with power availability or reliability). Thesecategories will drive a completely different set ofchoices when decisions must be made regardingwhat loads to put on the generator set.

Code Mandated: These applications are typicallythose judged by authorities as emergency orlegally required standby, where life safety and life

support are paramount. These types of applica-tions may be stipulated in building codes or codesspecific to life safety, and typically involve facili-ties such as health care (hospitals, nursing care,clinics), high rise construction, and places ofassembly (theaters, assembly halls, sportingfacilities, hotels). Typically, the generator set willprovide backup power to loads such as egresslighting, ventilation, fire detection and alarm sys-tems, elevators, fire pumps, public safety com-munication systems, and even industrial processwhere power loss creates a life safety or health

hazard. Other legally required systems are man-dated when it is determined that loss of the normalutility power constitutes a hazard or will hamperrescue or fire fighting operations. To determinethe minimum loads that must be supplied by thegenerator, confer with the local code authorityand related standards. Additional optional loadsmay be applied to the generator in most applica-tions if approved by the local code authority.

Optional Standby: This type of system installa-tion has become more frequent as power avail-ability has become more critical. These systemspower facilities like industrial and commercialbuildings and serve loads such as heating, refrig-eration, data processing communications, andcritical industrial processes. Generators areoften justifiable where loss of utility power couldcause discomfort or interruption of critical pro-cess threatening products or process equipment.





Prime and Continuous: Applications for genera-tor sets that supply prime or continuous duty pow-er are becoming increasingly prevalent in devel-oping countries and for many distributed powergeneration applications. Many opportunitiesexist with utilities on the generation side and utility

customers on the consumption side. Deregula-tion and more strict environmental regulationshave electric utilities seeking alternative powerproduction and distribution alternatives to newcentral generating plant construction like peakshaving and interruptible rate structures to satisfyincreasing demand. Utility customers are usingon–site generation to reduce utility peak demandand continue to pursue cogeneration opportuni-ties where simultaneous demand for both electricpower and heat exist.

In any case, one must be aware that generatorsets generally are a small power sourcecompared to the normal utility source and the loadoperating characteristics can have a profoundeffect on power quality if the generator is not sizedproperly. Given that a generator is a limited powersource, whenever loads are connected to or dis-connected from a generator, voltage and frequen-cy disturbances must be expected. These distur-bances must be maintained within limitsacceptable to all connected loads. In addition,voltage distortion of the generator output voltage

will result when non–linear loads producing har-monic currents are connected. This distortioncan be considerably greater when operating ongenerator than when the load is supplied from theutility/mains and will cause additional heating inboth the generator and the load equipment if notkept in check. Consequently, generators largerthan required to supply adequate load runningpower are needed to limit voltage and frequencydisturbance during transient loading and limit har-monic distortion where serving non–linear loadslike computers, UPSs and VFDs.

Generator sizing software programs now allowprecise generator set selection and provide ahigher level of confidence for purchasing a sys-tem large enough for your needs – and no larger.While most generator set sizing exercises arebest done with sizing programs such as GenSizefrom Cummins Power Generation (See Appendix

A) – or with the help of a manufacturer’s represen-tative – it is still instructive to know what goes intoselecting the right generator set for your applica-tion.

Besides connected load, numerous other factors

affect the generator set sizing; starting require-ments of loads such as motors and their mechani-cal loads, single–phase load imbalance, non–lin-ear loads such as UPS equipment, voltage diprestrictions, cyclic loads, etc.

Understanding Loads

Load Running and Starting Requirements

The power required by many load types can beconsiderably higher while starting the load thanrequired for continuous steady state running

(most motor driven loads that don’t employ sometype of soft start equipment). Some loads alsorequire higher peak power during operation thanwhile running (welding and medical imagingequipment, for example). Still other loads (non– linear loads like UPS, computers, VFDs and otherelectronic loads) cause excessive generator dis-tortion unless the generator is sized larger thanwhat is required to power the load. The powersource must be capable of supplying all operatingpower requirements of the load.

During starting or peak load operating conditions,sudden load transients can cause voltage andfrequency disturbances harmful to the connectedload or large enough to prevent successful start-ing or proper load operation if the generator isundersized. While some loads are quite tolerantof short term transient voltage and frequency dis-turbances, other loads are quite sensitive. Insome cases, the load equipment may have pro-tective controls that cause the load to shut downunder these conditions. Although not as critical,other effects like lights dimming or momentary

surging of elevators can be, at the least, disturb-ing.

A generator set is a limited power source both interms of engine power (kW) and generator volt– amperes (kVA), regardless of the type of excita-tion system. Because of this, load changes willcause transient excursions in both voltage and





frequency. The magnitude and duration of theseexcursions are affected by the characteristics ofthe load and the size of the generator relative tothe load. A generator set is a relatively highimpedance source when compared to the typicalutility transformer. See further information in Sec-

tion 4, Equipment Selection.

Load Step Sequencing

In many applications, it may be advisable to limitthe amount of load to be connected or started bythe generator set at any one time. Loads are com-monly stepped onto the generator set insequence to reduce the starting requirementsand, thus, the size of generator required. Thisrequires load control and equipment to switch theload onto the generator1. Multiple transferswitches are commonly used for this purpose.Individual transfer switches can be adjusted toconnect loads at different times using standardtime delay transfer settings to stagger loads. Afew seconds time delay to allow the generator tostabilize voltage and frequency is recommendedbetween load steps. This, of course, will meanthat any emergency or legally required loads willneed to be connected first to meet code require-ments. Loads requiring higher starting power, likelarge motor loads, should be started while mini-mum load is connected. UPS loads can be left tolast since the UPS load is being carried on battery.

With that basic background, individual load oper-ating characteristics are discussed below.

Load Types

Lighting Loads: Calculations of lighting are fairlystraightforward, a summation of the lamp or fix-ture wattage or required wattage for lighting cir-cuits, plus the wattage required for ballasts.Common lighting types are Incandescent – stan-dard bulb–type lamp assemblies that typically

use a tungsten filament, fluorescent – a ballastdriven ionized gas lamp – also apply for gas dis-charge lighting, and discharge – low–pressuresodium, high–pressure sodium, etc. Tables 3–1and 3–2 contain some useful representativedata.

1 Cummins Power Generation offers network–based cascading

load–control systems.

TYPE OF LIGHTING SPF RPF

Fluorescent 0.95 0.95

Incandescent 1.00 1.00

High Intensity Discharge 0.85 0.90

Table 3–1. Lighting Power Factors (Starting and

Running)

LAMP BALLAST

48 Inch T–12, 40 W, Preheat 10 W

48 Inch T–12, 40 W, RapidStart

14 W

High Output 40 W Fluorescent 25 W

Mercury, 100 W 18–35 W

Mercury, 400 W 25–65 W

Table 3–2. Ballast Power

Air Conditioning Loads : Air conditioning loadsare generally specified in tons. To estimate powerrequirements in kilowatts, a conversion of 2 HP/ ton is used as a very conservative estimate of thetotal load for a lower efficiency unit. If you want amore exact size and know the individual compo-nent motor loads in the A/C equipment, sum themindividually and come up with a demand factor forwhat loads are likely to start simultaneously.

Motor Loads : There is a wide variety of motortypes and types of loads connected to thosemotors, each of which affects the motor’s startingand running characteristics. Following is a dis-cussion of many of these differences and charac-teristics and their affects on generator set sizingchoices.

Low– and High–Inertia: The moment of inertia ofa rotating mass, such as a motor and its load, is ameasure of its resistance to acceleration by motorstarting torque. Starting torque requires moregenerator set engine power (SkW) than runningload. Rather than having to perform calculations,however, it is usually sufficient to broadly charac-terize loads as high–inertia loads or as low–iner-tia loads for the purpose of determining enginepower needed to start and accelerate motorloads. Therefore, low–inertia loads are those thatcan be accelerated when a service factor of 1.5 orless can be assumed, whereas, high–inertialoads are those where a service factor greater





than 1.5 must be assumed. A higher service fac-tor must also be assumed for mechanically unbal-anced or pulsating loads. Table 3–3 shows cate-gorizations of common loads.

Low–inertia Loads* High–InertiaLoads**

Fans and centrifugalblowers

Elevators

Rotary compressors Single– and Multi– Cylinder Pumps

Rotary andcentrifugal pumps

Single– and Multi– Cylinder

Compressors

Rock Crushers

Conveyers

Table 3–3. Rotating Inertia Summary

*Exceptionally large fans or pumps that work against tallheads may not qualify as low–inertia loads. If unsure,assume High–Inertia.

**High–inertia loads include mechanically pulsating andunbalanced loads.

Over 50 HP: A large motor started across–the– line with a generator set represents a low imped-ance load while at locked rotor or initial stalledcondition. The result is a high inrush current, typi-cally six times the rated (running) current. The

high inrush current causes generator voltage dip.This voltage dip is composed of the instanta-neous transient voltage dip and the recovery volt-age dip.

The instantaneous transient voltage dip occurs atthe instant the motor is connected to generatoroutput and is strictly a function of the relativeimpedances of the generator and the motor.Instantaneous voltage dip is the voltage dip pre-dicted by the voltage dip curves published on thealternator data sheets2. These dip curves pro-

vide an idea of what might be expected for theinstantaneous dip, assuming frequency isconstant. If the engine slows down due to a heavystarting kW requirement, the transient voltage dip

2 Voltage dig curves for Cummins Power Generation equipment

are available on the Power Suite Library CD.

may be exaggerated as the torque–matchingcharacteristic of the voltage regulator rolls offalternator excitation to help the engine recoverspeed.

Following detection of the instantaneous tran-

sient voltage dip, the generator excitation systemresponds by increasing excitation to recover torated voltage –– at the same time as the motor isaccelerating to running speed (assuming themotor develops enough torque). Motor torque,for induction motors, is directly proportional to thesquare of the applied voltage. Motor accelerationis a function of the difference between motortorque and the torque requirements of the load. Inorder to avoid excessive acceleration times, ormotor stall, the generator must recover to ratedvoltage as quickly as possible.

The manner in which generator voltage recoversis a function of the relative sizes of the generatorand motor, engine power (kW capacity) and gen-erator excitation forcing capability. Several milli-seconds after the initial transient voltage dip, thevoltage regulator applies full forcing voltage to thegenerator exciter resulting in a buildup of the maingenerator field current in accordance with theexciter and main field time constants. Generatorset components are designed and matched toachieve the shortest possible response time

while maintaining voltage stability and avoidingengine overload. Excitation systems thatrespond too quickly or that are too “stiff” can actu-ally overload the engine when starting largemotors. Depending on the severity of the load,the generator should recover to rated voltagewithin several cycles, or at most, a few seconds.

For motor starting applications, both the initialtransient voltage dip and the recovery voltageneed be considered. A generator should be sizedso that it will not exceed the initial transient volt-age dip specified for the project, and so that it willrecover to a minimum of 90 percent of rated out-put voltage with the full motor locked rotor kVAapplied. Thus, the motor can deliver approxi-mately 81 percent (0.9 x 0.9 = 0.81) of its ratedtorque during acceleration, which has proven





adequate for most starting applications. In lieu ofunique project specifications, a 35% starting volt-age dip is considered acceptable in a generatorset motor starting situation.

Various types of reduced–voltage motor starters

are available to reduce the starting kVA of a motorin applications where reduced motor torque isacceptable. Reducing motor starting kVA canreduce the voltage dip, the size of the generatorset and provide a softer mechanical start. As dis-cussed next, however, caution must be usedwhen applying these starters to generator sets.

Three–Phase Starting Methods: There are sev-eral methods available for starting three–phasemotors, as summarized in Table 3–4 and as elab-orated in the Appendix C – Reduced voltage

Motor Starting. The most common starting meth-od is direct, across–the–line (full voltage) starting.Motor starting requirements can be reduced byapplying some type of reduced–voltage or solid– state starter, resulting in a smaller recommendedgenerator set. However, caution must be usedwhen applying any of these reduce–voltage start-ing methods. Since motor torque is a function ofthe applied voltage, any method that reducesmotor voltage also reduces motor torque duringstarting. These starting methods should only beapplied to low–inertia motor loads unless it can be

determined that the motor will produce adequatetorque for accelerating during starting. Addition-

ally, these starting methods can produce veryhigh inrush currents when they transition fromstart to run (if the transition occurs before themotor reaches operating speed), resulting instarting requirements approaching an across– the–line start. If the motor does not reach near–

rated operating speed prior to transition, exces-sive voltage and frequency dips can occur whenemploying these starters with generator sets. Ifunsure how the starter and load will react,assume across–the–line starting.

Variable Frequency Drives (VFDs): Of all classesof non–linear load, variable frequency drives,which are used to control the speed of inductionmotors, induce the most distortion in generatoroutput voltage. Larger alternators are required toprevent alternator overheating due to the har-

monic currents induced by the variable frequencydrive, and to limit system voltage distortion bylowering alternator reactance.

For example, conventional current source invert-er type VFD loads on a generator must be lessthan approximately 50 percent of generatorcapacity to limit total harmonic distortion to lessthan 15 percent. More recently, Pulse WidthModulated type VFD’s have become increasinglymore cost effective and prevalent and inducesubstantially lower harmonics. The alternator

need only be oversized by about 40% for thesedrives.

STARTING METHOD

% FULLVOLTAGE

APPLIED (TAP)

% FULLVOLTAGE

kVA

% FULLVOLTAGETORQUE

SkVAMULTIPLYING

FACTOR SPF

Full Voltage 100 100 100 1.0 –

Reduced Voltage Auto-transformer

806550

644225

644225

0.640.420.25

– – –

Series Reactor 806550

806550

644225

0.800.650.50

– – –

Series Resistor 806550

806550

644225

0.800.650.50

0.600.700.80

Star Delta 100 33 33 0.33 –

Part Winding (Typical) 100 60 48 0.6 –

Wound RotorMotor

100 160* 100* 1.6* –

* – These are percents or factors of running current, which depend on the value of the series resistances added to the rotor windings.

Table 3–4. Reduced Voltage Starting Methods and Characteristics





For variable speed drive applications, size thegenerator set for the full nameplate rating of thedrive, not the nameplate rating of the drivenmotor. Harmonics may be higher with the driveoperating at partial load and it may be possiblethat a larger motor, up to the full capacity of the

drive, could be installed in the future.

NEMA Motor Code Letter: In North America, theNEMA standard for motors and generators (MG1)designates acceptable ranges for motor startingkVA with Code Letters “A” through “V.” Motordesign must limit starting (locked rotor) kVA to avalue within the range specified for the Code Let-ter marked on the motor. To calculate motor start-ing kVA, multiply motor horsepower by the valuein Table 3–5 that corresponds with the Code Let-ter. The values in Table 3–5 are the averages of

the specified ranges of values for the Code Let-ters.

CodeLetter Factor

CodeLetter Factor

CodeLetter Factor

A 2 H 6.7 R 15

B 3.3 J 7.5 S 16

C 3.8 K 8.5 T 19

D 4.2 L 9.5 U 21.2

E 4.7 M 10.6 V 23

F 5.3 N 11.8

G 5.9 P 13.2

Table 3–5. Multiplying Factors Corresponding with

Code Letters

Three–Phase Motor Design: In North America,design B, C, or D type motors are three–phasesquirrel–cage induction motors classified byNEMA (National Electrical Manufacturers Associ-ation) with respect to a maximum value for lockedrotor current and minimum values for locked rotortorque, pull–up torque and breakdown torque.High Efficiency type motors are premium–effi-ciency three–phase squirrel–cage inductionmotors with minimum torque values similar to

design B type motors, but with higher maximumlocked rotor current and higher nominal full–loadefficiency. See Table 3–6 for nominal standardvalues for Design B, C, D and High Efficiencymotors.

Single–Phase Motor Design: See Table 3–7 fornominal standard values for single–phase induc-tion motors.

Uninterruptible Power Supply Loads: A staticuninterruptible power supply (UPS) uses siliconcontrolled rectifiers (SCRs) or other static devicesto convert AC voltage to DC voltage. The DC volt-age is used to produce AC voltage through aninverter circuit at the output of the UPS. The DC

voltage is also used to charge batteries. the ener-gy storage medium for the UPS. The switchingSCRs at the input induce harmonic currents in thegenerator set’s alternator. The affects of thesecurrents include additional winding heating,reduced efficiency, and AC waveform distortion.The result is a requirement for a larger alternatorfor a given kW output from the genset.

UPS devices can also be sensitive to voltage dipand frequency excursions. When the rectifier isramping up, relatively broad swings in frequency

and voltage can occur without disrupting opera-tion. However, once the bypass is enabled, bothfrequency and voltage must be very stable or analarm condition will occur.

Past problems of incompatibility between genera-tor sets and static UPS devices led to many mis-conceptions about sizing generator sets for thistype of load. In the past, UPS suppliers recom-mended oversizing the generator set by two tofive times the UPS rating, but even then someproblems persisted. Since then, most UPS

manufacturers have addressed the problems ofincompatibility and it is now more cost effective torequire UPS devices to be compatible with thegenerator set than to significantly oversize thegenerator.

When sizing a generator use the nameplate rat-ing of the UPS, even though the UPS itself maynot be fully loaded, plus the battery charge rating.The UPS will typically have a battery chargingcapability of 10 to 50 percent of its UPS rating. Ifthe batteries are discharged when the UPS isoperating on the generator set, the generator setmust be capable of supplying both the output loadand the battery charging. Most UPSs have anadjustable current limit. If this limit is set at 110%

– 150% of UPS rating, that is the peak load thegenerator set will need to supply immediatelyafter a utility power outage. A second reason forusing the full UPS rating is that additional loads upto nameplate rating may be added to the UPS in





the future. The same applies to redundant UPSsystems. Size the generator set for the combinednameplate ratings of the individual UPS devicesin applications where, for example, one UPS isinstalled to back up another and the two are online at all times with 50 percent load or less.

Due to being non–linear loads, UPS equipmentinduces harmonics in the generator output. UPSdevices equipped with harmonic input filters havelower harmonic currents than those without. Har-monic filters must be reduced or switched outwhen the load on the UPS is small. If not, these

filters can cause leading power factor on the gen-erator set. See Leading Power Factor Load in theMechanical Design section. The number of recti-fiers (pulses) also dictates the degree of alterna-tor over–sizing required. A 12 pulse rectifier witha harmonic filter results in the smallest recom-

mended generator set.

Most UPS devices have a current–limiting func-tion to control the maximum load that the systemcan apply to its power supply, which is expressedas a percentage of the full load rating of the UPS.The total load which the UPS applies to its power

HP DESIGN B, C &D MOTORS HIGH EFFICIENCYMOTORS

FOR ALL MOTORS

NEMA CODELETTER*

EFFICIENCY(%)

NEMA CODELETTER*

EFFICIENCY(%)

STARTINGPF (SPF)

RUNNING PF(RPF)

1 N 73 N 86 0.76 0.70

1–1/2 L 77 L 87 0.72 0.76

2 L 79 L 88 0.70 0.79

3 K 83 L 89 0.66 0.82

5 J 84 L 90 0.61 0.85

7–1/2 H 85 L 91 0.56 0.87

10 H 86 K 92 0.53 0.87

15 G 87 K 93 0.49 0.88

20 G 87 K 93 0.46 0.89

25 G 88 K 94 0.44 0.89

30 G 88 K 94 0.42 0.89

40 G 89 K 94 0.39 0.90

50 G 90 K 95 0.36 0.90

60 G 90 K 95 0.36 0.90

75 G 90 K 95 0.34 0.90

100 G 91 J 96 0.31 0.91

125 G 91 J 96 0.29 0.91

150 G 91 J 96 0.28 0.91

200 G 92 J 96 0.25 0.91

250 G 92 J 96 0.24 0.91

300 G 92 J 96 0.22 0.92

350 G 93 J 97 0.21 0.92

400 G 93 J 97 0.21 0.92

500 &UP

G 94 J 97 0.19 0.92

Table 3–6. Three–Phase Motor Defaults: NEMA Code, EFF, SPF, RPF





HP NEMA CODE LET-TER*

EFFICIENCY (%) STARTING PF (SPF) RUNNING PF (RPF)

SPLIT–PHASE

1/6 U 70 0.8 0.66

1/4 T 70 0.8 0.69

1/3 S 70 0.8 0.701/2 R 70 0.8 0.70

PERMANENT SPLIT CAPACITOR (PSC)

1/6 G 70 0.8 0.66

1/4 G 70 0.8 0.69

1/3 G 70 0.8 0.70

1/2 G 70 0.8 0.72

CAPACITOR START/INDUCTION RUN

1/6 R 40 0.8 0.66

1/4 P 47 0.8 0.68

1/3 N 51 0.8 0.70

1/2 M 56 0.8 0.73

3/4 L 60 0.8 0.75

1 L 62 0.8 0.76

1–1/2 L 64 0.8 0.78

2 L 65 0.8 0.78

3 to 15 L 66 0.8 0.79

CAPACITOR START/CAPACITOR RUN

1/6 S 40 0.8 0.66

1/4 R 47 0.8 0.68

1/3 M 51 0.8 0.70

1/2 N 56 0.8 0.73

3/4 M 60 0.8 0.75

1 M 62 0.8 0.76

1–1/2 M 64 0.8 0.78

2 M 65 0.8 0.78

3 to 15 M 66 0.8 0.79

Table 3–7. Single–Phase Motor Defaults: NEMA Code, EFF, SPF, RPF

supply is controlled to that value by limiting its bat-

tery charging rate. If, therefore, the maximumload is limited to 125 percent and the UPS is oper-ating at 75 percent of rated capacity, batterycharging is limited to 50 percent of the UPS rating.Some UPS devices reduce the battery chargingrate to a lower value during the time that a genera-tor set is powering the UPS.

Battery Charger Loads: Battery Chargers typical-ly use silicon–controlled rectifiers (SCRs). A bat-tery charger is a non–linear load, requiring an

over–sized alternator to accommodate additional

heating and minimize voltage distortion causedby battery charger induced harmonic currents.The number of rectifiers (pulses) dictates thedegree of alternator over–sizing required. A 12pulse rectifier results in the smallest recom-mended generator set.

Medical Imaging Equipment (X–ray, Cat Scan,MRI): Imaging equipment such as X–Ray, CatScan and MRI produce unique starting and run-ning characteristics that must be considered





when sizing a generator set. Peak kVA load (kVPx ma) and allowable voltage dip are the essentialfactors for sizing a generator set for medicalimaging applications. Two additional factorsmust be understood for all medical imagingapplications.

First, when the medical imaging equipment ispowered by the generator set, the image may bedifferent than when it is powered by the commer-cial utility line. The reason for this is due to the dif-ference in voltage dip characteristics. As Figure3–1 illustrates, the dip will tend to be constantwhen the utility is the power source, and be deep-er and more variable when the generator set isthe power source. The generator set voltage reg-ulator’s attempt to regulate the voltage will alsoaffect the voltage dip characteristic.

Second, between the time the operator makesthe adjustment for the image and takes theimage, no large load changes should take placefrom elevators or air conditioning switching on oroff.

Medical imaging equipment is usually designedto be powered by the utility source. Most equip-ment, however, has a line voltage compensator,adjustable either by the installer or the operator.In applications where the generator set is the onlypower source, the line voltage compensator canbe adjusted for the voltage dip expected with the

generator set. When the imaging equipment hasbeen adjusted for utility power, the generator setwill have to duplicate the voltage dip of the utilityas closely a possible. From past experience, sat-isfactory images can be expected when the gen-erator (alternator) kVA rating is at least 2.5 times

the peak kVA of the imaging equipment. A volt-age dip of 5 to 10 percent can be expected whensizing on this basis. Peak kVA and required gen-erator set kVA for variously rated imaging equip-ment is listed in Table 3–8.

Fire Pump Applications 3: Special considerationmust be given to fire pumps due to their criticalstatus and special code requirements. The NorthAmerican National Electrical Code (NEC) con-tains requirements limiting voltage dip to 15 per-cent when starting fire pumps. This limit is

imposed so that motor starters will not drop outduring extended locked rotor conditions and sothat fire pump motors will deliver adequate torqueto accelerate pumps to rated speeds to obtainrated pump pressures and flows. The generatorset does not have to be sized to provide thelocked rotor kVA of the fire pump motor indefinite-ly. That would result in an oversized generatorset, which could lead to maintenance and reliabil-ity due to an under–utilized generator set.

3 This is Cummins Power Generation’s interpretation of the

1996 edition of NFPA Standard No. 20, Centrifugal Fire Pumps.Desi n en ineers should also review the standard itself.

20

40

60

80

100

TIME IN SECONDS

0 0.5 1.0 1.5

VOLTAGE DIP AS THE EQUIPMENT IS FIRINGWHEN IT IS POWERED BY THE UTILITY

VOLTAGE DIP AS THE EQUIPMENT IS FIRING

WHEN IT IS POWER BY A GENERATOR SET % O F N O – L O A D V O L T A G E

Figure 3–1. Voltage Dip in Medical Imaging Applications





IMAGING EQUIPMENT RATING PEAK kVA* MINIMUMGENERATOR kVA

Ma kVP

15 100 1.5 3.8

20 85 1.7 4.3

40 125 5.0 12.5

50 125 6.3 15.8

100 125 12.5 31.3

200 125 25.0 62.5

300 125 37.5 93.8

300 150 45.0 112.0

500 125 62.5 156.0

500 150 75.0 187.0

700 110 77.0 192.0

1200 90 108.0 270.0

* – Multiply the peak kVA by the power factor (PF) to obtain Peak kW. If PF is unknown, assume 1.0.

Table 3–8. Generator Set Requirements for Medical Imaging Applications

Whenever a reduced voltage starter is used for afire pump motor, regardless of the type, allowgenerator capacity for across–the–line starting.The fire pump controller includes either a manu-al–mechanical, manual–electrical, or automaticmeans to start the pump across–the–line in thecase of a controller malfunction.

The additional generation capacity can be man-aged, if practical, by providing automatic load– shedding controls on low–priority connectedloads so that otherwise idle generator set capac-ity for the fire pump may be used for those sameloads. The controls should be arranged to shedloads prior to starting the fire pump.

Another option is to consider a diesel engine driv-en fire pump rather than an electric motor pump.The economics generally favor electric motordriven pumps, but the fire protection engineermay prefer a diesel engine drive. That way, thefire protection system and the emergency powersystem are kept entirely separate. Some engi-

neers and insurers believe this improves the reli-ability of both systems. The cost of a transferswitch for the fire pump would be avoided. Thegenerator set does not have to be sized to providethe locked rotor kVA of the fire pump motor indefi-nitely. That could result in an oversized generatorset, which could experience maintenance andreliability issues from being under–utilized.

Load Characteristics

Load Voltage and Frequency Tolerances: Table3–9 summarizes the tolerance that various loadshave for changes in voltage and frequency.

Regenerative Power: The application of genera-tor sets to loads having motor–generator (MG)drives such as elevators, cranes and hoists,require the consideration of regenerative power.In these applications, the descent of the elevator

car or hoist is slowed by the motor–generatorwhich “pumps” electrical power back to thesource to be absorbed. The normal utility sourceeasily absorbs the “regenerated” power becauseit is an essentially unlimited power source. Thepower produced by the load simply serves otherloads reducing the actual load on the utility(mains). A generator set, on the other hand, is anisolated power source that has a limited capabilityof absorbing regenerative power. Regenerativepower absorption is a function of engine frictionhorsepower at governed speed, fan horsepower,

generator friction, windage and core losses (thepower required to maintain rated generator out-put voltage). The regenerative power rating of theset appears on the recommended generator setSpecification Sheet and is, typically, 10 to 20 per-cent of the generator set power rating. (The gen-erator drives the engine, which absorbs energythrough frictional losses.)





EQUIPMENT VOLTAGE FREQUENCY COMMENTS

InductionMotors

+/– 10% +/– 5% Low voltage results in low torque andincreased temperature.

High voltage results in increased torqueand starting amps.

Coils,Motor Starters%

+/–10 N/A The holding force of a coil and its timeconstant of decay are proportional to theampere–turns of the coil. Smaller coils

may drop out within these tolerances fortransient dip. A transient voltage dip of 30

to 40 percent for more than two cyclesmay cause coil dropout.

IncandescentLighting

+10%, –25% N/A Low voltage results in 65% light.

High voltage results in 50% life.

Low frequency may result in l ight flicker.

FluorescentLighting

+/– 10% N/A High voltage results in overheating.

HID Lighting +10%, –20% N/A Low voltage results in extinguishment.

High voltage results in overheating.

Static UPS +10%, –15% +/– 5% No battery discharge down to –20% volt-age.

UPS are sensitive to a frequency changerate (slew rate) greater than 0.5 Hz/sec.

Oversizing of the generator may be neces-sary to limit harmonic voltage distortion.

VariableFrequency

Drives (VFD)

+10%, –15% +/– 5% VFD are sensitive to a frequency changerate greater than 1 Hz/sec.

Oversizing of the generator may be neces-sary to limit harmonic voltage distortion.

If voltage does not recover to 90 percent, undervoltage protective devices may lockout, overcurrent devices

may interrupt, reduced voltage starters may lockout or step and motors may stall or not have acceptableacceleration.

Table 3–9. Typical Voltage and Frequency Tolerances

An insufficient regenerative power rating for theapplication can result in excessive elevatordescent speed and overspeeding of the genera-tor set.

NOTE: Excessive regenerative loads can cause a generator set to overspeed and shut down. Applica- tions that are most susceptible to this type of problem are small buildings where the elevator is the major load on the generator set.

Generally, the regeneration problem can besolved by making sure there are other connectedloads to absorb the regenerative power. Forexample, in small buildings where the elevator isthe major load, the lighting load should be trans-

ferred to the generator before transferring the ele-vator. In some cases auxiliary load banks withload bank controls may be needed to help absorbregenerative loads.

Load Power Factor (PF): Inductances andcapacitances in AC load circuits cause the pointat which the sinusoidal current wave passes

through zero to lag or lead the point at which thevoltage wave passes through zero. Capacitiveloads, overexcited synchronous motors, etc.cause leading power factor, where current leadsvoltage. Lagging power factor, where currentlags voltage, is more typically the case and is aresult of the inductance in the circuit. Power fac-





tor is the cosine of the angle by which currentleads or lags voltage, where one full sinusoidalcycle is 360 degrees. Power factor is usuallyexpressed as a decimal figure (0.8) or as a per-centage (80%). Power factor is the ratio of kW tokVA. Therefore:

kW = kVA x PF

Note that three–phase generator sets are ratedfor 0.8 PF loads and single–phase generator setsfor 1.0 PF loads. Loads which cause power fac-tors lower than those at which generators arerated may cause GenSize to recommend a largeralternator or generator set to serve the load prop-erly.

Reactive loads that cause leading power factor

can be problematic, causing damage to alterna-tors, loads, or tripping protective equipment. Themost common sources of leading power factorare lightly loaded UPS systems using input lineharmonic filters or power factor correctiondevices (capacitor banks) used with motors.

Leading power factor load must be avoided withgenerator sets. The system capacitancebecomes a source of generator excitation andloss of voltage control can become a problem.Always switch power factor correction capacitorson and off the system with the load. See Leading

Power Factor Loads in the Electrical Design sec-tion.

Single–Phase Loads and Load Balance: Singlephase loads should be distributed as evenly aspossible between the three phases of a three– phase generator set in order to fully utilize gener-ator capacity and limit voltage unbalance. Forexample, as little as a 10 percent single–phaseload unbalance may require limiting the three– phase balanced load to not more than 75 percentof rated capacity. To help prevent overheating

and premature insulation failure in three–phasemotors, voltage unbalance should be kept belowabout two percent. See Allowable Single–PhaseLoad Unbalance Calculation in the Electrical Design section.




354 EQUIPMENT SELECTION


Overview

When the decision has been made as to genera-tor set(s) size and load sequence, the task ofchoosing the equipment for the job can begin.

This section deals with various generator setequipment for a complete and functional installa-tion. Functional characteristics, criteria forchoices and optional equipment needed are dis-cussed.

AC Alternators

Voltage

Low voltage: The application largely determinesthe generator set voltage selected. In emergencyand standby applications, generator output volt-age usually corresponds to the utilization voltageof the loads. Most commercially used voltagesand connection configurations are available asstandard options from alternator manufacturers.Some rare–use voltages may require specialwindings which may require considerable leadtimes to produce. Most alternators have voltageadjustment of at least ±5% from the nominal volt-

age specified to allow adjustment to specific siterequirements. See the Table of World Voltages inAppendix B .

Medium voltage: 1 In prime power or base loadapplications, or when overall application condi-tions are conducive, medium voltage generatorsets (greater than 600 volts) are being used withmore frequency. Generally, medium voltagesshould be considered when output would exceed2,000 amps from a low voltage generator. Anoth-er criteria driving medium voltage use is the size/

capacity of power switching equipment andamount of conductors required vs. low voltage.While medium voltage equipment will be more

1 Medium voltage alternators are available on Cummins Power

Generation products rated 750 kW and larger.

expensive, the conductors required (on the orderof 10–20 times less ampacity) combined with

reduced conduit, support structures, and installa-tion time, can offset the higher alternator cost.

Insulation and Ratings

Generally, alternators in the range from 20 kW to2,000 kW have NEMA Class F or Class H windinginsulation. Class H insulation is designed to resisthigher temperatures than Class F. Alternator rat-ings are referred to in terms of temperature riselimits. Alternators with Class H insulation havekW and kVA output ratings that remain within the

class temperature rises of 80° C, 105° C, 125° Cand 150° C above an ambient of 40° C. An alter-nator operated at its 80° C rating will have longerlife than at its higher temperature ratings. Lowertemperature rise rated alternators for a given gen-erator set rating will result in improved motorstarting, lesser voltage dips, greater non–linear orimbalanced load capability, as well as higher faultcurrent capability. Most Cummins Power Gener-ation generator sets have more than one size ofalternator available, making it possible to match awide range of applications.

Many alternators for a specific generator set willhave multiple ratings such as 125/105/80 (S,P,C).This means that alternator choice will operatewithin a different temperature limit depending onthe generator set rating, i.e. it will remain within125° C temperature rise at the Standby rating,within 105° C rise at the Prime rating and within80° C rise at the Continuous rating.

Windings and Connections

Alternators are available in various winding and

connections configurations. Understandingsome of the terminology used will help in makingthe choice that best suits an application.





Reconnectable: Many alternators are designedwith individual lead–outs of the separate phasewindings that can be reconnected into WYE orDelta configurations. These are often referred toas 6–lead alternators. Often, reconnectablealternators have six separate windings, two in

each phase, that can be reconnected in series orparallel, and wye or delta configurations. Theseare referred to as 12–lead reconnectable. Thesetypes of alternators are primarily produced forflexibility and efficiency in manufacturing and areconnected and tested at the factory to the desiredconfiguration.

Broad Range : Some alternators are designed toproduce a wide range of nominal voltage outputssuch as a range from 208 to 240 or 190 to 220volts with only an adjustment of excitation level.

When combined with the reconnectable feature,this is termed Broad Range Reconnectable .

Extended Range: This term refers to alternatorsdesigned to produce a wider range of voltagesthan broad range. Where a broad range may pro-duce nominally 416–480 volts, an extendedrange may produce 380–480 volts.

Limited Range: As the name suggests, limitedrange alternators have a very limited nominalvoltage range adjustment (for example 440–480volts) or may be designed to produce only onespecific nominal voltage and connection such as480 volt WYE.

Increased Motor Starting : This term is used todescribe a larger alternator or one with specialwinding characteristics to produce a higher motorstarting current capability. Although as men-tioned earlier, increased motor starting capabilitywill also be achieved by choosing a lower temper-

ature rise limit alternator.

Fundamentals and Excitation

It is desirable to have some understanding of thefundamentals of AC generators and generatorexcitation systems with respect to transient load-ing response, interaction of the voltage regulatorwith the load, and response of the excitation sys-tem to generator output faults.

A generator converts rotating mechanical energyinto electrical energy. It consists essentially of a

rotor and a stator, as shown in the cross section inFigure 4–1. The rotor carries the generator field(shown as four–pole), which is turned by theengine. The field is energized by a DC sourcecalled the exciter, which is connected to the “+”and “–” ends of the field windings. The generatoris constructed such that the lines of force of themagnetic field cut perpendicularly across the sta-tor windings when the engine turns the rotor,inducing voltage in the stator winding elements.The voltage in a winding element reverses eachtime the polarity changes (twice each revolution

in a four–pole generator). Typically, a generatorhas four times as many “winding slots” as shown

N

S

–+

SÇ Ç Ç

Ç Ç Ç

N

stator wind-ings

rotormagnetic lines of

force

stator

Figure 4–1. Four-Pole Generator Cross Section





and is “wound” to obtain a sinusoidal, alternating,single– or three–phase output.

The induced voltage in each winding elementdepends on the strength of the field (which couldbe represented by a higher density of the lines of

force), the velocity with which the lines of force cutacross the winding elements (rpm), and the“stack length”. Therefore, in order to vary the out-put voltage of a generator of given size and oper-ating speed, it is necessary to vary the strength ofthe field. This is done by the voltage regulator,which controls the output current of the exciter.

Generators are equipped with self–excited orseparately–excited (PMG) excitation systems.

Self–Excited Generators: The excitation system

of a self–excited generator is powered, via theautomatic voltage regulator (AVR), by tapping(shunting) power from the generator power out-put. The voltage regulator senses generator out-put voltage and frequency, compares them to ref-erence values and then supplies a regulated DCoutput to the exciter field windings. The exciterfield induces an AC output in the exciter rotor,which is on the rotating, engine–driven generatorshaft. Exciter output is rectified by the rotatingdiodes, also on the generator shaft, to supply DCfor the main rotor (generator field). The voltageregulator increases or decreases exciter currentas it senses changes in output voltage and fre-

quency due to changes in load, thus increasing ordecreasing the generator field strength. Genera-tor output is directly proportional to field strength.Refer to Figure 4–2.

Typically, a self–excited generator excitation sys-

tem is the least expensive system available froma manufacturer. It provides good service under alloperating conditions when the generator set issized properly for the application. The advantageof a self–excited system over a separately–ex-cited system is that the self–excited system isinherently self protecting under symmetrical shortcircuit conditions because the field “collapses”.Because of this, a main line circuit breaker for pro-tecting the generator and the conductors to thefirst level of distribution may not be considerednecessary, further reducing the installed cost of

the system.

The disadvantages of a self excited system are:

• It might be necessary to select a larger gen-erator in order to provide acceptable motorstarting performance.

• Self–excited machines rely on residual mag-netism to energize the field. If residual mag-netism is not sufficient, it will be necessary to“flash” the field with a DC power source.

• It might not sustain fault currents longenough to trip downstream circuit breakers.

AUTOMATICVOLTAGE

REGULATOR

MAIN ROTOR

EXCITERROTOR

ANDSTATOR

MAIN STATOR

ELECTRICAL POWER OUTPUT

ROTATINGMECHANICAL

POWERINPUT

SENSINGAND POWER

Figure 4–2. Self-Excited Generator





AUTOMATICVOLTAGE

REGULATOR

MAIN ROTOR

EXCITERROTOR

ANDSTATOR

PMGROTOR

ANDSTATOR

MAIN STATOR

ELECTRICAL POWER OUTPUTSENSING

ROTATINGMECHANICAL

POWERINPUT

Figure 4–3. Separately-Excited (PMG) Generator

Separately–Excited Generators: The excitationsystem of a separately–excited generator is simi-lar to that of a self–excited generator except that aseparate permanent magnet generator (PMG)located on the end of the main generator shaftpowers the voltage regulator. Refer to Figure4–3. Because it is a separate source of power, theexcitation circuit is not affected by the loads on thegenerator. The generator is capable of sustainingtwo to three times rated current for approximatelyten seconds. For these reasons, separately–ex-cited generator excitation systems are recom-mended for applications where enhanced motorstarting capability, good performance with non– linear loads or extended duration short circuit per-formance are necessary.

With this excitation system it is necessary to pro-tect the generator from fault conditions becausethe generator is capable of operating to destruc-tion. The Power Command Control System withAmpSentrytprovides this protection by regulat-ing sustained short circuit current and shuttingdown the generator set in the event fault currentpersists but before the alternator is damaged.See Electrical Design for further information on

this subject.

Transient Loading: A generator set is a limitedpower source both in terms of engine power (kW)and generator volt–amperes (kVA), regardless ofthe type of excitation system. Because of this,load changes will cause transient excursions in

both voltage and frequency. The magnitude andduration of these excursions are affected princi-pally by the characteristics of the load and the sizeof the alternator relative to the load. A generatorset is a relatively high impedance source whencompared to the typical utility transformer.

A typical voltage profile on load application andremoval is shown in Figure 4–4. At the left side ofthe chart the steady–state no–load voltage isbeing regulated at 100 percent of rated voltage.When a load is applied the voltage dips immedi-ately. The voltage regulator senses the voltagedip and responds by increasing the field current to

recover rated voltage. Voltage recovery time isthe duration between load application and thereturn of voltage to the envelope of voltage regu-lation (shown as ± 2%). Typically, initial voltagedip ranges from 15 to 45 percent of nominal volt-age when 100 percent of generator set rated load(at 0.8 PF) is connected in one step. Recovery tonominal voltage level will occur in 1–10 secondsdepending on the nature of the load and thedesign of the generator set.

The most significant difference between a gener-

ator set and a utility (mains) is that when a load issuddenly applied to a utility (mains) there is typi-cally not a frequency variation. When loads areapplied to a generator set the machine rpm (fre-quency) dips. The machine must sense thechange in speed and readjust its fuel rate to regu-late at its new load level. Until a new load and fuel





STEADYSTATELOAD

VOLTAGE

STEADY

STATENO-

LOADVOLT-AGE

VOLTAGERECOVERY

TIME (LOADAPPLIed)

TIME

VOLTAGERECOVERYTIME (LOADREMOVed)

TRANSIENT VOLTAGEOVERSHOOT

LOAD APPLIED

LOAD REMOVED

MINIMUMPEAK-TO-

PEAK VOLT-AGE

VOLTAGESINEWAVE

TRANSIENTVOLTAGE DIP

ENVELOPE OF VOLTAGEREGULATION ±2%

Figure 4–4. Typical Voltage Profile on Load Application and Removal

rate match is achieved, frequency will be differentthan nominal. Typically, frequency dip rangesfrom 5 to 15 percent of nominal frequency when100 percent of rated load is added in one step.Recovery may take several seconds.

Note: Not all generator sets are capable of accepting 100% block load in one step.

Performance varies between generator setsbecause of differences in voltage regulator char-acteristics, governor response, fuel systemdesign engine aspiration (natural or turbo-charged), and how engines and generators arematched. An important goal in generator setdesign is limiting voltage and frequency excur-sions to acceptable levels.

Generator Saturation Curves: G enerator satura-tion curves plot generator output voltage for vari-ous loads as main field winding current is

changed. For the typical generator shown, theno–load saturation curve A crosses the generatorset rated voltage line when field current is approx-imately 18 amperes. In other words, approxi-mately 18 amperes of field current is required tomaintain rated no–load generator output voltage.

The full–load saturation curve B shows thatapproximately 38 amperes of field current isrequired to maintain rated generator output volt-age when the full–load power factor is 0.8. SeeFigure 4–5.

Excitation System Response: Field current can-not be changed instantaneously in response to

load change. The regulator, exciter field, andmain field all have time constants that have to beadded. The voltage regulator has a relatively fastresponse, whereas the main field has a signifi-cantly slower response than the exciter fieldbecause it is many times larger. It should be notedthat the response of a self–excited system will beapproximately the same as that of a separately– excited system because the time constants forthe main and exciter fields are the significant fac-tors in this regard, and they are common to bothsystems.

Field forcing is designed in consideration of allexcitation system components to optimize recov-ery time. It must be enough to minimize recoverytime, but not so much as to lead to instability(overshoot) or overcome the engine (which is alimited source of power). See Figure 4–6.





