Substation Operation Aand Maintenance Mannuals

8/11/2019 Substation Operation Aand Maintenance Mannuals

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CONTENTS

1 Substations and Switchyards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Introduction to Substations and Switchyards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Basic Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Substations: Protective Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Regulation, Monitoring, and Communication Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Switchyards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Switchyard Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2 Safety in Substations and Switchyards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Hazards and Safety Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Safety Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Electrical Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Chemical Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Personal Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Using Support Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Dangers and Accidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Safety Review. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3 Power Transformers, Part 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33Transformer Principles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Power Transformers, Current Transformers, and Potential Transformers . . . . . . . . . . . . . . . . . . . . . 35

Power Transformer Cooling Systems, Self-Cooled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Power Transformers Cooling Systems, Forced Air/Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4 Power Transformers, Part 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Visual Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Inspection of a Transformers Exterior Condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Inspection of a Transformers Sealing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Inspection of a Transformers Cooling System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Gas and Oil Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Testing for Combustible Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Testing for Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Testing Oil Insulating Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Tap Changers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

No-Load Tap Changers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Load Tap Changers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Tap Changer Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64De-Energizing, Isolating, and Grounding a Power Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Tap Changer Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Physical Condition of the Tap Changer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Mechanical Operation of the Tap Changer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Electrical Operation of the Tap Changer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Turns Ratio Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Calculating the Turns Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Identifying Bushing Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Performing the Turns Ratio Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Insulation Resistance Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72


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Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72Test Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

5 New Power Transformer Inspection and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75On-Car Inspections and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Moving a New Power Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

On-Site Inspections and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

6 Power Transformer Turns Ratio Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87The Purpose of Transformer Turns Ratio Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Test Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Evaluating Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

7 Power Transformer Oil Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99The Purpose of Transformer Oil Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Oil Dielectric Test Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Dielectric Breakdown Strength Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101Oil Sample Taking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Lab Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

8 Power Transformer Insulation Resistance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113The Purpose of Insulation Resistance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115Test Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

Evaluating Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

9 Power Transformer Temperature Indicator Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127Temperature Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127Temperature Indicator Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132Heater Circuit Testing, Part 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

Heater Circuit Testing, Part 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

10 Power Transformer Pressure Relay Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143Sudden Pressure Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Fault Pressure Relays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

Testing a Sudden Pressure Relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148Testing a Fault Pressure Relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

11 Circuit Breaker Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157Introduction to Circuit Breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

Air-Magnetic and Air-Blast Circuit Breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

Oil and Vacuum Circuit Breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162Gas-Blast and Gas-Puffer Breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Solenoid and Motor/Spring Operating Mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

Pneumatic and Hydraulic Operating Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

12 Circuit Breaker Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175General Circuit Breaker Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Operating Mechanism Maintenance, Part 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179


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Operating Mechanism Maintenance, Part 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

Air-Magnetic and Vacuum Breaker Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

Oil Circuit Breaker Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

13 New Circuit Breaker Inspections and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199Receiving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203Post-Installation Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206

Proof Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

14 SF6 Gas Properties and Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .213Properties of SF6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

Personal Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215Handling SF6 Gas and Its Decomposition Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Cleanup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

15 Vacuum Bottle Hi-Pot Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225Vacuum Interrupter Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

Test Principles, Precautions, and Preparations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227Hi-Pot Test Setup and Steps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231Watching for Signs of Breakdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

16 Circuit Breaker Time-Travel Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .237Purpose and Principles of Time-Travel Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

Circuit Breaker Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

Circuit Breaker Time Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

Circuit Breaker Travel Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

17 Circuit Breaker Time-Travel Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .249Time-Travel Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

Drop-Bar Recorder Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253Light-Beam Recorder Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

Digital Timer/Analyzer Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263

18 Circuit Breaker Time-Travel Test Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .267Time-Travel Recordings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

Electrical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270Mechanical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

Velocities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

19 Contact Resistance Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .279The Purpose of Contact Resistance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

Test Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283Test Procedures and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

20 Capacitors and Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .289Function of Capacitors and Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

Clearing Capacitor Banks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292

Capacitor Bank Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

Capacitor Resistor and Insulator Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300Capacitor Capacitance Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302


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vi

Shunt Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305

Series Reactors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

21 Voltage Regulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .313Voltage Regulator Operation, Part 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

Voltage Regulator Operation, Part 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

Voltage Regulator Control, Part I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319Voltage Regulator Control, Part 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322

Field Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

Field Control Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326Regulator Replacement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

22 Protective Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333Introduction to Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

Overcurrent Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336

Directional Overcurrent Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340

Reclosing Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343Voltage Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

Auxiliary Relays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347

Solid-State Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

23 Protective Relays, Transmission Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .351Introduction to Protective Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

Differential Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354Transfer Tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359

Distance Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

Zoned Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

Pilot Wire Relaying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366Breaker Failure Relaying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369

24 Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .373Control Functions, Modes, and Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

Voltage Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376

Distribution Feeder Fault Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377Transmission and Subtransmission Feeder Fault Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380