RATED VOLTAGE

10 20 30 40 50

A B

FIELD CURRENT (AMPERES)

O U T

P U T V O L T A G E

Figure 4–5. Typical Generator Saturation Curves

TIME

N0-LOAD FIELDCURRENT

FULL-LOAD FIELD

CURRENT

T1

T2

CHARACTERISTIC RESPONSE WITHDAMPENED FIELD FORCING

(RECOVERY TIME T1)

F I E L D C U R R E N T CHARACTERISTIC

RESPONSE WITH

FIELD FORCING

CHARACTERISTICRESPONSE WITHOUT

FIELD FORCING(RECOVERY TIME T2)

Figure 4–6. Excitation System Response Characteristics

Motor Starting Response: When motors are

started, a starting voltage dip occurs which con-sists primarily of an instantaneous voltage dipplus a voltage dip as a result of excitation systemresponse. Figure 4–7 illustrates these two com-ponents which together, represent the transientvoltage dip. The instantaneous voltage dip is sim-ply, the product of motor locked rotor current andgenerator set sub–transient reactance. Thisoccurs before the excitation system can respondby increasing field current and is therefore notaffected by the type of excitation system. This ini-tial voltage dip may be followed by further dipcaused by the “torque matching” function of thevoltage regulator which “rolls off” voltage tounload the engine if it senses a significant slowingdown of the engine. A generator set must bedesigned to optimize recovery time while avoid-ing instability or lugging the engine.

Locked Rotor kVA: Motor starting current (locked

rotor) is about six times rated current and doesnot drop off significantly until the motor nearlyreaches rated speed as shown in Figure 4–8.This large motor “inrush” current causes genera-tor voltage dip. Also, the engine power required tostart the motor peaks at about three times ratedmotor power when the motor reaches approxi-mately 80 percent of rated speed. If the enginedoes not have three times the rated power of themotor the voltage regulator will “roll off” generatorvoltage to unload the engine to a level it can carry.As long as motor torque is always greater thanload torque during the period of acceleration, themotor will be able to accelerate the load to fullspeed. Recovery to 90 percent of rated voltage(81 percent motor torque) is usually acceptablebecause it results in only a slight increase in motoracceleration time.





100

90

80

70

TIME (SECONDS)0 1 2

INSTANTANEOUS VOLTAGE DIP(Ims x X′′d)

X′′d — GENERATOR SET SUB-TRANSIENT REACTANCE

Xms — LOCKED-ROTORMOTOR REACTANCE

EAC — GENERATORVOLTAGE

VOLTAGE IF MOTOR STARTING KVA IS MAIN-TAINED AND EXCITATION IS NOT CHANGED

SYSTEM REACTANCES ON STARTING A MOTOR

VOLTAGE “ROLL OFF“ CAUSED BY “TORQUEMATCHING“ FUNCTION OF REGULATOR

STARTING VOLTAGE DIP

P E R C E N

T R A T E D G E N E R A T O R V O L T A G E

IMS – INSTANTANEOUS STARTING CURRENT

Figure 4–7. Transient Voltage Dip





1

2

3

4

5

6

PER UNIT MOTOR ROTATING SPEED

0.2 0.4 0.6 0.8 1.0

POWERFACTOR

POWER

FULL-VOLTAGEMOTOR TORQUE

LOADTORQUE

MOTORCURRENT

0.2

0.4

0.6

0.8

1.0

MOTOR TORQUE MUST BEGREATER THAN LOAD

TORQUE TO ACCELERATETHE LOAD TO FULL SPEED

P E R U N I T T O R

Q U E , P O W E R , C U R R E N T

P O W E R F

A C T O R ( L A G G I N G )

TORQUE RESERVE

Figure 4–8. Typical Across-the-Line Motor Starting Characteristics(Assumes 100% of Nominal Voltage at Motor Terminals)

Sustained Voltage Dip: Following the relativelyshort (typically less than 10 cycles but as much asseveral seconds), steep transient voltage dip is asustained period of voltage recovery as shown inFigure 4–9. The maximum motor starting kVA on

the generator set Specification Sheet is the maxi-mum kVA the generator can sustain and still

recover to 90 percent of rated voltage, as shownby Figure 4–10. It should be noted that this iscombined performance of the alternator, exciter,and AVR only. The motor starting performance ofa particular generator set depends on the engine,

governor and voltage regulator as well as thegenerator.





SUSTAINED VOLTAGE DIP90% VOLTAGE RECOVERED

RMS VOLTAGE

TYPICAL TRANSIENT VOLT-AGE DIP

Figure 4–9. Sustained Voltage Dip

500 1000 1500 2000 2500 3000 3500

10

20

30

40

200 250 300 350 400 450

CODE F MOTOR HORSEPOWER

240/480 V, 60 HERTZ, 3-PHASE GENERATOR KVA OUTPUT AVAILABLE FORMOTOR STARTING (LOCKED ROTOR)

MAXIMUM KVA THIS GENERATORWILL SUSTAIN AND STILL RECOVER

TO 90% VOLTAGE.TRANSIENT VOLTAGE DIP WILL BE

APPROXIMATELY 30%

Figure 4–10. Typical NEMA Generator Chart of Transient Voltage Dip vs. Motor Starting KVA

Fault Response: The short circuit fault responseof self– and separately–excited generators is dif-ferent. A self–excited generator is referred to as a“collapsing field” generator because the field col-lapses when the generator output terminals areshorted (either 3 phase short or shorted L–Lacross the sensing phases). A separately–ex-cited generator can sustain the generator fieldduring a short circuit because excitation is pro-vided by a separate permanent magnet genera-

tor. Figure 4–11 shows the typical three–phasesymmetrical short circuit current response ofself– and separately–excited generators. Initialshort circuit current is nominally 8 to10 timesrated generator current and is a function of thereciprocal of the generator sub–transient reac-tance, 1/X′′d. For the first few cycles (A), there ispractically no difference in response betweenself–and separately–excited generators becausethey follow the same short circuit current decre-





ment curve as field energy dissipates. After thefirst few cycles (B), a self–excited generator willcontinue to follow the short circuit decrementcurve down to practically zero current. A sepa-rately–excited generator, because field power isderived independently, can sustain 2.5 to 3 times

rated current with a 3–phase fault applied. Thiscurrent level can be maintained for approximately10 seconds without damage to the alternator.

Figure 4–12 is another way to visualize the differ-ence in response to a three–phase fault. If thegenerator is self–excited, voltage and current will“collapse” to zero when current is increasedbeyond the knee of the curve. A separately–ex-cited generator can sustain a direct shortbecause it does not depend on generator outputvoltage for excitation power.

Short Circuit Winding Temperatures: The prob-lem to consider in sustaining short circuit currentis that the generator could be damaged before acircuit breaker trips to clear the fault. Short circuitcurrents can rapidly overheat generator statorwindings. For example, an unbalanced L–N short

on a separately excited generator designed tosustain three times rated current results in a cur-rent of about 7.5 times rated current. At that cur-rent level, assuming an initial winding tempera-ture of about 155_C, it can take less than fiveseconds for the windings to reach 300_C—theapproximate temperature at which immediate,permanent damage to the windings occurs. Anunbalanced L–L short takes a few seconds longerto cause the windings to reach 300_C, and a bal-anced three–phase short takes a little more time.See Figure 4–13. Also see Alternator Protection

in the Electrical Design section.

SEPARATELY-EXCITEDGENERATOR

SELF-EXCITEDGENERATOR

A B8 TO 10TIMESRATED

CURRENT

3 TO 4

TIMESRATED

CURRENT

SYMMETRICAL SHORTCIRCUIT INITIATED

Figure 4–11. Symmetrical Three-Phase Short Circuit Response

100

75

50

25

0

MULTIPLE OF RATED GENERATOR CURRENT

SEPARATELY-EXCITEDGENERATOR

1 2 3 4

SELF-EXCITEDGENERATOR

Figure 4–12. Short Circuit Capability





5 SEC 10 SEC 15 SEC 20 SEC155° C

225° C

300° C

355° C

455° C

TIME

S T A T O R T E M P E R A T U R E

Figure 4–13. Approximate Short Circuit Winding Temperatures

As the reader can see from this lengthy subsec-tion on fundamentals and excitation, only twobasic forms of excitation systems influence awide variety of performance characteristics.Steady state operation, transient conditions,motor starting, fault response and more areaffected by this system. These characteristiceffects are important in system performancestudies. Below is a brief summary of the differen-tiating characteristics of self– and separately– excited systems.

SSelf Excited – Higher Voltage Dips – Collapsing Field – Single Phase Average Sensing – Lower Tolerance for Non Linear Loads – Lesser Capable Motor StarterSSeparately Excited

– Lower Voltage Dips – Sustained Fault Current – Three Phase RMS Sensing – Better Non–Linear Load Immunity – Better Motor Starter

Engines

Governors

Mechanical Governors: Mechanical governors,as the name suggests, control engine fuelingbased on mechanical sensing of engine RPMthrough flyweights or similar mechanisms. These

systems exhibit about 3–5 percent speed droopfrom no load to full load inherent in the design.This type of system is generally the least expen-sive and is suitable for applications where the fre-quency droop is not a problem for the loads beingserved. Some but not all generator sets haveoptional mechanical governing available.

Electronic Governors: Electronic governors areused for applications where isochronous (zerodroop) governing is required or where active syn-

chronizing and paralleling equipment is specified.Engine RPM is usually sensed by electromagnet-ic sensor and the engine fueling controlled bysolenoids driven by electronic circuits. These cir-cuits, whether self contained controllers or part ofa microprocessor generator set controller, utilizesophisticated algorithms to maintain precisespeed (and so frequency) control. Electronic gov-ernors allow generator sets to recover faster fromtransient load steps than mechanical governorsdo. Electronic governors should always be usedwhen the loads include UPS equipment.

Modern engines, especially diesel engines withfull authority electronic fueling systems, are onlyavailable with electronic governing systems. Thedemand or regulation requirements to achieveincreased fuel efficiency, low exhaust emissionsand other advantages, require the precise controlafforded by these systems.





Engine Starting Systems

Battery Starting: Battery starting systems forgenerator sets are usually 12 volt or 24 volt. Typi-cally with smaller sets using 12 volt systems andlarger machines using 24 volt systems. Figure4–14 illustrates typical battery–starter connec-tions. Consider the following choosing or sizingbatteries and related equipment:

• Batteries must have enough capacity (CCA,Cold Cranking Amps) to provide the crankingmotor current indicated on the recom-mended generator set Specification Sheet.The batteries may be either lead–acid ornickel–cadmium. They must be designatedfor this use and may have to be approved bythe local authority having jurisdiction.

• An engine–driven alternator with integral

automatic voltage regulator is normally pro-vided to recharge the batteries during opera-tion.

• For most generator set power systems, auxil-iary, float–type battery charger, powered bythe normal power source, is desirable orrequired to keep the batteries fully chargedwhen the generator set is not running. Floatbattery chargers are required for emergencystandby systems.

• Codes usually specify a maximum batterycharging time. The following rule–of–thumb

can be used to size auxiliary battery char-gers:

Required BatteryCharging Amps

=1.2 x Battery Amp–HoursRequired Charging Hours

• Local codes may require battery heaters tomaintain a minimum battery temperature of50_F (10_C) if the generator set is subject tofreezing ambient temperatures. See furtherinformation under Accessories and Options

(this section), Standby Heating Devices forGenerator Sets.

• Standard generator sets usually include bat-tery cables, and battery racks are available.

Relocating of Starting Batteries: If batteries are

mounted at a further distance from the starterthan the standard cables allow, the cables mustbe designed accordingly. Total resistance, cablesplus connections, must not result in an excessivevoltage drop between the battery and the startermotor. Engine recommendations are that totalcranking circuit resistance, cables plus connec-tions, not exceed 0.00075 ohms for 12 volts sys-tems and 0.002 ohms for 24 volt systems. Seethe following example calculation.

Example Calculation: A generator set has a

24–VDC starting system to be powered by two12–volt batteries connected in series (Figure4–14). Total cable length is 375 inches, includingthe cable between the batteries. There are sixcable connections. Calculate the required cablesize as follows:

1. Assume a resistance of 0.0002 ohms for thestarter solenoid contact (RCONTACT).

2. Assume a resistance of 0.00001 ohms foreach cable connection (RCONNECTION), total ofsix.

3. Based on the formula that:• Maximum Allowable Cable Resistance

= 0.002 – RCONNECTION – RCONTACT

= 0.002 – 0.0002 – (6 x 0.00001)= 0.00174 ohms

4. Refer to Figure 4–15 for AWG (AmericanWire Gauge) cable resistances. In this exam-ple, as shown by the dashed lines, the small-est cable size that can be used is 2–#1/0AWG cables in parallel.





–

+

–

12 VOLTBATTERIES

STARTERSOLENOID

POSITIVE (+) BATTERYCABLE CONNECTION

NEGATIVE (–) BATTERYCABLE CONNECTION

STARTERMOTOR

+

Figure 4–14. Typical Electric Starter Motor Connections (24 Volt System Shown)

R E S I S T A N C E ( O H M S )

LENGTH OF CABLE IN INCHES (METERS)

100(2.54)

200(5.08)

300(7.62)

400(10.16)

500 600(15.24)

700(17.76)(12.70)

.0004

.0002

.0006

.0010

.0012

.0014

.0016

.0018

.0024

.0026

.0028

.0030

.0032

.0034

.0036

.0038

.0040

.0022

.0020

.0008

#4 #3 #2 #1 #1/0 #2/0#3/0

2–#1/0

2–#2/0

Figure 4–15. Resistance vs. Length for Various AWG Cable Sizes





muffler

to push-button start-ing switch

from air

tank

air starter

pressuregauge

24 volt airstarting valve

pushbutton startingvalve

relayvalve

air inlet

lubricator(connected to

injector drain line)

Figure 4–16. Typical Piping Arrangement for an Air Starter

Air Starting: Compressed air engine starting sys-tems are available for some larger generator sets.Air starting may be preferred for some prime pow-er applications assuming compressed air is readi-ly available. Figure 4–16 shows a pipingarrangement for a typical air starter system. Thefollowing items should be considered for deter-mination of equipment needs when installing anair starter system:

• The engine manufacturer should be con-

sulted for recommendations regarding airhose size and the minimum tank volumerequired for each second of cranking. Tanksize will depend on the minimum crankingtime required. All of the starters availablefrom Cummins Power Generation have amaximum pressure rating of 150 psig(1035 kPa).

• Air tanks (receivers) should be fitted with adrain valve of the screw–out, tapered–seattype (other types are unreliable and a com-mon source of air leaks). Moisture can dam-age starter components.

• All valves and accessories in the systemshould be designed for diesel air starting ser-vice.

• Pipe fittings should be of the dry seal typeand should be made up with thread sealant.Teflon tape is not recommended as it does

not prevent thread loosening and can be asource of debris that can clog valves.

Note: Batteries, although of much less capacity, will still be required for engine control and monitoring systems when air starting is used.





Controls

Relay–Based

Until a few years ago relay–based control sys-tems were common on nearly all generator sets.They can be designed to provide either manual orfully automatic starting plus basic generatorprotection functions. They may include sufficientequipment to meet local code requirements forgenerator sets.

Relay–based systems (see Figure 4–17) controlengine starting and operational functions, moni-tor engine and alternator functions for failures orout–of–specification performance, and providegauges, metering, and annunciation for userinterface. Functions such as alternator voltagecontrol are performed by a separate AVR circuit

board. Similarly, a separate controller circuitoperates electronic governing and other optionalequipment. There are numerous optional fea-tures available to enhance performance and con-trol to add functionality for special tasks such asinterface to paralleling equipment and to monitoradditional equipment functions such as fueltanks, coolant, or batteries.

Figure 4–17. Two–Wire Control Interface Panel

Some generator sets are equipped with hybridrelay/solid–state control systems (see Figure4–18). These controls provide more functionality

than pure relay–based systems, but are still limit-ed in their ability to provide complex control oradvanced operation interfaces.

Figure 4–18. Detector 12tControl InterfacePanel

Electronic (Microprocessor) Based

Modern day demands for a high level of perfor-mance, enhanced functionality, control of sophis-

ticated systems and network interfaces requirethe capabilities of microprocessor based controlsystems. The age of microprocessors and com-puters has enabled the development of fully inte-grated, electronic microprocessor based controlssuch as the Power Command (see Figure 4–19)control series from Cummins Power Generation.The Power Command system integrates engineoperation, alternator control and monitoring func-tions of a fully equipped relay based control, pluselectronic governing and voltage regulation alongwith many additional features and capabilities.

Full monitoring of electrical output characteris-tics, kW, kVA, kVAR, over and under voltage,reverse power and more, allows for total control ofthe power producing system.

Figure 4–19. Power Command MicroprocessorSystem





“Full Authority” Electronics

Advanced engine designs incorporate sophisti-cated fuel delivery systems, ignition or injectiontiming control, and active performance monitor-ing and adjustment. These systems and func-tions are required to achieve fuel efficiency andlow exhaust emissions. “Full authority” enginesas they are often referred to, require equallysophisticated microprocessor systems to operateand control these functions. A more advancedversion of the Power Command control incorpo-rates dynamic engine control capability with fea-tures and functionality of the previously men-tioned version, plus many added features (seeFigure 4–20). On generator sets with “full author-ity” electronic engines, this type of advanced con-trol system is an integral part of the engine–gen-erator package and there is no option for relaybased or other control systems.

Figure 4–20. Power Command Full Authority

Electronic

Control Options

Optional equipment for electronic control sys-tems include all functions needed for control andmonitoring for paralleling of multiple generatorsets to each other and to utilities (mains). Inter-mediate type, paralleling upgradable controls arealso available.

The available network interface capability forthese types of controls can be an important fea-ture to consider as optional equipment. The net-work capability provides for remote monitoringand control of the generator set as well as integra-tion into building and power system automationsystems.

Optional relay packages for control of peripheralequipment, are also available.

Accessories and Options

Control Safeties and Annunciators

Relay based control and monitoring systemsavailable on many generator sets can includemultiple warning and shutdown alarms forengine/generator protection. Optional equipmentis usually required for full monitoring or remoteannunciation as well on–set AC metering. Addi-tional equipment is required if network commu-nications are desired, but this usually has limitedcapability. With the advent of complex electronicengine and alternator control requirements plusincreased levels of diagnostic and service data,systems can run up against the capability limita-

tions of these control system types.

Electronic control and monitoring systems, thatare often standard equipment on many generatorsets, include a full menu of integrated warningand shutdown alarms to protect the engine/gen-erator equipment and communicate thosealarms. Some of these alarms are customerselectable or programmable. All alarms can bedisplayed on the control panel or at a remote loca-tion. The remote annunciation is accomplishedthrough various means:

1. Relay contact outputs for common or individ-ual alarms.

2. Annunciator panels specifically designed forthe control system, driven by various types ofnetwork interfaces.

3. Communication through Local Area Net-works or modem connections to remotemonitoring locations using PC based soft-ware.

Codes may require different levels of annunci-

ation for different types of applications. Criticallife safety (U.S. NFPA 110 Level 1) or all otheremergency/standby (U.S. NFPA 110 Level 2) andequivalent codes specify the minimum annunci-ation required for those applications. Othercodes may also have specific requirements.Refer to the individual codes in force for annunci-





ation requirements. Power Command controlfrom Cummins Power Generation are designedto meet or exceed these types of requirementsand numerous additional other standards (Referto the specification sheet for the Power Com-mand control for details.)

Main–Line Circuit Breakers

Circuit breakers of both the molded case type andpower circuit type may be used for generator sets.Molded case breakers are generally availablemounted directly on the generator set. However,many circuit breakers must be mounted in a sepa-rate enclosure mounted on a wall or pedestal.Sizes can range from 10 to 2500 amperes and aresuitable for mounting in an output box directly onthe generator set. Power circuit breakers areavailable in sizes from 800 to 4,000 amps and arelarger, faster–operating, and considerably moreexpensive than molded case breakers. Power cir-cuit breakers are usually mounted on a free– standing panel next to the generator set insteadof on the set because of their size and susceptibil-ity to vibration damage. When main line breakersare needed for a project, the project specificationshould include the type of breaker, type of trip unit,and rating basis (continuous or non–continuous).See the Electrical Design section for more infor-mation regarding choices of circuit breakers.

Molded Case Switches : In cases where a discon-necting means is desired but protection for thegenerator or conductors is not required (i.e. thisprotection is afforded by AmpSentrytor by usinga self excited generator), a molded case switch isoften used in place of a circuit breaker. Theseswitches have the same contacts and switchingmechanisms as circuit breakers but no trip cur-rent sensing. The switch will also provide a con-nection location and lugs for connection of loadconductors.

Entrance Boxes : An entrance box is essentially acircuit breaker box without a CB. If no circuitbreaker is needed or desired, the entrance boxprovides additional space for conductor entrance,routing and connection.

Multiple Circuit Breakers : Multiple breakers areoften required and are available from the factoryon most generator sets. Standard options avail-able are two mounted circuit breakers (except on

the largest alternator). On certain alternators andgensets it is simply not practical or there is noroom to mount circuit breaker enclosures. Con-sult manufacturer representatives for availabilityon specific equipment. Special orders can beconsidered for mounting three or more breakers

onto some generator sets but usually this drivesthe use of a wall mounted or free standing dis-tribution panel.

Batteries and Battery Chargers

Perhaps the most critical sub–system, on a gen-erator set, is the battery system for engine start-ing and generator set control. Proper selectionand maintenance of batteries and battery char-gers is essential for system reliability.

The system consists of batteries, battery racks, a

battery charger powered by the normal electricpower source during standby and an engine–driv-en battery charging alternator which rechargesthe batteries and provides DC power for the con-trol system when the generator set is running.

When generator sets are paralleled, the batterybanks for the individual sets are often paralleledto provide control power for the paralleling sys-tem. The manufacturer of the paralleling systemshould always be consulted to determine suitabil-ity of the engine control power system for this ser-

vice because battery bank voltage dip may dis-rupt some paralleling control systems and requirethe use of separate–station batteries for the par-alleling equipment.

Batteries should be located as close as possibleto the generator set to minimize starting circuitresistance. The location should allow easy servic-ing of the batteries and minimize exposure towater, dirt and oil. A battery enclosure must pro-vide ample ventilation so that explosive gasesgiven off by the battery can dissipate. Codes in

seismic zones require battery racks that havespecial features to prevent battery electrolytespillage and breakage during an earthquake.

The systems designer should specify the type ofbattery system (usually limited to lead–acid orNiCad as explained below) and the battery sys-tem capacity. The required battery systemcapacity depends on the size of the engine (dis-placement), minimum engine coolant, lube oil





and battery temperatures expected (see StandbyHeating Devices for Generator Sets below), theengine manufacturer’s recommended lube oilviscosity, and the required number and durationof cranking cycles1. The generator set suppliershould be able to make recommendations based

on this information.

Lead–acid batteries are the most commonly cho-sen type of battery for generator sets. They arerelatively economical and provide good service inambient temperatures between 0° F (–18° C) and100° F (38° C). Lead–acid batteries can berecharged by conventional battery chargerswhich may be wall–mounted close to the genera-tor set or in an automatic transfer switch (if thegenerator set is NOT part of a paralleling system).The charger should be sized to recharge the bat-

tery bank in approximately 8 hours while provid-ing all the control power needs of the system.

A lead–acid battery may be of the sealed “mainte-nance–free” or flooded–cell type. Maintenancefree batteries withstand maintenance neglect bet-ter but are not as easily monitored and main-tained as flooded–cell batteries.

All lead–acid batteries are required to be chargedat the job site prior to their initial use. Even mainte-nance–free batteries do not retain charge indefi-nitely. Flooded–cell batteries require addition ofelectrolyte at the job site and will rise to approxi-mately 50 percent of the fully charged conditionshortly after electrolyte is added to the battery.

NiCad (nickel–cadmium) battery systems areoften specified where extreme high or low ambi-ent temperature is expected because their perfor-mance is less affected by temperature extremesthan that of lead–acid batteries. NiCad batterysystems are considerably more expensive thanlead–acid batteries but have a longer service life.

A major disadvantage of NiCad battery systemsis that disposal may be difficult and expensivebecause the battery materials are consideredhazardous. Also, NiCad batteries require special

1 NFPA 110 applications require either two 45 second continu-

ous cranking cycles with a rest period between, or two cycles of

three 15 second cranking periods with 15 second rest between.

battery chargers in order to bring them to the full– charge level. These chargers must be providedwith filters to reduce “charger ripple” which candisrupt engine and generator control systems.

Exhaust Systems and Mufflers

Two primary elements drive exhaust and mufflersystem choices, noise level, of course, andaccommodating the relative movement betweenthe exhaust system and the generator set.

Noise regulations or preferences are primarydrivers for muffler choices. Exhaust system andmuffler choices also obviously depend on wheth-er the generator set is indoors or outdoors. Anoutdoor weather protective housing supplied by agenerator set manufacturer usually will have vari-ous muffler options and usually with the muffler

mounted on the roof. Muffler options are oftenrated as industrial, residential or critical depend-ing on their attenuation. Acoustic housings usual-ly include an integral muffler system as part of theoverall acoustic package. For more informationon noise and understanding sound levels seeSection VI Mechanical Design .

A key element regarding the overall exhaust sys-tem is that the generator set vibrates, i.e. moveswith respect to the structure it is housed within.Therefore a flexible piece of exhaust pipe or tube

is required at the generator set exhaust outlet.Indoor systems with long runs of exhaust tube willalso require allowance for expansion in order toavoid damage to both the exhaust system and tothe engine exhaust manifolds or turbo chargers.

Another consideration for exhaust system equip-ment is in regard to measurement of the exhaustgas temperatures. The engine exhaust systemmay be fitted with thermocouples and monitoringequipment to accurately measure the engine ex-haust temperature for the purpose of service

diagnosis or to verify the engine is operating atload level sufficient to prevent light load opera-tional problems. See Appendix E. Maintenance and Service for more information.





Housings (Canopies)

Housing generally can be categorized in threetypes, weather protective (sometimes referred toas skin–tight), acoustic, and walk–in enclosures.The names are for the most part self explanatory.

Weather protective: Sometimes referred to asskin tight, these housings protect and can securethe generator set, often available with lockablelatches. Incorporated louvers or perforated pan-els allow for ventilation and cooling air flow. Little,if any sound attenuation is achieved and some-times there can be added vibration induced noise.These housing types will not retain heat or holdtemperature above ambient.

Acoustic: Sound attenuating housings are speci-fied based on a certain amount of noise attenua-

tion or a published external sound level rating.Noise levels must be specified at a specific dis-tance and to compare noise levels they all mustbe converted to the same distance base. Soundattenuation takes material and space so be cer-tain that unit outline drawings applied include theproper acoustic housing information.

While some of these enclosure designs will exhib-it some insulation capability to hold heat, this isnot the intent of their design. If maintenance ofabove ambient temperatures are required, a

walk–in enclosure is needed.

Walk–in: This term encompasses a wide varietyof enclosures that are custom built to individualcustomer specifications. Often they includesound attenuation, power switching and monitor-ing equipment, lighting, fire extinguishing sys-tems, fuel tanks, and other equipment. Thesetypes of enclosures are constructed both as dropover, single unit and as integral units with largedoors or removable panels for service access.These enclosures can be built with insulation and

heating capability.

Coastal Regions: Another consideration regard-ing housings is if the unit is in a coastal region. Acoastal region is defined as within 60 miles of asaltwater body. In these areas steel housings,

even when specially coated, skids, fuel tanks, etc.are more susceptible to corrosion from saltwatereffects. The use of optional aluminum gensetenclosures and skirts (where offered) are reocm-mended in coastal regions.

Note: Placement of outdoor housings (especially acoustic housings) inside buildings is not a recommended practice for two primary reasons. One,acoustic housings utilize the excess fan restriction capability to achieve sound reduction through ventilation baffling. Therefore there is little or no restriction capability remaining for any air ducts, louvers or other equipment that will invariably add restriction. Two, the exhaust systems of outdoor housings are not necessarily sealed systems, i.e. they have clamped, slip fit

joints in lieu of threaded or flanged fittings. These clamped fittings can let exhaust escape into the room.

Alternative Cooling and Ventilating Configu-rations

Liquid–cooled engines are cooled by pumpingcoolant (a mixture of water and anti–freeze)through passages in the engine cylinder blockand heads by means of an engine–driven pump.The engine, pump and radiator or liquid–to–liquidheat exchanger form a closed, pressurized cool-ing system. It is recommended that, wheneverpossible, the generator set include this type offactory–mounted radiator for engine cooling andventilation. This configuration results in the low-

est system cost, best system reliability and bestoverall system performance. Further, themanufacturer of these generator sets can proto-type test to verify system performance.

Cooling System Ratings: Most Cummins PowerGeneration generator sets have optional coolingsystem ratings available on the factory mountedradiator models. Cooling systems designed tooperate in 40° C and 50° C ambient temperatureare often available. Check individual unit specifi-cation sheets for performance or availability.

These ratings have a maximum static restrictioncapability associated to them, see Ventilation inthe Mechanical Design section for more informa-tion on this subject.





Note: Be cautious when comparing cooling system ratings that the rating is based on ambient temperature not air–on–radiator. An air–on–radiator rating restricts the temperature of the air flowing into the radiator and does not allow for air temperature increase due to the radiated heat energy of the engine and alternator.Ambient rated system accounts for this increase in

temperature in their cooling capability.

Remote Cooling Alternatives: In some applica-tions, the air flow restriction could be too great,because of long duct runs for example, for anengine–driven radiator fan to provide the air flowrequired for cooling and ventilation. In suchapplications, and where fan noise is a consider-ation, a configuration involving a remote radiatoror a liquid–to–liquid heat exchanger should beconsidered. In these applications, a large volumeof ventilating air flow is still required to remove the

heat rejected by the engine, generator, muffler,exhaust piping and other equipment so as tomaintain the generator room temperature atappropriate levels for proper system operation.

Remote Radiator: A remote radiator configura-tion requires careful system design to provideadequate engine cooling. Close attention must bepaid to details such as the friction and static headlimitations of the engine coolant pump and toproper deaeration, filling and draining of the cool-ant system, as well as containment of any anti–

freeze leaks.

Heat Exchanger: A liquid–to–liquid heatexchanger configuration requires close attentionto the design of the system that provides themedium for cooling the heat exchanger. It shouldbe noted that local water conservation and envi-ronmental regulations may not permit city waterto be used as the cooling medium and that in seis-mic risk regions city water could be disrupted dur-ing an earthquake.

See the Mechanical Design section for moredetailed information regarding cooling alterna-tives.

Lubricating Oil Level Maintenance Systems:

Lubricating oil maintenance systems may bedesirable for applications where the generator setis running under prime power conditions, or inunattended standby applications which may run

for greater than the normal number of hours. Oillevel maintenance systems do not extend the oilchange interval for the generator set, unless spe-cial filtration is also added to the system.

Standby Heating Devices for Generator Sets

Cold Start and Load Acceptance: A critical con-cern of the system designer is the time it takes theemergency or standby power system to sense apower failure, start the generator set and transferthe load. Some codes and standards for emer-gency power systems stipulate that the generatorset must be capable of picking up all the emergen-cy loads within ten seconds of power failure.Some generator set manufacturers limit the coldstarting performance rating to a percentage of thestandby rating of the generator set. This practicerecognizes that in many applications, only a por-tion of the total connectable load is emergencyload (non–critical loads are permitted to be con-nected later), and that it is difficult to start andachieve full–load acceptance with diesel genera-tor sets.

The Cummins Power Generation design criteriafor cold starting and load acceptance is that thegenerator set be capable of starting and pickingup all emergency loads up to the standby ratingwithin ten seconds of power failure. This level ofperformance presumes that the generator set is

located within a minimum ambient temperature of40_F (4_C) and that the set is equipped with

coolant heaters. This must be accomplished byinstalling the generator set in a heated room orenclosure. Outdoor, weather protective enclo-sures (including those termed “skin tight”) aregenerally not insulated and thus make it difficult tomaintain a warm generator set in cooler ambienttemperatures.

Below 40_F (4_C), and down to –25_F(–32_C), most Cummins Power Generation

generator sets will start but may not accept load inone step within ten seconds. If a generator setmust be installed in an unheated enclosure in alocation with low ambient temperatures, thedesigner should consult with the manufacturer.The facility operator is responsible for monitoring





operation of the generator set coolant heaters (alow coolant temperature alarm is required byNFPA 110 for this purpose) and obtaining the opti-mum grade of fuel for ambient conditions.

Generator sets in emergency power applications

are required to start and pick up all emergencyloads within 10 seconds of a power failure.Engine coolant heaters are usually necessaryeven in warm ambients, especially with dieselgenerator sets, to meet such requirements. NFPA110 has specific requirements for Level 1 sys-tems (where system failure can result in seriousinjury or loss of life):

• Coolant heaters are required unless the gen-erator room ambient will never fall below 70°F (21° C).

• Coolant heaters are required to maintain theengine block at not less than 90° F (32° C) ifthe generator room ambient can fall to 40° F(4° C), but never below. Performance at low-er temperatures is not defined. (At lowerambient temperatures the generator set maynot start in 10 seconds, or may not be able topick up load as quickly. Also, low tempera-ture alarms may signal problems becausethe coolant heater is not maintaining blocktemperature at a high enough level for a10–second start.)

•Battery heaters are required if the generatorroom ambient can fall below 32° F (0° C).

• A low engine temperature alarm is required.• Coolant heaters and battery heaters must be

powered by the normal source.

Coolant Heaters: Thermostatically controlledengine coolant heaters are required for fast start-ing and good load acceptance on generator setsthat are used in emergency or standby applica-tions2. It is important to understand that the cool-

2 US Code Note: For Level 1 emergency power systems,

NFPA 110 requires that engine coolant be kept at a minimum of90o F (32o C). NFPA110 also requires that heater failure moni-

toring be provided in the form of a low engine temperature

alarm.

ant heater is typically designed to keep the enginewarm enough for fast and reliable starting andload pick–up, not to heat the area around the gen-erator set. So, in addition to the operating coolantheater on the engine, ambient air around the gen-erator set should be maintained at a minimum of

40F (10C)3. If the ambient space around the gen-erator set is not maintained at this temperature,considerations should be given to the use of spe-cial fuel type or fuel heating (for diesel gensets),alternator heaters, control heaters, and batteryheaters.

Failure of the water jacket heater or reduction ofthe ambient temperature around the engine willnot necessarily prevent engine starting, but willaffect the time it takes for the engine to start andhow quickly load can be added to the on–site

power system. Low engine temperature alarmfunctions are commonly added to generator setsto alert operators to this potential system–operat-ing problem.

Water jacket heaters (see Figure 4–21) are amaintenance item, so it can be expected that theheating element will be required to be changed atsome times during the life of the installation. Inorder to replace the heater element without drain-ing the entire cooling system of the engine, heaterisolation valves (or other means) should be pro-

vided.

Jacket water heaters can operate at considerablyhigher temperatures than engine coolant lines, soit is desirable to use high quality silicon hoses, orbraided hose to prevent premature failure of cool-ant hoses associated with the water jacket heater.Care should be taken in the design of the coolantheater installation to avoid overhead loops in thehose routing that can result in air pockets thatmight cause system overheating an failure.

3 Canadian Code Note: CSA282–2000 requires that generator

sets used in emergency application are always installed in such

a way that the generator set is in a 10C (40F) minimum environ-

ment.





Engine coolant heaters normally operate whenthe generator set is not running, so they are con-nected to the normal power source. The heatershould be disabled whenever the generator set isrunning. This may be done by any number ofmeans, such as an oil pressure switch, or with log-

ic from the generator set control.

Figure 4–21. Water Jacket Heater Installation.Note Heater Isolation Valve, Hose Type, and Hose

Routing.

Oil and Fuel Heaters: For applications where thegenerator set will be exposed to low ambient tem-peratures (less than 0° F [–18° C]), lube oil heat-ers and fuel line and fuel filter heaters for prevent-ing fuel waxing may also be necessary.

Anti–Condensation Heaters: For applicationswhere the generator set will be exposed to highhumidity or fluctuating temperatures around thedeploying, heaters for the generator and controlbox are recommended to prevent condensation.Condensation in the control box, on the control

circuits or on generator windings can cause cor-rosion, deterioration of circuit paths and genera-tor winding insulation and even cause short cir-cuits and premature insulation failure.

Fuel Tanks (Diesels)

Day tanks: Tanks at or near the generator setfrom which the generator set draws its fuel arecalled day tanks (although they do not necessari-ly contain sufficient fuel for a day’s operation).These are used as a convenience or when it is notpractical to draw directly from the primary fuelstorage system. The distance to, the heightabove or below, or the size of the primary tank arereasons for using a day tank. All diesel engineshave limitations as to fuel lift capability (or fueldraw restriction), fuel head pressure (both supplyand return) and fuel supply temperature. The fuelis transferred from the primary tank to the daytank using a transfer pump often controlled by anautomatic system utilizing level sensors in theday tank. If the tank is small, the fuel return ispumped back into the primary fuel tank to avoidoverheating of the fuel. See fuel systems in theMechanical Design section.

Sub–base tanks: Usually larger than day tanks,these tanks are either built into the base frame ofthe generator set or constructed so that the gen-erator set chassis can be mounted directly onto it.

These tanks hold an amount of fuel for a specifiednumber of hours of operation such as 12 or 24hour sub–base tank. Sub–base tanks are oftendual–wall, incorporating a secondary tank aroundthe fuel container for the purpose of fuel contain-ment in case of a primary tank leak. Many localregulations require secondary fuel containmentsuch as dual–wall construction along with fullmonitoring of primary and secondary containers.

Mounting Vibration Isolators

To reduce vibrations transmitted to the building ormounting structure, often generator sets aremounted on vibration isolators. These isolatorscome in spring or rubber pad styles, the mostcommon being spring type. Vibration isolationperformance is generally 90% or higher and com-monly in excess of 95%. Weight capacity and cor-





rect placement are critical to performance. In thecase of larger generator sets with sub–base tanksthe isolators are frequently placed between thetank and the base frame.

Power Switching Equipment

Power transfer or switching equipment such astransfer switches or paralleling gear, while not thesubject of this manual, is an essential part of astandby power system. It is mentioned here toaccentuate the importance of consideration anddecisions about this equipment early in a project.The scheme of power switching for a projectrelates directly to the generator set rating (seePreliminary Design), the control configurationand the accessory equipment that may berequired for the generator set. For more specificinformation regarding this subject, refer to otherapplication manuals: T011 – Power Transfer Sys- tems and T016 – Paralleling and Paralleling Switchgear .

Devices Required for Generator Set Paralleling: Generator sets in paralleling applications shouldbe equipped with the following to enhance perfor-mance and protect the system from normallyoccurring faults:

• Paralleling suppressors to protect the gener-ator excitation system from the effects of

out–of–phase paralleling.• Loss of field protection that disconnects the

set from the system to prevent possible sys-tem failure.

• Reverse power protection that disconnectsthe set from the system so that engine failuredoes not cause a reverse power conditionthat could damage the generator set or dis-able the rest of the system.

• Electronic isochronous governing to allowuse of active synchronizers and isochronousload sharing equipment.

• Equipment to control the reactive outputpower of the generator set and properlyshare load with other operating generatorsets. This may include cross current com-pensation or reactive droop controls.

• Var/PF controller to actively control the reac-

tive output power of the generator set in utility(mains) paralleling applications.

Relay based or relay/solid state integrated con-trols will require added equipment to accomplishthe preceding requirements.

From the standpoint of convenience and reliabil-ity, a microprocessor based integrated controlcontaining all of the above functions (such as theCummins Power Generation Power Commandcontrol system) is desirable.

Additional Equipment Needs

In certain applications, such as prime or continu-ous power, medium voltage, utility paralleling andothers, additional equipment may be desired orrequired and is generally available as optional orspecial order. Some of these include;

• RTDs, resistive temperature measurementdevices in the alternator windings to monitorwinding temperature directly.

• Thermistors on the end turns of the alternator

to monitor winding temperature.• Differential CTs to monitor for winding insula-tion breakdown.

• Ground fault monitoring and protection.• Pyrometers for exhaust temperature mea-

surement.• Engine crankcase breather vapor recirculat-

ing systems.




585 ELECTRICAL DESIGN

5 ELECTRICAL DESIGN

Overview

The electrical design and planning of the on–sitegeneration system is critical for proper systemoperation and reliability. This section coversinstallation design of the generator and relatedelectrical systems, their interface with the facility,and topics regarding load and generator protec-tion. One key element for understanding andcommunication of the electrical system design isa one–line diagram such as the one depicted inFigure 2–1.

The electrical installation of the generator set and

its accessories must follow the Electrical Code inuse by local inspection authorities. Electricalinstallation should be done by skilled, qualified,and experienced electricians/contractors.

Design Considerations

In view of the wide differences in applications,facilities, and conditions, the details of wiring andovercurrent protection of the electrical distributionsystem for on–site generation must be left to engi-neering judgement. There are however, somegeneral guidelines to consider in the design.

• The design of the electrical distribution foremergency on–site generation systemsshould minimize interruptions due to internalproblems such as overloads and faults. Sub-sets of this are providing for selective coor-dination of overcurrent protective devicesand deciding on the number and location ofthe transfer switch equipment used in thesystem. To provide protection from internalpower failures the transfer switch equipmentshould be located as close to the load utiliza-

tion equipment as practical.• Physical separation of the generator feeders

from the normal wiring feeders to preventpossible simultaneous destruction as a resultof a localized catastrophe such as a fire,flooding, or shear force.

• Bypass–isolation transfer switch equipmentso that transfer switches can be maintainedor repaired without disruption of critical loadequipment.

• Provisions for permanent load banks or tofacilitate connection to temporary load banks

without disturbing permanent wiring, such asa conveniently located spare feeder breaker,to allow for exercising the generator setunder a substantial load.

Note: Load banks installed in front of the genset radiator must be supported from the floor or other building structure, not from the radiator or duct adapter. These genset components may not be designed to support the weight or cantilever of the load bank.

• Load–shed circuits or load priority systems incase of reduced generator capacity or loss ofa single unit in paralleled systems.

• Fire protection of conductors and equipmentfor critical functions, such as fire pumps, ele-vators for fire department use, egress light-ing for evacuation, smoke removal or pres-surization fans, communication systems,etc.

• The security and accessibility of switch-boards and panelboards with overcurrentdevices, and transfer switch equipment in theon–site generator distribution system.

• Provisions for the connection of temporary

generators (portable rental generator sets)for periods when the permanently–installedgenerator set is out of service or whenextended normal power outages make it nec-essary to provide power for other loads(space air conditioning, etc.).

Electrical Connections

General

Vibration Isolation: All generator sets vibrate dur-ing normal operation, a simple fact that must be

addressed. They are either designed with inte-gral isolators or the entire skid is mounted onspring isolators to allow movement and to isolatevibrations from the building or other structure.Greater movement can also occur upon suddenload change or fault event and during startup orshutdown. Therefore, all connections to the gen-erator set, mechanical and electrical, must beable to absorb the vibration movement and start-





up/shutdown movements. Power output, controlfunction, annunciation, and accessory circuits allrequire stranded flexible leads and flexible con-duits between the generator set and the building,mounting structure, or foundation.

Large stiff cables may not provide sufficient abilityto bend even though they are considered flexible.This is also true of some conduit types, for exam-ple certain liquid–tight conduits that are quite stiff.Also keep in mind that cables or conduits are notcompressible along their length so flexibility inthat dimension must be accommodated with suffi-cient length, offsets or bends.

Further, the electrical connection points on thegenerator set – bushings, bus–bars, terminalblocks, etc. – are not designed to absorb these

movements and related stresses. (This is againespecially notable for large stiff cables or stiff“flexible” conduits. Failure to allow sufficient flexi-bility will result in damage to enclosures, leads,cables, insulation, or connection points.

Note: Simply adding flex conduit or cabling may not result in sufficient capability to absorb the vibration movement of a generator set. Cables and flexible conduits vary in flexibility and will not stretch or compress.This condition can be addressed by including at least one bend between the generator output enclosure and the structure (cement floor, raceway,wall, etc.) to allow

for three dimensional movement.

Seismic Areas: In seismic risk areas, specialelectrical installation practices are required,including seismic mounting of equipment. Themass, center of gravity, and mounting dimensionsof the equipment is indicated on the outline draw-ings.

Control Wiring: AC and DC control wiring (to theremote control equipment and remote annuncia-tors) must be run in separate conduit from thepower cables to minimize power circuit interfer-ence in the control circuit. Stranded conductorsand a section of flexible conduit must be used forconnections at the set.

Accessory Branch Circuits: Branch circuits mustbe provided for all accessory equipment neces-sary for operation of the generator set. These cir-cuits must be fed either from the load terminals of

an automatic transfer switch or from the genera-tor terminals. Examples of accessories includethe fuel transfer pump, coolant pumps for remoteradiators, and motorized louvers for ventilation.

Branch circuits, fed from the normal power panel-

board, must be provided for the battery chargerand coolant heaters, if used. See Figure 5–1.

AC Power Connections at Generator

Verify a proper match of the number of conduc-tors per phase and their size with the publishedlug capacities of the equipment (circuit breakersand transfer switches).

A main disconnect device (circuit breaker/switch)should be supervised and arranged to activate analarm when it is open. Some suppliers will initiate

a “not in auto” alarm when the CB is open.

Connection options at the generator can includethe following:

Generator–Mounted Molded Case Circuit Break- ers (Thermal–Magnetic or Solid–State): Connec-tions can be made to a generator–mounted circuitbreaker. The circuit breaker selected must haveadequate interrupting capability based on theavailable short circuit current. With a single gen-erator set the maximum available first cycle sym-

metrical short circuit current is typically in therange of 8 to 12 times the rated current. For a spe-cific generator it equals the reciprocal of the gen-erator per unit subtransient reactance, or 1/X′′d.Use the minimum tolerance of subtransient reac-tance from the specific generator manufacturer’sdata for the calculation.

Generator–Mounted Disconnect (Molded Case)Switch: Connections can be made to a genera-tor–mounted disconnect switch. This is allowablewhere the generator includes an inherent means

of generator overcurrent protection, such as Pow-er Command. The switch is not intended to inter-rupt fault level currents, having an interrupting rat-ing sufficient only for the load currents.

Generator Terminals: Connections may be madeto the generator terminals where no generator– mounted circuit breaker or disconnect switch isrequired and where the generator includes aninherent means of generator overload protection.





AC POWER TOEMERGENCY LOADS

AC POWER TO REMOTEVENT OR RADIATOR FAN2

DC STARTSIGNAL

FROM ATS

DC SIGNALSTO REMOTE

ANNUNCIATOR

NORMALAC POWER

TO CONTROLBOX HEATER

SET RUNNINGSIGNALS

NORMAL AC POWERTO GENERATOR

HEATER

NORMAL ACPOWER TO LUBE

OIL HEATER

NORMAL ACPOWER TOBATTERYHEATER

NORMAL ACPOWER TOBATTERYCHARGER

NORMAL AC POWER

TO COOLANT HEATER

DC SIGNALSTO GENERATORCONTROL AND

REMOTE

ANNUNCIATOR

DAY TANKFUEL PUMP

DC POWERTO BATTERY

AC POWER TODAY TANK

FUEL PUMP2

NOTES:

1. WHEN A CUMMINS POWER GENERATION ATS (AUTOMATIC TRANSFER SWITCH) IS USED, THE BATTERY CHARGER CAN BE SUPPLIED WITH THEATS. ATS MOUNTED BATTERY CHARGERS CANNOT BE USED IN PARALLELING APPLICATIONS.

2. THESE LOADS CAN BE POWERED DIRECTLY OFF THE GENERATOR (WITH APPROPRIATE OVERCURRENT PROTECTION) OR FROM THE LOADSIDE OF THE FIRST PRIORITY ATS.

3. THE ITEMS IN ITALICS ARE NOT ALWAYS USED.

4 NETWORK INTERCONNECT MAY REPLACE SIGNALS FOR SOME CONTROL INTERCONNECTIONS.

REMOTEEMERGENCY

STOP

DC SIGNALS TO REMOTE

ANNUNCIATOR

BATTERYCHARGER1

NETWORKINTERFACE

Figure 5–1. Typical Generator Set Control and Accessory Wiring





AC Power Conductors

The generator set AC output connects to fieldinstalled conductors sized as required by the loadcurrents, the application, and codes. The con-ductors from the generator terminals to the firstovercurrent device are considered tap conduc-tors, and allowed to run short distances withoutshort circuit protection. A generator circuit break-er may be provided at the load end of the genera-tor supply conductors (for example, parallelingbreakers in the paralleling switchboard or mainbreaker in a distribution panel) and still provideoverload protection for the conductors.

If the generator set is not factory–supplied with amain–line circuit breaker, the ampacity of thefield–installed AC phase conductors from thegenerator output terminals to the first overcurrentdevice should be at least equal to 115 percent ofthe rated full–load current, without temperature oraltitude de–ratings. The ampacity of the conduc-tors may be 100 percent of rated full–load currentif the generator set is equipped with Power Com-

mand. The generator set manufacturer will speci-fy line–ampere ratings of a specific generator setat the specific voltage required. If unknown, cal-culate using one of the following formulae:

ILINE =kW • 1000

VL–L • 0.8 • 1.73

ORkVA • 1000

VL–L • 1.73

ILINE =

Where:ILINE = Line Current (amps).kW = Kilowatt rating of the genset.kVA = kVA rating on the genset.VL–L = Rated line–to–line voltage.

See schematics (a) and (b) in Figure 5–2. Thelength of run for generator tap conductors to thefirst overcurrent device should be kept as short aspossible (generally not more than 25 – 50 feet).

NOTE: If the generator is supplied with leads, the size of the leads may be smaller than required for field– installed conductors because generator leads have type CCXL or similar, high temperature insulation rated at or above 125 _C.

GEN

GEN

GEN*

115% OF GENERATOR FULL-LOAD AMPERES

MAY BE 100% GENERATOR FLA WITHPOWER COMMAND

115% OFGENERATORFULL-LOADAMPERES

EQUAL TO OR GREATERTHAN GENERATORBREAKER RATING

* – FACTORYMOUNTED CIRCUIT

BREAKER

(a) No Main-Line Circuit Breaker

(b) Remote Main-Line Circuit Breaker

(c) Generator Mounted Main-Line Circuit Breaker

EQUAL TO OR GREATERTHAN REMOTE

BREAKER RATING

TO THE AUTOMATIC TRANSFER SWITCHES



Figure 5–2. Feeder Ampacity





If the generator set is factory–equipped with amain–line circuit breaker, the ampacity of thefield–installed AC phase conductors connectedto the load terminals of the circuit breaker shouldbe equal to or greater than the circuit breaker rat-ing. See Schematic (c) in Figure 5–2.

The minimum ampacity of the neutral conductoris generally permitted to be equal to or greaterthan the calculated maximum single–phaseunbalance of the load. Where a significant por-tion of the load is non–linear, the neutral should besized in accordance with anticipated neutral cur-rent but never less than 100 percent rated. Thegenerator neutral supplied by Cummins PowerGeneration is equal in ampacity to the phase con-ductors.

Note: Medium voltage cable (greater than 600 VAC)must be installed and terminated exactly as recommended by the cable manufacturer, by persons who have learned the procedures through training and practice under close supervision.

Voltage Drop Calculations: Conductor imped-ance due to resistance and reactance causesvoltage to drop in an AC circuit. To obtain the per-formance expected of load equipment, conduc-tors usually should be sized so that voltage doesnot drop more than 3 percent in a branch or feed-er circuit or more than 5 percent overall between

the service drop and the load equipment. Whileexact calculations are complex, reasonably closeapproximations can be made using the followingrelation:

VDROP = (IPHASE • ZCONDUCTOR)VRATED

Example Calculation: Calculate percentage volt-age drop in 500 feet of 1/0 AWG copper cable insteel conduit supplying a 3–phase, 100 kW, 480volt, (line–to–line) load imposing a 0.91 PF (Pow-

er Factor).

Z(ohms) =L [(R • pf)+X (1–pf2)]

(1000 • N)

Where:Z = Impedance of conductorR = Resistance of conductorX = Reactance of conductor

L = conductor length in feetN = number of conductors per phasepf = power Factor

R = 0.12 ohms/1000 feet (NEC Chapter 9, Table9, Resistance for 1/0 AWG copperconductors in steel conduit.)

X = 0.055 ohms/1000 feet (NEC Chapter 9, Table9, Reactance for 1/0 AWG copperconductors in steel conduit.)

Z =500 [0.12 • 0.91) + 0.055 (1–0.912)]

(1000 • 1)

= 0.066 percent

IPHASE = kW

= 120.3 amps

1000.48 • 1.73kV • 1.73

=

VDROP (%) =120.3 • 0.066

100• 480

= 1.65 percent

Allowable Single–Phase Load Unbalance: Single–phase loads should be distributed asevenly as possible between the three phases of athree–phase generator set in order to fully utilizethe rated capacity (kVA and kW) of the set and to

limit voltage unbalance. Figure 5–3 can be usedto determine the maximum permissible percent-age of unbalanced single–phase load, as illus-trated by the example calculation.

Single phase power can be taken up to 67 percentof the three–phase rating on Cummins PowerGeneration generator sets, up through 200/175kW.

Generally, the larger the generator set, the lowerthe percentage of single–phase power that canbe taken. Figure 5–3 includes single–phase per-centage lines for Cummins Power Generationintermediate–size Frame–4 and Frame–5 gener-ators. Confirm the frame size by referring to theapplicable Alternator Data Sheet referenced bythe generator set Specification Sheet. Single– phase load unbalance should not exceed 10 per-cent.





0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

SINGLE-PHASE LOAD AS PERCENTAGE OF THREE-PHASE kVA RATING

T H R E E

- P H A S E L O A D A S P E R C E N T A G E O F T H R E E - P H A S E k V A R A T I N G

use THIS LINE FOR200 Kw and less

Use this line for frame-4 gen-erators

Use this line for frame-5 gen-erators

Figure 5–3. Allowable Unbalanced Single-Phase Load(Typical Three–Phase Generator From Cummins Power Generation)





Example Calculation: Find the maximum single– phase load that can be powered in conjunctionwith a total three–phase load of 62 kVA by a gen-erator set rated 100kW/125 kVA.

1. . Find the three–phase load as a percentage

of the generator kVA rating:

=

125 kVAThree–Phase

Load Percentage62 kVA • 100% = 50%

2. Find the percentage of allowable single– phase load, as shown by the arrows in Fig-ure 5–3. In this case, it is approximately 34percent of the three–phase rating.

3. Find the maximum single–phase load:

= 100%Maximum SinglePhase Load 125 kVA • 34% = 42.5 kVA

4. Note, as follows, that the sum of the three– phase and maximum permissible single– phase loads is less than the kVA rating of thegenerator set:

62 kVA + 42.5 kVA = 104.5 kVA

and

104.5 kVA < 125 kVARating of theGenerator Set

NOTE: Unbalanced loading of a generator set causes unbalanced phase voltages. The levels of load unbalance anticipated by these guidelines should not result in harm to the generator set itself. The corresponding levels of voltage unbalance, however, may not be acceptable for loads such as three–phase motors.

Because of unbalanced phase voltages, criticalloads should be connected to the phase that thevoltage regulator uses as the reference voltage(L1 –L2 as defined in the generator set schematic)when only one phase is used as a reference.

Leading Power Factor Load

Three phase generator sets are rated for continu-ous operation at 0.8 PF (lagging) and can operatefor short periods of time at lower power factors,such as when starting motors. Reactive loadsthat cause leading power factor can provideexcitation power to the alternator, and if highenough, can cause alternator voltage to riseuncontrollably, damaging the alternator or loads

or tripping protective equipment. Figure 5–4 is atypical alternator curve of reactive power (kVAR)capability. A reasonable guideline is that a gener-ator set can carry up to 10 percent of its ratedkVAR capability in leading power factor loadswithout being damaged or losing control of output

voltage.

The most common sources of leading power fac-tor are lightly loaded UPS systems with input fil-ters and power factor correction devices formotors. Loading the generator set with laggingpower factor loads prior to the leading power fac-tor loads can improve stability. It is also advisableto switch power factor correction capacitors onand off with the load. It is generally impractical tooversize a generator set (thus reducing the per-centage of nonlinear load) to correct for this prob-

lem.

System and Equipment Grounding

The following is a general description of systemand equipment grounding for AC generators per-manently installed within a facility. While this isintended as a guide, it is important to follow localelectrical code.

System Grounding (Earthing): System grounding(earthing) is the intentional grounding of the neu-tral point of a wye–connected generator, the cor-

ner of a delta–connected generator, or the mid– point of one–phase winding of a delta–connectedgenerator, to ground (earth). It is most common toground the neutral point of a wye–connected gen-erator and bring out the neutral (grounded circuitconductor) in a three–phase, four–wire system.

A corner–grounded delta system has a groundedcircuit conductor that is not a neutral. It also has a“wild leg” that must be identified by orange colorcoding and connected to the middle pole of three– phase equipment.

Solid Grounding: A solidly grounded system isgrounded directly by a conductor (the groundingelectrode conductor) with no intentional imped-ance to earth (grounding electrode). This methodis typically used and required by electrical codeon all low voltage systems (600 volts and below)with a grounded circuit conductor (most often aneutral) that serves L–N loads.





PER UNIT kVAR

P E R U N I T k W

1.0 PF 0.8 PF LAGGING

0.2

0.4

0.6

0.8

1.0

0.20.20.4 0.40.6 0.60.8 0.81.0 1.00.0

0.99 PF LEADING

UnstableVoltageRegion

LEADING LAGGING

0.2

0.4

0.6

0.8

1.0

AcceptableSteady State

Operating Region

Figure 5–4. Typical Steady State Alternator Reactive Power Capability Curve

Correct grounding in standby systems that aresolidly grounded is a function of the transferswitch equipment used (solid neutral or switchedneutral). See Figure 5–5.

As shipped, the neutral terminal of a CumminsPower Generation generator is not bonded to

ground. If the generator is a separately derivedpower source (i.e. 4–pole transfer switch) thenthe neutral will have to be bonded to ground and agrounding electrode conductor connected to thegrounding electrode system by the installing elec-trician.

If the generator neutral connects to a service– supplied grounded neutral, typically at the neutralblock of a 3–pole transfer switch, then the genera-tor neutral should not be grounded at the genera-tor. In this case, the electrical code may require asign to be placed at the service supply indicatingthat the generator neutral is grounded at thatlocation.

Impedance (Resistance) Grounding : A ground-ing resistor is permanently installed in the pathfrom the neutral point of the generator to thegrounding electrode. This method is occasionallyused on three–phase, three–wire systems (nogrounded circuit conductor) operating at 600 voltsor below, where it is desirable to maintain continu-

ity of power with the first and only accidentalground fault. Delta–wye transformers may beused in the distribution system to derive a neutralfor line–to–neutral load equipment.

Typically, a high–resistance grounded, low volt-age system uses a grounding resistor sized tolimit ground fault current, at line–to–neutral volt-age, to 25, 10, or 5 amps nominal (continuoustime rating). Ground fault detection and alarmsysetms are also typically installed.





3-POLE ATS

3-POLE ATS

4-POLE ATS

GENERATOR SET

GENERATOR SET

GENERATOR SETSERVICE ENTRANCE

SERVICE ENTRANCE

SERVICE ENTRANCE

LOAD

or

LOAD

LOAD

THREE-PHASE, THREE-WIRE UTILITY, THREE-POLE ATS

Generator Neutral may be solidly grounded, resistance grounded or ungrounded with a three-wire

system

THREE-PHASE, FOUR-WIRE UTILITY, THREE-POLE ATS

Generator Neutral is grounded at service entrance only with a three-pole ATS

THREE-PHASE, FOUR-WIRE UTILITY, FOUR-POLE ATS

Generator Neutral must be solidly grounded when a separately derived source with a four-pole ATS

Figure 5–5. Typical One-Line Diagrams of Alternative System Grounding Methods





Select a grounding resistor based on:

1. Voltage Rating: Phase–to–phase voltage(system voltage) divided by the square rootof three (1.73).

2. Current Rating: Low enough to limit damage

but high enough to reliably operate the pro-tective relaying.3. Time Rating: Most often 10 seconds for pro-

tective relayed systems, and extended timefor non–relayed systems.

NOTE: Low–resistance grounding is recommended on generator systems operating from 601 through 15,000 volts in order to limit the level of ground fault current (most often 200–400 amps) and permit time for selective coordination of protective relaying. See Fig-ure 5–6 and Medium Voltage Grounding.

Ungrounded : No intentional connection is madebetween the AC generator system and earth.This method is occasionally used on three– phase, three–wire systems (no grounded circuitconductor) operating at 600 volts or below, whereit is required or desirable to maintain continuity ofpower with one ground fault, and qualified serviceelectricians are on site. An example would besupplying a critical process load. Delta–wyetransformers may be used in the distribution sys-tem to derive a neutral for line–to–neutral loadequipment.

Equipment Grounding (Earthing): Equipmentgrounding (earthing) is the bonding together andconnection to ground (earth) of all non–currentcarrying (during normal operation) metallic con-duit, equipment enclosures, generator frame, etc.Equipment grounding provides a permanent,continuous, low–impedance electrical path backto the power source. Proper grounding practicallyeliminates “touch potential” and facilitates clear-ing of protective devices during ground faults. Amain bonding jumper at the source bonds the

equipment grounding system to the grounded cir-cuit conductor (neutral) of the AC system at asingle point. A grounding connection location is

provided on the alternator frame or, if a set– mounted circuit breaker is provided, a groundingterminal is provided inside the circuit breakerenclosure. See Figure 5–7.

Selective Coordination

Selective coordination : is the positive clearing ofa short circuit fault at all levels of fault current bythe overcurrent device immediately on the line– side of the fault, and only by that device. “Nui-sance clearing” of a fault by overcurrent devicesupstream of the one closest to the fault causesunnecessary disruption of unfaulted branches inthe distribution system and may cause the emer-gency system to start unnecessarily.

Electrical power failures include external failures,such as utility outage or brownout and internal

failures within a building distribution system, suchas a short circuit fault or overload that causes anovercurrent protection device to open the circuit.Because emergency and standby generator sys-tems are intended to maintain power for selectedcritical loads, the electrical distribution systemshould be designed to maximize continuity ofpower in the event of a fault within the system.The overcurrent protection system should there-fore be selectively coordinated.

Overcurrent protection for the equipment and

conductors that are part of the emergency orstandby power system, including the on–site gen-erator, should follow applicable electrical codes.However, where the emergency power systemserves loads that are critical to life safety, as inhospitals or high–rise buildings, more priorityshould be given to maintaining the continuity ofpower than to protecting the emergency system.For example, it would be more appropriate tohave an alarm–only indication of an overload orground fault than to have a circuit breaker open toprotect the equipment if the result would be the

loss of emergency power to loads critical for life– safety.





G

ES209

G

TO LOADS

MEDIUM VOLTAGESWITCHGEAR

INSULATED NEUTRAL(ISOLATED FROM GROUND)

EQUIPMENTGROUND

NEUTRAL

GROUNDINGRESISTOR

CURRENTSENSING

GFP

UTILITY SUPPLY TRANSFORMER(SOLIDLY GROUNDED)

MEDIUM VOLTAGEGENERATOR

GROUNDINGELECTRODE

51G

L

L

Figure 5–6. Typical Low-Resistance Grounding System for a Medium Voltage Generator Set and LoadTransfer Equipment





G

UTILITYSUPPLY TRANSFORMER

(SOLIDLY GROUNDED SYSTEM)

SERVICEDISCONNECT

UNGROUNDEDCIRCUIT

CONDUCTOR(PHASE)

GROUNDEDCIRCUIT

CONDUCTOR(NEUTRAL)

SYSTEMGROUNDINGELECTRODE

GROUNDINGELECTRODECONDUCTOR

EQUIPMENTGROUNDINGCONDUCTOR

MAINBONDINGJUMPER

L N G NL

3-PHASE, 4-WIRESERVICE

UTILITYSERVICE

EQUIPMENT

Figure 5–7. Typical System and Equipment Grounding Connections at the Utility Service Equipment





For the purposes of coordination, the availableshort circuit current in the first few cycles from agenerator set is important. This current is inde-pendent of the excitation system and is solelydependent on the magnetic and electrical charac-teristics of the generator itself. The maximum first

cycle bolted three–phase, symmetrical short cir-cuit current (Isc) available from a generator at itsterminals is:

ISC P.U. =1

X”d

EAC is the open circuit voltage and X′′d is the per– unit direct axis subtransient reactance of the gen-erator. A typical Cummins Power Generationgenerator set will deliver 8 to12 times its rated cur-rent on a three–phase bolted fault, regardless ofthe type of excitation system used. (Refer to thegenerator set Specification Sheets and alternatordata sheets for X′′d.)

Generator reactances are published in per unit toa specified base alternator rating. Generatorsets, however, have various base ratings. There-fore, to convert per unit reactances from the alter-nator base to the generator set base use the fol-lowing formula:

P.U.Znew=P.U.Zgiven

base kVgiven

base kVnew base kVAgiven

base kVAnew2

Example Calculation: Find X′′d (alternator sub-transient reactance) for Cummins Power Genera-tion Model 230DFAB diesel generator set rated230 kW/288 kVA at 277/480 VAC. BulletinS–1009a for this model references AlternatorData Sheet No. 303. ADS No. 303 indicates thatX′′d = 0.13 for the alternator at a full–load ratingpoint of 335 kW/419 kVA and 277/480 VAC(125_C temperature rise). Substituting these val-ues into the preceding equation:

X”d(Genset) = X”d(ADS)

kVADSkVGenset

2

kVAADS

kVAGenset

X”d(Genset) = 0.130.48

2

419288

0.48= 0.089

Equipment Location Recommendations: It is rec-ommended for selective coordination that trans-fer switches be located on the load side of thebranch circuit overcurrent device, where possibleon the line side of a branch circuit panel board.With the transfer switch located on the load side of

the branch circuit overcurrent device, faults onthe load side of the transfer switch will not result inunfaulted branches of the emergency systembeing transferred to the generator along with thefaulted branch.

This recommendation is consistent with the rec-ommendations for overall reliability to physicallylocate transfer switches as close to the loadequipment as possible, and to divide the emer-gency system loads into the smallest circuitspractical using multiple transfer switches.

A second recommendation is to use a sustaininggenerator (PMG excitation) to positively clearmolded case branch circuit breakers. A sustain-ing generator can provide an advantage in clear-ing molded case circuit breakers of the same cur-rent rating but different time–currentcharacteristics.

Fault and Overcurrent Protectionwith Generator Sets

Sizing a Main–Line Generator CircuitBreaker

Sizing a main–line generator circuit breaker usu-ally follows one of three approaches:

The most common approach is to size the circuitbreaker equal to or the next rating up from thegenerator full–load current rating. For example,an 800–ampere circuit breaker would be selectedfor a generator with a 751–ampere full load cur-rent rating. The advantage in this approach is oneof cost; the cables and distribution panel or trans-

fer switch can be sized to the breaker rating of 800amperes. If the circuit breaker is standard rated(80% continuous) it may open automatically atlevels below the generator full–load current rat-ing. However, the generator set is not likely to berun near or at full kW load and at rated power fac-tor long enough to trip the breaker in actual use.Alternatively, a 100% rated 800–ampere circuitbreaker may be used that will carry 800 amperescontinuously.





A second approach using standard (80% continu-ous) rated circuit breakers is to oversize the cir-cuit breaker by 1.25 times the generator full loadcurrent. For example, a 1000–ampere circuitbreaker would be selected for a generator with a751–ampere full load current rating (751 amperes

x 1.25 = 939 amperes, the next higher standardbreaker rating equals 1000 amperes). A breakerselected this way should not trip under full kWload at rated power factor (rated kVA). The disad-vantage of this approach is that the cables anddistribution panel or transfer switch would need tobe sized up to at least 1000 amperes.

Yet a third approach is to size the circuit breakeras the result of the design calculations for a feederand its overcurrent device –– recognizing that theprincipal purpose of the circuit breaker is to pro-

tect the feeder conductors. Feeder ampacity andovercurrent device rating are calculated by sum-ming the load currents of the branch circuits multi-plied by any applicable demand factors (DF) thatare allowed by applicable electrical codes. With- out allowing for future capacity , the minimumrequired feeder ampacity for a typical generatorset application involving both motor and non–mo-tor loads must equal or exceed:

• 1.25 x continuous non–motor load current,plus

• 1.00 x DF (demand factor) x non–continu-ous, non–motor load current, plus• 1.25 x largest motor full–load current, plus• 1.00 x sum of full–load currents of all other

motors.

Because the generator set is sized for both start-ing (surge) and running load, and may also besized to include future capacity, the generator setfull–load current may be greater than the calcu-lated ampacity of the generator feeder conduc-tors and circuit breaker. If this is the case, consid-er increasing both the feeder conductor ampacityand the circuit breaker rating so that the breakerwill not trip at full generator nameplate current.This would also provide future capacity for theaddition of branch circuits.

NOTE: Feeder conductor ampacity is regulated and determined by codes, such as NFPA or CSA. While it is based on generator and CB capacity, other critical fac-

tors are also applied. Refer to applicable codes for correct feeder conductor sizing.

NOTE: Extended full–load testing may trip a main–line circuit breaker sized at or below the full–load current rating of the generator set.

Generator Set Sources

When the energy for the emergency system isprovided by a generator set, it is necessary to pro-vide branch circuit breakers (usually of themolded case type) with a high probability of trip-ping, regardless of the type of fault which couldoccur in a branch circuit.

When a generator set is subjected to a phase–to– ground fault, or some phase–to–phase faults, itwill supply several times more than rated current,

regardless of the type of excitation system. Gen-erally, this trips the magnetic element of a branchcircuit breaker and clears the fault. With a self– excited generator set, there are instances ofthree–phase faults and certain phase–phasefaults where the output current of the generatorwill initially rise to a value of about 10 times ratedcurrent, and then rapidly decay to a value wellbelow rated current within a matter of cycles. Witha sustaining (PMG) generator set, the initial faultcurrents are the same, but the current decays to asustained short circuit current ranging from about

3 times rated current for a three–phase fault toabout 7–1/2 times rated current for a phase–to– ground fault.

The decay in fault current of a self–excited gener-ator requires that branch circuit breakers unlatchand clear in the 0.025 seconds during which themaximum current flows. A branch circuit breakerthat does not trip and clear a fault can cause theself–excited generator to collapse, interruptingpower to the un–faulted branches of the emer-gency system. A sustaining (PMG) generatordoes not collapse and has the advantage of pro-viding about three times rated current for severalseconds, which should be sufficient for clearingbranch circuit breakers.





Using the full load current ratings of the generatorset and of the branch circuit breaker, the followingmethod determines if a branch breaker will trip ona three–phase or phase–to–phase symmetricalfault. The method only determines if tripping ispossible under short circuit conditions with the

available fault current, and does not guaranteetripping for all values of fault current (in arcingfaults, for instance, where fault impedance ishigh).

Because most circuit breaker charts express cur-rent as a percentage of the breaker rating, theavailable fault current must be converted to a per-centage of the circuit breaker rating. Use the fol-lowing formula to determine the available faultcurrent as a percentage of the circuit breaker(CB) rating for an AC generator capable of deliv-

ering 10 times rated current initially (X′′d = 0.10),ignoring circuit impedance between the genera-tor and the breaker:

= Rated CB AmpsFault Current as% of CB rating

10•Rated Generator Amps •100%

Consider the effect of a fault (short circuit) on a100 ampere branch circuit breaker when power issupplied by a generator set having a rated currentof 347 amperes. In this example, the fault currentavailable for the first 0.025 seconds, regardless of

excitation system, is:

=

100Fault Current

as % of CB rating10 • 347 • 100% = 3470%

If the AC generator is of the type that can sustainthree times rated current, use the following formu-la to determine the approximate current availableas a percentage of the circuit breaker rating:

=

100Sustained Currentas % of CB rating

3 • 347 • 100% = 1040%

Figures 5–8 and 5–9 show the results with two100 ampere thermal–magnetic molded case cir-cuit breakers having different trip characteristics,“A” and “B.” With trip characteristic “A” (Figure5–8), the initial fault current of 3470% will trip the

breaker within 0.025 seconds. With trip charac-teristic “B” (Figure 5–9), the breaker may not tripwith the 3470% current available initially, but willtrip in approximately three seconds if fault currentis sustained at 1040% of the breaker rating (threetimes the generator rating). The conclusion is

that a sustaining (PMG) generator offers anadvantage in providing sufficient fault current toclear branch circuit breakers.

The application of the generator, its excitationsystem, and operating voltage, determine theextent of overload protection provided for genera-tors and the protective devices used.

NOTE: The following discussion applies for single– unit installations, 2000 kW and below. Refer to Cum- mins Power Generation publication T–016, Paralleling and Paralleling Switchgear, for protection require-

ments of multiple generators in parallel.

Overload Protection of Generators

In low voltage (600 volts and below) emergency/ standby applications where critical loads arebeing served and the generator set runs a rela-tively small number of hours per year, the mini-mum protection requirements of applicable elec-trical codes should be met. Beyond that, thespecifying engineer should consider the tradeoffbetween equipment protection and continuity of

power to critical loads, and may decide to providemore than the minimum level of protection.

In low–voltage prime power or interruptibleapplications, the loss of power that would resultfrom operation of the protective devices may betolerable and, therefore, a higher level of equip-ment protection would be appropriate.

Protection Zone: The zone of protection for gen-erators includes the generator and the conduc-tors from the generator terminals to the first over-current device; a main–line overcurrent device (if

used), or the feeder overcurrent device bus.Overcurrent protection for the generator shouldinclude protection for short circuit faults anywherewithin this zone.





Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç


























1 0

2 0

3 0

4 0

5 0

1 0 0

1 0 0 0

1 0 0 0 0

5 0 0 0

5 0 0

.01

.02

.05

.1

.5

1

5

10

50

100

500

1000 5 0 0 0 0

1 0 0 0 0 0

T I M E I N S E C O N D S

CURRENT IN PERCENT OF CIRCUIT BREAKER TRIP UNIT RATING

3470%WILLTRIP

Figure 5–8. Fault Effect on a 100 Ampere Breaker with Trip Characteristic “A”

On the downstream side of the feeder bus, stan-dard practice for overcurrent protection of con-ductors and equipment applies. The ratio of gen-erator rated current to the rating of downstreamovercurrent devices, multiplied by the short circuitcurrent available from the generator in the firstfew cycles, should be sufficient for tripping these

devices within one to two cycles.

Emergency/Standby Systems 600 Volts and Below: The minimum generator overload protec-tion required by applicable electrical codes is rec-ommended for Emergency/Standby applications

600 volts and below. Typically, this means thegenerator should be provided with phase over-current devices such as fuses or circuit breakers,or be protected by inherent design, such as Pow-erCommand AmpSentryt. In some applications,the electrical code may also require ground faultindication.





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1 0

2 0

3 0

4 0

5 0

1 0 0

1 0 0 0

1 0 0 0 0

5 0 0 0

5 0 0

.01

.02

.05

.1

.5

1

5

10

50

100

500

1000 5 0 0 0 0

1 0 0 0 0 0

T I M E I N

S E C O N D S

CURRENT IN PERCENT OF CIRCUIT BREAKER TRIP UNIT RATING

1040%WILLTRIP

3470%MAYNOTTRIP

SUSTAININGGENERATOR

CURRENT

Figure 5–9. Fault Effect on a 100 Ampere Breaker with Trip Characteristic “B”

Generator Circuit Breaker: Conventional practiceon generators without inherent overcurrentprotection is to provide a molded case circuitbreaker (MCCB), either thermal–magnetic or sol-id–state, sized to protect the generator feeder

conductors, in order to satisfy electrical coderequirements for generator overload protection.However, a typical thermal–magnetic MCCBsized to carry generator rated current does notprovide effective generator protection. Generally,if circuit breakers are used for generator protec-tion, a solid–state circuit breaker with full adjust-ments (Long time, Short time and Instantaneous,LSI) will be required to coordinate the breakerprotection curve within the generator thermal

capability curve. Where the generator is pro-tected by inherent design, as generators withPowerCommand Amp Sentryt, the use of amain–line circuit breaker for generator overloadprotection is not required.

There are other reasons to consider use of a cir-cuit breaker; including protecting the generatorfeeder conductors, and to have a disconnectingmeans. In order to improve the overall reliabilityof the system, a disconnecting means may beprovided by a molded case switch or other non– automatic means.





Inherent Design, Balanced Faults: A self–excited(Shunt) generator may be considered to be pro-tected by inherent design since it is not capable ofsustaining short circuit current into balancedthree–phase faults long enough for serious dam-age to occur to the generator. Considering the

need for high reliability of power to critical loads,use of shunt excitation is sometimes consideredsufficient to meet the minimum generator protec-tion required by electrical code by inherent designand make generator overcurrent protectivedevices (fuses or circuit breakers) unnecessary.

Note: In America, the electrical code permits generator feeder conductors, appropriately sized at 115 percent of generator rated current, to be run short distances without overcurrent protection for the conductors.

A generator with PMG excitation, but withoutPowerCommand, is capable of sustaining shortcircuit current with an unbalanced or balancedfault. If overcurrent devices downstream of thegenerator should fail to clear a balanced three– phase short circuit fault, the PMG excitation sys-tem includes an over–excitation shutdown func-tion that will serve as “backup”. Thisover–excitation function will shut down the volt-age regulator after about 8 to10 seconds. Thisbackup protection is suitable for three–phasefaults only and may not protect the generator from

damage due to single–phase faults.

PowerCommand Controls and AmpSentry: Pow-erCommand uses a microcontroller (micropro-cessor) with three–phase current sensors to con-tinuously monitor current in each phase. Undersingle– or three–phase fault conditions, current isregulated to approximately 300 percent of thegenerator rating. The microcontroller integratescurrent vs. time and compares the result to astored generator thermal damage curve. Beforereaching the damage curve, the microcontroller

protects the generator by shutting down excita-tion and the engine. Figure 5–10 shows the AmpSentry protection curve1 as available for use inprotection and coordination studies. The alterna-tor thermal damage curve is shown on the rightside of the Amp Sentry protection curve. An over-

1 Power Command Amp Sentry protection curve is avail-

able from Cummins Power Generation representatives;

order form R–1053.

load current of 110 percent of rated for 60 sec-onds causes an overload alarm and operation ofload shed contacts. An overload above 110% willcause the protective response at a time deter-mined by the inverse time protection curve.These controls provide generator protection over

the full range of time and current, from instanta-neous short circuits, both single and three phase,to overloads of several minutes in duration. Interms of selective coordination one importantadvantage of Amp Sentry versus a main circuitbreaker is that Amp Sentry includes an inherentdelay of about 0.6 seconds for all fault currentsabove 4 per unit. This delay allows the instanta-neous response of downstream breakers to clearfaults without tripping the generator off–line, pro-viding selective coordination with the first level ofdownstream breakers.

Ground Fault Indication/Protection: In America,the electrical code requires an indication of aground fault on emergency and standby (life safe-ty) generators that are solidly grounded, operat-ing at more than 150 volts to ground, and withmain overcurrent devices rated 1000 amperes ormore. If required, standard practice in emergen-cy/standby applications is to provide a latchingindication only of a ground fault, and not to trip acircuit breaker. Although ground fault protectionof equipment that opens a main generator circuit

breaker may be provided, it is not required bycode nor recommended on emergency (life safe-ty) generators.

Proper operation of ground fault sensors on gen-erator sets typically requires that the generator isseparately–derived and the use of a 4–pole(switched neutral) transfer switch2.

Prime Power and Interruptible, 600 Volts and Below: The generator overcurrent protectionrequired by the North American electrical code isrecommended for prime power and interruptibleapplications 600 volts and below. Typically, thismeans the generator should be provided withphase overcurrent devices such as fuses or cir-cuit breakers, or be protected by inherent design.

2 See Cummins Power Generation publication T–016,

Paralleling and Paralleling Switchgear.





1 2 3 4 5 1 0

2 0

3 0

4 0

5 0

1 0 0

1 0 0 0

5 0 0

.1

.5

1

5

10

50

100

500

1000

110% OVERLOAD THRESHOLD(Amp Sentry Disabled Below 110% Rated Current)

CURRENT IN MULTIPLES OF GENERATOR SET RATING

Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í







.1

.5

1

5

10

50

100

500

1000

1 2 3 4 5 1 0

2 0

3 0

4 0

5 0

1 0 0

1 0 0 0

5 0 0

FormNo.R-1053

CURRENT IN MULTIPLES OF GENERATOR SET RATING

ALTERNATOR THERMAL DAMAGE THRESHOLD

Figure 5–10. PowerCommand Control AmpSentry Time-Over-Current Characteristic Curve Plus AlternatorDamage Curve. (Note: This curve is applicable to all Cummins PowerCommand ) Generator Sets.)

Units equipped with the PowerCommand control

with AmpSentry provide this protection. If a high-er level of protection is desired, PowerCommandalso provides the following inherent protectionson all phases:

• Short circuit• Over voltage• Under voltage• Loss of field• Reverse power

As stated previously, PowerCommand control

with AmpSentry provides the overcurrent andloss of field protection inherent in it design.

Medium Voltage, All Applications

In medium voltage applications (601 – 15,000volts), the standard practice of providing genera-tor protection will not typically compromise thereliability of the power supply since selectivity of





devices is achievable. The cost of the investmentin equipment also warrants a higher level ofprotection. The basic minimum protectionincludes (see Figure 5–11):

• Three phase backup overcurrent sensing

(51V)• One backup ground time–overcurrent relay(51G)

• Field loss sensing (40)• Three phase instantaneous overcurrent

sensing for differential protection (87).

Refer to ANSI/IEEE Standard No. 242 for additional information about overcurrent protection of these generators.

Surge Protection of Medium–Voltage Genera- tors: Consideration should be given to protectingmedium–voltage generators against voltagesurges caused by lightning strikes on the distribu-tion lines and by switching operations. Minimumprotection includes:

• Line arrestors on the distribution lines• Surge arrestors at the terminals of the gener-

ator• Surge capacitors at the terminals of the gen-

erator• Strict adherence to good grounding practice.

LOW VOLTAGE PROTECTION,

PRIME POWER

MEDIUM VOLTAGE PROTECTION,

TYPICAL MINIMUM

51V 40

GEN

51V

GEN

51G

(3)

(3)(3)

(3)

(3)

(3)

(3)

87 51G

Figure 5–11. Typical Protective Scheme




786 MECHANICAL DESIGN

6 MECHANICAL DESIGN

Foundation and Mounting

Generator Set Mounting and Vibration Isola-tion

The installation design must provide a properfoundation to support the generator set, and toprevent damaging or annoying levels of vibrationenergy from migrating into the building structure.In addition, the installation should assure that thesupporting infrastructure for the generator setdoes not allow vibration from the generator set tomigrate into the stationary portion of the equip-ment.

All components that physically connect to thegenerator set must be flexible in order to absorb

the vibration movement without damage. Com-ponents that require isolation include the engineexhaust system, fuel lines, AC power supply wir-ing, load wiring, control wiring (which should bestranded, rather than solid core), the generatorset (from the mounting pad), and ventilation airducts (for generator sets with skid–mountedradiators) (See Figure 6–1). Lack of attention toisolation of these physical and electrical intercon-nection points can result in vibration damage tothe building or the generator set, and failure of thegenerator set in service.

Figure 6–1. Anti–Vibration Provisions for a Typical Generator Set





The generator set engine, alternator, and othermounted equipment are typically mounted on askid–base assembly. The skid–base assembly isa rigid structure that provides both structuralintegrity and a degree of vibration isolation. Thefoundation, floor, or roof must be able to support

the weight of the assembled generator set and itsaccessories (such as a sub–base fuel tank), aswell as resist dynamic loads and not transmitobjectionable noise and vibration. Note that inapplications where vibration isolation is criticalthe assembled weight of the package mightinclude a massive mounting foundation (SeeFoundation Provisions in this section.)

Physical size, weight, and mounting configura-tions vary greatly between manufacturers andbetween various sizes of equipment. Consult the

manufacturer’s installation instructions for thespecific model installed for detailed informationon weights and mounting dimensions1.

Foundation Provisions

Slab Floor: For many applications, a massivefoundation is not necessary for the generator set.Gensets with integral vibration isolators canreduce transmitted vibrations by 60–80% andplacing steel spring isolators between the gensetand slab can isolate greater than 95% of vibra-tions (see vibration isolators later in this section).

If vibration transmission to the building is not acritical concern, the major issue will be installingthe generator set so that its weight is properlysupported and so that the unit can be easily ser-viced. A concrete pad should be poured on top ofa concrete floor to raise the generator set to aheight that makes service convenient and tomake housekeeping around the unit easier.

• The pad should be constructed of reinforcedconcrete with a 28–day compressivestrength of at least 2500–psi (17,200 kPa).

• The pad should be at least 6 inches (150 mm)deep and extend at least 6 inches (150 mm)beyond the skid on all sides.

1 Detailed information on Cummins Power Generation products

can be found on the Cummins Power Suite, or may be obtained

from any authorized distributor.

See generator set manufacturer’s drawings forphysical locations of fuel lines, control and powerinterconnections and other interfaces that areplanned to be cast into the concrete. These inter-faces vary considerably from supplier to supplier.

Vibration isolators should be secured to themounting pad with Type J or L bolts (rag or rawlbolts) set into the concrete pad. Positioning of“cast in” bolts is problematic, since even smallerrors in location can cause time consumingredrilling of the skid base. Some generator setdesigns allow use of concrete anchor bolts.These would require the mounting points to becarefully laid out based on actual location of themounting points on the generator set and isola-tors.

The mounting pad for the generator set should belevel and flat to allow for proper mounting andadjustment of the vibration isolation system.Verify that the mounting pad is level lengthwise,widthwise, and diagonally.

Piers (Plinth): Alternatively, the generator set canbe mounted on concrete piers (plinth) orientedalong the length of the skid of the generator set.This arrangement allows easy positioning of adrip pan underneath the generator set, and allowsmore room for servicing of the generator set. Thepiers should be physically attached to the floor.

Vibration Isolating Foundation

In applications where the amount of vibrationtransmission to the building is highly critical,mounting the generator set on a vibration isolat-ing foundation may be required. In this case,additional considerations are necessary. Figure6–2 illustrates a typical vibration isolating founda-tion.

• The weight (W) of the foundation should be at

least 2 times (and up to 5–10 times) theweight of the set itself to resist dynamic load-ing. (The weight of fuel in a sub–base fueltank should not be considered to be contrib-uting to the weight required of a vibration iso-lating foundation even though the isolatorsare between the tank and the generator set.)





Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â









Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç





Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

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Á

Á

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Á

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Á

Á

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Á

Á

Á

Á

Á

Á É É É É

É É É É

É É É É É É É É É É É É

É É É É É É É É É É É É

1/2 INCH (13 mm)CLEARANCE FILLED

WITH SEALER

SPRING-TYPE VIBRATIONISOLATOR ANCHORED

WITH TYPE J OR L BOLTS(SEE DETAIL)

2500 PSI (173 kPa) REINFORCEDCONCRETE FOUNDATION

AT LEAST 8 INCHES (200 mm)OF SAND OR GRAVEL

DETAIL OF TYPE J OR L BOLTANCHORING

É É

É É

É É

É É Ç Ç Ç Ç Ç Ç Ç

Ç Ç Ç Ç Ç Ç Ç





Figure 6–2 Typical Vibration Isolating Foundation

• The foundation should extend at least 6 inch-es (150 mm) beyond the skid on all sides.This determines the length (l) and width (w)of the foundation.

• The foundation should extend at least 6 inch-

es (150 mm) above the floor to make serviceand maintenance of the generator set easier.• The foundation must extend below the frost

line to prevent heaving.• The foundation should be reinforced con-

crete with a 28–day compressive strength ofat least 2500 psi (17,200 kPa).

• Calculate the height (h) of the foundationnecessary to obtain the required weight (W)by using the following formula:

h =W

d • l • w

Where:

h = Height of the foundation in feet (meters).l = Length of the foundation in feet (meters).w = Width of the foundation in feet (meters).d = Density of Concrete – 145 lbs/f3 (2322

kg/M3)W = Total wet weight of Genset in lbs (kg).