Station Fault Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382

Source Circuit Fault Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

Routine Checks of Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

25 Substation Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .391Substation DC Control System Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391

Cell Components and Electrochemical Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394Cell and Battery Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398

Battery Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401

26 Substation Battery Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .405Voltage and Resistance Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405

Specific Gravity Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407Integrity and Capacity Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410

Impedance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415


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vii

27 Substation Battery Chargers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .419Charger Functions and Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419DC Control System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420

Freshening Charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421

Float and Equalizing Charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424

Charger Inspection and Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426

28 Substation Battery, Cell and Charger Replacement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .429Cell Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429Replacing Battery Cells. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

Battery Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432

Auxiliary Battery and Auxiliary Battery Trailer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432

Battery Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436Inspecting New Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436

Placing New Cells on the Battery Rack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437

Preparing Electrical Contact Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438Making Intercell Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439

Battery Charger Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440Taking the Existing Charger Out of Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440

Installing a New Charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441


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Substations and Switchyards

1

CHAPTER

1


Electricity is a necessity of modern life. Transmission and distribution (T&D) systems provide electricity

to consumers wherever and whenever it is needed. Two of the major components of a typical T&D systemare substations and switchyards.

This chapter examines the role that substations and switchyards play in a T&D system and discusses someof the equipment that is commonly used in substations and switchyards. Security and safety precautionsassociated with substations and switchyards are also covered when appropriate.

Introduction to Substations and Switchyards

Major Components of a Transmission and Distribution System

The major components of a transmission anddistribution system typically include transmissionlines, distribution lines, substations, and switch-

yards. Transmission lines carry electricity from the

generating plant where it is produced, and distri-bution lines carry electricity to the houses, offices,and industries where it is used.

The distances between generating plants andconsumers are often too great to allow electricity

to be carried directly from the plants to theconsumers. To carry electricity over long distances,transmission and distribution systems need voltage

changing substations, which are referred to in thisprogram as substations. An example of a substa-

tion is shown in Figure 1-1. At substations, voltageis increased for efficient transmission over longdistances or decreased for distribution to nearbycustomers.

Besides changing voltage for transmission ordistribution, a transmission and distributionsystem must also be able to ensure that users will

continue to receive electricity even if part of thesystem fails. To meet this rquirement, circuits

Figure 1-1. Substation.

Figure 1-2. Switchyard.


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11

Shunt reactors are used to improve substationefficiency by adding inductive load to counterbal-ance capacitive loads. A shunt reactor, like the one

shown in Figure 1-33, looks like a power trans-former, except that the bushings on a shunt reactor

are connected with the source circuit; there are nomajor connections leading out of a shunt reactor(such as the secondary connections on a powertransformer).

Monitoring Equipment

Monitoring equipment is used to provide a meansof watching substation equipment and systems

for problems so that they can be limited andcorrected. Commonly used types of monitoringequipment include potential transformers, current

transformers, meters, and relays.

Potential transformers

Potential transformers are devices that reduce linevoltage to a proportionally lower and safer voltage

for metering and relaying. A potential transformer,like the one shown in Figure 1-34, normally has alarge porcelain bushing that insulates the higher

voltage conductor going into the transformer. Thetransformer itself is usually enclosed in a metalhousing. The output wires of the transformers are

enclosed in conduit to protect them. These wiresconnect to meters or relaying equipment in acontrol house.

Potential transformers come in many shapesand sizes. They are sometimes difficult to distin-

guish from other devices such as some currenttransformers and surge arrestors. For this reason,potential transformers are often identified in

substations by signs like the one shown in Figure1-35.

Current Transformers

In contrast to potential transformers, which

reduce line voltage, current transformers reduceline current to a proportionally lower currentfor metering or relaying. Current transformers

can look like potential transformers or surge arrestors. One identifying feature on the currenttransformer shown in Figure 1-36 is a large canister on top of the bushing with a conductor

Figure 1-32. Capacitor bank.

Figure 1-33. Shunt reactor.

Bushings

Source circuit

Shunt reactor

Figure 1-34. Potential transformer.

Bushing

Transformer housing

Conduit


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Power Transformers, Part 1

49

are not always forced-oil/forced-air cooled.

Power transformers with other kinds of coolingsystems can also be gas sealed. Figure 3-36 showsa gas-sealed, self-cooled/forced-air-cooled power

transformer. The cooling system is recognizable by

the combination of the radiator and the fan.Regardless of the type of cooling system that agas-sealed power transformer has, the gas sealsystem works in basically the same way. The simpli-fied illustration in Figure 3-37 represents the

sealing system of a gas-sealed power transformer.The components of the sealing system are a gascylinder, two pressure regulators, two gauges, and a

pressure relief device.

The windings in a gas-sealed power transformer

are completely covered by oil. The rest of theenclosure is filled with gas, which is suppliedthrough tubing from the cylinder. The regulators

ensure that gas is supplied at a pressure slightlyabove atmospheric pressure. This slight positivepressure keeps air and moisture from leaking into

the enclosure.