• The total weight of the generator set, coolant,fuel, and foundation usually results in a soilbearing load (SBL) of less than 2000 lbs/ft2

(9800 kg/m2)psi (96 kPa). Although this iswithin the load bearing capacity of most soils,always find out the allowable SBL by check-

ing the local code and the soil analysis reportfor the building. Remember to include theweight of coolant, lubricant, and fuel (if appli-cable) when performing this calculation. Cal-culate the SBL by using the following formu-la:

SBL (psi) =W

l • w • 144

SBL (kPa) =W • 20.88

l • w

Sample Calculations (US units):

A 500kW genset weights approximately 10,000pounds (4540 kg) wet (i.e., including coolant andlubricants). Skid dimension is 10 feet (3 meters)long and 3.4 feet (1 meter) wide.

l = 10 + (2 • 0.5) = 11 feetw = 3.4 + (2 • 0.5) = 4.4 feetFoundation weight = 2 • 10,000 = 20,000 lbsTotal weight = genset + foundation

SBL = 30,00011 • 4.4

=10,000 + 20,000 = 30,000 lbs

= 620 lbs/ft2

Vibration Isolators

The engine and alternator of a generator set mustbe isolated from the mounting structure where it isinstalled. Some generator sets, particularlysmaller kW models, utilize neoprene/rubbervibration isolators that are inserted into themachine between the engine/alternator and theskid2. The skid of these generator sets usually

can be bolted directly to the foundation, floor, orsub–structure. Other generator sets may be pro-vided with a design that features the engine/alter-

2 Cummins Power Generation generator sets (200/175 kW and

smaller) have rubber vibration isolators located between the

skid and the engine–generator assembly and do not require

use of external vibration isolators for most applications.

nator solidly attached to the skid assembly. Gen-erator sets that do not include integral isolationshould be installed using vibration isolationequipment such as pad, spring, or air isolators.

NOTE: Bolting a generator set that does not include

integral isolators directly to the floor or foundation will result in excessive noise and vibration; and possible damage to the generator set, the floor, and other equipment. Vibrations can also be transmitted through the building structure and damage the structure itself.

Pad Isolators: Pad–type isolators are comprisedof layers of flexible materials designed to dampenvibration levels in non–critical applications, suchas those on grade or for generator sets mountedin their own outdoor enclosure, or where integralisolators are used with a generator set. Pad isola-tors vary in their effectiveness, but are approxi-

mately 75% efficient. Depending on construction,they may also vary in effectiveness with tempera-ture, since at cold temperatures the rubber isolat-ing medium is much less flexible than at highertemperatures.

Spring Isolators: Figure 6–3 illustrates a steelspring vibration isolator of the type required formounting generator sets that do not include inte-gral vibration isolators. Depicted are the bottomrubber pad, isolator body, securing bolts, supportspring, adjusting screw, and locking nut.

These steel spring isolators can damp up to 98percent of the vibration energy produced by thegenerator set. Locate the isolators as shown onthe generator set manufacturer’s documentation.The isolators may not be located symmetricallyaround the perimeter of the generator set,because they are required to be located with con-sideration of the center of gravity of the machine.The number of isolators required varies with theratings of the isolators and the weight of the gen-erator set. See Figure 6–4.

When the machine is mounted on a sub–basefuel tank, the type of vibration isolators required toprotect the sub–base fuel tank depends on thestructure of the tank and the level of vibrationforce created by the machine. If synthetic rubbervibration isolators are installed between the en-gine/generator and the skid, additional vibration





isolation is not usually required between the ma-chine and the subbase tank. However, the natu-ral frequency of the sub–base fuel tank at thepoints of attachment to the genset should be 200Hz or greater. If the engine/alternator is solidly at-tached to the skid, additional vibration isolation

between the skid and a sub–base tank is neededto protect the sub–base tank and adequately iso-late the building from vibration. In all cases, followthe manufacturer’s recommendations for thespecific genset and sub–base tank combination.

Adjusting ScrewLocking Nut

Isolator Body

Support Spring

Securing Bolts

Rubber Pad

Figure 6–3. Typical Steel Spring Vibration Isolator

Figure 6–4. A Generator Set Mounted With Spring–Type Vibration Isolators





Spring–type vibration isolators must be properlyselected and installed to provide effective isola-tion. The weight of the generator set should com-press the isolator sufficiently to allow freedom ofmotion without allowing the isolator to “bottomout” during operation. This is accomplished by

choosing the isolators and their number based onthe isolator’s weight rating and the total weight ofthe generator set.

The isolator should be positively anchored to themounting pad for the generator set using Rag (Lor J bolts) or Rawl (concrete anchor) bolts.

Air Isolators: An air isolator (or air spring) is a col-umn of gas confined in a container designed toutilize the pressure of the gas as the forcemedium of the spring. Air isolators can provide a

natural frequency lower than can be achievedwith elastomeric (rubber) and with specialdesigns lower than helical steel springs. Theyprovide leveling capability by adjusting the gaspressure within the spring.

Air isolators require more maintenance, and tem-perature limitations are more restrictive than forhelical springs. Stiffness of air isolators varieswith gas pressure and is not constant, as is thestiffness of other isolators. As a result, the naturalfrequency does not vary with load to the samedegree as other methods of isolation. A failure ofthe air supply system or leak can cause the isola-tors to fail completely.

Dampening in air isolators is generally low with acritical dampening ratio in the order of 0.05 orless. This dampening is provided by flexure in thediaphragm or sidewall by friction, or by dampingin the gas. Incorporating capillary flow resistance(adding an orifice to the flow) may increase damp-ing between the cylinder of the air isolator and theconnecting surge tanks.

Isolators Used in Seismic Locations: Additionalfactors must be considered for equipmentinstalled in seismic areas. In addition to their typi-cal role of protecting buildings or equipment frommachine induced vibration, during a seismicevent vibration isolators must also ensure that theequipment remains anchored and does not breakfree of the structure it is attached to.

In seismic areas, vibration isolators are oftenused between the genset skid–base and thestructure it is attached to. Seismic isolator mustbe captive, meaning they restrain the generatorset from excessive movement and must be strongenough to withstand the seismic forces encoun-

tered. Vibration isolators suitable for use in theseapplications are available in both synthetic rubberand steel spring types.

Vibration isolators, if installed between the en-gine/alternator and skid, must also adequatelysecure the engine/alternator to the skid. Normallythese types of isolators are of the synthetic rubbertype and must be of a “captive” design so as to ad-equately secure the equipment. The manufactur-er or supplier of the equipment should be con-sulted to determine suitability to the specific

application.

Whenever seismic events are a consideration, aqualified structural engineer should be consulted.

Earthquake Resistance

Cummins Power Generation generator sets,when properly mounted and restrained, are suit-able for application in recognized seismic riskregions. Special design considerations are nec-essary for mounting and restraining equipment ofthe mass density typical of generator sets. Gen-

erator set weight, center of gravity, and mountingpoint locations are indicated on Cummins PowerGeneration generator set outline drawings.

Components such as distribution lines for elec-tricity, coolant, and fuel must be designed to sus-tain minimal damage and to facilitate repairsshould an earthquake occur. Transfer switches,distribution panels, circuit breakers and associat-ed controls for critical applications3 must be capa-ble of performing their intended functions duringand after the anticipated seismic shocks, so spe-

cific mounting and electrical connection provi-sions must be considered.

3 US CODE NOTE: NFPA110 requires these features for Level

1 and Level 2 systems.





Power and Control Wiring Strain Relief

Power wiring and especially control wiring shouldbe installed with the wiring supported on themechanical structure of the generator set or con-trol panel, and not the physical connection lugs orterminations. Strain relief provisions, along withthe use of stranded control wiring rather thansingle core wiring help to prevent failure of the wir-ing or connections due to vibration. See ElectricalConnections in Electrical Design.

Exhaust System

Exhaust System General Guidelines

The function of the exhaust system is to conveyengine exhaust safely outside the building and todisperse the exhaust fumes, soot, and noise

away from people and buildings. The exhaust

system must be designed to minimize backpres-sure on the engine. Excessive exhaust restrictionwill result in increased fuel consumption, abnor-mally high exhaust temperature and failuresrelated to high exhaust temperature as well asexcessive black smoke.

See Figure 6–5 and 6–6. Exhaust systemdesigns should consider the following:

• Schedule 40 black iron pipe may be used forexhaust piping. Other materials that areacceptable include prefabricated stainlesssteel exhaust systems.

Figure 6–5: Typical Features of an Exhaust System for a Generator Installed Inside a Building.





• Flexible, seamless corrugated stainlesssteel exhaust tubing at least 24 inches (610mm) long must be connected to the engineexhaust outlet(s) to allow for thermal expan-sion and generator set movement and vibra-tion whenever the set is mounted on vibration

isolators. Smaller sets with integral vibrationisolation that are bolted directly to the floormust be connected by seamless corrugatedstainless steel exhaust tubing at least 18inches (457 mm) long. Flexible exhaust tub-ing must not be used to form bends or to com-pensate for incorrectly aligned exhaust pip-ing.

• Generator sets may be provided withthreaded exhaust, slip–type exhaust, orflange–type exhaust connections. Threaded

and flanged connections are less likely toleak but more costly to install.

• Isolated non–combustible hangers or sup-ports, NOT the engine exhaust outlet, mustsupport mufflers and piping. Weight on theengine exhaust outlet can cause damage tothe engine exhaust manifold or reduce thelife of the turbocharger (when used), and can

cause vibration from the generator set to betransmitted into the building structure. Theuse of mounts with isolators further limitsvibration from being induced into the buildingstructure.

• To reduce corrosion due to condensation, amuffler (silencer) should be installed as closeas practical to the engine so that it heats upquickly. Locating the silencer close to theengine also improves the sound attenuationof the muffler. Pipe bend radii should be aslong as practical.


Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

FLEXIBLETUBING

VERTICALDISCHARGE WITH

RAIN CAP

CONDENSATEDRAIN

LONG-RADIUSPIPE BEND

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á É É É É É É É É É É É É É É É É É É É É É É É É É É É É É É

MUFFLER SUPPORTEDINDEPENDENTLY OF THE ENGINEBY NON-COMBUSTIBLE STRAPS

APPROVED THIMBLETO PROTECT

COMBUSTIBLE WALL

PREVAILING WINDS

Figure 6–6. Typical Exhaust System





• Exhaust tubing and piping should be of thesame nominal diameter as the engineexhaust outlet (or larger) throughout theexhaust system. Verify that the piping is ofsufficient diameter to limit exhaust backpres-sure to a value within the rating of the specific

engine used. (Different engines have differ-ent exhaust sizes and different backpressurelimitations4.) Piping of smaller diameter thanthe exhaust outlet must never be used. Pip-ing that is larger than necessary is more sub-

ject to corrosion due to condensation thansmaller pipe. Piping that is too large alsoreduces the exhaust gas velocity availablefor dispersing the exhaust gases up and intothe outdoor wind stream.

• All engine exhaust system componentsshould include barriers to prevent dangerous

accidental contact. Exhaust piping and muf-flers should be thermally insulated to preventburns from accidental contact, preventactivation of fire detection devices and sprin-klers, reduce corrosion due to condensation,and reduce the amount of heat radiated tothe generator room. Expansion joints,engine exhaust manifolds, and turbochargerhousings, unless water cooled, must neverbe insulated. Insulating exhaust manifoldsand turbochargers can result in material tem-peratures that can destroy the manifold and

turbocharger, particularly in applicationswhere the engine will run a large number ofhours. Routing of exhaust piping at least 8feet (2.3 meters) above the floor will also helpto prevent accidental contact with theexhaust system.

• Exhaust piping must be routed at least 9inches (230 mm) from combustible construc-tion. Use approved thimbles where exhaustpiping must pass through combustible wallsor ceilings (Figure 6–7 and 6–8).

• The exhaust system outlet direction shouldalso be carefully considered. Exhaustshould never be directed toward the roof of abuilding or toward combustible surfaces.Exhaust from a diesel engine is hot and willcontain soot and other contaminants that canadhere to surrounding surfaces.

4 Exhaust system size and other exhaust data for specific

generator sets is described in the Cummins Power Suite.

• Locate the exhaust outlet and direct it awayfrom the ventilation air intakes.

• If noise is a factor direct the exhaust outletaway from critical locations.

• Exhaust pipe (steel) expands approximately0.0076 inches per foot of pipe for every

100°F rise in exhaust gas above ambienttemperature (1.14 mm per meter of pipe per100° C rise). It is required that exhaustexpansion joints be used to take up expan-sion in long, straight runs of pipe. Expansion

joints should be provided at each point wherethe exhaust changes direction. The exhaustsystem should be supported so that expan-sion is directed away from the generator set.Exhaust temperatures are supplied by theengine or generator set manufacturer for thespecific engine used5.

ExhaustThimble

Figure 6–7: Generator Set Exhaust System Fea-

tures. Dual Side Inlet Silencer, Flex Connectors,Exhaust Thimbles, and Mounting Hangers are

Shown.

5 Exhaust gas data for Cummins Power Generation products is

available in the Power Suite CD package.





VENT HOLES TOWARD HEAT SOURCE

HEAT DISPERSEMENT AREA

HIGH TEMPERATURE

INSULATION

MOUNTING PLATE

Figure 6–8: Typical Thimble Construction for Combustible Wall Installations.

• Horizontal runs of exhaust piping shouldslope downwards, away from the engine, tothe out–of–doors or to a condensate trap.

• A condensate drain trap and plug should beprovided where piping turns to rise vertically.Condensate traps may also be provided witha silencer. Maintenance procedures for thegenerator set should include regular drainingof condensate from the exhaust system.

• Provisions to prevent rain from entering theexhaust system of an engine that is not oper-ating should be provided. This might includea rain cap or exhaust trap (Figure 6–9 and6–10) on vertical exhaust outlets. Horizontalexhaust outlets may be cut off at an angleand protected with birdscreen. Rain capscan freeze closed in cold environments, dis-abling the engine, so other protectivedevices may be best for those situations.

• A generator set should not be connected toan exhaust system serving other equipment,including other generator sets. Soot, corro-sive condensate, and high exhaust gas tem-peratures can damage idle equipmentserved by a common exhaust system.

• Exhaust backpressure must not exceed theallowable backpressure specified by theengine manufacturer6. Excessive exhaust

6 Exhaust backpressure information for specific Cummins Power

Generation generator sets can be found in the Cummins Power

Suite, or may be obtained from an authorized Cummins distribu-

tor.

backpressure reduces engine power andengine life and may lead to high exhaust tem-peratures and smoke. Engine exhaust back-pressure should be estimated before the lay-out of the exhaust system is finalized, and itshould be measured at the exhaust outletunder full–load operation before the set isplaced in service.

• See Exhaust Silencer Performance else-where in this section for information onexhaust silencers and various selection crite-ria for these devices.

WARNING: Engine exhaust contains soot and carbon monoxide, an invisible, odorless, toxic gas. The exhaust system must terminate outside the building at a location where engine exhaust will disperse away from buildings and building air intakes. It is highly recommended that the exhaust system be carried up as high as practical on the downwind side of buildings in order to discharge straight up to maximize dispersal.Exhaust should also discharge on the radiator air discharge side of the building to reduce the likelihood of exhaust gases and soot being drawn into the generator room with the ventilating air.

NOTE: Some codes specify that the exhaust outlet terminate at least 10 feet (3 meters) for the property line, 3 feet (1 meter) from an exterior wall or roof, 10 feet (3 meters) from openings into the building and at least 10 feet (3 meters) above the adjoining grade.





Figure 6–9. A Simple Exhaust System Fitted With a Rain Cap to Prevent Rain From Entering the Exhaust.

EXHAUST STACK (14

IN)

EXHAUST RAIN SHIELD(16 IN)

(4 x 14)56

14

Figure 6–10. A Fabricated Rain Shield for Vertical Genset Exhaust Stack. Dimensions Shown are for a Typical14–Inch Exhaust.





Exhaust System Calculations

Example Exhaust Backpressure Calculation (US Units): The layout of an exhaust system in Figure6–11 specifies a 5–inch (125–mm) diameter by24–inch (610 mm) long flexible tube at the engineexhaust outlet, a critical grade muffler with a6–inch (150–mm) diameter inlet, 20 feet (610 m)of 6–inch (150–mm) diameter pipe and one6–inch (150 mm) diameter long–radius elbow.The generator set Specification Sheet indicatesthat the engine exhaust gas flow is 2,715 cfm(cubic feet per minute)(76.9 m3 /min) and that themaximum allowable exhaust back pressure is 41inches (1040 mm) WC (water column).

This procedure involves determining the exhaustback pressure caused by each element (flexibletubes, mufflers, elbows, and pipes) and thencomparing the sum of the back pressures with themaximum allowable back pressure.

1. Determine the exhaust backpressurecaused by the muffler. Figure 6–12 is agraph of typical muffler exhaust backpres-sures. For more accurate calculations obtain

data from the muffler manufacturer. To useFigure 6–12:

a Find the cross–sectional area of the mufflerinlet using Table 6–1 (0.1963 ft2 in this exam-ple).

b Find the exhaust gas flow rate from the

engine manufacturer7. For this example2715 cfm is given.

c Calculate exhaust gas velocity in feet perminute (fpm) by dividing exhaust gas flow(cfm) by the area of the muffler inlet, as fol-lows:

Gas Velocity =2715 cfm

0.1963 ft2= 13,831 fpm

d Using Figure 6–12, determine the back pres-sure caused by this flow in the specific muf-fler used.In this example, the dashed lines in Figure

6–12 show that the critical grade muffler willcause a back pressure of approximately 21.5inches W.C.

3) 20 feet of 6–inch Pipe 20 ft

7 Exhaust gas data for Cummins Power Generation products is

in the Cummins Power Suite.


Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

5 INCH FLEXIBLETUBING

6 INCHLONG-RADIUS

ELBOW

É É É É É É É É É É É É É É É É É É É É É É É É É É É

4 ft

6 INCH CRITICALSILENCER 16 ft

24”

Figure 6–11. Sample Exhaust System for Calculation.





2. Find the equivalent lengths of all fittings andflexible tube sections by using Table 6–2.1) 24 inch flexible tube 4 ft2) 6–inch long radius elbow 11 ft

3. Find the back pressure at the given exhaustflow per unit length of pipe for each nominal

pipe diameter used in the system. In thisexample, 5 inch and 6 inch nominal pipe isused. Following the dashed lines in Figure6–13, 5 inch pipe causes a back pressure ofapproximately 0.34 inches WC per foot and 6inch pipe approximately 0.138 inches WCper foot.

4. Add the total back pressures for all elementsof the example, as follows:

1) 5 inch flexible tube (4•0.34) 1.42) long–radius elbow (11•0.138) 1.53) 20 feet of 6–inch pipe (20•0.138) 2.84) muffler 21.5Total Restriction (inches WC) 27.2

The calculation indicates that the piping layout isadequate in terms of exhaust back pressure sincethe sum of the back pressures is less than themaximum allowable back pressure of 41 InchesWC.

NOTE: On engines with dual exhaust, the exhaust flow as listed on genset specification sheets from Cummins Power Generation is total flow of both banks. The listed value must be divided by 2 for correct calculation for dual exhaust systems.

DIAMETER OF MUFFLERINLET (INCHES)

AREA OF MUFFLERINLET (FT2)

DIAMETER OF MUFFLERINLET (INCHES)

AREA OF MUFFLERINLET (FT2)

2 0.0218 8 0.3491

2.5 0.0341 10 0.5454

3 0.0491 12 0.7854

3.5 0.0668 14 1.069

4 0.0873 16 1.396

5 0.1363 18 1.767

6 0.1963

Table 6–1. Cross Sectional Areas of Openings of Various Diameter

TYPE OF FITTING NOMINAL INCH (MILLIMETER) PIPE SIZE

2(50)

2–1/2(65)

3(80)

3.5(90)

4(100)

5(125)

6(150)

8(200)

10(250)

12(300)

14(350)

16(400)

18(450)

905StandardElbow

5.2(1.6)

6.2(1.9)

7.7(2.3)

9.6(2.9)

10(3.0)

13(4.0)

15(4.6)

21(6.4)

26(7.9)

32(9.8)

37(11.3)

42(12.8)

47(14.3)

905MediumRadius Elbow

4.6(1.4)

5.4(1.6)

6.8(2.1)

8(2.4)

9(2.7)

11(3.4)

13(4.0)

18(5.5)

22(6.7)

26(7.9)

32(9.8)

35(10.7)

40(12.2)

905Long RadiusElbow

3.5(1.1)

4.2(1.3)

5.2(1.6)

6(1.8)

6.8(2.1)

8.5(2.6)

10(3.0)

14(4.3)

17(5.2)

20(6.1)

24(7.3)

26(7.9)

31(9.4)

455Elbow 2.4(0.7)

2.9(0.9)

3.6(1.1)

4.2(1.3)

4.7(1.4)

5.9(1.8)

7.1(2.2)

6(1.8)

8(2.4)

9(2.7)

17(5.2)

19(5.8)

22(6.7)

TEE, Side Inlet orOutlet

10(3.0)

12(3.7)

16(4.9)

18(5.5)

20(6.1)

25(7.6)

31(9.4)

44(13)

56(17)

67(20)

78(23.8)

89(27.1)

110(33.5)

18 Inch FlexibleTube

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

3(0.9)

24 Inch FlexibleTube

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

4(1.2)

Table 6–2. Equivalent Lengths of Pipe Fittings in Feet (Meters)





26

24

22

20

18

16

14

12

10

8

6

4

2

CRITICAL GRADE MUFFLERS

RESIDENTIAL GRADE MUFFLERS

INDUSTRIAL GRADE MUFFLERS

0

2 , 0 0 0

4 , 0 0 0

6 , 0 0 0

8 , 0 0 0

1 0 , 0 0 0

1 2 , 0 0 0

1 4 , 0 0 0

1 6 , 0 0 0

EXHAUST GAS VELOCITY, FEET (METERS) PER MINUTE)

E X H A U

S T B A C K P R E S S U R E , I N C H E S ( M I L L I M E T E R S ) W A T E R C O L U M N

(660)

(610)

(560)

(508)

(451)

(406)

(356)

(305)

(254)

(203)

(152)

(102)

(51)

( 6 1 0 )

( 1 2 1 9 )

( 1 8 2 9 )

( 2 4 3 8 )

( 3 0 4 8 )

( 3 6 5 8 )

( 4 2 6 7 )

( 4 8 7 7 )

Figure 6–12. Typical Muffler Exhaust Back Pressure vs. Gas Velocity





0.01

0.05

0.10

0.50

1.00

0.02

0.03

0.04

0.20

0.30

0.40

2 (50)

2.5 (65)

3 (80)

3.5 (90)

4 (100)

5 (125)

6 (150)

8 (200)

10 (250)

12 (300)

1 0 0 2

0 0

3 0 0

4 0 0

5 0 0

1 , 0 0 0

2 , 0 0 0

3 , 0 0 0

4 , 0 0 0

5 , 0 0 0

1 0 , 0 0 0

2 0 , 0 0 0

EXHAUST FLOW CUBIC FEET (CUBIC METERS) PER MINUTE

E X H A U S T B A C K P R E S S

U R E I N C H E S ( M I L I M E T E R S ) W A T E R

C O L U M N P E R F O O T O F P I P E L E N G T H

(25.4)

(12.7)

(10.1)

(7.6)

(5.1)

(2.5)

(1.3)

(1.0)

(0.76)

(0.51)

(0.25)

( 2 . 8 3 )

( 5 . 6 6 )

( 8 . 5 0 )

( 1 1 . 3 3 )

( 1 4 . 1 6 )

( 2 8 . 3 )

( 5 6 . 6 )

( 8 5 . 0 )

( 1 1 3 )

( 1 4 2 )

( 2 8 3 )

( 5 6 6 )

14 (350)

16 (400)

Figure 6–13. Exhaust Back Pressure in Nominal Inch (mm) Pipe Diameters





Engine Cooling

Liquid–cooled engines are cooled by pumping acoolant mixture through passages in the enginecylinder block and head(s) by means of anengine–driven pump. The most common genera-

tor set configuration has a mounted radiator andan engine–driven fan to cool the coolant and ven-tilate the generator room. Alternative methods forcooling the coolant include skid–mounted liquid– to–liquid heat exchangers, remote radiator, aremote liquid–to–liquid heat exchanger, and cool-ing tower configurations.

Cooling systems for reciprocating engine–drivengenerator sets have the following common char-acteristics, regardless of the heat exchangerused, to remove heat from the engine. These

include:

• The engine portion of the cooling system is aclosed, pressurized (10–14 psi/69.0–96.6kPa) system that is filled with a mixture ofclean, soft (demineralized) water, ethyleneor propylene glycol, and other additives.Engines should not be directly cooled byuntreated water, since this will cause corro-sion in the engine and potentially impropercooling. The “cold” side of the cooling sys-tem can be served by a radiator, heatexchanger, or cooling tower.

• The engine cooling system must be properlysized for the ambient and components cho-sen. Typically the top tank temperature of thesystem (temperature at the inlet to theengine) will not exceed 220° F (104° C) forstandby applications, and 200° F (93° C) forprime power installations.

• The cooling system must include deaerationand venting provisions to prevent buildup ofentrained air in the engine due to turbulentcoolant flow, and to allow proper filling of theengine cooling system. This means that in

addition to the primary coolant inlet and out-let connections, there are likely to be at leastone set of vent lines terminated at the “top” ofthe cooling system. Consult the enginemanufacturer’s recommendations for thespecific engine used for detailed require-ments8. See Figure 6–14 for a schematic

8 Requirements for venting and deaeration of specific Cummins

engines are found in Cummins documents AEB.

representation of the cooling and vent lineson a typical engine.

• A thermostat on the engine typically is usedto allow the engine to warm up and to regu-late engine temperature on the “hot” side ofthe cooling system.

• The cooling system design should accountfor expansion in the volume of coolant as theengine temperature increases. Coolantexpansion provisions for 6% over normal vol-ume is required.

• The system must be designed so that there isalways a positive head on the engine coolantpump.

• Proper flows for cooling depend on minimiz-ing the static and friction head on the enginecoolant pump. The generator set will not coolproperly if either the static or friction head lim-

itations of the coolant pump are exceeded.Consult the engine manufacturer for infor-mation on these factors for the specific gen-erator set selected. See Cooling Pipe SizingCalculations in this section for specificinstruction on sizing coolant piping and cal-culating static and friction head.

• Engine and remote cooling systems shouldbe provided with drain and isolation provi-sions to allow convenient service and repairof the engine. See example drawings in thissection for locations of drains and valves typ-

ically used in various applications.

Skid–Mounted Radiator

A generator set with a skid–mounted radiator(Figure 6–15) is an integral skid–mounted cool-ing and ventilating system. The skid–mountedradiator cooling system is often considered to bethe most reliable and lowest cost cooling systemfor generator sets, because it requires the leastamount of auxiliary equipment, piping, controlwiring, and coolant, and minimizes work to bedone at the jobsite on the generator set cooling

system. The radiator fan is usually mechanicallydriven by the engine, further simplifying thedesign. Electric fans are used in some applica-tions to allow more convenient control of theradiator fan based on the temperature of theengine coolant. This is particularly useful inseverely cold environments.





FILL/PRESSURECAP

RADIATORVENT TUBE

FROM ENGINE VENT LINE(5% OF COOLANT FLOW)

FILL NECK WITH VENTHOLE TO CREATE

THERMAL EXPANSIONSPACE

TOP TANK VOLUMEMUST EQUAL 10% OFTOTAL SYSTEM VOL-

UME (DRAWDOWNCAPACITY) PLUS 5%

FORTHERMAL EXPANSION

DEAERATED/FILL/MAKEUPCOOLANT FROM FROM TOP TANK

(ABOVE BAFFLE PLATE) TOLOWEST POINT IN SYSTEM

HOT COOLANT FROM

ENGINE TO RADIATOR(BELOW BAFFLEPLATE)

SEALEDBAFFLEPLATE

Figure 6–14. Deaeration Type of Radiator Top Tank

COOLAIR

HOTAIR



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AIR INLET

RADIATOR

FLEXIBLE DUCT CONNECTOR WIND/NOISE BARRIER

ENGINE-DRIVEN FAN

PREVAILING WINDS

ENGINE-DRIVENCOOLANT PUMP

Figure 6–15. Factory-Mounted Radiator Cooling





Since the genset manufacturer typically designsskid–mounted cooling systems, the system canbe prototype tested to verify the overall perfor-mance of the system in a laboratory environment.An instrumented, controlled, laboratory environ-ment is useful in easily verifying the performance

of a cooling system. Often physical limitations ata project site can limit the accuracy or practicalityof design verification testing.

The major disadvantage of the skid–mountedradiator is the requirement to move a relativelylarge volume of air through the generator room,since the air flow through the room must be suffi-cient for evacuating heat radiated from the gener-ator set and for removing heat from the enginecoolant. See Ventilation in this section for detailsof ventilation system design and calculations

related to ventilation system design. The enginefan will often provide sufficient ventilation for theequipment room, eliminating the need for otherventilating devices and systems.

Remote Radiator

Remote radiator systems are often used whensufficient ventilation air for a skid–mounting cool-ing system can not be provided in an application.Remote radiators do not eliminate the need for generator set room ventilation, but they will reduce it. If a remote radiator cooling system is

required, the first step is to determine what type ofremote system is required. This will be deter-mined by calculation of the static and friction headthat will be applied to the engine based on itsphysical location.

If calculations reveal that the generator set cho-sen for the application can be plumbed to aremote radiator without exceeding its static andfriction head limitations, a simple remote radiatorsystem can be used. See Figure 6–16.

If the friction head is exceeded, but static head isnot, a remote radiator system with auxiliary cool-ant pump can be used. See Figure 6–14 andRemote Radiator With Auxiliary Coolant Pump, inthis section.

If both the static and friction head limitations of theengine are exceeded, an isolated cooling systemis needed for the generator set. This mightinclude a remote radiator with hot well, or a liquid– to–liquid heat exchanger–based system.

Whichever system is used, application of aremote radiator to cool the engine requires care-ful design. In general, all the recommendationsfor skid mounted radiators also apply to remoteradiators. For any type of remote radiator system,consider the following:

• It is recommended that the radiator and fanbe sized on the basis of a maximum radiatortop tank temperature of 200o F (93o C) and a115 percent cooling capacity to allow for foul-ing. The lower top tank temperature (lower

than described in Engine Cooling) compen-sates for the heat loss from the engine outletto the remote radiator top tank. Consult theengine manufacturer for information on heatrejected to the coolant from the engine, andcooling flow rates9.

• The radiator top tank or an auxiliary tankmust be located at the highest point in thecooling system. It must be equipped with: anappropriate fill/pressure cap, a system fill lineto the lowest point in the system (so that thesystem can be filled from the bottom up), anda vent line from the engine that does not haveany dips or traps. (Dips and overhead loopscan collect coolant and prevent air from vent-ing when the system is being filled.) Themeans for filling the system must also belocated at the highest point in the system,and a low coolant level alarm switch must belocated there.

• The capacity of the radiator top tank or auxil-iary tank must be equivalent to at least 17percent of the total volume of coolant in thesystem to provide a coolant “drawdowncapacity” (11percent) and space for thermal

expansion (6 percent). Drawdown capacityis the volume of coolant that can be lost byslow, undetected leaks and the normal reliev-ing of the pressure cap before air is drawninto the coolant pump. Space for thermalexpansion is created by the fill neck when acold system is being filled. See Figure 6–14.

9 Information on Cummins Power Generation products is pro-

vided in the Cummins Power Suite.





* – THE VENT LINE MUST NOT HAVE ANY DIPS OR TRAPS THAT WILL COLLECT COOLANT AND PREVENT AIR FROM VENTING WHEN THE SYSTEM IS BEING

FILLED WITH COOLANT.

** – THE FILL/MAKEUP LINE MUST BE ROUTED DIRECTLY TO THE LOWEST POINT IN THE PIPING SYSTEM SO THAT THE SYSTEM CAN BE FILLED FROM

THE BOTTOM UP AND NOT TRAP AIR.

VENTILATINGAIR INLET



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7–12 PSI (48-83 kPa)PRESSURE CAP

REMOTERADIATOR

VENTILATINGFAN

VENTLINE*

PREVAILING WINDS

HOT COOLANT LINETO RADIATOR

DRAIN VALVE ATLOWEST POINT

IN SYSTEM

COOLANTRETURN TO

ENGINE

SYSTEMFILL/MAKEUP

LINE**

HOT AIR

SAE 20R1 OR EQUIVALENTHOSE DOUBLE CLAMPED

AT BOTH ENDS WITH“CONSTANT-TORQUE“

HOSE CLAMPS

GATE ORBALL VALVESTO ISOLATEENGINE FORSERVICING

Figure 6–16. Remote Radiator Cooling (Deaeration Type System, See Figure 6–14)





• To reduce radiator fin fouling, radiators thathave a more open fin spacing (nine fins orless per inch) should be considered for dirtyenvironments.

• Coolant friction head external to the engine(pressure loss due to pipe, fitting, and radia-

tor friction) and coolant static head (height ofliquid column measured from crankshaftcenterline) must not exceed the maximumvalues recommended by the enginemanufacturer10. See the example calcula-tion in this section for a method of calculatingcoolant friction head. If a system configura-tion cannot be found that allows the engine tooperate within static and friction head limita-tions, another cooling system type should beused.

NOTE: Excessive coolant static head (pressure) can cause the coolant pump shaft seal to leak. Excessive coolant friction head (pressure loss) will result in insufficient engine cooling.

• Radiator hose 6 to 18 inches (152 to 457mm)long, complying with SAE 20R1, or an equiv-alent standard, should be used to connectcoolant piping to the engine to take up gener-ator set movement and vibration.

• It is highly recommended that the radiatorhoses be clamped with two premium grade“constant–torque” hose clamps at each end

to reduce the risk of sudden loss of enginecoolant due to a hose slipping off under pres-sure. Major damage can occur to an engine ifit is run without coolant in the block for just afew seconds.

• A drain valve should be located at the lowestpart of the system.

• Ball or gate valves (globe valves are toorestrictive) are recommended for isolatingthe engine so that the entire system does nothave to be drained to service the engine.

• Remember that the generator set must elec-

trically drive remote radiator fan, ventilatingfans, coolant pumps, and other accessoriesrequired for operation in remote coolingapplications. So, the kW capacity gained bynot driving a mechanical fan is generally con-

10 Data for Cummins engines is in the Power Suite.

sumed by the addition of electrical devicesnecessary in the remote cooling system.Remember to add these electrical loads tothe total load requirement for the generatorset.

• See Ventilation General Guidelines and

Heat Exchanger or Remote RadiatorApplications, both in this section, concerninggenerator room ventilation when remotecooling is used.

Deaeration Type Remote Radiator System

A deaeration type of radiator top tank (also knowas a sealed top tank) or auxiliary tank must be pro-vided. In this system, a portion of the coolant flow(approximately 5 percent) is routed to the radiatortop tank, above the baffle plate. This allows airentrained in the coolant to separate from the cool-

ant before the coolant returns to the system. Con-sider the following:

• Engine and radiator vent lines must rise with-out any dips or traps that will collect coolantand prevent air from venting when the sys-tem is being filled. Rigid steel or high densitypolystyrene tubing is recommended for longruns, especially if they are horizontal, to pre-vent sagging between supports.

• The fill/makeup line should also rise withoutany dips from the lowest point in the piping

system to the connection at the radiator toptank or auxiliary tank. No other piping shouldbe connected to it. This arrangement allowsthe system to be filled from bottom up withouttrapping air and giving a false indication thatthe system is full. With proper vent and fillline connections, it should be possible to fillthe system at a rate of at least 5 gpm (19L/Min) (approximately the flow rate of a gar-den hose).

Remote Radiator with Auxiliary Coolant

PumpA remote radiator with an auxiliary coolant pump(Figure 6–17) can be used if coolant frictionexceeds the engine manufacturer’s maximumrecommended value, and static head is withinspecifications. In addition to the considerationsunder Remote Radiators, consider the following:





Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç Ç

AUXILIARYCOOLANT PUMP

BYPASS GATEVALVE

GATE OR BALL VALVES TO ISOLATEENGINE FOR SERVICING

RADIATORVENT LINE

7–12 PSIPRESSURE CAP

AUXILIARY TANKALTERNATIVE TO A DEAERATION-TYPE

RADIATOR. VOLUME CAPACITY MUST BE ATLEAST 15% OF SYSTEM COOLANT VOLUME

REMOTE RADIATORASSEMBLY

ENGINE VENTLINE

SYSTEM FILL/MAKEUPLINE

HOT COOLANT LINETO RADIATOR

COOLANT RETURNTO ENGINE

Figure 6–17. Remote Radiator With Auxiliary Coolant Pump and Auxiliary Tank

• An auxiliary pump and motor must be sizedfor the coolant flow recommended by theengine manufacturer and develop enoughpressure to overcome the excess coolantfriction head calculated by the method shownin the previous example.

NOTE: One foot of pump head (pump manufacturer’s data) is equivalent to 0.43 PSI of coolant friction head

(pressure loss) or one foot of coolant static head (height of liquid column).

• A bypass gate valve (globe valves are toorestrictive) must be plumbed in parallel withthe auxiliary pump, for the following reasons: – To allow adjustment of the head devel-

oped by the auxiliary pump (the valve isadjusted to a partially–open position to





recirculate some of the flow backthrough the pump).

– To allow operation of the generator setunder partial load if the auxiliary pumpfails (the valve is adjusted to a fully openposition).

• Coolant pressure at the inlet to the enginecoolant pump, measured while the engine isrunning at rated speed, must not exceed themaximum allowable static head shown onthe recommended generator set Specifica-tion Sheet. Also, for deaeration type coolingsystems (230/200 kW and larger generatorsets), auxiliary pump head must not forcecoolant through the make–up line into theradiator top tank or auxiliary tank. In eithercase, the pump bypass valve must beadjusted to reduce pump head to an accept-

able level.• Since the engine of the generator set doesnot have to mechanically drive a radiator fan,there may be additional kW capacity on theoutput of the generator set. To obtain the netpower available from the generator set, addthe fan load indicated on the generator setSpecification Sheet to the power rating of theset. Remember that the generator set mustelectrically drive the remote radiator fan, ven-tilating fans, coolant pumps, and otheraccessories required for the set to run for

remote radiator applications. So, the kWcapacity gained by not driving a mechanicalfan is generally consumed by the addition ofelectrical devices necessary in the remotecooling system.

Remote Radiator With Hot Well

A remote radiator with a hot well (Figure 6–18)can be used if the elevation of the radiator abovethe crankshaft centerline exceeds the allowablecoolant static head on the recommended genera-tor set Specification Sheet. In a hot well system,

the engine coolant pump circulates coolantbetween engine and hot well and an auxiliarypump circulates coolant between hot well andradiator. A hot well system requires carefuldesign.

In addition to the considerations under RemoteRadiator, consider the following:

• The bottom of the hot well should be abovethe engine coolant outlet.

• Coolant flow through the hot well/radiator cir-cuit should be approximately the same ascoolant flow through the engine. The radiatorand the auxiliary pump must be sized accord-

ingly. Pump head must be sufficient to over-come the sum of the static and friction headsin the hot well/radiator circuit.

NOTE: One foot of pump head (pump manufacturer’s data) is equivalent to 0.43 PSI of coolant friction head (pressure loss) or one foot of coolant static head (height of liquid column).

• The liquid holding capacity of the hot wellshould not be less than the sum of the follow-ing volumes: – ¼ of the coolant volume pumped per

minute through the engine (e.g., 25 gal-lons if the flow is 100 gpm) (100 liters ifthe flow is 400 l/min), plus

– ¼ of the coolant volume pumped perminute through the radiator (e.g., 25 gal-lons if the flow is 100 gpm) (100 liters ifthe flow is 400 l/min), plus

– Volume required to fill the radiator andpiping, plus 5 percent of total system vol-ume for thermal expansion.

• Careful design of the inlet and outlet connec-tions and baffles is required to minimize cool-

ant turbulence, allow free deaeration andmaximize blending of engine and radiatorcoolant flows.

• Coolant must be pumped to the bottom tankof the radiator and returned from the top tank,otherwise the pump will not be able to com-pletely fill the radiator.

• The auxiliary pump must be lower than thelow level of coolant in the hot well so that it willalways be primed.

• The radiator should have a vacuum reliefcheck valve to allow drain down to the hot

well.• The hot well should have a high volumebreather cap to allow the coolant level to fallas the auxiliary pump fills the radiator andpiping.





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AUXILIARY COOLANT PUMP FORHOT WELL/RADIATOR CIRCUIT

REMOTE RADIATORASSEMBLY

VACUUM BREAK

HOT WELL

BREATHER CAP

ENGINEVENT LINE

HOT ENGINECOOLANT

RETURNTO ENGINE

BAFFLES

PUMP COOLANTTO RADIATORBOTTOM TANK

Figure 6–18. Remote Radiator With Hot Well and Auxiliary Coolant Pump





• Remember that the generator set must elec-trically drive remote radiator fan, ventilatingfans, coolant pumps and other accessoriesrequired for operation in remote coolingapplications. So, the kW capacity gained bynot driving a mechanical fan is generally con-

sumed by the addition of electrical devicesnecessary in the remote cooling system.Remember to add these electrical loads tothe total load requirement for the generatorset.

Multi–Loop Engine Cooling–Remote Radia-tors

Some engine designs incorporate more than onecooling loop and therefore require more than oneremote radiator or heat exchanger circuit forremote cooling applications. These engines uti-

lize various approaches to achieve Low Tempera-ture Aftercooling (LTA) of the intake air for com-bustion. A primary reason behind the creation ofthese designs is their affect on improvement ofexhaust emissions levels. Not all of these enginedesigns however are easily adaptable for remotecooling.

Two–Pump Two–Loop: A common approach forlow temperature aftercooling is to have two com-plete and separate cooling circuits with two radia-tors, two coolant pumps and separate liquid cool-

ant for each. One circuit cools the engine water jackets, the other cools the intake combustion airafter turbocharging. For remote cooling, theseengines require two complete separate remoteradiators or heat exchangers. Each will have itsown specifications of temperatures, pressurerestrictions, heat rejection, etc. that must be metin the remote systems. This data is available fromthe engine manufacturer. Essentially, two circuitsmust be designed, each require all the consider-ations of, and must meet all the criteria of a singleremote system. See Figure 6–19.

Note: Radiator placement for the LTA circuit can be critical to achieving adequate removal of heat energy required for this circuit. When the LTA and jacket water radiators are placed back to back with a single fan, the LTA radiator should be placed upstream in the air flow so as to have the coolest air traveling over it.

One–Pump, Two–Loop : Occasionally enginedesigns accomplish low temperature aftercoolingthrough the use of two cooling circuits within theengine, two radiators but only one coolant pump.These systems are not recommended for remotecooling applications due to the difficulty of achiev-

ing balanced coolant flows and thus proper cool-ing of each circuit.

Air–to–Air Aftercooling: Another approach toachieving low temperature aftercooling is to usean air–to–air radiator cooling circuit instead of anair–to–liquid design as described above. Thesedesigns route the turbocharged air through aradiator to cool it before entering the intake man-ifold(s). These systems are not generally recom-mended for remote cooling for two reasons. First,the entire system piping and radiator are operate

under turbocharged pressure. Even the smallestpinhole leak in this system will significantlydecrease turbo charger efficiency and is unac-ceptable. Second, the length of the air tube run tothe radiator and back will create a time lag inturbocharging performance and potentially resultin pressure pulses that will impede proper perfor-mance of the engine.

Radiators for Remote Radiator Applications

Remote Radiators : Remote radiators are avail-able in a number of configurations for generator

set applications. In all cases, the remote radiatoruses an electric motor–driven fan that should befed directly from the output terminals of the gener-ator set. A surge tank must be installed at thehighest point in the cooling system. The capacityof the surge tank must be at least 5% of the totalsystem cooling capacity. The pressure capinstalled there is selected based on the radiatorsizing. Vent lines may also need to be routed tothe surge tank. A sight glass is a desirable featureto display level of coolant in the system. It shouldbe marked to show normal level cold and hot. A

coolant level switch is a desirable feature to indi-cate a potential system failure when coolant levelis low.

Some remote radiator installations operate withthermostatically controlled radiator fans. If this isthe case, the thermostat is usually mounted at theradiator inlet.





Engine RadiatorOutlet

LTA RadiatorOutlet

Side–by–Side Engine/Low Temperature Aftercooling Radiators

Figure 6–19. A Horizontal Remote Radiator and Aftercooler Radiator

Radiators may be either horizontal type (radiator

core is parallel to mounting surface) or verticaltype (radiator core is perpendicular to mountingsurface) (Figure 6–19). Horizontal radiators areoften selected because they allow the largestnoise source in the radiator (the mechanical noiseof the fan) to be directed up, where it is likely thatthere are no receivers that may be disturbed bythe noise. However, horizontal radiators can bedisabled by snow cover or ice formation, so theyare often not used in cold climates.

Remote radiators require little maintenance, but

when they are used, if they are belt driven, annualmaintenance should include inspection and tight-ening of the fan belts. Some radiators may usere–greasable bearings that require regular main-tenance. Be sure that the radiator fins are cleanand unobstructed by dirt or other contaminants.

Skid–Mounted Heat Exchanger: The engine,

pump and liquid–to–liquid heat exchanger form aclosed, pressurized cooling system (Figure6–20). The engine coolant and raw cooling water(the “cold” side of the system) do not mix. Consid-er the following:

• The generator set equipment room willrequire a powered ventilating system. SeeVentilation in this section for information onthe volume of air required for proper ventila-tion.

• Since the engine of the generator set does

not have to mechanically drive a radiator fan,there may be additional kW capacity on theoutput of the generator set. To obtain the netpower available from the generator set, addthe fan load indicated on the generator setSpecification Sheet to the power rating of the





HOT AIR



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RAW WATERSUPPLY

RAW WATERDISCHARGE

ENGINE-MOUNTEDHEAT EXCHANGER

PREVAILING WINDS

VENTILATING FANVENTILATING AIR INLET

FLEXIBLEWATER CONNECTIONS

Figure 6–20. Factory-Mounted Heat Exchanger Cooling

set. Remember that the generator set mustelectrically drive remote radiator fan, venti-lating fans, coolant pumps and other acces-sories required for the set to run for remoteradiator applications. So, the kW capacitygained by not driving a mechanical fan isgenerally consumed by the addition of elec-trical devices necessary in the remote cool-ing system.

• A pressure–reducing valve must be providedif water source pressure on the cold side ofthe system exceeds the pressure rating ofthe heat exchanger. Consult heat exchangermanufacturer for heat exchanger informa-tion11.

11 Data for heat exchangers provided on Cummins Power

Generation products that are provided with factory–mounted

heat exchangers is available in the Cummins Power Suite.

• The heat exchanger and water piping mustbe protected from freezing if the ambienttemperature can fall below 32 F (0 C).

• Recommended options include a thermo-static water valve (non–electrical) to modu-late water flow in response to coolant tem-perature and a normally closed (NC)battery–powered shut off valve to shut off thewater when the set is not running.

• There must be sufficient raw water flow toremove the Heat Rejected To Coolant indi-cated on the generator set SpecificationSheet. Note that for each 1° F rise in temper-ature, a gallon of water absorbs approxi-mately 8 BTU (specific heat). Also, it is rec-ommended that the raw water leaving theheat exchanger not exceed 140° F (60° C).Therefore:





Raw WaterRequired (gpm)

Heat Rejected

∆ T ( F) • c

Btumin

8 BtuF–Gallon

=

Where:∆ T = Temperature rise of water across core

c = Specific heat of water

If a set rejects 19,200 BTU per minute andthe raw water inlet temperature is 80° F,allowing a water temperature rise of 60° F:

Raw Water Required =19,200

60 • 8= 40 gpm

Dual Heat Exchanger Systems: Dual heatexchanger cooling systems (Figure 6–21) can bedifficult to design and implement, especially if a

secondary cooling system such as a radiator isused to cool the heat exchanger. In these situa-tions the remote device might be significantlylarger than expected, since the change in temper-ature across the heat exchanger is relativelysmall. These systems should be designed for the

REMOTERADIATOR



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É É É É É É É É É É É É É É É É É É É É É É É É É É É É

PRESSURE CAPHEAT EXCHANGERHOT COOLANT OUT

TO SECONDARYEXCHANGER

DRAIN VALVE ATLOWEST POINT

IN SYSTEM

COOLANTRETURN TO

HEATEXCHANGER

Figure 6–21. Dual Heat Exchanger System (With Secondary Liquid–to–Air Cooler)





specific application, considering the require-ments of the engine, liquid to liquid heat exchang-er, and remote heat exchanger device12.

Cooling Tower Applications: Cooling tower sys-tems can be used in applications where the ambi-

ent temperature does not drop below freezing,and where the humidity level is low enough toallow efficient system operation. Typical arrange-ment of equipment is shown in Figure 6–22.

Cooling tower systems typically utilize a skid– mounted heat exchanger whose “cold” side toplumbed to the cooling tower. The balance of thesystem is composed of a “raw” water pump (theengine cooling pump circulates coolant on the“hot” side of the system) to pump the coolingwater to the top of the cooling tower, where it is

cooled by evaporation, and then returned to the12 Skid–mounted heat exchangers provided by Cummins

Power Generation are typically not suitable for use in dual

heat exchanger applications. Dual heat exchanger arrange-

ments require carefully matched components.

generator set heat exchanger. Note that the sys-tem requires make–up water provisions, sinceevaporation will continuously reduce the amountof cooling water in the system. The “hot” side ofthe heat exchanger system is similar to thatdescribed earlier under skid mounted heat

exchanger.

Fuel Cooling with Remote Radiators

Generator sets occasionally include fuel coolersto meet the requirements for specific engines. Ifan engine is equipped with a separate fuel cooler,these cooling requirements must be accommo-dated in the cooling system design. It is not oftenfeasible to, and often against code to pipe fuel to aremote location. One approach would be toinclude a radiator and fan for fuel cooling withinthe generator space and account for the heatrejection in the room ventilation design. Anothermight be a heat exchanger type fuel cooling sys-tem utilizing a remote radiator or separate watersupply for the coolant side.

ALT

ENGINE

HE

NRV

NRV

Figure 6–22. Diagram of Representative Cooling Tower Application





Cooling Pipe Sizing Calculations

The preliminary layout of piping for a remoteradiator cooling system shown in Figure 6–16calls for 60 feet of 3–inch diameter pipe, threelong sweep elbows, two gate valves to isolate theradiator for engine servicing and a tee to connectthe fill/makeup line. The recommended genera-tor set Specification Sheet indicates that coolantflow is 123 GPM and that the allowable frictionhead is 5 PSI.

This procedure involves determining the pres-sure loss (friction head) caused by each elementand then comparing the sum of the pressurelosses with the maximum allowable friction head.

1. Determine the pressure loss in the radiatorby referring to the radiator manufacturer’s

data. For this example, assume the pressureloss is 1 psi at a flow of 135 gpm.

2. Find the equivalent lengths of all fittings andvalves by using Table 6–3 and add to thetotal run of straight pipe.

Three Long Sweep Elbows–3 x 5.2 15.6

Two Gate Valves (Open)–2 x 1.7 3.4

Tee (Straight Run) 5.2

60 Feet Straight Pipe 60.0

Equivalent Length of Pipe (Feet) 84.2

3. Find the back pressure at the given flow perunit length of pipe for the nominal pipe diam-eter used in the system. In this example, 3inch nominal pipe is used. Following thedashed lines in Figure 6–23, 3 inch pipecauses a pressure loss of approximately1.65 psi per 100 foot of pipe.

4. Calculate the pressure loss in the piping asfollows:

Piping Loss = 84.2 feet x 1.65 psi = 1.39 psi100 feet

5. The total system loss is the sum of the pipingand radiator losses:

Total Pressure Loss = 1.39 psi piping + 1.00psi radiator = 2.39 psi

TYPE OF FITTING NOMINAL INCH (MILLIMETER) PIPE SIZE

1/2(15)

3/4(20)

1(25)

1–1/4(32)

1–1/2(40)

2(50)

2–1/2(65)

3(80)

4(100)

5(125)

6(150)

905Std. Elbow orRun of Tee Reduced½.

1.7(0.5)

2.1(0.6)

2.6(0.8)

3.5(1.1)

4.1(1.2)

5.2(1.6)

6.2(1.9)

7.7(2.3)

10(3.0)

13(4.0)

15(4.6)

905Long SweepElbow or Straight

Run Tee

1.1(0.3)

1.4(0.4)

1.8(0.5)

2.3(0.7)

2.7(0.8)

3.5(1.1)

4.2(1.3)

5.2(1.6)

6.8(2.1)

8.5(2.6)

10(3.0)

455Elbow 0.8(0.2)

1.0(0.3)

1.2(0.4)

1.6(0.5)

1.9(0.6)

2.4(0.7)

2.9(0.9)

3.6(1.1)

4.7(1.4)

5.9(1.8)

7.1(2.2)

Close Return Bend 4.1(1.2)

5.1(1.6)

6.5(2.0)

8.5(2.6)

9.9(3.0)

13(4.0)

15(4.6)

19(5.8)

25(7.6)

31(9.4)

37(11.3)

TEE, Side Inlet orOutlet

3.3(1.0)

4.2(1.3)

5.3(1.6)

7.0(2.1)

8.1(2.5)

10(3.0)

12(3.7)

16(4.9)

20(6.1)

25(7.6)

31(9.4)

Foot Valve andStrainer

3.7(1.1)

4.9(1.5)

7.5(2.3)

8.9(2.7)

11(3.4)

15(4.6)

18(5.5)

22(6.7)

29(8.8)

36(11.0)

46(14.0)

Swing Check Valve,Fully Open

4.3(1.3)

5.3(1.6)

6.8(2.1)

8.9(2.7)

10(3.0)

13(4.0)

16(4.9)

20(6.1)

26(7.9)

33(10.1)

39(11.9)

Globe Valve, Fully

Open

19

(5.8)

23

(7.0)

29

(8.8)

39

(11.9)

45

(13.7)

58

(17.7)

69

(21.0)

86

(26.2)

113

(34.4)

142

(43.3)

170

(51.8)Angle Valve, Fully

Open9.3

(2.8)12

(3.7)15

(4.6)19

(5.8)23

(7.0)29

(8.8)35

(10.7)43

(13.1)57

(17.4)71

(21.6)85

(25.9)

Gate Valve, FullyOpen

0.8(0.2)

1.0(0.3)

1.2(0.4)

1.6(0.5)

1.9(0.6)

2.4(0.7)

2.9(0.9)

3.6(1.1)

4.7(1.4)

5.9(1.8)

7.1(2.2)

Table 6–3. Equivalent Lengths of Pipe Fittings and Valves in Feet (Meters)





COOLANT FLOW – U.S. Gallons Per Minute (liters/min)

0.1

0.5

1.0

5.0

0.2

0.3

0.4

2.0

3.0

4.02 (50) 2.5 (65) 3 (80) 4 (100) 5 (125)

6 (150)

1.5 (40)

P R E S S U R E L O S S (

P S I P E R 1 0 0 F O O T O F P I P E L E N G T H )

1 0

2 0

3 0

4 0

5 0

1 0 0

2 0 0

4 0 0

5 0 0

1 , 0 0 0

3 0 0

( k P a P e r 3 0 M e t e r s o f P i p e L e n g t h )

(35)

(3.5)

(7.0)

(1.4)

(2.1)

(5.9)

(14)

(21)

(28)

(0.7) ( 3 8 )

( 7 6 )

( 1 1 4 )

( 1 5 0 )

( 1 9 0 )

( 3 8 0 )

( 7 6 0 )

( 1 5 0 0 )

( 1 9 0 0 )

( 3 8 0 0 )

( 1 1 4 0 )

Figure 6–23. Frictional Pressure Losses for Inch (mm) Diameter Pipes

6. The calculation for this example indicatesthat the layout of the remote radiator coolingsystem is adequate in terms of coolant fric-tion head since it is not greater than theallowable friction head. If a calculation indi-cates excessive coolant friction head, repeat

the calculation using the next larger pipesize. Compare the advantages and disad-vantages of using larger pipe with that ofusing an auxiliary coolant pump.

Coolant Treatment: Antifreeze (ethylene or pro-pylene glycol base) and water are mixed to lowerthe freezing point of the cooling system and toraise the boiling point. Refer to Table 6–4 for

determining the concentration of ethylene or pro-pylene glycol necessary for protection against thecoldest ambient temperature expected. Anti-freeze/water mixture percentages in the range of30/70 to 60/40 are recommended for mostapplications.

NOTE: Propylene glycol based antifreeze is less toxic than ethylene based antifreeze, offers superior liner protection and eliminates some fluid spillage and disposal reporting requirements. However, it is not as effective coolant as ethylene glycol, so cooling system capacity (maximum operating temperature at full load)will be diminished somewhat by use of propylene glycol.





Cummins Power Generation generator sets,125/100 kW and larger, are equipped withreplaceable coolant filtering and treating ele-ments to minimize coolant system fouling andcorrosion. They are compatible with most anti-freeze formulations. For smaller sets, the anti-

freeze should contain a corrosion inhibitor.

Generator sets with engines that have replace-able cylinder liners require supplemental coolantadditives (SCAs) to protect against liner pittingand corrosion, as specified in the engine and gen-erator set operator’s manuals.

Ventilation

General Guidelines

Ventilation of the generator room is necessary to

remove the heat expelled from the engine, alter-nator and other heat generating equipment in thegenset room, as well as to remove potentiallydangerous exhaust fumes and to provide com-bustion air. Poor ventilation system design leads

to high ambient temperatures around the genera-tor set that can cause poor fuel efficiency, poorgenerator set performance, premature failure ofcomponents, and overheating of the engine. Italso results in poor working conditions around themachine.

Selection of the intake and exhaust ventilationlocations is critical to the proper operation of thesystem. Ideally, the inlet and exhaust allow theventilating air to be pulled across the entire gener-ator room. The effects of prevailing winds mustbe taken in to consideration when determiningexhaust air location. These effects can seriouslydegrade skid–mounted radiator performance. Ifthere is any question as to the wind speed anddirection, blocking walls can be used to preventwind blowing into the engine exhaust air outlet

(See Figure 6–24). Care should also be taken toavoid ventilation exhausting into a recirculationregion of a building that forms due to prevailingwind direction.

MIXTURE PERCENTAGES (ANTIFREEZE/WATER)

MIXTURE BASE0/100 30/70 40/60 50/50 60/40 95/5

FREEZING POINT32° F(0° C)

4° F(–16° C)

–10° F(–23° C)

–34° F(–36° C)

–65° F(–54° C)

8° F(–13° C)

ETHYLENE GLYCOL

BOILING POINT212° F

(100° C)220° F

(104° C)222° F

(106° C)226° F

(108° C)230° F

(110° C)345° F

(174° C)

FREEZING POINT32° F(0° C)

10° F(–12° C)

–6° F(–21° C)

–27° F(–33° C)

–56° F(–49° C)

–70° F(–57° C)

PROPYLENE GLYCOL

BOILING POINT212° F

(100° C)216° F

(102° C)219° F

(104° C)222° F

(106° C)225° F

(107° C)320° F

(160° C)

Table 6–4. Freezing and Boiling Points vs. Concentration of Antifreeze





Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

COOLAIR

HOTAIR


Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á


PREVAILING WINDS

RADIATOR WIND/NOISEBARRIER

ENGINE-DRIVENFAN

THERMOSTATICALLYCONTROLLED LOUVER

NOT LESS THANHEIGHT OF RADIATOR

OUTLET AIRDAMPER

MEASURE STATIC PRESSURE WITH-IN 6 INCHES (150 mm) OF THERADIATOR. SEE Figure NO TAG

FLEXIBLE DUCTCONNECTOR

INLET AIRDAMPER

Figure 6–24. Factory-Mounted Radiator Cooling

Ventilating air that is polluted with dust, fibers, orother materials may require special filters on theengine and/or alternator to allow proper operationand cooling, particularly in prime power applica-tions. Consult the factory for information on use ofgenerator sets in environments that includechemical contamination.

Engine crankcase ventilation systems canexhaust oil–laden air into the generator set room.The oil can then be deposited on radiators or oth-

er ventilation equipment, impeding their opera-tion. Use of crankcase ventilation breather trapsor venting of the crankcase to outdoors is bestpractice.

Attention should be give to the velocity of intakeair brought into the generator set room. If the airflow rate is too high, the generator sets will tend topull rain and snow into the generator set room

when they are running. A good design goal is tolimit air velocity to between 500–700 f/min(150–220 m/min).

In cold climates, the radiator exhaust air can berecirculated to modulate the ambient air tempera-ture in the generator set room. This will help thegenerator set warm up faster, and help to keepfuel temperatures higher than the cloud point ofthe fuel. If recirculation dampers are used, theyshould be designed to “fail closed”, with the main

exhaust dampers open, so that the generator setcan continue to operate when required. Design-ers should be aware that the generator set roomoperating temperature will be very close to theoutdoor temperature, and either not route waterpiping through the generator set room, or protectit from freezing.





As ventilating air flows through an equipmentroom, it gradually increases in temperature, par-ticularly as it moves across the generator set.See Figure 6–25. This can lead to confusion asto temperature ratings of the generator set andthe overall system. Cummins Power Generation

practice is to rate the cooling system based on theambient temperature around the alternator. Thetemperature rise in the room is the differencebetween the temperature measured at the alter-nator, and the outdoor temperature. The radiatorcore temperature does not impact the systemdesign, because radiator heat is moved directlyout of the equipment room.

A good design goal for standby applications is tokeep the equipment room at not more than 125° F(50° C). However, limiting generator set room

temperature to 100° F (40° C) will allow the gener-ator set to be provided with a smaller, less expen-sive skid–mounted radiator package, and elimi-nate the need for engine de–rating due toelevated combustion air temperatures13. Be surethat the design specifications for the generatorset fully describe the assumptions used in thedesign of the ventilation system for the generatorset.

13 .Check the engine manufacturer’s data for information

on derating practice for a specific engine. Information on

Cummins Power Generation products is on the Power

Suite.

The real question then becomes, “What is themaximum temperature of outdoor air when thegenerator set will be called to operate?” This issimply a question of the maximum ambient tem-perature in the geographic region where the gen-erator set is installed.

In some areas of the northern United States forexample, the maximum temperature is likely tonot exceed 90° F. So, a designer could select theventilation system components based on a 10° Ftemperature rise with a 100° F generator set cool-ing system, or based on a 35° F temperature risewith a 125° F generator cooling system.

The key to proper operation of the system is to besure that the maximum operating temperatureand temperature rise decisions are carefully

made, and that the generator set manufacturerdesigns the cooling system (not just the radiator)for the temperatures and ventilation required.

The result of improper system design is that thegenerator set will overheat when ambient temper-atures and load on the generator set is high. Atlower temperatures or lower load levels the sys-tem may operate properly.

Air Flow Out

Air Flow In

90F 110F

125F

Figure 6–25. Typical Air Temperature Surrounding an Operating Genset





Air Flow Calculations

The required air flow rate to maintain a specifictemperature rise in the generator room isdescribed by the formula:

m =

Q

cp T d

Where:m = Mass flow rate of air into the room;

ft3 /min (m3 /min)Q = Heat rejection into the room from the

genset and other heat sources; BTU/min(MJ/min).

cp = Specific heat at constant pressure;0.241 BTU/lb– ° F (1.01x10 –3 MJ/kg– ° C).∆T = Temperature rise in the generator setroom over outdoor ambient; ° F (° C).

d = Density of air; 0.0754 lb/ft3 (1.21 kg/m3).Which can be reduced to:

0.241 • 0.0754 • ∆ Tm =

Q 55.0Q(ft3 /min)= ∆ T

OR:

Q

(1.01 • 103) • 1.21 • ∆ Tm =

818Q(m3 /min)= ∆ T

The total airflow required in the room is the calcu-lated value from this equation, plus the combus-tion air required for the engine14.

In this calculation the major factors are obviouslythe heat radiated by the generator set (and otherequipment in the room) and the allowable maxi-mum temperature rise.

Since the heat rejection to the room is fundamen-tally related to the kW size of the generator setand that rating is controlled by building electricalload demand, the major decision to be made bythe designer regarding ventilation is what allow-

able temperature rise is acceptable in the room.

14 Data required for calculations for specific Cummins Power

Generation generator sets can be found on the Cummins Pow-

er Suite. There may be significant differences in the variables

used in these calculations for various manufacturer’s products.

Field Testing of Ventilation Systems

Since it is difficult to test for proper operation, onefactor to view in system testing is the temperaturerise in the room under actual operating condi-tions, vs. the design temperature rise. If the tem-perature rise at full load and lower ambient tem-peratures is as predicted, it is more probable thatit will operate correctly at higher ambients andload levels.

The following procedure can be used for prelimi-nary qualification of the ventilation systemdesign:

1. Run the generator set at full load (1.0 powerfactor is acceptable) long enough for theengine coolant temperature to stabilize. Thiswill take approximately 1 hour.

2. With the generator set still running at ratedload, measure the ambient air temperature ofthe generator set room at the air cleaner inlet.

3. Measure the outdoor air temperature (in theshade).

4. Calculate the temperature differencebetween the outdoor temperature and thegenerator set room.

5. Verify that the design temperature rise of thegenerator room is not exceeded, and that themaximum top tank temperature of the engineis not exceeded.

If either the design temperature rise or top tanktemperature is exceeded, more detailed testing ofthe facility or corrections in the system design willbe required to verify proper system design.

Skid–Mounted Radiator Ventilation

In this configuration (Figure 6–24), the fan drawsair through inlet air openings in the opposite walland across the generator set and pushes itthrough the radiator which has flanges for con-necting a duct to the outside of the building.

Consider the following:

• The location of the generator room must besuch that ventilating air can be drawn directly





from the outdoors and discharged directly tothe outside of the building. Ventilation airshould not be drawn from adjacent rooms.Exhaust should also discharge on the radia-tor air discharge side of the building to reducethe likelihood of exhaust gases and soot

being drawn into the generator room with theventilating air.

• Ventilating air inlet and discharge openingsshould be located or shielded to minimize fannoise and the effects of wind on airflow.When used, the discharge shield should belocated not less than the height of the radia-tor away from the ventilation opening. Betterperformance is achieved at approximately 3times the radiator height. In restricted areas,turning vanes will help to reduce the restric-tion caused by the barriers added to the sys-

tem. When these are used, make provisionsfor precipitation run–off so that it is not routedinto the generator room.

• The airflow through the radiator is usuallysufficient for generator room ventilation. Seethe example calculation (under Air Flow Cal-culations in this section) for a method ofdetermining the airflow required to meetroom air temperature rise specifications.

• Refer to the recommended generator setSpecification Sheet for the design airflowthrough the radiator and allowable airflow

restriction. The allowable air flow restric-tion must not be exceeded. The staticpressure (air flow restriction) should be mea-sured, as shown in Figures 6–24, 6–26, and6–27, to confirm, before the set is placed inservice, that the system is not too restrictiveThis is especially true when ventilating air issupplied and discharged through long ducts,restrictive grilles, screens, and louvers.

• Rules of thumb for sizing ventilation air inletsand outlets have been applied or even pub-lished in the past but have more recentlybeen largely abandoned. Due to large varia-tion in louver performance and greaterdemands on installations for space, noise,etc., these rules of thumb have proven to beunreliable at best. Generally, louvermanufacturers have charts of restriction ver-sus airflow readily available. These chartscombined with duct design and any otherrestriction can be easily compared to thepublished specifications for the generator set

for a reliable method of determing accept-able restriction levels.

• For installations in North America, refer to theASHRAE (American Society of Heating,Refrigeration and Air Conditioning Engi-neers) publications for recommendations on

duct design if air ducts are required for theapplication. Note that the inlet duct musthandle combustion airflow (see the Specifi-cation Sheet) as well as ventilating airflowand must be sized accordingly.

• Louvers and screens over air inlet and outletopenings restrict airflow and vary widely inperformance. A louver assembly with narrowvanes, for example, tends to be more restric-tive than one with wide vanes. The effectiveopen area specified by the louver or screenmanufacturer should be used.

• Because the radiator fan will cause a slightnegative pressure in the generator room, it ishighly recommended that combustion equip-ment such as the building heating boilers notbe located in the same room as the generatorset. If this is unavoidable, it will be necessaryto determine whether there will be detrimen-tal effects, such as backdraft, and to providemeans (extra large room inlet openings and/ or ducts, pressurizing fans, etc.) to reducethe negative pressure to acceptable levels.

• In colder climates, automatic dampers

should be used to close off the inlet and outletair openings to reduce heat loss from thegenerator room when the generator set is notrunning. A thermostatic damper should beused to recirculate a portion of the radiatordischarge air to reduce the volume of cold airthat is pulled through the room when the setis running. The inlet and outlet dampersmust fully open when the set starts. Therecirculating damper should close fully at 60°F (16° C).

• Other than recirculating radiator dischargeair into the generator room in colder climates,all ventilating air must be discharged directlyoutside the building. It must not be used toheat any space other than the generatorroom.

• A flexible duct connector must be provided atthe radiator to prevent exhaust air recircula-tion around the radiator, to take up generatorset movement and vibration, and preventtransmission of noise.





Note: Duct adapters or radiator shrouds may not be designed to support weight or structure beyond that of the flexible duct adatper. Avoid supporting additional weight/equipment with the duct adapter or radiator shroud without sufficient analysis of strength and vibration considerations.

• Typically a generator set with a Skid– Mounted radiator is designed for full–powercooling capability in an ambient temperatureof 40° C while working against an externalcooling air flow resistance of 0.50 inch WC(Point A, Figure 6–27). External airflow

resistance is that caused by ducts, screens,dampers, louvers, etc. Operation in ambienttemperatures higher than the design temper-ature can be considered (Point B, Figure6–27, for example) if derating is acceptableand/or resistance to cooling airflow is less

than the resistance under which the coolingcapability was tested. (Less resistancemeans greater airflow through the radiator,offsetting the effect of higher air temperatureon radiator cooling capability.) Close con-sultation with the factory is required to attainacceptable generator set cooling capabilityin an elevated ambient temperature.

INCLINEDMANOMETER

0.01 IN WCACCURACY

LEAVE THE OTHER END OFTHE MANOMETER OPEN TO

THE GENERATOR ROOM

—STATIC PRESSURE PROBE—1/4 IN (6 mm) COPPER TUBE WITH PLUGGED END

AND 1/16 IN (1.5 mm) CROSS-DRILLED HOLES

ORIENT THE TIP PARALLEL WITH THE AIRSTREAM IN RADIATOR DISCHARGE DUCT WITHIN

6 INCHES (150 mm) OF THE RADIATOR

Figure 6–26. Recommended Instrumentation for Measuring Air Flow Restriction

100%

MAX

TEMP

40° CSTANDARD RATING @

40° C & 0.50 INCH WC

PERCENT RATED POWER

A M B I E N T T E M P E R A T U R E

POSSIBLE OPERATING POINT @ 0.00 INCH WC,

ELEVATED TEMPERATURE & REDUCED POWER

A

B

Figure 6–27. Figure Cooling Capability in Elevated Ambients





HOT AIR



Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á

Á Á


INLET AIR DAMP-ER

ENGINE-MOUNTED HEAT EXCHANGER

PREVAILING WINDS

VENTILATINGFAN

Figure 6–28. Ventilation for a Heat Exchanger Cooling System

Ventilating Heat Exchanger or RemoteRadiator Applications

A heat exchanger (Figure 6–28), or remote radia-tor cooling system might be selected because ofnoise considerations or because the air flowrestriction through long ducts would be greaterthan that allowed for the engine–driven radiatorfan. Consider the following:

• Ventilating fans must be provided for the gen-erator room. The ventilating fans must havethe capacity of moving the required flow ofventilating air against the airflow restriction.

See the following example calculation for amethod of determining the airflow requiredfor ventilation.

• A remote radiator fan must be sized primarilyto cool the radiator. Depending on its loca-tion, it might also be used to ventilate thegenerator room.

• The fan and air inlet locations must be suchthat the ventilating air is drawn forward overthe set.

In general, remote cooling systems have moreparasitic loads, so slightly less kW capacity isavailable from the generator set in those applica-tions. Remember to add the parasitic loads to thetotal load requirements for the generator set.

Example Ventilating Air Flow Calculation

The recommended generator set SpecificationSheet indicates that the heat radiated to the roomfrom the generator set (engine and generator) is4,100 BTU/min. The muffler and 10 feet of 5–inchdiameter exhaust pipe are also located inside thegenerator room. Determine the airflow required

to limit the air temperature rise to 30° F.

1. Add the heat inputs to the room from allsources. Table 6–5 indicates that the heatloss from 5–inch exhaust pipe is 132 BTU/ min per foot of pipe and 2,500 BTU/min fromthe muffler. Add the heat inputs to the roomas follows:Heat rejection from generator set 4,100Heat from Exhaust Pipe–10 x 132 1,320





Heat from Muffler 2,500Total Heat to Generator Room(BTU/Min) 7,920

2. The required airflow to account for heatrejection in the room is proportional to the

total heat input divided by the allowable roomair temperature rise (See Ventilation earlierin this section):

m =55 • 7920 = 14,520 ft3 /min

30

55 • Q

∆ T=

Fuel Supply

Diesel Fuel Supply

Diesel engine–driven generator sets are general-ly designed to operate on ASTM D975 number 2diesel fuel. Other fuels may be suitable for shortterm operation, if the fuel meets the quality andphysical characteristics described in Table 6–6.Consult engine manufacturer for use of otherfuels.

Care should be taken in the purchase of fuel andfilling of tanks to prevent ingress of dirt and mois-ture into the diesel fuel system. Dirt will clog injec-tors and cause accelerated wear in the finelymachined components of the fuel system. Mois-ture can cause corrosion and failure of thesecomponents.

Diesel generator sets consume approximately0.07 gal/hr per rated–kW (0.26 liters/hr per rated– kW) of fuel at full load, based on their standby rat-ing. For example, a 1000 kW standby generatorset will consume approximately 70 gal/hr (260

liters/hr) of fuel. The main fuel tank for a dieselgenerator set may be either a sub–base tank(mounted under the generator set skid), or aremote fuel tank. If the main (bulk) fuel tank isremote from the generator set, an intermediate(day) tank may be required to properly supply the

generator set. There are considerable differ-ences in engine capabilities between suppliers,so the fuel system design should be reviewed forthe specific generator set installed at a site.

The primary advantage of sub–base fuel tanks isthat the system can be factory designed andassembled to minimize site work. However, theymay not be a practical (or possible) selectionbased on main fuel tank capacity requirementsand code limitations, and the ability to access thetank for re–filling. When selecting a sub–base

fuel tank, be aware that the generator set controlsystem and other service maintenance pointsmay be raised to an impractical height. This mayrequire structures to be added to the installationto allow convenient service or meet operationalrequirements.

Because of the limitations of the mechanical fuelpumps on most engines, many installations thatrequire remote main (bulk) fuel tanks will alsorequire intermediate (day) tanks. The main tankmay be either above the generator set, or below it,

and each of these installations will require slightlydifferent intermediate tank designs and fuel con-trol systems.

Figures 6–29 and 6–30 illustrate typical dieselfuel supply systems.

PIPE DIAMETERINCHES (mm)

HEAT FROM PIPEBTU/MIN-FOOT (kJ/Min-Meter)

HEAT FROM MUFFLERBTU/MIN (kJ/Min)

1.5 (38) 47 (162) 297 (313)

2 (51) 57 (197) 490 (525)

2.5 (64) 70 (242) 785 (828)

3 (76) 84 (291) 1,100 (1,160)3.5 (98) 96 (332) 1,408 (1,485)

4 (102) 108 (374) 1,767 (1,864)

5 (127) 132 (457) 2,500 (2,638)

6 (152) 156 (540) 3,550 (3,745)

8 (203) 200 (692) 5,467 (5,768)

10 (254) 249 (862) 8,500 (8,968)

12 (305) 293 (1,014) 10,083 (10,638)

Table 6–5. Heat Losses From Uninsulated Exhaust Pipes and Mufflers





PROPERTY SPECIFICATIONS GENERAL DESCRIPTION

Viscosity(ASTM D445)

1.3–1.5 centisokes (mm/sec) at 40° C(104° F)

The injection system works most effectively when the fuel has theproper ”body” or viscosity. Fuels that meet the requirements of ASTM

1–D or 2–D fuels are satisfactory with Cummins fuel systems.

Cetane Number(ASTM D613)

42 minimum above C (32° F)45 minimum below 0° C (32° F)

Cetane number is a measure of the starting and warm–up characteris-tics of a fuel. In cold weather or in service with prolonged low loads, a

higher cetane number is desirable.

Sulphur Content(ASTM D129 or 1552) Not to exceed 0.5 mass percent (see note) Diesel fuels contain varying amounts of various sulphur compoundswhich increase oil acidity. A practical method of neutralizing high acidsfrom higher sulphur is to change oil more frequently or use a higher

TBN oil (TBN = 10 to 20) or both.The use of high sulphur fuel (above 0.5 mass percent )will result in

sulfate formation in the exhaust gas under high load continuous condi-tions. High sulphur fuel will also shorten the life of certain components

in the exhaust system, including the oxidation catalyst.

Active Sulphur(ASTM D130)

Copper strip corrosion not to exceed No.2rating after three hours at 50° C (122° F)

Some sulphur compounds in fuel are actively corrosive. Fuels with acorrosion rating of three or higher can cause corrosion problems.

Water andSediment

(ASTM D1796)

Not to exceed 0.05 volume percent The amount of water and solid debris in the fuel is generally classifiedas water and sediment. It is good practice to filter the fuel while it isbeing put into the fuel tank. More water vapor condenses in partiallyfilled tanks due to tank breathing caused by temperature changes.

Filter elements, fuel screens in the fuel pump, and fuel inlet connec-tions on injectors, must be cleaned or replaced whenever they

become dirty. These screens and filters, in performing their intended

function, will become clogged when using a poor or dirty fuel and willneed replacing more often.

Carbon Residue(Ramsbottom, ASTMD254 or Conradson,

ASTM D189)

Not to exceed 0.35 mass percent on 10volume percent residuum

The tendency of a diesel fuel to form carbon deposits in an engine canbe estimated by determining the Ramsbottom or Conradson carbonresidue of the fuel after 90 percent of the fuel has been evaporated.

Density(ASTM D287)

42–30 degrees API gravity at 60° F(0.816–0.876 g/cc at 15° C)

Gravity is an indication of the high density energy content of the fuel.A fuel with a high density (low API gravity) contains more BTUs per

gallon than a fuel with a low density (higher API gravity). Under equaloperating conditions, a higher density fuel will yield better fuel econo-

my than a low density fuel.

Cloud Point(ASTM D97)

6° C (10° F) below lowest ambient temper-ature at which fuel expected to operate.

The cloud point of the fuel is the temperature at which crystals of par-affin wax first appear. Crystals can be detected by a cloudiness of the

fuel. These crystals will cause a filter to plug.

Ash(ASTM D482)

Not to exceed 0.02 mass percent (0.05percent with lubricating oil blending)

The small amount of non–combustible metallic material found inalmost all petroleum products is commonly called ash.

Distillation(ASTM D86)

The distillation curve must be smooth andcontinuous.

At least 90 percent of the fuel must evaporate at less than 360° C(680° F). All of the fuel must evaporate at less than 385° C (725° F).

Acid Number(ASTM D664)

Not to exceed 0.1 Mg KOH per 100ML Using fuel with higher acid numbers can lead to higher levels of wearthan is desirable. The total acid number is located in ASTM D664

Lubricity 3100 grams or greater as measured byUS Army scuffing BOCLE test or Wear

Scar Diameter (WSD) less than 0.45mmat 60° C (WSD less than 0.38mm at

25° C) as measured by HFRR method.

Lubricity is the ability of a liquid to provide hydrodynamic and/orboundary lubrication to prevent wear between moving parts.

NOTE: Federal or local regulations may require a lower sulphur content than is recommended in this table. Consult all application regulationsbefore selecting a fuel for a given engine application.

Table 6–6. Diesel Fuel Specifications





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5 % E x p a n s i o n S p a c e

( M i n i m u m )

C o n s t r u c t i o n , L o c a t i o n , I n s t a l l a t i o n ,

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a n d I n s p e c t i o n M u s t C o m p

l y W i t h

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a r r a n g e d s o t h a t t h e h i g h e s t f u e l l e v e l d o e s n o t e x c e e d t h e

m a x i m u m

h e i g h t a b o v e t h e f u e l i n j e c t o r s s p e c i f i e d f o r t h e

e n g i n e . T h e l o w e s t l e v e

l m u s t n o t f a l l b e l o w t h e s p e c i f i e d l i f t

h e i g h t o f t h e e n g i n e f u e l l i f t p u m p . I n “ c r i t i c a l s t a r t ” a p p l i c a t i o n s ,

t h e l o w e s t l e v e l s h o u l d

n o t b e l e s s t h a t 6 i n c h e s ( 1 5 0 m m )

a b o v e t h e e n g i n e f u e l p

u m p i n l e t t o m a k e s u r e t h e r e i s n o a i r

i n t h e f u e l l i n e d u r i n g s t a r t u p .

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e f o r d r a i n i n g o r p u m p i n g o u t w a t e r a n d

s e d i m e n t f r o m t h e b o t t o

m s o f a l l s u p p l y t a n k s a n d d a y t a n k s .

F l o a t S w i t c h O p e r a t e d

S i p h o n - B r e a k S o l e n o i d

V a l v e

S u p p l y P i p i n g

( B l a c k I r o n )

S c r e e n e d

F i l l P i p e C a p

( O u t s i d e )

S c r e e n e d

V e n t C a p

( O u t s i d e )

R

e t u r n P i p i n g


A p p r o v e d F l e x i b l e

F u e l H o s e s

F l o a t

S w i t c h

M a n u a l

S h u t o f f

V a l v e

F l o a t S w i t c h

O p e r a t e d

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V a l v e

1 2 0 M e s h

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S t r a i n e r

O p t i o n a l F l o a t

S w i t c h O p e r a t e d

O v e r f l o w P u m p

M a n u a l P r i m i n g B a l l

V a l v e — S e l f C l o s i n g

S c r e e n e d

V e n t C a p

( O u t s i d e )

F i g u r e 6 – 2 9 . T y p i c a l F u e l S

u p p l y S y s t e m — S u p p l y T a n k A b o v

e G e n e r a t o r S e t





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i a m e t e r L a r g e r t h a n S u p p l y

C o n s t r u c t i o n , L o c a t i o n , I n s t a l l a t i o n

,

V e n t i n g , P i p i n g , L e a k C o n t a i n m e n t

a n d I n s p e c t i o n M u s t C o m p l y W i t h

A l l A p p l i c a b l e C o d e s

D A Y T A N K

N o t e : T h e f u e l s u p p l y t a n k , d a y t a n k o r o t h e r r e s e r v o i r m u s t b e a r r a n g e d s o

t h a t t h e h i g h e s t f u e l l e v e l d o e s n o t e x c e e d t h e m a x i m u m h e i g

h t a b o v e t h e f u e l

i n j e c t o r s s p e c i f i e d f o

r t h e e n g i n e . T h e l o w e s t l e v e l m u s t n

o t f a l l b e l o w t h e

s p e c i f i e d l i f t h e i g h t o f t h e e n g i n e f u e l l i f t p u m p . I n “ c r i t i c a l s t a r t ” a p p l i c a t i o n s ,

t h e l o w e s t l e v e l s h o u

l d n o t b e l e s s t h a t 6 i n c h e s ( 1 5 0 m m ) a

b o v e t h e e n g i n e

f u e l p u m p i n l e t t o m a

k e s u r e t h e r e i s n o a i r i n t h e f u e l l i n e d

u r i n g s t a r t u p .

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a d e f o r d r a i n i n g o r p u m p i n g o u t w a t e r a n d s e d i m e n t f r o m

t h e b o t t o m s o f a l l s u p p l y t a n k s a n d d a y t a n k s .

5 % E x p a n s i o n S p a c e ( M i n i m u m

)

S c r e e n e d

V e n t a n d

F i l l P i p e C a p s

( O u t s i d e )

F l o a t S w i t c h , P u m

p ,

S o l e n o i d V a l v e a n d

1 2 0 M e s h F u e l S t r a i n e r

S u p p l y P i p i n g

( B l a c k I r o n

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R e t u r n P i p i n g


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r o v e d F l e x i b l e

F u e l H o s e s

A u x i l i a r y P u m p

I f R e q u i r e d

F i g u r e 6 – 3 0 . T y p i c a l F u e l S u p p l y S y s t e m — S u p p l y T a n k B e l o w G

e n e r a t o r S e t





The following should be considered when design-ing and installing any diesel fuel supply system:

• Fuel supply tank capacity, construction, loca-tion, installation, venting, piping, testing, andinspection must comply with all applicable

codes and their local interpretation15

. Localenvironmental regulations generally requiresecondary containment (called a “rupturebasin”, “dike”, or “bund”) to prevent leakingfuel from entering the soil or the sewer sys-tem. The secondary containment area willnormally include features to sense andsound an alarm when the main tank is leak-ing.

• Location should be chosen with consider-ation for accessibility for refilling and whethersupply lines will need to be heated (in cold cli-

mates).• The fuel supply tank must hold enough fuel torun the set for the prescribed number ofhours16 without refueling. Tank sizing cal-culations can be based on the hourly fuelconsumption rates, tempered with the knowl-edge that full load operation of most genera-tor sets is rare. Other considerations for tanksizing include the duration of expected poweroutages vs. availability of fuel deliveries andthe storage life of the fuel. The storage life fordiesel fuel is 1–1/2 to 2 years, when properlymaintained.

• Fuel supply tanks must be adequatelyvented to prevent pressurization. There maybe both primary and emergency ventingrequirements in a tank, depending on localcodes and interpretations. They also musthave provisions for manually draining orpumping out water and sediment, and haveat least a five–percent expansion space toprevent spillage when the fuel warms up.

• The fuel lift pump, day tank transfer pump orfloat valve seat should be protected from fuelsupply tank debris by a pre–filter or sedimentbowl with a 100 to 120 mesh element.

• For emergency power systems, codes mightnot permit the fuel supply to be used for any

15 US CODE NOTE: In North America, NFPA Standards

No. 30 and No. 37 are typical.

16 US CODE NOTE: NFPA110 defines number of

required operating hours as the Class of an installation.

Typical requirements are 2 hours if for emergency egress

from the building, 8 hours for the duration of most outages.

other purpose, or may specify a draw–downlevel for other equipment that guarantees thefuel supply for emergency power use.

• The Cetane rating of No. 2 heating oil is nothigh enough for dependable starting of dieselengines in cold weather. Therefore, sepa-

rate supply tanks for emergency power andbuilding heating systems might be required.

• Separate fuel return lines to the day tank orsupply tank must be provided for each gener-ator set in a multiple–set installation to pre-vent pressurizing the return lines of idle sets.Also, a fuel return line must not include ashutoff device. Engine damage will occur ifthe engine is run with the line shut off.

• A day tank is required whenever pipe frictionand/or supply tank elevation, either belowthe fuel pump inlet or above the fuel injectors,

would cause an excessive fuel inlet or returnrestriction. Some generator set models areavailable with an integral skid–mounted orsub–base day tank.

NOTE: Where generator sets are paralleled or must satisfy short emergency start–time requirements, it is a requirement that a fuel tank or reservoir be located such that the lowest possible fuel level is not less than 6 inches (150 mm) above the fuel pump inlet. This will prevent air from accumulating in the fuel line while the set is not running, eliminating the period during startup when the air has to be purged. Options are available

on some models for eliminating this requirement.

• Day tank fuel temperature limits may beexceeded in some applications when thewarm fuel from the engine is returned to theday tank. As fuel temperature increases, fueldensity and lubricity decrease, reducingmaximum power output and lubrication offuel handling parts such as pumps and injec-tors. One solution is to pipe the fuel back tothe supply tank rather than to the day tank.Other designs might require a fuel cooler toreduce the return fuel temperature to a safelevel for return to the day tank. Consult theengine manufacturer for more information onthe engine used, and its return fuel require-ments17.

• The day tank fuel transfer pump capacity andsupply piping should be sized on the basis of

17 In general, Cummins engines may be installed with the fuel

return plumbed to the day tank. The location of the return line

varies with the engine provided.





the maximum fuel flow indicated on the rec-ommended generator set SpecificationSheet.

• Use Table 6–6 as a guide for diesel fuelselection to obtain best performance.

• All fuel systems should have provisions for

containment of fuel if a tank leaks, and alsofor situations where it is “overfilled”.

• Consider means to manually fill tanks if autotank filling system fails.

• The supply pump from the main tank may bea duplex type to improve system reliability.

• Local fire codes may include specific require-ments for the generator set, such as meansto prevent fuel flow into the generator setroom if a fire is sensed, and means to returnfuel to the main tank if a fire occurs in the gen-erator set room.

Diesel Fuel Piping

• Diesel fuel lines should be constructed fromblack iron pipe. Cast iron and aluminum pipeand fittings must not be used because theyare porous and can leak fuel. Galvanizedfuel lines, fittings, and tanks must not be usedbecause the galvanized coating is attackedby the sulfuric acid that forms when the sulfurin the fuel combines with tank condensate,resulting in debris that can clog fuel pumpsand filters. Copper lines should not be used

because fuel polymerizes (thickens) in cop-per tubing during long periods of disuse andcan clog fuel injectors. Also, copper lines areless rugged than black iron, and thus moresusceptible to damage.

Note: Never use galvanized or copper fuel lines, fittings or fuel tanks. Condensation in the tank and lines combines with the sulfur in the diesel fuel to produce sulfuric acid. The molecular structure of the copper or galvanized lines or tanks reacts with the acid and con- taminates the fuel.

• Approved flexible fuel hose must be used forconnections at the engine to take up genera-tor set movement and vibration.

• Piping from a day tank to the engine shouldrun “down hill” all the way from the tank to theengine, with no overhead loops that canallow air to be entrained in the system.

• Fuel system piping should be properly sup-ported to prevent vibration and breakage dueto vibration. The piping should not run closeto heating pipes, electrical wiring, or engineexhaust system components. The pipingsystem design should include valves at

appropriate locations to allow isolation ofsystem components for repair without drain-ing the entire fuel system.

• Piping systems should be regularlyinspected for leaks and general condition.The piping system should be flushed beforeoperation of the engine to remove dirt andother impurities that could damage theengine. Use of plugged “T” connections rath-er than elbows allows for easier cleaning ofthe piping system.

• The engine manufacturer’s data indicates

the maximum fuel inlet and return restric-tions, the maximum fuel flow, supply andreturn, and the fuel consumption. Table 6–7indicates minimum hose and pipe sizes forconnections to a supply tank or day tankwhen it is within 50 feet (15 meters) of the setand at approximately the same elevation.

Hose and pipe size should be based on the maxi-mum fuel flow rather than on the fuel consump-tion. It is highly recommended that the fuel inletand return restrictions be checked before thegenerator set is placed in service.

Max Fuel Flow RateGPH (L/hr)

FlexHoseNo.*

NPSPipe

Size (in)

DN PipeSize(mm)

Less than 80 (303) 10 ½ 15

81–100 (304–378) 10 ½ 15

101–160 (379–604) 12 ¾ 20

161–230 (605–869) 12 ¾ 20

231–310 (870–1170) 16 1 25

311–410 (1171–1550) 20 1–1/4 32

411–610 (1550–2309) 24 1–1/2 40

611–920 (2309–3480) 24 1–1/2 40

* Generic fuel hose suppliers’ size specification.

Table 6–7. Minimum Fuel Hose and Pipe Sizes; Upto 50 Feet (15 Meters) Equivalent Length.





Sub–Base Fuel Tank

When a generator set is mounted on a sub–basefuel tank, the vibration isolators must be installedbetween the generator set and the fuel tank. Thefuel tank must be able to support the weight of theset and resist the dynamic loads. It is requiredthat the tank be mounted such that an air space isprovided between the bottom of the tank and thefloor underneath to reduce corrosion and permitvisual inspections for leaks.

Day Tanks

When an intermediate day tank is required in anapplication, it is typically sized for approximately 2hours of operation for the generator set at fullload. (Subject to code limitations for fuel in thegenerator set equipment room.) Multiple genera-

tor sets may be fed from one day tank, but it is pre-ferred that there be one day tank for each genera-tor set in the system. The day tank should belocated as close to the generator set as is practi-cal. Position the tank to allow for manually fillingthe tank, should it become necessary.

The height of the day tank should be sufficient toput a positive head on the engine fuel pump.(Minimum level in tank not less than 6 inches [150mm] above engine fuel inlet.) The maximumheight of fuel in the day tank should not be suffi-

cient to put a positive head on the engine fuelreturn lines.

Fuel return line location in the day tank is differentdepending on the type of engine used. Someengines require the fuel to be returned above themaximum tank level, others require fuel to bereturned to the tank at the bottom (or below theminimum tank level). The engine manufacturersupplies these specifications.

Important features, either required or desired, ofday tanks include:

• Rupture basin or bund. (Option, but requiredby law in many areas.)

• Float switch used for tank filling to control: asolenoid valve, if the bulk tank is above theday tank, or a pump, if the bulk tank is belowthe day tank.

• Vent pipe, same size as fill, routed to highestpoint in system.

• Drain valve.

• Level gage or sight glass.• Low level alarm (option).• High level float switch to control: the sole-

noid, if the bulk tank is above the day tank, orthe pump control, if the bulk tank is below theday tank.

• Overflow to bulk tank if the tank is below theday tank.

Local laws and standards often control day tankconstruction as well as federal codes so it isessential to check with the local authority.

Gaseous Fuel Supply

See section 2 of this manual for informationregarding general advantages and disadvan-tages of gaseous fuel systems compared to otheravailable alternatives.

Gaseous fueled generator sets (also called“spark–ignited generator sets”) may utilize natu-ral gas or liquid–propane (LP) gas, or both. Dualfuel systems with natural gas as primary fuel andpropane as a backup can be used in seismic riskareas and where there is concern that a naturalevent could disrupt a public utility gas system.

Regardless of the fuel used, the primary factors insuccessful installation and operation of a gas fuelsystem are:

• The gas supplied to the generator set mustbe of acceptable quality.

• The gas supply must have sufficient pres-sure. Care must be taken to be sure that thegas supply at the generator set , not just at thesource, is of proper pressure for operation.The specified pressure must be availablewhile the generator set is running at full load.

• The gas must be supplied to the genset insufficient volume to support operation of thegenerator set. This is normally a matter ofselecting fuel line size to be large enough totransport the volume of fuel needed. For LPvapor–withdrawal fuel systems the size andtemperature of the fuel tank also affects thisrequirement.

Failure to meet the minimum requirements of thegenerator set in these areas will result in theinability of the generator set to operate, or inabilityto carry rated load, or poor transient performance.





Gaseous Fuel Quality

Gaseous fuels are actually a mixture of severaldifferent hydrocarbon gases such as methane,ethane, propane, and butane; other gaseous ele-ments such as oxygen and nitrogen; vaporizedwater; and various contaminants, some of whichare potentially damaging to an engine over time.The quality of the fuel is based on the amount ofenergy per unit volume in the fuel and the amountof contaminants in the fuel.

Energy Content: One of the most important char-acteristics of the gaseous fuel used in a generatorset is the heat value of the fuel. The heat value ofa fuel describes how much energy is stored in aspecific volume of the fuel. Gaseous fuel has alow heat value (LHV) and a high heat value(HHV). The low heat value is the heat available todo work in an engine after the water in the fuel isvaporized. If the low heat value of a fuel is too low,even if a sufficient volume of fuel reaches theengine, the engine will not be able to maintain fulloutput power, because sufficient energy is notavailable in the engine to convert to mechanicalenergy. If the LHV is below 905 BTU/ft3 theengine may not produce rated power at standardambient temperature conditions.

If the local fuel has a higher energy content than1000 BTU/ft3, the actual flow requirements in cu

ft/min will be lower and the pressure requirementsdrop slightly. Conversely if the local fuel has alower energy content than 1000 BTU/ ft3, theactual flow requirements in ft3 /min will be higherand a higher minimum supply pressure will beneeded to meet published performance for anygiven generator set

Each engine may have slightly different perfor-mance characteristics based on the type of fuelprovided, due to differences in engine compres-sion ratio, and whether the engine is naturally

aspirated or turbocharged.

Pipeline Natural Gas: The most common fuel forgenerator sets is called “Pipeline natural gas”. Inthe US, “dry pipeline natural gas” has specificqualities, based on federal requirements. In othercountries, pipeline gas may vary in content, sofuel characteristics should be verified prior to use

with a generator set. US pipeline gas is a mixturecomposed of approximately 98% methane andethane with the other 2% being hydrocarbonssuch as propane and butane, nitrogen, carbondioxide, and water vapor. “Dry” means that it isfree of liquid hydrocarbons such as gasoline, but

NOT that it is free of water vapor. Dry pipeline gastypically has a LHV of 936 BTU/ft3, and a HHV of1,038 BTU/ft3.

Field Gas: The composition of “Field natural gas”varies considerably by region and by continent.Careful analysis is necessary prior to using fieldnatural gas in an engine. Field natural gas cancontain “heavier” hydrocarbon gases such aspentane, hexane, and heptane, which mayrequire derating of the output of the engine. Othercontaminants, such as sulfur, may also be pres-

ent in the fuel. A typical field gas might have aLHV of 1203 BTU/ft3, and a HHV of 1,325 BTU/ft3.

Propane (LPG): Propane is available in twogrades, either commercial, or special duty. Com-mercial propane is used where high volatility isrequired. Not all spark–ignition engines will oper-ate acceptably with this fuel due to its volatility.Special duty propane (also called HD5) is a mix-ture of 95% propane and other gases such asbutane that allow better engine performance dueto the reduction pre–ignition due to reduced vola-

tility. Special duty propane fuel gas that meets theASTM D 1835 specification for special–duty pro-pane (equivalent to HD–5 propane of Gas Pro-ducers Association Standard 2140) is suitable formost engines. Propane has a LHV of approxi-mately 2,353 BTU/ft3, and an HHV of 2,557 BTU/ ft3. The higher heating value of the fuel necessi-tates mixing of different volumes of air in the fuelsystem for propane vs. natural gas applications,so dual fuel engines essentially have two fuelarrangements for this purpose.

Contaminants: The most harmful contaminants ingaseous fuels are water vapor and sulfur.

Water vapor is damaging to an engine because itmay cause uncontrolled burning, pre–ignition, orother effects that can damage an engine. Liquidvapor or droplets must be removed from the fuelprior to entry into the engine by use of a “dry filter”







8.5:1 Compression Ratio 10.5:1 Compression Ratio

Methane (C1) 100 100

Ethane (C2) 100 100

Propane (C3) 10 2

ISO–Butane (IC4) 7 0.2

Hydrogen (H2) 7 trace

Normal Butane (NC4) 3 0.2

ISO–Pentane (IC5) 3 0.2

Normal Pentane (NC5) 1 0.1

Hexane (C6) 1 0.1

Heptane (C7) 1 0.1

Table 6–8. Maximum Allowable Percentages for Engine Fuel Combustibles

8.5:1 Compression Ratio 10.5:1 Compression Ratio

Methane NA NA

Ethane NA NA

Propane 5% *

Iso-butane 2% *

*High compression ratio turbocharged engines cannot consume any propane or iso–butane.

Table 6–9. Maximum Allowable Percentages of Constituent Gases Before Derating Turbocharged Engines

Generator Set Fuel System Design

Figure 6–31 illustrates the typical gas line com-ponents in an automatic–transfer, dual–fuel sys-tem (natural gas and LPG). Single fuel systems(natural gas or LPG) use the noted portions of thecomponents on this drawing. Not shown is theLPG vaporizer supplied with Cummins PowerGeneration generator sets equipped for liquidwithdrawal of LPG (engine–mounted on outdoorsets only). Service pressure regulators, dry gasfilters and manual shutoff valves are typically pro-vided by the installer but are available as acces-sories from Cummins Power Generation.

Site Fuel System Design

The following should be considered when instal-ling a natural gas and/or LPG fuel system:

• Gaseous–fuel supply system design, materi-als, components, fabrication, assembly,installation, testing, inspection, operationand maintenance must comply with all appli-cable codes19.

19 In North America, NFPA Standards No. 30, No. 37, No. 54

and No. 58 are typical.

• The layout and sizing of gas piping must beadequate for handling the volume of gasrequired by the generator set and all otherequipment, such as building heating boilers,supplied by the same source. Full–load gasflow (see the recommended generator set

Specification Sheet) must be available at notless than the minimum required supply pres-sure, typically from 5 to 10 inches WC (watercolumn), depending on model. Final deter-mination of pipe sizes must, however, bebased upon the method approved by theauthority having jurisdiction (see NFPA No.54).

• Most installations will require a service gaspressure regulator. Gas supply pressureshould not exceed 13.8 or 20 inches WC,depending on model, at the inlet to the gener-

ator set. Depending on distribution gas pres-sure, more than one stage of pressure regu-lation may be required. High–pressure gaspiping is not permitted inside buildings (5psig for natural gas and 20 psig for LPG,unless higher pressures are approved by theauthority having jurisdiction). Gas pressureregulators must be vented to the outdoorsaccording to code.





* THE GAS PRESSURE SWITCH CAUSES THE NATURAL GAS SOLENOID VALVE TO CLOSE AND THE PROPANE GAS SOLENOID VALVE TO OPEN UPONLOSS OF NATURAL GAS SUPPLY PRESSURE TO CONTINUE GENERATOR SET OPERATION WITHOUT INTERRUPTION. RETURN TO NATURAL GAS IS

AUTOMATIC WHEN SUPPLY PRESSURE IS RESTORED.

GAS-AIRMIXER

SECONDARYGAS PRESSURE

REDUCINGFLOW VALVE

PROPANE GASFLOW ADJUSTING

VALVE(DUAL FUEL ONLY)

FUEL CHANGE GASPRESSURE SWITCH(DUAL FUEL ONLY)

NORMALLY CLOSED NAT-URAL GAS SOLENOID

VALVE (LISTED SAFETYSHUTOFF VALVE)

PRIMARYPROPANE GAS SER-

VICE PRESSUREREGULATOR

NORMALLY CLOSEDPROPANE GAS SOLENOID

VALVE (LISTED SAFETYSHUTOFF VALVE)

SWITCH B+ TERMINALOF ENGINE CONTROL

SECONDARYGAS PRESSURE

REDUCING FLOWVALVE

MANUALSHUTOFF

VALVE

NATURAL GAS 5 TO 30LBS. (34 TO 270 kPa)

INLET PRESSURE

DRYFUEL

FILTER

MANUALSHUTOFF

VALVE

DRYFUEL

FILTER

VAPORIZED LP GAS 5 TO30 LBS. (34 TO 207 kPa)

INLET PRESSURE

PRIMARYNATURAL GAS

SERVICE PRESSUREREGULATOR

APPROVED FLEXIBLEFUEL HOSE

ATMOSPHERICVENT

Figure 6–31. Typical Gaseous Fuel System





• The pressure regulator installed on the sup-ply line at the gas source for generatorapplications should never be a “pilot” regula-tor. A “pilot” style regulator is the type wherethe regulator requires a pressure line fromthe regulator housing to the downstream gas

pipe to “sense” when downstream pressurehas dropped. Pilot regulators do not workbecause the response time is unacceptablecompared to the large–instantaneouschanges in demand from the generator set.

• Approved flexible fuel hose must be used forconnections at the engine to take up genera-tor set movement and vibration.

• Most codes require both manual and electric(battery–powered) shutoff valves ahead ofthe flexible fuel hose(s). The manual valveshould be of the indicating type.

• A dry fuel filter should be installed in each lineas shown in Figure 6–31 to protect the sensi-tive pressure regulating components and ori-fices downstream from harmful foreign sub-stances carried along in the gas stream (rust,scale, etc.).

• An LPG fuel supply system must be dedi-cated for the emergency power system if it isthe required alternative fuel.

• An LPG vaporizer heated by engine coolantis factory installed on Cummins Power Gen-eration generator sets equipped for a liquid–

withdrawal of LPG. Because high pressure(20 psig or greater) gas piping is not per-mitted inside buildings, generator setsequipped for liquid withdrawal of LPG mustnot be installed inside the building. (Weath-er–protective housings for outdoor installa-tion are available for most LPG models.)

• The rate of vaporization in an LPG tankdepends upon the outdoor air temperature,unless the tank is equipped with a heater,and the quantity of fuel in the tank. Even oncold days outdoor air heats and vaporizesLPG (mostly through the wetted tank sur-face) when air temperature is higher thanLPG temperature. Withdrawing vaporcauses tank temperature and pressure todrop. (At –37° F [–38° C] LPG has zero vaporpressure.) Unless there is enough fuel andenough heat available from ambient air, thevaporization rate will drop off, as the genera-tor set runs, to less than that required to con-tinue running properly.

Gaseous Fuel System Calculations FuelPressure

Tank Size: Use Figure 6–32 as a quick referencefor sizing an LPG tank on the basis of the lowestambient temperature expected. For example, ona 40F day, withdrawal at 1000 ft3 /h requires a2000 gallon tank at least half full. Note: In many

instances the amount of fuel required for proper vapor-

ization is far greater than that required for the number

of hours of operation stipulated by code.

For instance, in an NFPA 110 Class 6 application,there must be enough fuel for the generator set torun for 6 hours before refilling the tank. LPG yieldsapproximately 36.5 cubic feet of gas per gallon ofliquid. If the generator set withdrawal rate is1000 ft3 /h:

FuelConsumedin 6 hours

=164 gallons1000 ft3 /hr • 6 hours

36.5 ft3 /gal=

In this instance the tank must be sized for at least2000 gallons based on the lowest expected tem-perature rather than on the fuel consumed in 6hours (164 gallons).

Gas Pipe Sizing: Sizing of gas piping for properfuel delivery, both flow and pressure, can becomequite complex. However, a simplified method, as

with other piping for exhaust and coolant, is toconvert all fittings, valves, etc. to equivalentlengths of pipe in the diameter(s) being consid-ered. The total equivalent length can then berelated to flow capacity.

Table 6–3, Equivalent Lengths of Pipe Fittingsand Valves applies to gas as well as liquid piping.Tables 6–10 through 6–14 show maximum gascapacity for equivalent length for various pipesizes. Tables 6–10 through 6–14 are reproducedfrom NFPA 54–2002, National Fuel Gas Code,

and are selected considering the general fuel sys-tem operating requirements for generator sets.Tables are included for natural gas, propane liq-uid withdrawal and propane vapor withdrawalunder specified conditions. Consult NFPA 54 orother applicable codes for other operating condi-tions or other fuel system installation require-ments.





A calculation of minimum pipe size is fairlystraightforward:

• Make a list of al the fittings and valves in aproposed system and sum their equivalentlengths using the table.

• Add to this total, all lengths of straight pipe toarrive at a total equivalent length.

• Choose the applicable table based on thefuel system.

• Obtain the maximum fuel requirements forthe specific generator set(s) from the

manufacturer’s specification sheets. Con-vert to ft3 /hr as needed (Be cognizant of BTUcontent as discussed earlier in this section.)

• Locate the equivalent length of pipe (or nextlarger equivalent length) in the left hand col-umn. Move across to the columns to where

the number is as large or larger than the totalequivalent length calculated above. At thetop of that column is the minimum nominalpipe size or tubing size required for the sys-tem as designed.

1 0 0

1 0 0 0

L P G T A N K S I Z E ( G A L L O N S )

LPG VAPORIZATION RATE (CUBIC FEET PER HOUR)

10,000

1000

100

100,000

1 0 , 0 0 0

500

5000

50,000

5 0 0

5 0 0 0

–10° F

–20° F

0° F

10° F

20° F

30° F

40° F

50% FULL

Figure 6–32. Minimum LPG Tank Size (50% Full) Required to Maintain 5 PSIG at Specific Withdrawal Rate andMinimum Expected Winter Temperature





Gas: NaturalInlet Pressure: 0.5 psi or lessPressure Drop: 0.5 in. w.c.Specific Gravity: 0.60

Pipe Size (in.)

Nominal 1/4 3/8 1/2 3/4 1 1 1/4 1 1/2 2 2 1/2 3 4

Actual ID (0.364) (0.493) (0.622) (0.824) (1.049) (1.380) (1.610) (2.067) (2.469) (3.068) (4.026)Length

(ft) Maximum Capacity in Cubic Feet of Gas per Hour

10 43 95 175 360 680 1400 2100 3950 6300 11000 23000

20 29 65 120 250 465 950 1460 2750 4350 7700 15800

30 24 52 97 200 375 770 1180 2200 3520 6250 12800

40 20 45 82 170 320 660 990 1900 3000 5300 10900

50 18 40 73 151 285 580 900 1680 2650 4750 9700

60 16 36 66 138 260 530 810 1520 2400 4300 8800

70 15 33 61 125 240 490 750 1400 2250 3900 8100

80 14 31 57 118 220 460 690 1300 2050 3700 7500

90 13 29 53 110 205 430 650 1220 1950 3450 7200

100 12 27 50 103 195 400 620 1150 1850 3250 6700

125 11 24 44 93 175 360 550 1020 1650 2950 6000

150 10 22 40 84 160 325 500 950 1500 2650 5500

175 9 20 37 77 145 300 460 850 1370 2450 5000

200 8 19 35 72 135 280 430 800 1280 2280 4600

Table 6–10. Natural Gas Schedule 40 Iron Pipe Sizing20

20 Reprinted with permission from NFPA 54–2002, National Fuel Gas Code , Copyright 2002, National Fire Protection Association, Quincy,

MA 02169. This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only

by the standard in its entirety.





Gas: NaturalInlet Pressure: 0.5 psi or lessPressure Drop: 0.5 in. w.c.Specific Gravity: 0.6 0

Tube Size (in.)

K & L 1/4 3/8 1/2 5/8 3/4 1 1 1/4 1 1/2 2 2 1/2

Nominal ACR 3/8 1/2 5/8 3/4 7/8 1 1/8 1 3/8 1 5/8 2 1/8 2 5/8Outside 0.375 0.500 0.625 0.750 0.875 1.125 1.375 1.625 2.125 2.625

Inside* 0.305 0.402 0.527 0.652 0.745 0.995 1.245 1.481 1.959 2.435

Length(ft) Maximum Capacity in Cubic Feet of Gas per Hour

10 27 55 111 195 276 590 1062 1675 3489 6173

20 18 38 77 134 190 406 730 1151 2398 4242

30 15 30 61 107 152 326 586 925 1926 3407

40 13 26 53 92 131 279 502 791 1648 2916

50 11 23 47 82 116 247 445 701 1461 2584

60 10 21 42 74 105 224 403 635 1323 2341

70 9.3 19 39 68 96 206 371 585 1218 2154

80 8.6 18 36 63 90 192 345 544 1133 2004

90 8.1 17 34 59 84 180 324 510 1063 1880

100 7.6 16 32 56 79 170 306 482 1004 1776

125 6.8 14 28 50 70 151 271 427 890 1574

150 6.1 13 26 45 64 136 245 387 806 1426

175 5.6 12 24 41 59 125 226 356 742 1312

200 5.2 11 22 39 55 117 210 331 690 1221

250 4.7 10 20 34 48 103 186 294 612 1082

300 4.2 8.7 18 31 44 94 169 266 554 980

* Table capacities are based on Type K copper tubing inside diameter (shown), which has the smallest inside di-ameter of the copper tubing products.

Table 6–11. Natural Gas Semi–Rigid Copper Tubing Sizing21

21 Reprinted with permission from NFPA 54–2002, National Fuel Gas Code, Copyright 2002, National Fire Protection Association , Quincy,







Gas: Undiluted PropaneInlet Pressure: 11.0 in. w.c.

ressure rop: . n. w.c.Specific Gravity: 1.50Special Use: Pipe sizing between single or second stage (low pressure regulator) and appliance.

Pipe Size (in.)

Nominal Inside 1/2 3/4 1 1 1/4 1 1/2 2 3 3 1/2 4

Actual: 0.622 0.824 1.049 1.38 1.61 2.067 3.068 3.548 4.026

Length (ft) Maximum Capacity in Thousands of Btu per Hour

10 291 608 1145 2352 3523 6786 19119 27993 38997

20 200 418 787 1616 2422 4664 13141 19240 26802

30 160 336 632 1298 1945 3745 10552 15450 21523

40 137 287 541 1111 1664 3205 9031 13223 18421

50 122 255 480 984 1475 2841 8004 11720 16326

60 110 231 434 892 1337 2574 7253 10619 14793

80 94 197 372 763 1144 2203 6207 9088 12661100 84 175 330 677 1014 1952 5501 8055 11221

125 74 155 292 600 899 1730 4876 7139 9945

150 67 140 265 543 814 1568 4418 6468 9011

200 58 120 227 465 697 1342 3781 5536 7712

250 51 107 201 412 618 1189 3351 4906 6835

300 46 97 182 373 560 1078 3036 4446 6193

350 42 89 167 344 515 991 2793 4090 5698

400 40 83 156 320 479 922 2599 3805 5301

Table 6–12. Propane Vapor Schedule 40 Iron Pipe Sizing22








Gas: Undilute PropaneInlet Pressure: 11.0 in w.c.Pressure Drop: 0.5 in. w.c.Specific Gravity: 1.50Special Use: Sizing between single or second stage (low pressure regulator) and appliance

Tube Size (in.)

K & L 1/4 3/8 1/2 5/8 3/4 1 1 1/4 1 1/2 2 2 1/2

Nominal ACR 3/8 1/2 5/8 3/4 7/8 1 1/8 1 3/8 1 5/8 2 1/8 2 5/8

Outside 0.375 0.500 0.625 0.750 0.875 1.125 1.375 1.625 2.125 2.625

Inside* 0.305 0.402 0.527 0.652 0.745 0.995 1.245 1.481 1.959 2.435

Length(ft) Maximum Capacity in Cubic Feet of Gas per Hour

10 45 93 188 329 467 997 1795 2830 5895 10429

20 31 64 129 226 321 685 1234 1945 4051 7168

30 25 51 104 182 258 550 991 1562 3253 5756

40 21 44 89 155 220 471 848 1337 2784 4926

50 19 39 79 138 195 417 752 1185 2468 4366

60 17 35 71 125 177 378 681 1074 2236 3956

70 16 32 66 115 163 348 626 988 2057 3639

80 15 30 61 107 152 324 583 919 1914 3386

90 14 28 57 100 142 304 547 862 1796 3177

100 13 27 54 95 134 287 517 814 1696 3001

125 11 24 48 84 119 254 458 722 1503 2660

150 10 21 44 76 108 230 415 654 1362 2410

175 10 20 40 70 99 212 382 602 1253 2217

200 8.9 18 37 65 92 197 355 560 1166 2062

225 8.3 17 35 61 87 185 333 525 1094 1935

250 7.9 16 33 58 82 175 315 496 1033 1828

275 7.5 15 31 55 78 166 299 471 981 1736

300 7.1 15 30 52 74 158 285 449 936 1656

* Table capacities are based on Type K copper tubing inside diameter (shown), which has the smallest inside di-ameter of the copper tubing products.

Table 6–13. Propane Vapor Semi–Rigid Copper Tubing Sizing23








EquivalentLen th of

Schedule 40 Iron Pipe Size, in.: Nominal (Inside Diameter)

Pipe, ft. 1/2 3/4 1 1 1/4 1 1/2 2 3 3 1/2 4

(0.622) (0.824) (1.049)

(1.38)

(1.61) (2.067) (3.068)

(3.548) (4.026)

30 733 1532 2885 5924 8876 17094 48164 70519 98238

40 627 1311 2469 5070 7597 14630 41222 60355 84079

50 556 1162 2189 4494 6733 12966 36534 53492 74518

60 504 1053 1983 4072 6100 11748 33103 48467 67519

70 463 969 1824 3746 5612 10808 30454 44589 62116

80 431 901 1697 3484 5221 10055 28331 41482 57787

90 404 845 1593 3269 4899 9434 26583 38921 54220

100 382 798 1504 3088 4627 8912 25110 36764 51216

150 307 641 1208 2480 3716 7156 20164 29523 41128

200 262 549 1034 2122 3180 6125 17258 25268 35200

250 233 486 916 1881 2819 5428 15295 22395 31198

300 211 441 830 1705 2554 4919 13859 20291 28267

350 194 405 764 1568 2349 4525 12750 18667 26006

400 180 377 711 1459 2186 4209 11861 17366 24193

450 169 354 667 1369 2051 3950 11129 16295 22700

500 160 334 630 1293 1937 3731 10512 15391 21442

600 145 303 571 1172 1755 3380 9525 13946 19428

700 133 279 525 1078 1615 3110 8763 12830 17873

800 124 259 488 1003 1502 2893 8152 11936 16628

900 116 243 458 941 1409 2715 7649 11199 15601

1000 110 230 433 889 1331 2564 7225 10579 14737

1500 88 184 348 713 1069 2059 5802 8495 11834

2000 76 158 297 611 915 1762 4966 7271 10128

Table 6–14. Propane Schedule 40 Iron Pipe Sizing, Liquid Withdrawal – Maximum Capacity of Pipe in Cubic Feetof Gas per Hour. Pipe size recommendations are based on schedule 40 black iron pipe.

Reducing Noise in Generator SetApplications

The Science of Noise

Noise Level Measurement and Decibel/dB(A)Units: One unit of measurement for sound is thedecibel (dB). The decibel is a convenient numberon a logarithmic scale expressing the ratio of twosound pressures, comparing the actual pressure

to a reference pressure.Noise regulations are generally written in terms of“decibels ‘A’ scale” or dB(A). The “A” denotes thatthe scale has been “adjusted” to approximatehow a person perceives the loudness of sound.Loudness depends on sound pressure level(amplitude) and frequency. Figure 6–33 showstypical noise levels associated with various sur-roundings and noise sources.

Accurate and meaningful sound level data arepreferably measured in a “free field site” to collectnoise data. A “free field”, as distinguished from a“reverberant field”, is a sound field in which theeffects of obstacles or boundaries on sound prop-agated in that field are negligible. (Generally thismeans the objects or barriers are far away, do notreflect toward the test area and/or are coveredwith adequate sound absorption materials.)Accurate noise measurements also require that

the microphone be placed outside the “near field.”“Near field” is defined as the region within onewave length, or two times the largest dimension ofthe noise source, whichever is greater. Noisemeasurements for community regulations shouldnot be made in the near field. Engineers’ noisespecifications should call for sound pressure levelmeasurements in the free field, 7 meters (21 feet)or greater.







DIFFERENCE IN dB(A) BETWEEN VALUES BEING ADDED1 2 3 4 5 6 7 8 9 10

0.2

0.4

0.6

0.8

1.0

2.0

3.0

1.2

1.4

1.61.8

2.2

2.4

2.6

2.8

d B ( A ) T O A D D T O T H E G R E A T E R V A L U E

Figure 6–34. Graph Of Values For Adding Noise Levels

Figure 6–34 can be used, as follows, to estimatethe noise level from multiple noise sources:

1. Find the difference in dB(A) between two ofthe sources (any pair). Locate that value onthe horizontal scale as shown by the verticalarrow, move up to the curve and over to thevertical scale as shown by the horizontalarrow. Add this value to the larger dB(A) val-ue of the pair.

2. Repeat Step 1 between the value just deter-mined and the next value. Keep repeatingthe process until all sources have beenaccounted for.

For example, to add 89 dB(A), 90.5 dB(A), and 92dB(A):

– Subtract 90.5 dB(A) from 92 dB(A) for a dif-ference of 1.5 dB(A). As the arrows show inFigure 6–34, corresponding to the differenceof 1.5 dB(A) is the value of 2.3 dB(A) whichshould be added to 92 dB(A) for a new value

of 94.3 dB(A). – Likewise, subtract 89 dB(A) from the new val-

ue of 94.3 dB(A) for a difference of 5.3 dB(A). – Finally, add the corresponding value of 1.1

dB(A) to 94.5 dB(A) for a total of 95.6 dB(A).

Alternatively, the following formula can be used toadd sound pressure levels measured in dB(A):

dBA2

10

dBAtotal =

10

dBA1

10 +...+10+10

dBAn

1010 • log10

Effect of Distance : In a “free field,” sound leveldecreases as distance increases. If, for example,a second sound measurement is taken twice asfar from the source, the second reading will beapproximately 6 dB(A) less than the first (fourtimes less). If the distance is cut in half, the sec-

ond reading will be approximately 6 dB(A) greater(four times greater). For the more general case, ifthe sound pressure level (SPL1) of a source atdistance d1 is known, the sound pressure level(SPL2) at distance d2 can be found as follows:

SPL2 = SPL1 – 20 • log10 d2

d1

For example, if the sound pressure level (SPL1) at21 meters (d1) is 100 dB(A), at 7 meters (d2), the

sound pressure level (SPL2) will be:

SPL2 = 100dBA – 20 • log10

7

21

= 100 – 20 • (–0.477)

= 100 + 9.5 = 109. 5 dBA





50

60

70

80

90

100

110

10 1005020 200(33)

DISTANCE FROM SOURCE IN METERS (FEET)(66)

7(23) (164) (330) (660)

L O U D N E S s I N d B ( A )

Figure 6–35. Decrease In Loudness As Distance Increases (Free Field)

To apply the distance formula (above) to genera-tor set data published by Cummins Power Gener-ation, the background noise level must be at least10 dB(A) below the noise level of the generatorset and the installation must approximate a freefield environment.

Figure 6–35 can be used as an alternative to theformula for estimating the sound level at variousdistances, such as to the property line. For exam-ple, as shown by the dashed arrows, if the noiserating on the recommended generator set Speci-fication Sheet is 95 dB(A) (at 7 meters), the noiselevel 100 meters away will be approximately 72dB(A).

To use Figure 6–35, draw a line parallel to theslanted lines from the known dB(A) value on thevertical scale line to the vertical line for the speci-fied distance. Then draw a horizontal line back tothe vertical scale line and read the new dB(A) val-ue.

Generator Set Noise

Generator set applications are susceptible toproblems associated with noise levels, due to theinherent high levels of noise produced by operat-ing generator sets. Codes and standards havebeen enacted to protect property owners or usersfrom objectionable levels of noise from other

properties.

In general, required noise levels at a property lineare often in the low 60s or high 50s (depending ontime of day), while untreated generator set noiselevels can approach 100dBA. The generator setnoise may be amplified by site conditions, or theambient noise level existing at the site may pre-vent the generator set from meeting requirednoise performance levels. (In order to accuratelymeasure the noise level of any source, the noisesource must be more than 10 dBA louder than the

ambient around it.)





The noise level produced by a generator set at aproperty line is predictable if the generator set isinstalled in a free field environment. In a free fieldenvironment, there are no reflecting walls to mag-nify the noise produced by the generator set, andthe noise level follows the “6 dBA reduction for

doubling distance” rule. If the property line is with-in the near field of a generator set the noise levelmay not be predictable. A near field environmentis any measurement taken within twice the largestdimension of the noise source.

Reflecting walls and other hard surfaces magnifythe noise level that may be sensed by a receiver.For example, if a generator set is placed next to ahard surfaced wall, the noise level perpendicularto the wall will be approximately twice theexpected sound power of the generator set in a

free field environment (i.e., a generator set oper-ating with a 68 dBA noise level would measure 71dBA next to a reflecting wall). Putting a generatorset in a corner further magnifies the noise levelsensed.

Noise ordinances are often only enforced by com-plaint, but the high cost of retrofitting a site fornoise reduction makes it a good idea to assessnoise performance requirements early in thedesign cycle, and designing into the site the mostcost effective sound attenuation provisions.

See section Table 2–2 for representative outsidenoise data.

Reducing Structure–Transmitted Noise

Vibrating structures create sound pressurewaves (noise) in the surrounding air. Connec-tions to a generator set can cause vibrations in thebuilding structure, creating noise. Typically,these include the skid anchors, radiator dis-charge air duct, exhaust piping, coolant piping,fuel lines, and wiring conduit. Also, the walls of a

generator set housing can vibrate and causenoise. Figure 6–1 shows ways of minimizingstructure–transmitted noise by proper vibrationisolation.

Mounting a generator set on spring–type vibra-tion isolators effectively reduces vibration trans-mission. Vibration isolation practice is describedin Vibration Isolators at the beginning of this chap-ter.

Flexible connections to exhaust pipe, air duct,fuel line, coolant pipe (remote radiator or heatexchanger systems) and wiring conduit effective-ly reduce vibration transmission. All generatorset applications require the use of flexible con-nections to the generator set.

Reducing Airborne Noise

Airborne noise has a directional characteristicand is usually the most apparent at the high end ofthe frequency range.

SThe simplest treatment is to direct the noise,such as a radiator or exhaust outlet, awayfrom receivers. For example, point the noiseup vertically so that people at grade level willnot be in the sound path.

S. Line–of–sight barriers are effective in block-ing noise. Barriers made of materials with

high mass materials such as concrete, filledcement block, or brick, are best. Be careful toeliminate sound paths through cracks indoors or room (or enclosure) access pointsfor exhaust, fuel, or electrical wiring.

SSound absorbing (acoustic) materials areavailable for lining air ducts and coveringwalls and ceilings. Also, making noise travelthrough a 90–degree bend in a duct reduceshigh frequency noise. Directing noise at a

wall covered with sound absorbing materialcan be very effective. Fiberglass or foammay be suitable, based on factors such ascost, availability, density, flame retardance,resistance to abrasion, aesthetics and clean-ability. Care should be taken to select materi-als that are resistant to the effects of oil andother engine contaminants.

SA concrete block enclosure is an excellentbarrier to all noise. The blocks may be filledwith sand to increase the mass of the walland thus increase noise attenuation.

SRemote radiator arrangements can be usedto limit air flow and to move the radiator fannoise source to a location that is less likely tobe objectionable to receivers. Remote radia-tor installations can be supplied with lowspeed fans to minimize noise from theassembly.





Sound Attenuated Enclosures (Canopies)

Generator sets that are installed out of doors maybe provided with integral sound attenuated enclo-sures. These enclosures effectively form a “room”around the generator set and can effectivelyreduce the noise level produced by the machine.

In general, the price of the enclosure is directlyrelated to the sound attenuation required. So, thegreater the level of sound attenuation required,the greater the cost of the enclosure. It is notuncommon for enclosure costs to approach thecost of the generator set that it protects.

It should also be recognized that there may be aprice in terms of generator set performance byuse of high levels of sound attenuation. Carefullytest sound attenuated machines for proper ven-

tilation system and load–carrying performance.

Note: Be cautious when comparing cooling system ratings that the rating is based on ambient temperature not air–on–radiator. An air–on–radiator rating restricts the temperature of the air flowing into the radiator and does not allow for air temperature increase due to the radiated heat energy of the engine and alternator.Ambient rated system accounts for this increase in temperature in their cooling capability.

Exhaust Silencer Performance

Generator sets are almost always provided withan exhaust silencer (muffler) to limit exhaustnoise from the machine. Exhaust silencers comein a wide variety of types, physical arrangements,and materials.

Silencers are generally grouped into either cham-ber–type silencers, or spiral type devices. Thechamber type devices can be designed to bemore effective, but the spiral types are oftenphysically smaller, and may have suitable perfor-mance for the application.

Silencers may be constructed of cold–rolled steelor stainless steel. Cold–rolled steel silencers areless expensive, but more susceptible to corrosionthan stainless steel silencers. For applicationswhere the silencer is mounted indoors, and pro-tected with insulation (lagging) to limit heat rejec-tion, there is little advantage for the stainless vari-ety.

Silencers can be provided in the following physi-cal configurations:

• End in/end out; probably the most commonconfiguration.

• Side in/end out; often used to help to limit

ceiling height requirements for a generatorset.

• Dual side inlet/end out; used on “V” enginesto eliminate need for an exhaust header, andminimize ceiling height requirements.

Silencers are available in several different noiseattenuation “grades”; commonly called: “industri-al”, “residential”, and “critical”. Note that theexhaust noise from a generator set may not bethe most objectionable noise source on themachine. If the mechanical noise is significantly

greater than the exhaust noise, selection of ahigher performance silencer may not improve thenoise level present at the site.

In general, the more effective a silencer is atreducing exhaust noise, the greater the level ofrestriction on the engine exhaust. For longexhaust systems, the piping itself will providesome level of attenuation.

Typical Silencer Attenuation

Industrial Silencers: 12–18 dBA

Residential Silencers: 18–25 dBA

Critical Silencers: 25–35 dBA

Fire Protection

The design, selection and installation of fireprotection systems is beyond the scope of thismanual due to of the wide range of factors to con-sider, such as building occupancy, codes, and theefficacy of various fire protection systems. Con-sider the following, however:

• The fire protection system must comply with

the requirements of the authority having jurisdiction, such as the building inspector,fire marshal or insurance carrier.





• Generator sets that are used for emergencyand standby power should be protected fromfire by location or by the use of fire–resistantconstruction in the generator set room. Insome locations, generator room constructionfor installations that are considered to be

necessary for life safety must have a two– hour fire resistance rating24,25. Some loca-tions will also require feeder fire protection.Consider use of automatic fire doors ordampers for the generator set room.

The generator set room must be ventilated ade-quately to prevent buildup of engine exhaustgases or flammable fuel supply gas.

• The generator room should not be used forstorage purposes.

•Generator rooms should not be classified ashazardous locations (as defined by the NEC)solely by reason of the engine fuel.

• The authority having jurisdiction will usuallyclassify the generator set as a low heatappliance when use is only for brief, infre-quent periods, even though exhaust gastemperature may exceed 1000° F (538° C).Where exhaust gas temperature mayexceed 1000° F (538° C), some diesels andmost gas engines may be classified as highheat appliances and may require exhaustsystems rated for 1400° F (760° C) opera-tion. Consult the engine manufacturer forinformation on exhaust temperatures.

• The authority having jurisdiction may specifythe quantity, type, and sizes of approved por-table fire extinguishers required for the gen-erator room.

• A manual emergency stop station outside thegenerator room or remote from a generatorset in an outside enclosure would facilitateshutting down the generator set in the eventof a fire or other type of emergency.

• Typical liquid fuel systems are limited to 660

gallons (2498 liters) inside of a building.However, the authority having jurisdictionmay enforce much more stringent restric-tions on the amount of fuel that can be stored

24 CODE NOTE: In the US, NFPA110 requires that generator

sets used in Level 1 emergency systems be installed in a room

with a 2–hour fire resistance rating. Other emergency systems

are required to have 1–hour fire resistance ratings.

25 CODE NOTE: In Canada, CSA282–2000 requires that a

room with 1–hour fire resistance rating protect emergency pow-

er systems that are installed in buildings.

inside a building. Also, exceptions may bemade to allow use of larger amounts of fuel ina generator set room, especially if the gener-ator set room has properly designed fireprotection systems.

• Fuel tanks located inside buildings and

above the lowest story or basement shouldbe diked in accordance with NFPA standardsand environmental regulations.

• The generator set should be exercised peri-odically as recommended under at least 30percent load until it reaches stable operatingtemperatures. It should also be run undernearly full load at least once a year to preventfuel from accumulating in the exhaust sys-tem.

Equipment Room Design

General Considerations

Generator sets should be installed according toinstructions provided by the generator setmanufacturer, and in compliance with applicablecodes and standards.

General guidelines for room design:

• Most generator sets will require access forservice to both sides of the engine as well asthe control/alternator end of the machine.

Local electrical codes may require specificworking space for electrical equipment, but ingeneral, allow for working space equal to thewidth of the genset on both sides and rear.

• Location of fuel system, or electrical distribu-tion system components may require addi-tional working space. See fuel supplyrequirements elsewhere in this section formore information on that subject.

• There should be access to the generator setroom (or outdoor enclosure) that allows thelargest component in the equipment to beremoved (almost always the engine).Access may be through wide doorways, orvia removable inlet or exhaust air louvers. Anideal design will allow moving the generatorset as a package into the equipment room.

Roof–top Installations: With more pressure onbuilding cost, it is becoming more common tolocate generator sets on roof–tops. These instal-lations can be successfully accomplished if the








1417 APPENDIX

Start/Run from the Windows desktop, select theCD ROM drive and run Setup.exe. The GenSizesoftware is designed to run in a Windows NT, 95,98, or 2000 operating system environment. Thebrowser function for the Library CD is optimizedfor Internet Explorer 5.0 and Adobe Acrobat 4.0

(included on the CD). After installation is com-plete, a New Project dialog box will appear – Select New Project.

Project Parameters

The first step in sizing and selecting an engine– generator set is to establish project parameters.At a minimum, the generator set must be sized tosupply the maximum load starting steady–staterunning requirements of the connected loadequipment.

To set the default project parameters, select Pro- jects from the top tool bar, then New ProjectDefault Parameters at the bottom of the pull– down menu. The resulting dialog box, Figure

7–1, shows New Project Parameters that areapplied to all new projects and can be altered tosuit your preferences. The project parameters fora single or an existing project can be changedwithout altering the default parameters by high-lighting the project name then selecting Projects,

Edit, and then the parameters tab.

Following is an explanation of the project parame-ters and the default entries shown in the dialogbox.

Number of Generator Sets Running In Parallel: The default value is 1. If the total load is greaterthan the capacity of a single generator set, insert2, 3, or more as appropriate. If the total load isabove 1000 kW, it may be advantageous to paral-lel generator sets for higher reliability and opera-

tional flexibility. When the total load is 300 kW orless, however, it is usually not cost–effective toparallel generator sets – although it is technicallyfeasible.

Figure 7–1. GenSize–New Project Parameters Dialog Box




1427 APPENDIX

Minimum Genset Load/Capacity: Running a gen-erator set under light load can lead to enginedamage and reduced generator set reliability.Cummins Power Generation does not recom-mend running generator sets at less than 30 per-cent of rated load –– this is the default setting in

GenSize. Load banks should be used to supple-ment the regular loads when loading falls belowthe recommended value. A generator set shouldnot run at less than 10 percent of rated load forany extended period.

Maximum Voltage Dip (Starting and Peak): Asyou reduce the maximum allowable voltage dipduring initial startup, or when loads cycle underautomatic controls or have high peak surges, thesize of the recommended generator setincreases. Choosing a lower allowable voltage

dip results in a larger recommended generatorset. However, setting allowable voltage dips ofmore than 40 percent can lead to relay and con-tactor malfunctions. The default Maximum Volt-age Dip in GenSize is 35 percent.

Maximum Frequency Dip: As you reduce themaximum allowable frequency dip, you increasethe size of the recommended generator set.Since a generator set is a limited power source(compared to a utility), voltage and frequencyexcursions will occur during transient loading

events. The generator set must be sized to limitthese excursions to an appropriate level for prop-er load performance. The default Maximum Fre-quency Dip in GenSize is 10 percent. This num-ber may have to be set lower when supplyingfrequency–sensitive loads, such as UPS sys-tems. Check with the UPS manufacturer for infor-mation on the UPS system’s sensitivity to fre-quency excursions when operating on a standbygenerator set.

Altitude and Ambient Temperature: Based ongeographic location, the size of the generator setthe software recommends may be increased for agiven level of performance as altitude and/orambient temperature increase. The default val-ues are an altitude of 500 feet (152 meters) andan ambient temperature of 77° F (25° C).

Sound Attenuation: The default setting is None.However, a Quiet Site generator set may beselected. Quiet Site units include special exhaustsilencers, a sheet metal housing with sound atte-nuating insulation, and/or intake and dischargedampers. Not all models are available in a Quiet

Site configuration. When selecting Sound Atten-uation, GenSize generator set recommendationswill be limited to standard optional packagesavailable from the factory. Your local distributor,however, should be consulted for any other soundattenuation needs.

Maximum Alternator Temperature Rise: A maxi-mum allowable temperature rise over an ambientof 40° C (104° F) can be specified for the alterna-tor windings. GenSize will recommend engine– alternator combinations that limit the alternator

temperature rise to the specified temperaturewhen powering the specified connected loads. Itmay be desirable to use lower temperature risealternators in applications that contain significantnon–linear loads, where better motor starting isrequired, or in prime duty applications. Thedefault setting is 125° C. Note that, when youselect a lower temperature rise alternator, youmay increase the size of the recommended gen-erator set to accommodate a larger alternator.

Fuel: The default fuel is Diesel. Other choices of

available fuels are Natural gas and Liquid Pro-pane Gas. An “Any Fuel” choice is availablewhich allows GenSize to compare the perfor-mance of all available fuel choices.

Note: For gaseous fuels requirements above approximately 150/140 kW, consult the distributor.

Frequency: Specify the required operating fre-quency. Generator sets are configured for either50 Hz or 60 Hz. The default value is 60 Hz.

Phase: Select either a single– or three–phase

generator set. The default setting is three–phase.If selecting single–phase, only single–phaseloads are allowed. Selecting single–phase willalso limit the number of available models sincelarger generator sets are not available with




1437 APPENDIX

single–phase generators. The default three– phase selection permits single–phase loads butGenSize assumes that the single–phase loadswill be balanced across the three phases.

Duty: GenSize makes a recommendation based

on the standby or prime power rating of the gener-ator set, derating appropriately for site conditions.The default setting is Standby. For further discus-sion and illustration of system and generator setratings see Preliminary Design section.

A standby power system is an independent powersystem that supplies a facility in the event of a fail-ure of the normal power source. (It is assumedthat the generator set is isolated from the utilityservice.) The standby power rating is applicablefor emergency power duty for the duration of a

typical power interruption. No overload capabilityis available for this rating.

A prime power system is an independent powersystem for supplying electric power in lieu of pur-chasing power from a commercial utility. (It isassumed that the generator set is isolated fromthe utility service, or that utility service is unavail-able.) The prime power rating is the maximumpower available at variable load for an unlimitednumber of hours. A minimum of 10 percent over-load capability is available for prime power ratingsper engine rating standards BS 5514 and DIN6271. Not every generator set configuration isavailable for prime duty.

When generator sets are paralleled with a utilityservice for an extended period of time, theyshould not be operated in excess of their baseload rating. Generally the base load rating of agenerator set is significantly lower than its primepower rating. Base load ratings for generator setsare available from the factory or your local Cum-mins Power Generation distributor.

Voltage: Available voltage choices are a functionof selected frequency. Default values are277/480, Series Wye.

Entering Loads

The next and most important step in sizing a gen-erator set is identifying every type and size of loadthe generator set will power. As with most opera-tions in GenSize, the loads can be entered either

from the menu under Projects, Add New Load, orfrom the icons located on the tool bar. Afterselecting a load type, the load entry form willappear. Each load form will open with load char-acteristic defaults which can all be changed.Enter all of the required information. If you are

unsure what any of the items are, check the onlineHelp for an explanation. As each load is entered,they will appear in a list on the left side of thescreen under the project you are working on.Selecting (with a mouse click) one of the loads inthe list will display the load operating characteris-tics on the right of the screen. Double clicking aload icon will open the load entry form for that loadand you can edit the load from here. The followingis intended to help you understand load parame-ters and the way they are calculated by GenSize.

Identify all of the different type and size loads thegenerator set will need to support. If you havemore than one load of a given size and type, youonly need to enter it once, unless you want eachof the loads to carry a different description. Thequantity of each load can be set when you enterthe load in the step starting sequence. Asdescribed later in this section

Cummins Power Generation has researched thestarting and running characteristics of many ofthe common loads and have included defaults for

these load characteristics in GenSize. You canchoose to use the defaults or, if you know thecharacteristics of your load are different, changethe load characteristic. If you have a load typeother than what is identified in GenSize, use amiscellaneous load to define the load starting andrunning requirements.

Based on the load characteristics, GenSize cal-culates values for running kW (RkW), runningkVA (RkVA), starting kVA (SkVA), starting kW(SkW), starting power factor (SPF), peak kVA(PkVA), peak kW (PkW), and running amps(RAmps). When non–linear loads are present, itmay be necessary to over–size the alternator,and GenSize calculates a value for the alternatorkW (AkW) for the load.

Note that when entering single–phase loads on athree–phase generator set, GenSize assumesthat all three phase loads will be balanced amongthe three phases. Therefore, the single–phase




1447 APPENDIX

loads are converted to an equivalent three–phaseload for sizing purposes. This results in thesingle–phase load current being distributedacross the three phases so the single–phase loadcurrent is divided by 1.73. When a single phaseload is entered for a three phase set application,

the actual single phase current will be displayedin the load entry form, but when the load isentered into a step (the step load is the balancedload applied to the generator), the step load cur-rent is converted to the equivalent three phasecurrent.






1467 APPENDIX

Light Load Calculations

Three different light load types can be entered:

Fluorescent – A low–pressure mercury type discharge lamp where most of the light is emitted by an excitedlayer of fluorescent material. The same load characteristics are used for ballast or electronic types. Bothare non–linear loads, but GenSize ignores the non–linearity for this load type since this is usually a smallpart of the total connected load.

Incandescent – Standard bulb type lamp assemblies, which use a filament to create light.

Discharge (HID) – Lamps that produce light by passing a current through a metal vapor; includes high pres-sure sodium, metal halide, and mercury vapor discharge lighting.

RkW If kVA entered: RkW = kVA x RPFIf Ramps entered: 1∅ RkW = (Ramps x voltage x RPF) ÷ 1000

3∅ RkW = (Ramps x voltage x RPF x 1.73) ÷ 1000RkVA If RkW entered: RkVA = RkW ÷ RPF

If Ramps entered: 1∅ RkVA = (Ramps x voltage) ÷ 1000

3∅ RkVA = (Ramps x voltage x 1.73) ÷ 1000RPF Running power factor as entered or defaultSkW SkW = RkW for incandescence and florescence

SkW = 0.75 x RkW for HIDSkVA SkVA = SkW ÷ SPFSPF SPF = RPF, except for HID where default SPF = 0.85AkW AkW = RkWRamps 1∅ Ramps = (RkW x 1000) ÷ (voltage x RPF)

3∅ Ramps = (RkW x 1000) ÷ (voltage x RPF x 1.73)

Air Conditioner Load Calculations

GenSize simply converts tons to horsepower for sizing air conditioning loads at 2 HP/ton as a conservative

estimate of the total load for a lower efficiency unit. If you want a more exact size and know the individualcomponent motor loads in the A/C equipment, enter them individually and come up with a demand factor forwhat loads are likely to start simultaneously.

RkW RkW = AC Tons x 2 x 0.746RkVA RkVA = RkW ÷ RPFRPF Running power factor as entered or default from databaseSkW High Inertia SkW = SkVA x SPF

Low Inertia SkW = SkVA x SPF x 0.6SkVA SkVA = HP x (LRkVA/HP) x SkVA factor, where

LRkVA/HP is the average kVA/HP for the NEMA Code letter of the motor, and SkVA fac-tor is 1.0 for full voltage starting, or from reduced voltage starting table (see Reduced Volt

age Starting Method)SPF As entered, or default values from database by HP and starting method

For loads that are designated to automatically cycle on and off:PkW PkW = SkWPkVA PkVA = SkVA

AkW (non–VFD) AkW = RkW except solid–state starter where AkW = 2.0 x RkW unless a bypasscontactor is used, then AkW = RkW

AkW (VFD) Conventional AC Inverter: AkW = 2.0 x RkWPulse Width Modulated: AkW = 1.4 x RkW




1477 APPENDIX

DC Drive: AkW = 2.0 x RkWRamps 1∅ Ramps = (HP x 746) ÷ (voltage x Eff. x RPF)

3∅ Ramps = (HP x 746) ÷ (1.73 x voltage x Eff. x RPF)

Battery Charger Load Calculations

A battery charger is a silicon–controlled rectifier (SCR) assembly used to charge batteries. A battery char-ger is a non–linear load requiring an oversized alternator.

RkW RkW = RkVA x RPFRkVA RkVA = (Output kVA x Recharge Rate) ÷ EfficiencyRPF Running power factor as entered or defaultSkW SkW = RkWSkVA SkVA = RkVASPF SPF = RPFAkW For 3 pulse, AkW = 2.5 x RkW

For 6 pulse, AkW = 1.4 x RkWFor 12 pulse, AkW = 1.15 x RkWWith input filter, AkW = 1.15 x RkW

Ramps 1∅ Ramps = (RkVA x 1000) ÷ voltage3∅ Ramps = (RkVA x 1000) ÷ (voltage x 1.73)

Medical Imaging Load Calculations

GenSize calculates a peak voltage dip for when a medical imaging load is operated. This dip must be limit-ed to 10% to protect the quality of the image. If the peak voltage dip is set higher in the project parameters,GenSize will automatically lower it and notify you. The generator set is then sized to limit the voltage dip to10% when the medical imaging equipment is operated with all other loads running. If multiple medicalimage loads are used, the peak voltage dip is calculated for the single largest load and assumes only thesingle largest load will be operated at any one time.

Note that GenSize assumes that the medical imaging equipment is not being operated while loads are start-ing, so the starting voltage dip is calculated separately and is allowed to exceed 10%.

RkW If RkVA entered: RkW = RkVA x RPFIf Ramps entered: 1∅ RkW = (Ramps x voltage x RPF) ÷ 1000

3∅ RkW = (Ramps x voltage x RPF x 1.73) ÷ 1000RkVA If Ramps entered: RkVA = RkW ÷ RPFRPF Running power factor as entered or defaultSkW SkW = RkWSkVA SkVA = SkW ÷ SPFPkW PkW = PkVA x SPFPkVA As entered, or 1∅ PkVA = (Pamps x voltage) ÷ 1000

3∅ PkVA = (Pamps x voltage x 1.73) ÷ 1000

SPF SPF = SkVA ÷ SkWAkW AkW = RkWRamps 1∅ Ramps = (RkVA x 1000) ÷ voltage

3∅ Ramps = (RkVA x 1000) ÷ (voltage x 1.73)

Motor Load Calculations

If the motor load is powered by a variable speed or variable frequency drive or is an AC drive on a DC motor,select Variable Frequency Drive (VFD). A VFD is a non–linear load requiring an oversized alternator tomatch the running load requirements. On the other hand, since VFDs ramp the load on, the starting require-




1487 APPENDIX

ments will be reduced compared to a motor started across the line. Select PWM if the VFD is of the pulsewidth modulated type. PWM type VFDs require less oversizing than non–PWM types.

Motor starting requirements can be reduced by applying some type of reduced voltage or solid state starter.Application of these devices can result in smaller generator set recommendations. However, caution mustbe used when applying any of these starting methods. First of all, motor torque is a function of the applied

voltage and all of these methods result in lower voltage during starting. These starting methods should onlybe applied to low inertia motor loads unless it can be determined the motor will produce adequate accelerat-ing torque during starting. Additionally, these starting methods can produce very high inrush currents whenthey transition from start to run if the transition occurs prior to the motor reaching very near operating speed,resulting in starting requirements approaching an across the line start. GenSize assumes the motor reach-es near rated speed before this transition, ignoring these potential inrush conditions. If the motor does notreach near rated speed prior to transition, excessive voltage and frequency dips can occur when applyingthese starters to generator sets. If unsure how your starter and load will react, use across–the–line starting.

For across–the–line motor starting, select low inertia load if you know the load requires low starting torqueat low speeds. This will reduce the starting kW requirements for the generator set and can result in a smallerset. Low inertia loads are typically centrifugal fans and pumps. If unsure, use high inertia (leave low inertia

unselected).

RkW If HP entered: RkW = (HP x 0.746) ÷ Running EfficiencyIf kW entered: RKW = kW ÷ Running EfficiencyIf Ramps entered: 1∅ RkW = (Ramps x voltage x RPF x Efficiency) ÷ 1000

3∅ RkW = (Ramps x voltage x RPF x Efficiency x 1.73) ÷ 1000RkVA RkVA = RkW ÷ RPFRPF Running power factor as entered or default from databaseSkW High Inertia SkW = SkVA x SPF

Low Inertia SkW = SkVA x SPF x 0.6SkVA SkVA = HP x (LRkVA/HP) x SkVA factor, where LrkVA/HP is the average kVA/HP for the

NEMA Code letter of the motor, and SkVA factor is 1.0 for full voltage starting, or fromreduced voltage starting table (see Reduced Voltage Starting Method)

SPF As entered, or default values from database by HP and starting method

For loads that are designated to automatically cycle on and off:PkW PkW = SkWPkVA PkVA = SkVA


AkW (VFD) Conventional AC Inverter: AkW = 2.0 x RkWPulse Width Modulated: AkW = 1.4 x RkWDC Drive: AkW = 2.0 x RkW

Ramps 1∅ Ramps = (HP x 746) ÷ (voltage x Efficiency x RPF)3∅ Ramps = (HP x 746) ÷ (1.73 x voltage x Efficiency x RPF)

Fire Pump Load Calculations

GenSize will size the generator limiting the peak voltage dip to 15% when starting the fire pump,with allother non–surge loads running. This is to meet North American fire code requirements. The generator setdoes not have to be sized to provide the locked rotor kVA of the fire pump motor indefinitely. That wouldresult in an oversized generator set, which could experience maintenance and reliability issues from beingunder–utilized.

Whenever a reduced voltage starter is used for a fire pump motor, the user should consider sizing foracross–the–line starting because the fire pump controller includes either a manual–mechanical, manual–




1497 APPENDIX

electrical, or automatic means to start the pump across–the–line in the case of a controller malfunction.GenSize will not disallow use of reduced voltage starters for fire pumps, however.

RkW If HP entered: RkW = HP x 0.746 ÷ Running EfficiencyIf kW entered: RkW = kW ÷ Running EfficiencyIf Ramps entered: 1∅ RkW = (Ramps x voltage x RPF x Efficiency) ÷ 1000

3∅ RkW = (Ramps x voltage x RPF x Efficiency x 1.73) ÷ 1000RkVA RkVA = RkW ÷ RPFRPF Running power factor as entered or default from databaseSkW High Inertia SkW = SkVA x SPF

Low Inertia SkW = SkVA x SPF x 0.6SkVA SkVA = HP x (LRkVA/HP) x SkVA factor, where

LrkVA/HP is the average kVA/HP for the NEMA Code letter of the motor, andSkVA factor is 1.0 for full voltage starting, or from reduced voltage starting table (seeReduced Voltage Starting Method)

SPF As entered, or default values from database by HP and starting methodPkW PkW = SkWPkVA PkVA = SkVA


AkW (VFD) Conventional AC Inverter: AkW = 2.0 x RkWPulse Width Modulated: AkW = 1.4 x RkWDC Drive: AkW = 2.0 x RkW

Ramps 1∅ Ramps = (HP x 746) ÷ (voltage x Efficiency x RPF)3∅ Ramps = (HP x 746) ÷ (1.73 x voltage x Efficiency x RPF)

UPS Load Calculations

A static UPS uses silicon controlled rectifiers (SCR) or another static device to convert AC voltage to DC forcharging batteries, and an inverter to convert DC to conditioned AC power to supply the load. A UPS is anon–linear load and may require an oversized alternator. Some incompatibility problems between genera-

tor sets and static UPSs have led to many misconceptions about sizing the generator set for this type ofload. Past problems did occur, and the recommendation from UPS suppliers at that time was to oversize thegenerator set from two to five times the UPS rating. Even then some problems persisted, and since thenthose incompatibility problems have been addressed by most UPS manufacturers. It is more cost effectiveto require generator compatibility of the UPS supplier than to oversize the generator.

If the batteries are discharged when the UPS is operating on the generator set, the generator set must becapable of supplying the rectifier for battery charging and the inverter to supply the load. A second reason touse the full UPS rating is that additional UPS load may be added in the future up to the nameplate rating.The non–linear load sizing factors used by GenSize are based on the level of harmonics the UPS induces inthe generator output with the UPS fully loaded. Since the harmonics increase at lighter loads, selecting thelarger capacity alternator helps to offset this effect.

For multiple redundant UPS systems, size the generator set for the combined nameplate ratings of the indi-vidual UPSs. Redundant system applications are those where one UPS is installed to back up another andthe two are on–line at all times with 50% or less load.

UPS equipment often has varying power quality requirements depending on the operating mode. When therectifier is ramping up, often relatively broad frequency and voltage swings can occur without disruptingequipment operation. However, when the bypass is enabled, both frequency and voltage must be veryconstant, or an alarm condition will occur. This occurs when rapidly changing UPS input frequency results






1517 APPENDIX

User Defined Load Calculations

RkW If kW entered: RkW = KwIf kVA entered: RkW = kVA x RPFIf Ramps entered: 1∅ RkW = (Ramps x voltage x RPF) ÷ 1000

3∅ RkW = (Ramps x voltage x RPF x 1.73) ÷ 1000RkVA If kW entered: RkVA = RkW

÷RPF

If RkVA entered: RkVA = kVAIf Ramps entered: 1∅ RkVA = (Ramps x voltage) ÷ 10003∅ RkVA = (Ramps x voltage x 1.73) ÷ 1000

RPF Running power factor as entered or defaultSkW If kW entered: SkW = kW

If kVA entered: SkW = SkVA x SPFIf Starting amps entered:1∅ SkW = (Ramps x voltage x RPF) ÷ 1000

3∅ SkW = (Ramps x voltage x RPF x 1.73) ÷ 1000SkVA SkVA = SkW ÷ SPFSPF SPF = RPF, except for HID where default SPF = 0.85 and RPF = 0.90PkW PkW = SkWPkVA PkVA = SkVAAkW AkW = RkWRamps 1∅ Ramps = (RkW x 1000) ÷ (voltage x RPF)

3∅ Ramps = (RkW x 1000) ÷ (voltage x RPF x 1.73)

Figure 7–2. GenSize Application Project Window




1527 APPENDIX

Entering Loads Into Steps

After entering the loads, you need to enter all ofthe project loads into Load Steps. Open the firstload step by clicking on the Steps folder on the leftof the screen. Note that initially, there are noloads in the Step. Step sequence loading canreduce the size of generator set required whenusing multiple steps. Multiple transfer switchescan be used to connect load to the generator setat different times, simply by adjusting the transfertime delays on the individual switches. Simplyallow a few seconds between steps to allow thegenerator set to stabilize with each load step.

To enter individual loads into the step, simply clickand drag the load over the step. Once the load isplaced into a step, you can set the load quantity inthe step by right clicking and selecting Set Quanti-ty from the drop down menu. Alternatively, eachtime you click and drag a load into the step, thequantity will increase.

To enter multiple loads into the step, click on theloads folder and all loads are listed on the rightside of the screen. Using the Shift or Ctrl key andthe mouse, select the desired loads, click on anyof the selected loads on the right, and drag to thestep. All of the selected loads should appear inthe step.

Use the tool bar to add one or more additionalsteps, as desired. You can view the loads andsteps using View on the menu to find out eitherwhich steps individual loads were placed in or toget a summary of all the loads in each step.

Load Step Considerations

For many applications, the generator set will besized to be able to pick up all of the loads in asingle step. For some applications it is advanta-geous to start the loads with the larger startingsurge requirements first, then after those loadsare running, to start the rest of the loads in differ-ent steps. The starting sequence of loads mightalso be determined by codes in which the emer-gency loads must come on first, then the standbyequipment, then the optional loads.

Starting step sequencing of generator sets maybe accomplished with transfer switches usingtransfer time delays, load sequencer, or othercontroller, such as a PLC. You may use this

application to tell your distributor how many start-ing steps your application requires. Remember,even though there is a controlled initial loadingsequence, there may be uncontrolled load stop-ping and starting of certain loads and you maywish to check surge loading under those condi-

tions.

Step Sequence Guidelines

Single Step Simultaneous Starting: One com-monly used approach is to assume that all con-nected loads will be started in a single step,regardless of the number of transfer switchesused. This assumption will result in the most con-servative (largest) generator set selection. Use asingle step load unless something will be added,such as multiple transfer switches with staggeredtime delays or a step load sequencer.

Single Step with a Diversity Factor: This is similarto simultaneous starting in a single step, exceptthat an estimated diversity factor, of perhaps80%, is applied to reduce the SkVA and SkWtotals to account for whatever automatic startingcontrols may be provided with the load equip-ment.

Multiple Step Sequence: Sequenced starting ofloads (where possible) will often permit the selec-tion of a smaller generator set. GenSize assumes

that adequate time is allowed between load stepsfor the generator set voltage and frequency to sta-bilize, typically 5–10 seconds.

Consider the following when controls or delaysare provided to step sequence the loads onto thegenerator set:

• Start the largest motor first.• When starting motors that use electronic

drives (VFD or VSD) the largest motor firstrule may not apply. Using electronic drives

for starting and running motors allows thedesigner to better control the actual loadapplied to the generator set by controlling themaximum current load, rate of load applica-tion, etc. The thing to remember about theseloads is that they are more sensitive to volt-age variation than motors that are started”across–the–line.”

• Load the UPS last. UPS equipment is typi-cally frequency sensitive, especially to the




1537 APPENDIX

rate of change of frequency. A pre–loadedgenerator set will be more stable in acceptingUPS load.

• For each step, the SkW required is the total ofthe RkW of the previous step(s) plus the SkWfor that step.

Recommendations and Reports

The following is intended to help you understandthe GenSize recommendation for a generator setand available reports that can be printed. Fig-ure 7–3 illustrates the default screen on whichGenSize makes its recommendation for thesingle Cummins Power Generation generator setmodel that most closely matches the current proj-ect parameters. This screen can be toggled withthe screen illustrated in Figure 7–4 on which allgenerator set models that match the parameters

can be viewed. You may find it helpful to view thelatter display to appreciate the differences in per-formance between all of the models that could dothe job, any of which you could select for the proj-ect. You can also print out Reports for distributionand review.

The recommended model(s) will be highlighted ingreen in the upper half of the screen. In the lowerhalf of the screen are displayed the parametersfor the recommended generator set. Theseinclude:

• Generator Set Requirements: This tab sum-marizes the Duty, Voltage, Altitude, Phase,Voltage Dips, and other parameters.

• Load Running/Surge Requirements: Thistab summarizes all of the load requirementsfor the project. Pct. Rated Load provides aquick way of determining how much genera-tor set running capacity is being used.

• Generator Set Configuration: This tab enu-merates the alternator frame size, number ofleads, whether the alternator is reconnect-

able, whether the alternator has anincreased capacity for motor starting, thevoltage range, whether the alternator has anextended stack, and whether the alternatorcan provide full single–phase output. It alsolists the engine model, displacement, num-ber of cylinders, fuel, and the altitude andambient temperature derating knees andslope values.

The report grid displays information about therecommended generator set and allows compari-son with other generator sets. Following is a dis-cussion of some of the important headings on thisgrid:

Site Rated Standby (Prime) kW: Displays the siterated standby or prime kW (prime power duty isalready derated 10 percent). If the display is red,the site rated kW is less than the load running kW,or the running load kW is less than 30 percent ofthe site rated set kW. A recommended generatorset must meet the running load requirement andrun at least 30 percent of rated capacity to be rec-ommended.

If the display is yellow , the load running kW is lessthan 30 percent of the site rated set kW. Running

generator sets at less than 30 percent of ratedload can be accomplished by lowering the mini-mum percent rated load value in the New ProjectParameters.

Site Rated Alternator Max kW (Temperature Rise): Displays the site–rated alternator kW forthe temperature rise selected in the current proj-ect parameters. If the display is red, the alterna-tor cannot maintain the temperature rise for yourconnected load requirement, either Running kWor Alternator kW.

Site Rated Alternator Max kVA (Temperature Rise): Displays the site rated alternator kVA forthe temperature rise set in the New ProjectParameters. If the display/column is red, thealternator cannot maintain your temperature risefor the load Running kVA requirement. The maxi-mum alternator rated kVA capacity is shown in thegrid.

The altitude knee for alternators, however, is1000m (3280 ft) and the temperature knee 40° C(104° F). Alternator Max kW will be derated 3%

per 500m (1640 ft) of altitude above the knee and3% per 5° C (9° F) of ambient temperature overthe knee.




1547 APPENDIX

F i g u r e 7 – 3 . R

e c o m m e n d e d G e n e r a t o r S e t W i n d

o w




1557 APPENDIX

F i g u r e 7 – 4 . A l l G e n e r a t o r S e t W i n d o w




1567 APPENDIX

Site Rated Max SkW and Max SkVA: Displays thesite–rated (derated when necessary for altitudeand ambient temperature) maximum SkW andSkVA the generator set configuration can accom-modate. If the display is red, the generator setcannot recover to a minimum of 90 percent of

rated voltage with required Step or Peak load.One of the sizing philosophies for surge loading isthat, with the surge load applied, the generatorset must be able to recover to 90 percent of ratedvoltage so that motors can develop adequateaccelerating torque. If the generator set recoversto 90 percent of rated voltage, a motor will devel-op 81 percent of rated torque, which has beenshown by experience to provide acceptablemotor starting performance.

If the display is yellow , the generator set can

recover to a minimum of 90 percent of rated volt-age with required surge load, but only becausethe surge requirement has been reduced. Gen-Size will reduce the surge requirement in recogni-tion of the fact that the generator set output volt-age is reduced while loads having starting powerrequirements approaching the maximum genera-tor set capacity are starting.

Temperature Rise At Full Load: Displays the tem-perature rise the alternator will not exceed whilesupplying load up to and including the generator

set full–load rating. Each individual generator setmodel will have one or more of the following tem-perature rise alternators available which may bespecified in the current project parameters: 80° C,105°C, 125° C and 150° C. Of course, the actualtemperature rise of an alternator is a function ofactual connected load. Therefore, GenSize mayrecommend a generator set with a lower or highertemperature rise option than specified in the NewProject Parameters since the set recommenda-tion is based on connected load. Connected loadmay be less than the full generator set capacity or,

in the case of non–linear loads, the alternator maybe required to be rated at greater than the setcapacity. In any case, the set recommendationwill limit the alternator temperature rise to thatspecified in the New Project Parameters.

Excitation: Displays the type of excitation systemto be supplied with a generator set. If the displayis red, the generator set is shunt excited and thepercentage of non–linear load exceeds 25 per-

cent of the load running requirement, RkW. ThePMG excitation system is recommended forapplications that have a high–linear load content.Unless the PMG option is unavailable, CumminsPower Generation does not recommend usingshunt excited generator sets if the non–linear

load requirement is more than 25 percent of thetotal load requirement.

The non–linear load requirement is calculated byadding the Running kW from all of the loadswhere Alternator kW exceeds Running kW . Thiswill be the case for UPS loads, variable frequencymotors, and solid state motor starters which arenot equipped with an automatic bypass. ThisAlternator kW sum is then divided by the sum ofthe Running kW from all of the loads.

Why a generator set may not be recommended: Several factors can cause a generator set to notbe recommended.

• Running kW requirement may exceed therating of the generator set. Project parame-ters such as altitude, ambient temperatureand prime power duty may cause the genera-tor set to be derated and fall below projectrequirements.

• The Running kW may be below the minimumof 10 to 30 percent of rated generator setcapacity, as specified in the current projectparameters (30 percent is default, as recom-mended by Cummins Power Generation).

• The surge kW requirement may exceed gen-erator capacity, which may have fallen belowproject requirements because of derating foraltitude and ambient temperature. Gen-Size uses the greater Cumulative kW andPeak kW to determine the load surge kW.

• The surge kVA exceeds generator set capac-ity. The surge kVA requirement is similar tothe surge kW requirement except that thereis no derating for altitude or ambient temper-

ature. GenSize uses the greater of cumula-tive kVA and Peak kVA (if any) to determinethe load surge kVA requirement.

• The alternator kW required exceeds thealternator capacity, which may be derated foraltitude and ambient temperature by the proj-ect parameters. The altitude knee for alter-nators, however, is 1000m (3280 ft) and thetemperature knee 40° C (104° F). Alternator




1577 APPENDIX

kW will be derated 3% per 500m (1640 ft) ofaltitude above the knee and 3% per 5° C(9° F) of ambient temperature over the knee.

• The alternator kVA required exceeds alterna-tor capacity, which can be derated by altitudeand temperature in the same way as the

alternator kW.• The total non–linear load requirementexceeds 25 percent of the total load require-ment. This will exclude shunt–excited gener-ators where PMG excitation is not available.The total non–linear load requirement is thesum of the Alternator kW values of all of thenon–linear loads.

• The calculated voltage and frequency dipsexceed the limits set in the current projectparameters. – Starting voltage dip is calculated using

the higher of two values: dip based onthe maximum Step kW or on the maxi-mum step kVA.

– Peak voltage dip is calculated only ifloads in the project exhibit a runningsurge (cyclic loads or loads like medicalimaging that have a high peak powerrequirement when they are operated.

– Frequency dip is calculated using thehigher of two values: maximum Step kWor Peak kW from loads which exhibit run-ning surge.

• The message, “No generator set is availablethat meets your running load requirements”usually means that something in the NewProject Parameters has been changed afterhaving specified the running load. Forinstance, you will get the message if youchange from diesel to natural gas fuel or fromno sound attenuation to Quite Site and therunning load you had specified exceeds thecapacity of the largest natural gas or Quite

Site generator set available. It may alsomean that your project falls into a “gap” in theCummins Power Generation product line. Atthis point, lowering the minimum percentrated load in the project parameters couldallow a recommended set. If this is the case,

contact your local Cummins Power Genera-tion distributor for help.

• The message, “No generator set is availablewhich meets your frequency or voltage diprequirements” generally means that thesurge requirement of some load step is forc-ing selection of such a large generator setthat the steady state running load falls below30 percent of the generator set capacity.Since Cummins Power Generation does notrecommend running at less than 30 percentof rated capacity, no set can be recom-

mended. At this point, you may have severalchoices: – Increase the allowable voltage or fre-

quency dip. – Reduce the minimum percent rated load

to less than 30 percent. – Apply loads in more steps to lower the

individual step surge load. – Provide reduced–voltage motor start-

ing. – Parallel generator sets. – Add loads that do not have a high start-

ing surge (lights, resistive loads, etc.).Reports

Several type of reports can be generated for theproject that is open, a Step/Load Detail, Stepsand Dips Detail, and a Recommended Generatorreport. These can be viewed on screen for reviewprior to completion, saved for submittal or printed.Figure 7–5 is an example of the RecommendedGenerator report.




1587 APPENDIX

Figure 7–5 Recommended Generator Report in View Mode.






1607 APPENDIX

Full Voltage Motor Starting

Starting: Full voltage, across–the–line starting is typical unless it is necessary to reduce motor starting kVAbecause of the limited capacity of the generator set or to limit voltage dip during motor starting. There is nolimit to the HP, size, voltage, or type of motor.

Application Notes: This method is most common because of its simplicity, reliability, and initial cost. Noteon the kVA and torque curves that starting kVA remains fairly constant until the motor almost reaches fullspeed. Also note that kW peaks at about 300 percent of rated kW near 80 percent of synchronous speed.

100

200

300

400

500

600

20 40 60 80 100

TYPICAL TORQUE AND KVA CURVES FORSQUIRREL CAGE INDUCTION MOTORS

KVA

TORQUE

SPEED (% SYNCHRONOUS)

k V A & T O R Q U E ( % F . L . )

MOTOR1

2

3

START: CLOSE 1–2–3RUN: NO CHANGE

MOTOR STARTING DIAGRAM

L I N E

Autotransformer Motor Starting, Open Transition

Starting: The autotransformer is in the circuit only during starting to reduce voltage to the motor. The open-ing of the circuit during transition can cause severe transients, which may even be able to cause nuisancetripping of circuit breakers.

Application Notes: Open transition switching of reduced voltage starters should be avoided in generator setapplications, especially when the motors are not brought up to full speed at the time of transition. The rea-son for this is that the motor slows down and gets out of synchronization during the switching transition. The

result is similar to paralleling generator sets out of phase. The kVA drawn immediately after switching canexceed starting kVA. Also note that the starting power factor is lower when an autotransformer is used.

100

200

300

400

500

600

20 40 60 80 100


KVA


k V

A & T O R Q U E ( % F . L . )

TORQUE

MOTOR

1 2

3

4

5

6

78

START: CLOSE 2–3–5–6–7RUN: OPEN 2–3–5–6–7; CLOSE 1–4–8


L I N E




1617 APPENDIX

Autotransformer Motor Starting, Closed Transition

Starting: The circuit is not interrupted during starting. During transfer, part of the autotransformer windingremains in the circuit as a series reactor with the motor windings.

Application Notes: Closed transition is preferred over open transition because of less electrical distur-bance. The switching, however, is more expensive and complex. It is the most commonly used reducedvoltage starting method for large motors with low load torque requirements, such as sewage lift pumps andchillers. The principle advantage is more torque per current than with other reduced voltage starting meth-ods. Operation can be automatic and/or remote. Also note that the starting power factor is lower when anautotransformer is used.

100

200300

400

500

600

20 40 60 80 100


KVA

TORQUE


k V A & T O

R Q U E ( % F . L . )

MOTOR

START: CLOSE 6–7–2–3–4TRANSFER: OPEN 6–7RUN: CLOSE 1–5


1

2

3

5

6

74

L I N E

Reactor Motor Starting, Closed Transition

Starting: Reactor starting has the advantage of simplicity and closed transition, but results in lower startingtorque per kVA than with autotransformer starting. Relative torque, however, improves as the motor accel-erates.

Application Notes: Reactor starting is generally not used except for large, high–voltage or high–currentmotors. The reactors must be sized for HP and voltage and may have limited availability. Typically, reactorstarting costs more than autotransformer starting for smaller motors, but is simpler and less expensive forlarger motors. Starting power factor is exceptionally low. Reactor starting allows a smooth start with almostno observable disturbance on transition and is well suited for applications such as centrifugal pumps orfans.

100

200

300

400

500

600

20 40 60 80 100


KVA


k V A & T O R Q U

E ( % F . L . )

TORQUE

MOTOR

START: CLOSE 1–2–3RUN: CLOSE 4–5–6


1

2

3

5

6

4 L I N E




1627 APPENDIX

Resistor Motor Starting, Closed Transition

Starting: Resistor starting is occasionally used for smaller motors where several steps of starting arerequired and no opening of motor circuits between steps is allowed.

Application Notes: Also available as a stepless transition starter which provides a smoother start. Resistorstarting is usually the least expensive with small motors. Accelerates loads faster because the voltageincreases with a decrease in current. Has a higher starting power factor.

100

200

300

400

500

600

20 40 60 80 100


TORQUE


k V A & T O R Q U E ( % F . L . )

KVAMOTOR

START: CLOSE 1–2–3

SECOND STEP: CLOSE 4–5–6THIRD STEP: CLOSE 7–8–9


1

2

3

5

6

4 7

8

9

L I N E

Star–Delta Motor Starting, Open Transition

Starting: Star–Delta starting requires no autotransformer, reactor, or resistor. The motor starts star–con-nected and runs delta–connected.

Application Notes: This starting method is becoming more popular where low starting torques are accept-able. It has the following disadvantages:

1. Open transition. Closed transition is available at extra cost.

2. Low torque.

3. No advantage when the motor is powered by a generator set unless the motor reaches synchronousspeed before switching. In applications where the motor does not reach synchronous speed, the generatorset must be sized to meet the surge.

100

200

300

400

500

600

20 40 60 80 100


KVA


k V A & T O R Q

U E ( % F . L . )

TORQUE

MOTOR

1

2

3

START: CLOSE 1–2–3–4–5–6RUN: OPEN 4–5–6; CLOSE 7–8–9


4 5 67

8

9

L I N E




1637 APPENDIX

Part Winding Motor Starting, Closed Transition

Starting: Part winding starting is less expensive because it requires no autotransformer, reactor, or resistorand uses simple switching. Available in two or more starting steps depending on size, speed, and voltage ofmotor.

Application Notes: Automatically provides closed transition. First, one winding is connected to the line;after a time interval, the second winding is paralleled with the first. Starting torque is low and is fixed by themotor manufacturer. The purpose of part winding is not to reduce starting current but to provide startingcurrent in smaller increments. There is no advantage to this method if the motor is powered by a generatorset unless the motor can reach synchronous speed before transition to the line.

100

200

300

400

500

600

20 40 60 80 100


KVA


k V A & T O R Q

U E ( % F . L . )

TORQUE

MOTOR

1

2

3

START: CLOSE 1–2–3RUN: CLOSE 4–5–6


4

5

6

L I N E

Wound Rotor Motor Starting

Starting: A wound rotor motor can have the same starting torque as a squirrel cage motor but with lesscurrent. It differs from squirrel cage motors only in the rotor. A squirrel cage motor has short circuit bars,whereas a wound rotor motor has windings, usually three–phase.

Application Notes: Starting current, torque, and speed characteristics can be changed by connecting theproper amount of external resistance into the rotor. Usually, wound rotor motors are adjusted so that thestarting kVA is about 1.5 times running kVA. This is the easiest type of motor for a generator set to start.

100

200

300

400

500

600

20 40 60 80 100

MOTORROTOR

1

2

3

START: CLOSE 1–2–3STEP #1: CLOSE 4–5STEP #2: cLOSE 6–7RUN: CLOSE 4–5–6


L I N E

4

5

6

7

8

9

RESISTORS

TYPICAL TORQUE AND KVA CURVES FORWOUND ROTOR MOTORS


k V A &

T O R Q U E ( % F . L . )

TORQUE

KVA




1647 APPENDIX

Synchronous Motor Starting

Starting: Synchronous motors can use most of the starting methods discussed. Synchronous motors rated20 HP and greater have starting characteristics similar to wound rotor motors.

Application Notes: Synchronous motors are in a class by themselves. There are no standards for perfor-mance, frame size, or connections. Motors rated 30 HP or less have high locked rotor currents. They canbe used in applications where power factor correction is desired. (Use the standard code letter when theactual letter is not known.)

General Application Note

If the reduced voltage motor starter has a time or rate adjustment, adjust the settings to obtain about twoseconds between taps. This allows time for the motor to approach rated speed and thus reduce the peakkVA at the time of switching, as shown below. Note that at the minimum setting there is not much improve-ment over full voltage starting.

In some applications the inrush current is so low that the motor shaft will not start to turn on the first tap, noreven the second. For those applications there is little reduction of starting kVA from the standpoint of the

generator set.

100

200

300

400

500

600


20 40 60 80 100

KVA PEAK AT MINIMUMTIME OR RATE SETTING

OF STARTER

KVA PEAK AT MAXIMUMTIME OR RATE SETTING

OF STARTER

FULL–VOLTAGEKVA CURVE

k V A ( % F . L . )




1657 APPENDIX

C. World Voltages and SuppliesCountry Frequency

(Hz)Supply Voltage Levels in Common Use (V)

Abu Dhabi(United Arab Emirates) 50 415/250Afghanistan 50;60 380/220;220

Algeria 50 10 kV; 5.5 kV;380/220; 220/127

Angola 50 380/220; 220Antigua 60 400/230;230

Argentina 50 13.2 kV;6.88 kV; 390/225;339/220;220

Australia

Austria

50

50

22 kV; 11 kV;6.6 kV; 440/250;415/240; 24020 kV; 10 kV; 5 kV;380/220; 220

Bahamas 60 415/240; 240/120;208/120; 120

Bahrain 50;60 11 kV; 400/230;380/220;230;220/110

Bangladesh 50 11 kV; 400/230; 230Barbados 50 11 kV; 3.3 kV;

230/115; 200/115

Belgium 50 15 kV; 6kV;380/220; 220/127, 220Belize 60 440/220; 220/110Bermuda 60 4.16/2.4 kV;

240/120; 208/120Bolivia 50;60 230/115;

400/230/220/110Botswana 50 380/220;220Brazil 50;60 13.8 kV; 11.2 kV;

380/220, 220/127Brunei 50 415/230Bulgaria 50 20 kV; 15 kV;

380/220; 220Burma 50 11 kV; 6.6 kV;

400/230; 230BurundiCambodia(Khmer Republic)

50 380/220; 208/120;120

Cameroon 50 15 kV; 320/220;220

Canada 60 12.5/7.2 kV;600/347; 240/120;208/120; 600;480; 240

Canary Islands 50 380/220; 230Cape Verde Islands 50 380/220; 127/220Cayman Islands 60 480/240; 480/227;

240/120; 208/120Central African Republic 50 380/220Chad 50 380/220; 220China 50 380/220 50Hz

Chile 50 380/220; 220

Colombia 60 13.2 kV; 240/120;120

Costa Rica 60 240/120; 120

Cuba 60 440/220; 220/110Cyprus 50 11 kV; 415/240;

240Czechoslovakia 50 22 kV; 15 kV; 6 kV;

3 kV; 380/220; 220Dahomey 50 15 kV; 380/220;

220Denmark 50 30 kV; 10 kV;

380/220;220Dominica(Windward Islands) 50 400/230Dominican Republic 60 220/100; 110Dubai (United ArabEmirates)

50 6.6 kV; 330/220;220

Ecuador 60 240/120; 208/120;220/127; 220/110

Country Frequency (Hz)

Supply Voltage Levels in Common Use (V)

Egypt (United ArabRepublic)

50 11 kV; 6.6 kV;380/220; 220

Eire (Republic ofIreland)

50 10 kV; 380/220; 220

El Salvador 60 14.4 kV; 2.4 kV;240/120

Ethiopia 50 380/220; 220Faeroe Islands(Denmark) 50 380/220Falkland Islands (UK) 50 415/230; 230Fiji 50 11 kV; 415/240;

240Finland 50 660/380; 500;

380/220; 220France 50 20 kV; 15 kV;

380/220; 380; 220; 127French Guiana 50 380/220French Polynesia 60 220; 100Gabon 50 380/220Gambia 50 400/230; 230Germany (BRD) 50 20 kV; 10 kV; 6 kV;

380/220; 220Germany (DDR) 50 10 kV; 6kV;

660/380; 380/220;220/127; 220; 127

Ghana 50 440/250; 250Gibraltar 50 415/240Greece 50 22 kV; 20 kV;

15 kV; 6.6 kV;380/220

Greenland 50 380/220Grenada (WindwardIslands)

50 400/230; 230

Guadeloupe 50;60 20 kV; 380/220; 220Guam (Mariana Islands) 60 13.8 kV; 4 kV;

480/277; 480;240/120; 207/120

Guatemala 60 13.8 kV; 240/120Guyana 50 220/110Haiti 60 380/220; 230/115;

230; 220; 115Honduras 60 220/110; 110Hong Kong (and

Kowloon)

50 11 kV;

346/200; 200Hungary 50 20 kV; 10 kV;380/220; 220

Iceland 50 380/220; 220India 50; 25 22 kV; 11kV;

440/250; 400/230;460/230; 230

Indonesia 50 380/220; 2201127Iran 50 20 kV; 11kV;

400/231; 380/220;220

Iraq 50 11 kV; 380/220; 220Israel 50 22kV; 12.6 kV;

6.3 kV; 400/230;230

Italy 50 20 kV; 15 kV;10 kV; 380/220;220/127; 220

Ivory Coast 50 380/220; 220Jamaica 50 4/2.3 kV; 220/110

Japan 50; 60 6.6 kV;200/100;22 kV; 6.6 kV;210/105; 200/100; 100

Jordan 50 380/220; 220Kenya 50 415/240; 240Korea Republic (South) 60 200/100; 100Kuwait 50 415/240; 240Laos 50 380/220Lebanon 50 380/220; 190/110;

220; 110Lesotho 50 380/220; 220Liberia 60 12.5/7.2 kV;

416/240; 240/120;208/120




1667 APPENDIX



Libyan Arab Republic 50 400/230; 220/127;230; 127

Luxembourg 50 20 kV; 15 kV;380/220; 220

Manila 60 20 kV; 6.24 kV;3.6 kV; 240/120

Martinique 50 220/127; 127Mauritania 50 380/220Mauritius 50 400/230; 230Macao 50 380/220; 220/110Malagassy Republic(Madagascar)

50 5 kV; 380/220;220/127

Malawi 50 400/230; 230Malaysia (West) 50 415/240; 240Mali 50 380/220; 220/127;

220; 127Malta 50 415/240Mexico 60 13.8 kV; 13.2 kV;

480/277; 220/127;220/120

Monaco 50 380/220; 220/127;220; 127

Montserrat 60 400/230; 230Morocco 50 380/220; 220/127

Mozambique 50 380/220Muscat and Oman 50 415/240; 240Naura 50 415/240Nepal 50 11 kV; 400/220; 220Netherlands 50 10 kV; 3 kV;

380/220; 220Netherlands Antilles 50; 60 380/220; 230/115;

220/127; 208/120New Caledonia 50 220New Zealand 50 11 kV; 415/240;

400/230; 440;240; 230

Nicaragua 60 13.2 kV; 7.6 kV;240/120

Niger 50 380/220; 220Negeria 50 15 kV; 11 kV;

400/230; 380/220;230; 220

Norway 50 20 kV; 10 kV; 5 kV;380/220; 230

Pakistan 50 400/230Panama 60 12 kV; 480/227;

240/120; 208/120Papua New Guinea 50 22 kV; 11 kV;

415/240; 240Paraguay 50 440/220; 380/220; 220Peru 60 10 kV; 6 kV; 225Philippines 60 13.8 kV; 4.16 kV;

2.4 kV; 220/110Poland 50 15 kV; 6 kV;

380/220; 220Portugal 50 15 kV; 5 kV;

380/220; 220Portuguese Guinea 50 380/220Puerto Rico 60 8.32 kV; 4.16 kV;

480; 240/120Qatar 50 415/240; 240

Reunion 50 110/220Romania 50 20 kV; 10 kV; 6 kV;

380/220; 220Rwanda 50 15 kV; 6.6 kV;

380/220; 220Sabah 50 415/240; 240Sarawak (EastMalaysia)

50 415/240; 240

Saudi Arabia 60 380/220; 220/127; 127Senegal 50 220/127; 127Seychelles 50 415/240Sierra Leone 50 11 kV; 400/230;

230Singapore 50 22 kV; 6.6 kV;

400/230; 230



Somali Republic 50 440/220; 220/110;230; 220; 110

South Africa 50; 25 11 kV; 6.6 kV;3.3 kV; 433/250;400/230; 380/220;500; 220

Southern Yemen (Aden) 50 400/230Spain 50 15 kV; 11 kV;380/220; 220/127;220; 127

Spanish Sahara 50 380/220; 110; 127Sri Lanka (Ceylon) 50 11 kV; 400/230;

230St. Helena 50 11 kV; 415/240St. Kitts Nevis Anguilla 50 400/230; 230St. Lucia 50 11 kV; 415/240;

240Saint Vincent 50 3.3 kV; 400/230; 230Sudan 50 415/240; 240Surinam 50; 60 230/115; 220/127;

220/110; 127; 115Swaziland 50 11 kV; 400/230; 230Sweden 50 20 kV; 10 kV; 6 kV;

380/220; 220

Switzerland 50 16 kV; 11 kV; 6 kV;380/220; 220Syrian Arab Republic 50 380/220; 200/115;

220; 115Taiwan (Republic ofChina)

60 22.8 kV;11.4 kV; 380/220;220/110

Tanzania (UnionRepublic of)

50 11 kV; 400/230

Thailand 50 380/220; 220Togo 50 20 kV; 5.5 kV;

380/220; 220Tonga 50 11 kV; 6.6 kV;

415/240; 240; 210Trinidad and Tobago 60 12kV; 400/230;

230/115Tunisia 50 15 kV; 10 kV;

380/220; 220Turkey 50 15 kV; 6.3 kV;

380/220; 220Uganda 50 11 kV 415/240; 240United Kingdom 50 22 kV; 11 kV;

6.6 kV; 3.3 kV;400/230; 380/220;240; 230; 220

Upper–Yolta 50 380/220; 220Uruguay 50 15 kV; 6 kV; 220USA 60 480/277; 208/120;

240/120USSR 50 380/230; 220/127

and higher voltagesVenezuela 60 13.8 kV; 12.47 kV;

4.8 kV; 4.16 kV;2.4 kV; 240/120;208/120

Vietnam (Republic of) 50 15 kV; 380/220;208/120; 220; 120

Virgin Islands (UK) 60 208; 120Virgin Islands (US) 60 110/220Western Samoa 50 415/240Yemen, Democratic(PDR)

50 440/250; 250

Yugoslavia 50 10 kV; 6.6 kV;380/220; 220

Zaire (Republic of) 50 380/220; 220Zambia 50 400/230; 230Zimbabwe 50 11 kV; 390/225; 225




1677 APPENDIX

D. Useful Formulas

TO OBTAIN: SINGLE–PHASE AC POWER THREE–PHASE AC POWER

kilowatts (kW) Volts x Amps x PF1000

Volts x Amps x PF x 1.732

1000

kVA Volts x Amps

1000

Volts x Amps x 1.732

1000

Amps (kVA unknown)

kW x 1000Volts x PF

kW x 1000Volts x PF x 1.732

Amps (kW unknown)

kVA x 1000Volts

kVA x 1000Volts x 1.732

Frequency (Hertz)

# poles x rpm

120

# poles x rpm

120

Reactive Power (kVAR) – –

Volts x Amps x 1 PF2

1000

Volts x Amps x 1.732 x 1 PF2

1000

% Voltage regulation

– – (for steady loads, fromNo–Load to Full–Load) VNL VFL

VFL

x 100 VNL VFL

VFL

x 100

% Frequency Regulation

– – (for steady loads fromNo–Load to Full–Load) FNL FFL

FFL

x 100 FNL FFL

FFL

x 100

Horsepower required to drive a generator kW

0.746 X Generator EfficiencykW

0.746 X Generator Efficiency

First cycle RMS short circuit current (±10%) Rated Amperes

pu XdRated Amperes

pu Xd

• “PF” refers to power factor, which isexpressed as a decimal fraction. For exam-ple, 80% power factor = 0.8 for the purposesof calculations. In general, single–phasegenerator sets are rated at 100% power fac-tor and three–phase generator sets at 80%power factor.

• “Volts” refers to line–to–line voltage.• “Amps” refers to line current in amperes.

•“F” refers to frequency. 0% frequency regu-lation is defined as isochronous.




1687 APPENDIX

E. Maintenance and Service

A well–planned program of preventative mainte-nance and service should be integral to thedesign of an on–site power system. Failure of astandby generator set to start and run could lead

to loss of life, personal injury, property damage,and loss of business income. Failure to start andrun due to low battery charge because of improp-er maintenance is the most common type of fail-ure. A comprehensive program carried out on ascheduled basis by qualified persons can preventsuch failures and their possible consequences.The maintenance and service programs mostgenerator set distributors offer on a contract basisshould be considered. Typically, they include per-formance of scheduled maintenance, repairs,parts replacement, and service documentation.

The maintenance schedule for prime power setsshould be on the basis of running time, as pub-lished by the manufacturer. Since standby setsrun infrequently, the maintenance schedule isusually in terms of daily, weekly, monthly, or lon-ger term tasks. See the manufacturer’s instruc-tions for details. In any case, scheduled mainte-nance should include:

Daily:

• Check for oil, coolant, and fuel leaks.

• Check operation of the engine coolant heat-er(s). If the block is not warm, the heaters arenot working and the engine might not start.

• Check to see that the switchgear is in theAUTOMATIC position and the generator cir-cuit breaker, if used, is closed.

Weekly:

• Check engine oil and coolant levels.• Check the battery charging system.

Monthly:

• Check for air cleaner restrictions.• Exercise the generator set by starting and

running it for at least 30 minutes under notless than 30% rated load. Lower load levelsare acceptable if the exhaust gas tempera-ture reaches a level sufficient to prevent en-gine damage. See Table 7–2 for minimumexhaust gas temperatures for Cummins

engines. Check for unusual vibrations,noises, and exhaust, coolant and fuel leakswhile the set is running. (Regular exercisingkeeps engine parts lubricated, improves

starting reliability, prevents oxidation of elec-trical contacts, and consumes fuel before itdeteriorates and has to be discarded.)

• Check for radiator restrictions, coolant leaks,deteriorated hoses, loose and deterioratedfan belts, non–functioning motorized–lou-vers and proper concentration of enginecoolant additives.

• Check for holes, leaks, and loose connec-tions in the air cleaner system.

• Check fuel level and fuel transfer pumpoperation.

• Check for exhaust system leaks and restric-tions, and drain the condensate trap.• Check all meters, gauges, and indicator

lamps for proper operation.• Check the battery cable connections and

battery fluid level and recharge the batteriesif specific gravity is less than 1.260.

• Check for ventilation restrictions in the inletand outlet openings of the generator.

• Check that all required service tools arereadily available.

Engne Family

Exhaust Stack Temperatures

Calibrated Thermocouple

B Series 550

C Series 600

LTA10 650

M11 650

NT(A)855 650

N14 650

QSX15 700

KTA19 650

VTA28 650

QST30 650

KTA38 650

QSK45 700

KTA50 700

QSK60 700

QSK178 700

Table 7–2. Recommended Minimum Exhaust StackTemperatures. (Exhaust gas temperature is mea-sured by thermocouple. Use of external temperaturesensing is not sufficiently accureate to verify exhausttemperature.)




1697 APPENDIX

Semi–Annually:

• Change engine oil filters.• Change the filter(s) in the coolant conditioner

circuit.• Clean or replace the crankcase breather fil-ter(s).

• Change the fuel filter(s), drain sediment fromfuel tanks, check flexible fuel hoses for cutsand abrasions and check the governor link-age.

• Check electrical safety controls and alarms.• Clean up accumulations of grease, oil, and

dirt on the generator set.• Check power distribution wiring, connec-

tions, circuit breakers, and transfer switches.

•Simulate a utility power outage. This will testthe ability of the set to start and assume therated load. Check the operation of the auto-matic transfer switches, related switchgearand controls, and all other components in thestandby power system.

Annually:

• Check the fan hub, pulleys, and water pump.• Clean the day tank breather.

• Check and torque the exhaust manifold andturbocharger fasteners.

• Tighten the generator set mounting hard-ware.

• Clean the generator power output and con-trol boxes. Check for and tighten all loose

wiring connectors. Measure and record gen-erator winding insulation resistances. Checkthe operation of the generator heater stripsand grease the bearings.

• Check the operation of the main generatorcircuit breaker (if used) by manually operat-ing it. Test the trip unit according to themanufacturer’s instructions.

• If the set is normally exercised at no–load orcarries only light loads, run the generator setfor at least three hours, including one hour atnear rated load.

• Conduct generator insulation tests annuallythroughout the life of the generator set. Initialtests done before final load connections aremade will serve as benchmarks for annualtests. These tests are mandatory for genera-tor sets rated above 600 VAC. Review ANSI/ IEEE Standard 43, Recommended Practicefor Testing Insulation Resistance of RotatingMachinery.






1717 APPENDIX

G. Glossary

AC (Alternating Current)Alternating current is electric current that alter-nates between a positive maximum value and anegative maximum value at a characteristic fre-quency, usually 50 or 60 cycles per second(Hertz).

AC GeneratorAC generator is the preferred term for referring toa generator that produces alternating current(AC). See Alternator and Generator.

Acoustic MaterialAcoustic material is any material considered interms of its acoustic properties, especially itsproperties of absorbing or deadening sound.

Active PowerActive power is the real power (kW) supplied bythe generator set to the electrical load. Activepower creates a load on the set’s engine and islimited by the power of the engine and efficiencyof the generator. Active power does the work ofheating, lighting, turning motor shafts, etc.

Air Circuit BreakerAn air circuit breaker automatically interrupts thecurrent flowing through it when that currentexceeds the trip rating of the breaker. Air is themedium of electrical insulation between electri-cally live parts and grounded (earthed) metalparts. Also see Power Circuit Breaker.

AnnunciatorAn annunciator is an accessory device used togive remote indication of the status of an operat-ing component in a system. Annunciators aretypically used in applications where the equip-ment monitored is not located in a portion of thefacility that is normally attended. The NFPA hasspecific requirements for remote annunciatorsused in some applications, such as hospitals.

AlternatorAlternator is another term for AC generator.

Amortisseur WindingsThe amortisseur windings of a synchronous ACgenerator are the conductors embedded in thepole faces of the rotor. They are connectedtogether at both ends of the poles by end rings.Their function is to dampen waveform oscillationsduring load changes.

AmpacityAmpacity is the safe current–carrying capacity ofan electrical conductor in amperes as defined bycode.

AmpereThe ampere is a unit of electric current flow. Oneampere of current will flow when a potential ofone volt is applied across a resistance of oneohm.

Apparent PowerApparent power is the product of current and volt-age, expressed as kVA. It is real power (kW)divided by the power factor (PF).

ArmatureThe armature of an AC generator is the assemblyof windings and metal core laminations in whichthe output voltage is induced. It is the stationarypart (stator) in a revolving–field generator.

Authority Having JurisdictionThe authority having jurisdiction is the individualwith the legal responsibility for inspecting a facili-ty and approving the equipment in the facility asmeeting applicable codes and standards.

Backup ProtectionBackup protection consists of protective deviceswhich are intended to operate only after otherprotective devices have failed to operate ordetect a fault.

Base LoadBase load is that portion of a building loaddemand which is constant. It is the “base” of thebuilding demand curve.

Black StartBlack start refers to the starting of a power sys-tem with its own power sources, without assis-tance from external power supplies.

Bumpless TransitionBumpless transition is make–before–break trans-

fer of an electrical load from one source to anoth-er where voltage and frequency transients arekept to a minimum.




1727 APPENDIX

BusBus can refer to the current–carrying copper barsthat connect the AC generators and loads in aparalleling system, to the paralleled output of theAC generators in a system or to a feeder in anelectrical distribution system.

CircuitA circuit is a path for an electric current across apotential (voltage).

Circuit BreakerA circuit breaker is a protective device that auto-matically interrupts the current flowing through itwhen that current exceeds a certain value for aspecified period of time. See Air Circuit Breaker,Main Breaker, Molded Case Circuit Breaker, andPower Circuit Breaker.

ContactorA contactor is a device for opening and closing

an electric power circuit.

Continuous LoadA continuous load is a load where the maximumcurrent is expected to continue for three hours ormore (as defined by the NEC for design calcula-tions).

Cross Current CompensationCross current compensation is a method of con-trolling the reactive power supplied by AC gener-ators in a paralleling system so that they shareequally the total reactive load on the bus withoutsignificant voltage droop.

CT (Current Transformer)Current transformers are instrument transformersused in conjunction with ammeters, control cir-cuits and protective relaying. They usually have5 ampere secondaries.

CurrentCurrent is the flow of electric charge. Its unit ofmeasure is the ampere.

Current Limiting FuseA current limiting fuse is a fast–acting device that,when interrupting currents in its current–limitingrange, will substantially reduce the magnitude ofcurrent, typically within one–half cycle, that wouldotherwise flow.

CycleA cycle is one complete reversal of an alternatingcurrent or voltage—from zero to a positive maxi-mum to zero again and then from zero to a nega-tive maximum to zero again. The number ofcycles per second is the frequency.

dB/dB(A) ScaleThe decibel (dB) scale used in sound level mea-surements is logarithmic. Sound level metersoften have several decibel weighting scales (A,B,C). The A–scale, dB(A), is the most commonlyused weighting scale for measuring the loudnessof noise emitted from generator sets.

Delta ConnectionDelta connection refers to a three–phase connec-tion in which the start of each phase is connectedto the end of the next phase, forming the Greekletter ∆.. The load lines are connected to the cor-ners of the delta.

Demand FactorThe demand factor is the ratio of actual load tothe potential total connected load.

Deviation FactorThe deviation factor is the maximum instanta-

neous deviation, in percent, of the generator volt-age from a true sine wave of the same RMS val-ue and frequency.

Dielectric StrengthDielectric strength is the ability of insulation towithstand voltage without rupturing.

Direct Current (DC)Direct current is current with no reversals inpolarity.

Differential RelayA differential relay is a protective device which is

fed by current transformers located at two differ-ent series points in the electrical system. Thedifferential relay compares the currents and picksup when there is a difference in the two whichsignifies a fault in the zone of protection. Thesedevices are typically used to protect windings ingenerators or transformers.

EarthingEarthing is the intentional connection of the elec-trical system or electrical equipment (enclosures,conduit, frames, etc.) to earth or ground.

Efficiency (EFF)Efficiency is the ratio of energy output to energyinput, such as the ratio between the electricalenergy input to a motor and the mechanical ener-gy output at the shaft of the motor.

Emergency SystemAn emergency system is independent power gen-eration equipment that is legally required to feedequipment or systems whose failure may presenta life safety hazard to persons or property.






1747 APPENDIX

InsulationInsulation is non–conductive material used toprevent leakage of electric current from a con-ductor. There are several classes of insulation inuse for generator construction, each recognizedfor a maximum continuous–duty temperature.

JerkRate of change of acceleration. Often used as ameasure of performance in elevator systems.

kVA (kilo–Volt–Amperes)kVA is a term for rating electrical devices. Adevice’s kVA rating is equal to its rated output inamperes multiplied by its rated operating voltage.In the case of three–phase generator sets, kVA isthe kW ouput rating divided by 0.8, the ratedpower factor. KVA is the vector sum of the activepower (kW) and the reactive power (kVAR) flow-ing in a circuit.

kVAR (kilo–Volt–Amperes Reactive)KVAR is the product of the voltage and theamperage required to excite inductive circuits. Itis associated with the reactive power which flowsbetween paralleled generator windings andbetween generators and load windings that sup-ply the magnetizing currents necessary in theoperation of transformers, motors, and otherelectromagnetic loads. Reactive power does notload the generator set’s engine but does limit thegenerator thermally.

kW (kilo–Watts)KW is a term used for power rating electricaldevices and equipment. Generator sets in theUnited States are usually rated in kW. KW,sometimes called active power, loads the genera-tor set’s engine.

kW• h (kilo–Watt–hour)This is a unit of electric energy. It is equivalent toone kW of electric power supplied for one hour.

Lagging Power FactorLagging power factor in AC circuits (a power fac-tor of less than 1.0) is caused by inductive loads,such as motors and transformers, which cause

the current to lag behind the voltage. See PowerFactor.

Leading Power FactorLeading power factor in AC circuits (0.0 to –1.0)is caused by capacitive loads or overexcited syn-chronous motors which cause the current to leadthe voltage. See Power Factor.

LegA leg is a phase winding of a generator, or aphase conductor of a distribution system.

Line–To–Line VoltageLine–to–line voltage is the voltage between anytwo phases of an AC generator.

Line–To–Neutral VoltageIn a 3–phase, 4–wire, Y–connected generator,line–to–neutral voltage is the voltage between aphase and the common neutral where the threephases are tied together.

Load FactorThe load factor is the ratio of the average load tothe generator set power rating.

Low VoltageIn the context of this manual, low voltage refersto AC system operating voltages from 120 to 600

VAC.

LuggingAttaching lugs (terminations) to the end of wires.

Main BreakerA main breaker is a circuit breaker at the input oroutput of the bus, through which all of the buspower must flow. The generator main breaker isthe device, usually mounted on the generator set,that can be used to interrupt generator set poweroutput.

Mains

Mains is a term used extensively outside theUnited States to describe the normal power ser-vice (utility).

Medium VoltageIn the context of this manual, medium voltagerefers to AC system operating voltages from 601to 15,000 VAC.

Molded Case Circuit BreakerA molded case circuit breaker automatically inter-rupts the current flowing through it when the cur-rent exceeds a certain level for a specified time.Molded case refers to the use of molded plastic

as the medium of electrical insulation for enclos-ing the mechanisms and for separating conduct-ing surfaces from one another and from ground-ed (earthed) metal parts.




1757 APPENDIX

MotoringIn paralleling applications, unless a generator setis disconnected from the bus when its enginefails (usually as a result of a fuel system prob-lem), the generator will drive (motor) the engine,drawing power from the bus. Reverse powerprotection which automatically disconnects a

failed set from the bus is essential for parallelingsystems. Also, in certain applications such aselevators, the load can motor the generator set ifinsufficient additional load is present.

NEC (National Electrical Code)This document is the most commonly referencedgeneral electrical standard in the United States.

NEMANational Electrical Manufacturers Association

NeutralNeutral refers to the common point of a Y–con-

nected AC generator, a conductor connected tothat point or to the mid–winding point of a single– phase AC generator.

NFPANational Fire Protection Association

Nonattainment AreasAreas of the country that consistently do not meetU.S. Environmental Protection Agency (EPA) airquality standards.

Nonlinear LoadA nonlinear load is a load for which the relation-

ship between voltage and current is not a linearfunction. Some common nonlinear loads arefluorescent lighting, SCR motor starters, andUPS systems. Nonlinear loads cause abnormalconductor heating and voltage distortion.

Octave BandIn sound pressure measurements (using anoctave band analyzer), octave bands are theeight divisions of the measured sound frequencyspectrum, where the highest frequency of eachband is twice that of its lowest frequency. Theoctave bands are specified by their center fre-quencies, typically: 63, 125, 250, 500, 1,000,2,000, 4,000 and 8,000 Hz (cycles per second).

OhmThe ohm is a unit of electrical resistance. Onevolt will cause a current of one ampere to flowthrough a resistance of one ohm.

One–Line DiagramA one–line diagram is a schematic diagram of athree–phase power distribution system whichuses one line to show all three phases. It isunderstood when using this easy to read drawingthat one line represents three.

Out–Of–PhaseOut–of–phase refers to alternating currents orvoltages of the same frequency which are notpassing through their zero points at the sametime.

Overload RatingThe overload rating of a device is the load inexcess of the nominal rating the device can carryfor a specified length of time without being dam-aged.

OvershootOvershoot refers to the amount by which voltage

or frequency exceeds the nominal value as thevoltage regulator or governor responds tochanges in load.

Parallel OperationParallel operation is the operation of two or moreAC power sources whose output leads are con-nected to a common load.

Peak LoadPeak load is the highest point in the kilowattdemand curve of a facility. This is used as thebasis for the utility company’s demand charge.

Peak ShavingPeak shaving is the process by which loads in afacility are reduced for a short time to limit maxi-mum electrical demand in a facility and to avoid aportion of the demand charges from the local util-ity.

PhasePhase refers to the windings of an AC generator.In a three–phase generator there are three wind-ings, typically designated as A–B–C, R–S–T orU–V–W. The phases are 120 degrees out ofphase with each other . That is, the instants atwhich the three phase voltages pass throughzero or reach their maximums are 120 degreesapart, where one complete cycle is considered360 degrees. A single–phase generator has onlyone winding.




1767 APPENDIX

PMG (Permanent Magnet Generator)A permanent magnet generator is a generatorwhose field is a permanent magnet as opposedto an electro–magnet (wound field). Used to gen-erate excitation power for separately excitedalternators.

Phase AnglePhase angle refers to the relation between twosine waves which do not pass through zero at thesame instant, such as the phases of a three– phase generator. Considering one full cycle to be360 degrees, the phase angle expresses how farapart the two waves are in relation to a full cycle.

Phase RotationPhase rotation (or phase sequence) describesthe order (A–B–C, R–S–T or U–V–W) of thephase voltages at the output terminals of a three– phase generator. The phase rotation of a gener-ator set must match the phase rotation of the nor-

mal power source for the facility and must bechecked prior to operation of the electrical loadsin the facility.

PitchPitch is the ratio of the number of generator sta-tor winding slots enclosed by each coil to thenumber of winding slots per pole. It is a mechan-ical design characteristic the generator designermay use to optimize generator cost verse voltagewave form quality.

PolePole is used in reference to magnets, which arebipolar. The poles of a magnet are designatedNorth and South. Because magnets are bipolar,all generators have an even number of poles.The number of poles determines how fast thegenerator will have to be turned to obtain thespecified frequency. For example, a generatorwith a 4–pole field would have to be run at 1800rpm to obtain a frequency of 60 Hz (1500 rpm for50 Hz).

Pole can also refer to the electrodes of a batteryor to the number of phases served by a switch orbreaker.

Power Circuit BreakerA power circuit breaker is a circuit breaker whosecontacts are forced closed via a spring–charged,over–center mechanism to achieve fast closing(5–cycle) and high withstand and interrupting rat-ings. A power circuit breaker can be an insulatedcase or power air circuit breaker.

PowerPower refers to the rate of performing work or ofexpending energy. Typically, mechanical poweris expressed in terms of horsepower and electri-cal power in terms of kilowatts. One kW equals1.34 hp.

Power Factor (PF)The inductances and capacitances in AC circuitscause the point at which the voltage wave passesthrough zero to differ from the point at which thecurrent wave passes through zero. When thecurrent wave precedes the voltage wave, a lead-ing power factor results, as in the case of capaci-tive loads or overexcited synchronous motors.When the voltage wave precedes the currentwave, a lagging power factor results. This is gen-erally the case. The power factor expresses theextent to which the voltage zero differs from thecurrent zero. Considering one full cycle to be360 degrees, the difference between the zeropoints can then be expressed as an angle. Pow-er factor is calculated as the cosine of the anglebetween zero points and is expressed as a deci-mal fraction (.8) or as a percentage (80%). It isthe ratio of kW and kVA. In other words kW =kVA x PF.

Radio InterferenceRadio interference refers to the interference withradio reception caused by a generator set.

Radio Interference SuppressionRadio interference suppression refers to themethods employed to minimize radio interfer-ence.

ReactanceReactance is the opposition to the flow of currentin AC circuits caused by inductances and capaci-tances. It is expressed in terms of ohms and itssymbol is X.

Reactive PowerReactive power is the product of current, voltageand the sine of the angle by which current leadsor lags voltage and is expressed as VAR (volts– amperes–reactive).

Real PowerReal power is the product of current, voltage andpower factor (the cosine of the angle by whichcurrent leads or lags voltage) and is expressedas W (watts).




1777 APPENDIX

ResistanceResistance is the opposition to the flow of currentin DC circuits. It is expressed in ohms and itssymbol is R.

RMS (Root Mean Square)The RMS values of a measured quantity such as

AC voltage, current and power are consideredthe “effective” values of the quantities. See Watt.

RotorA rotor is the rotating element of a motor or gen-erator.

RPMRevolutions Per Minute

SCR (Silicon Controlled Rectifier)An SCR is a three–electrode solid–state devicewhich permits current to flow in one directiononly, and does this only when a suitable potential

is applied to the third electrode, called the gate.

Selective CoordinationSelective coordination is the selective applicationof overcurrent devices such that short circuitfaults are cleared by the device immediately onthe line side of the fault, and only by that device.

Self–ExcitedAn alternator whose excitation system draws itspower from its own main AC output.

Separately ExcitedAn alternator whose excitation system draws its

power from a separate source (not its own out-put).

Service EntranceThe service entrance is the point where the utilityservice enters the facility. In low voltage systemsthe neutral is grounded at the service entrance.

Service FactorService factor is a multiplier that is applied to amotor’s nominal horsepower rating to indicate anincrease in power output (overload capacity) themotor is capable of providing under certain condi-tions.

Short CircuitA short circuit is generally an unintended electri-cal connection between current carrying parts.

Shunt ExcitedAn alternator that uses (shunts) a portion of itsAC output for excitation current.

Shunt TripShunt trip is a feature added to a circuit breakeror fusible switch to permit the remote opening ofthe breaker or switch by an electrical signal.

Sine WaveA sine wave is a graphical representation of a

sine function, where the sine values (usually they axis) are plotted against the angles (x axis) towhich they correspond. AC voltage and currentwave shapes approximate such a curve.

Soft LoadingSoft loading refers to the ramping of load onto oroff of a generator in a gradual fashion for the pur-pose of minimizing voltage and frequency tran-sients on the system.

Slow RateRate of change of frequency.

SoundSound is considered both in terms of the soundpressure waves travelling in air (pressures super-imposed on the atmospheric pressure) and thecorresponding aural sensation. Sound can be“structure–borne”, that is, transmitted through anysolid elastic medium, but is audible only at pointswhere the solid medium “radiates” the pressurewaves into the air.

Sound Level MeterA sound level meter measures sound pressurelevel. It has several frequency–weighted decibel(dB) scales (A, B, C) to cover different portions of

the range of measured loudness. Sound levelmeters indicate RMS sound, unless the measure-ments are qualified as instantaneous or peaksound level.

Sound Pressure Level (SPL)Sound pressure level refers to the magnitude ofthe pressure differential caused by a soundwave. It is expressed on a dB scale (A,B,C) ref-erenced to some standard (usually 10 –12 micro-bars).

Standby SystemA standby system is an independent power sys-tem that allows operation of a facility in the eventof normal power failure.

Star ConnectionSee Wye Connection.




1787 APPENDIX

Starting CurrentThe initial value of current drawn by a motorwhen it is started from standstill.

StatorThe stator is the stationary part of a generator ormotor. See Armature.

SurgeSurge is the sudden rise in voltage in a system,

–usually caused by load disconnect.

Surge SuppressorSurge suppressors are devices capable of con-ducting high transient voltages. They are usedfor protecting other devices that could bedestroyed by the transient voltages.

SynchronizationIn a paralleling application, synchronization isobtained when an incoming generator set is

matched with and in step to the same frequency,voltage, and phase sequence as the operatingpower source.

Telephone Influence Factor (TIF)The higher harmonics in the voltage wave shapeof a generator can cause undesirable effects ontelephone communications when power lines par-allel telephone lines. The telephone influencefactor is calculated by squaring the weightedRMS values of the fundamental and the non–tri-ple series of harmonics, adding them togetherand then taking the square root of the sum. Theratio of this value to the RMS value of the no–

load voltage wave is called the Balanced TIF.The ratio of this value to three times the RMSvalue of the no–load phase–to–neutral voltage iscalled the Residual Component RIF.

TransformerA transformer is a device that changes the volt-age of an AC source from one value to another.

UndershootUndershoot refers to the amount by which volt-age or frequency drops below the nominal valueas the voltage regulator or governor responds tochanges in load.

UtilityThe utility is a commercial power source that sup-plies electrical power to specific facilities from alarge central power plant.

VoltThe volt is a unit of electrical potential. A poten-tial of one volt will cause a current of one ampereto flow through a resistance of one ohm.

Voltage DipVoltage dip is the dip in voltage that results when

a load is added, occurring before the regulatorcan correct it, or resulting from the functioning ofthe voltage regulator to unload an overloadedengine–generator.

Voltage RegulationVoltage regulation is a measure that states thedifference between maximum and minimumsteady–state voltage as a percentage of nominalvoltage.

Voltage RegulatorA voltage regulator is a device that maintains thevoltage output of a generator near its nominal

value in response to changing load conditions.

WattThe watt is a unit of electric power. In direct cur-rent (DC) circuits, wattage equals voltage timesamperage. In alternating current (AC) circuits,wattage equals effective (RMS) voltage timeseffective (RMS) amperage times power factortimes a constant dependent on the number ofphases. 1,000 watts equal one kW.

Wye ConnectionsA Wye connection is the same as a star connec-tion. It is a method of interconnecting the phases

of a three–phase system to form a configurationresembling the letter Y. A fourth (neutral) wirecan be connected at the center point.

Zero SequenceZero sequence is a method of ground fault detec-tion that utilizes a sensor (CT) that encircles allthe phase conductors as well as the neutral con-ductors. The sensor will produce an output pro-portional to the imbalance of current ground faultin the circuit. This output is then measured by arelay to initiate circuit breaker tripping or groundfault alarm.

Zones of ProtectionZones of protection are defined areas within adistribution system that are protected by specificgroups.




179Index of Formulas,Tables, and Figures

Index of Formulas

Adding Sound Pressure Levels, 136

Air Flow Calculations, 113

Allowable Single–Phase Load Unbalance, 66

Available Short Circuit Current, 72

Calculate Height Foundation, 82

Converting PU Reactances, 72

Cooling Pipe Sizing Calculations, 108

Effect of Distance on Sound Pressure, 136

Exhaust Backpressure Calculation, 91

Fault Current as Percentage of CB Rating, 74

kW, kVA, and PF, 36

Line Current, 63

Propane Fuel Tank Size, 128

Raw Water Required for Heat Exchanger, 106

Required Battery Cable Size, 48

Required Battery Charging Amps, 48

Soil Bearing Load, 83

Voltage Drop Calculation, 64

Index of Tables

Table 2–1. Rating and System Types, 14

Table 2–2. Representative Outside Noise Levels, 23

Table 2–3. Typical Diesel Exhaust Emissions, 23Table 3–1. Lighting Power Factors (Starting and Run-

ning), 28

Table 3–2. Ballast Power, 28

Table 3–3. Rotating Inertia Summary, 29

Table 3–4. Reduced Voltage Starting Methods andCharacteristics, 30

Table 3–5. Multiplying Factors Corresponding withCode Letters, 31

Table 3–6. Three–Phase Motor Defaults: NEMA Code,EFF, SPF, RPF, 32

Table 3–7. Single–Phase Motor Defaults: NEMA Code,EFF, SPF, RPF, 33

Table 3–8. Generator Set Requirements for MedicalImaging Applications, 35

Table 3–9. Typical Voltage and Frequency Tolerances,36

Table 6–1. Cross Sectional Areas of Openings of Vari-ous Diameter, 93

Table 6–2. Equivalent Lengths of Pipe Fittings in Feet(Meters), 93

Table 6–3. Equivalent Lengths of Pipe Fittings andValves in Feet (Meters), 109

Table 6–4. Freezing and Boiling Points vs. Concentra-tion of Antifreeze, 111

Table 6–5. Heat Losses From Uninsulated ExhaustPipes and Mufflers, 118

Table 6–6. Diesel Fuel Specifications, 119

Table 6–7. Minimum Fuel Hose and Pipe Sizes; Up to50 Feet (15 Meters) Equivalent Length., 123, 171

Table 6–8. Maximum Allowable Percentages for En-gine Fuel Combustibles, 127

Table 6–9. Maximum Allowable Percentages of Constit-uent Gases Before Derating Turbocharged En-gines, 127

Table 6–10. Natural Gas Schedule 40 Iron Pipe Sizing – Maximum Capacity of Pipe in Cubic Feet of Gasper Hour. Pipe size recommendations are basedon schedule 40 black iron pipe. Recommendationsare based on NFPA 54, National Fuel Gas Code,Table 9.2., 131, 132, 133, 134

Table 6–12. Propane Schedule 40 Iron Pipe Sizing,Liquid Withdrawal – Maximum Capacity of Pipe inCubic Feet of Gas per Hour. Pipe size recommen-dations are based on schedule 40 black iron pipe.Recommendations are based on NFPA 54, Nation-al Fuel Gas Cod, 135

Table 7–1. Reduced Voltage Motor Starting Compari-son, 162




180Index of Formulas,Tables, and Figures

Index of Figures

Figure 2–1. Typical One–Line Diagram of an ElectricalDistribution System, 12

Figure 2–2. Standby Power Rating., 14

Figure 2–3. Unlimited Running Time Prime Power, 14

Figure 2–4. Limited Running Time Prime Power, 15

Figure 2–5. Base Load Power, 15

Figure 3–1. Voltage Dip in Medical Imaging Applica-tions, 31

Figure 4–1. Four–Pole Generator Cross Section, 36

Figure 4–2. Self–Excited Generator, 37

Figure 4–3. Separately–Excited (PMG) Generator, 38

Figure 4–4. Typical Voltage Profile on Load Applicationand Removal, 39

Figure 4–5. Typical Generator Saturation Curves, 40

Figure 4–6. Excitation System Response Characteris-tics, 40

Figure 4–7. Transient Voltage Dip, 41

Figure 4–8. Typical Across–the–Line Motor StartingCharacteristics, 42

Figure 4–9. Sustained Voltage Dip, 43

Figure 4–10. Typical NEMA Generator Chart of Tran-sient Voltage Dip vs. Motor Starting KVA, 43

Figure 4–11. Symmetrical Three–Phase Short CircuitResponse, 44

Figure 4–12. Short Circuit Capability, 44

Figure 4–13. Approximate Short Circuit Winding Tem-peratures, 45

Figure 4–14. Typical Electric Starter Motor Connec-

tions, 47Figure 4–15. Resistance vs. Length for Various AWG

Cable Sizes, 47

Figure 4–16. Typical Piping Arrangement for an AirStarter, 48

Figure 4–17. Two–Wire Control Interface Panel, 49

Figure 4–18. Detector 12 Control Interface Panel, 49

Figure 4–19. Power Command Microprocessor Sys-tem, 49

Figure 4–20. Power Command Full Authority Electron-ic, 50

Figure 4–21. Water Jacket Heater Installation. NoteHeater Isolation Valve, Hose Type, and Hose Rout-

ing., 56Figure 5–1. Typical Generator Set Control and Acces-

sory Wiring, 60

Figure 5–2. Feeder Ampacity, 61

Figure 5–3. Allowable Unbalanced Single–Phase Load, 63

Figure 5–4. Typical Steady State Alternator ReactivePower Capability Curve, 65

Figure 5–5. Typical One–Line Diagrams of AlternativeSystem Grounding Methods, 66

Figure 5–6. Typical Low–Resistance Grounding Sys-tem for a Medium Voltage Generator Set and LoadTransfer Equipment, 68

Figure 5–7. Typical System and Equipment Grounding

Connections at the Utility Service Equipment, 69Figure 5–8. Fault Effect on a 100 Ampere Breaker with

Trip Characteristic ”A”, 73

Figure 5–9. Fault Effect on a 100 Ampere Breaker withTrip Characteristic ”B”, 74

Figure 5–10. PowerCommand) Control AmpSentryETime–Over–Current Characteristic Curve Plus Al-ternator Damage Curve., 76

Figure 5–11. Typical Protective Scheme, 77

Figure 6–1. Anti–Vibration Provisions for a TypicalGenerator Set, 78

Figure 6–2 Typical Vibration Isolating Foundation, 80

Figure 6–3. Typical Steel Spring Vibration Isolator, 82

Figure 6–4. A Generator Set Mounted With Spring– Type Vibration Isolators, 82

Figure 6–5: Typical Features of an Exhaust System fora Generator Installed Inside a Building., 84

Figure 6–6. Typical Exhaust System, 85

Figure 6–7: Generator Set Exhaust System Features.,86

Figure 6–8: Typical Thimble Construction for Combus-tible Wall Installations., 87

Figure 6–9. A Simple Exhaust System Fitted With aRain Cap to Prevent Rain From Entering the Ex-haust., 88

Figure 6–10. A Fabricated Rain Shield for Vertical Gen-

set Exhaust Stack., 88Figure 6–11. Sample Exhaust System for Calculation.,

89

Figure 6–12. Typical Muffler Exhaust Back Pressurevs. Gas Velocity, 91

Figure 6–13. Exhaust Back Pressure in Nominal Inch(mm) Pipe Diameters, 92

Figure 6–14. Deaeration Type of Radiator Top Tank, 94

Figure 6–15. Factory–Mounted Radiator Cooling, 94

Figure 6–16. Remote Radiator Cooling (DeaerationType System, 96

Figure 6–17. Remote Radiator With Auxiliary CoolantPump and Auxiliary Tank, 98

Figure 6–18. Remote Radiator With Hot Well and Auxil-iary Coolant Pump, 100

Figure 6–19. A Horizontal Remote Radiator and After-cooler Radiator, 102

Figure 6–20. Factory–Mounted Heat Exchanger Cool-ing, 103

Figure 6–21. Dual Heat Exchanger System (With Sec-ondary Liquid–to–Air Cooler), 104

Figure 6–22. Diagram of Representative Cooling TowerApplication, 105




Figure 6–23. Frictional Pressure Losses for Inch (mm)Diameter Pipes, 107

Figure 6–24. Factory–Mounted Radiator Cooling, 109

Figure 6–25. Typical Air Temperature Surrounding anOperating Genset, 110

Figure 6–26. Recommended Instrumentation for Mea-

suring Air Flow Restriction, 113Figure 6–27. Figure Cooling Capability in Elevated Am-

bients, 113

Figure 6–28. Ventilation for a Heat Exchanger CoolingSystem, 114

Figure 6–29. Typical Fuel Supply System–Supply TankAbove Generator Set, 117

Figure 6–30. Typical Fuel Supply System–Supply TankBelow Generator Set , 118

Figure 6–31. Typical Gaseous Fuel System, 125

Figure 6–32. Minimum LPG Tank Size (50% Full) Re-quired to Maintain 5 PSIG at Specific WithdrawalRate and Minimum Expected Winter Temperature,127

Figure 6–33. Typical Noise Levels, 133

Figure 6–34. Graph Of Values For Adding Noise Lev-els, 134

Figure 6–35. Decrease In Loudness As Distance In-creases (Free Field), 135

Figure 7–1. GenSize–New Project Parameters DialogBox, 141

Figure 7–2. GenSize Application Project Window, 151

Figure 7–3. Recommended Generator Set Window,154

Figure 7–4. All Generator Set Window, 155

Figure 7–5 Recommended Generator Report in ViewMode., 158

Manual Aplicatii Grupuri T030body

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