When the transformer is operating, the windingsheat the oil, causing it to expand. As the expanding

oil compresses the gas, the pressure inside the

enclosure increases. If the pressure rises enoughto exceed a predetermined high value, the relief

device releases gas from the transformer enclosureto atmosphere. The release of gas continues untilpressure returns to an acceptable value.

When the transformer becomes cooler, forexample, during a period of reduced load, the

oil also becomes cooler, and it contracts. As theoil contracts, the pressure inside the transformerenclosure drops. If the pressure falls below a prede-

termined low value, a regulator adds gas from the

cylinder to the enclosure until the pressure returnsto an acceptable value.

The regulators and the relief device in a gas-sealedpower transformer regulate gas flow. The gauges indicate pressure. For example, the gaugeshown in Figure 3-38 indicates the pressure inside the gas cylinder. As gas in the cylinder is used,

the cylinder pressure drops. A low pressure reading means that the gas is running out, and thecylinder may need to be replaced.

Figure 3-35. Gas cylinder, regulators, gauges,

and pressure relief device.

Regulators

Gascylinder

Guage

Figure 3-36. Gas-sealed power transformer,Example 2.

Radiators

Gascylinder

Guage

Figure 3-37. Simplified representation of a

gas-sealed power transformer.

Regulators

Gascylinder

Oil Windings

Guage

Tubing

Pressure relief device


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Power Transformers, Part 2

65

Next, both selector switch A and selector switch B are rotated clockwise, so that selector switch

B slides over to tap 2, and selector switch A slides across tap N to the opposite end of the tap.(Selector switch A remains on tap N.) Since current is not flowing through selector switch B,there is no arcing as the switch changes taps.

Then, transfer switch B is closed, so that current flows across the reversing switch and the raise

tap, labeled R, from left to right through a portion of the tapped winding, across tap 2 andselector switch B, across transfer switch B, and out lead X0. Current continues to flow across theneutral tap, across selector switch A, across transfer switch A, and out lead X0.

Transfer switch A is then opened to interrupt current flow through selector switch A. Both

selector switch A and selector switch B are rotated clockwise, so that selector switch A slides overto tap 2, and selector switch B slides across tap 2 to the opposite end of the tap.

Once selector switch A is on tap 2, transfer switch A is closed, so that current again flows acrossselector switch A and transfer switch A and out lead X0. This completes the tap change. Thenew tap position is shown in Figure 4-18. With

the reversing switch in the Raise position and theselector switches on tap 2, a portion of the tappedwinding is added to the secondary winding. This

changes the ratio of secondary turns to primaryturns and effectively raises the secondary voltage.The first tap position that adds turns to the

secondary winding is called one-raise.

As the selector switches are moved clockwise tothe other taps, turns are added to the secondary to

raise the secondary voltage. When all of the tappedwindings are added, the tap changer is at the full-

raise position.

Figure 4-19 shows the tap changer at full-raise.

To lower the secondary voltage, the selectorswitches are rotated counterclockwise back to theneutral tap. Then, the reversing switch slides from

the Raise position (R) to the Lower position (L),and the selector switches rotate counterclockwisefrom tap N to tap 4.

Figure 4-20 shows the new tap position called:

on-lower.

When the reversing switch is in the Lower position, and the selector switches are on tap 4,current flows from left to right across the secondary winding, across the reversing switch and theLower tap, from right to left through part of the tapped winding, across tap 4 and the selector

switches, across the transfer switches, and out lead X0.

Figure 4-18. Tap changer at one-raise position.

Figure 4-19. Tap changer at full-raise position.


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Power Transformer Insulation Resistance Testing

121

between the high voltage winding and ground to be tested. Although the low voltage winding

is not included in this test, current leakage to the low voltage winding could affect the resis-tance measurement. To avoid this problem, a lead is connected to the guard (G) terminal of themegohmmeter and the low voltage (X) terminal of the transformer. The guard diverts current

that leaks to the low voltage windings so that this leakage current is not included in the test

measurement.

Connections for Testing the Resistance Between the Low Voltage Winding and Ground

The connections for testing the insulation resis-tance between the low voltage winding andground are illustrated in Figure 8-18. One test

lead is connected to the earth (-) terminal of themegohmmeter and to a transformer case ground.Another test lead is connected to the line (+)

terminal of the megohmmeter and to the lowvoltage (X) terminal of the transformer. A lead is

also connected between the guard (G) terminalof the megohmmeter and the high voltage (H)

terminal of the transformer to divert currentthat leaks to the high voltage winding so that thisleakage current is not measured.

Connections for Testing the Resistance Between the

Low Voltage Winding and the High Voltage Winding

The connections for testing the resistance betweenthe low voltage winding and the high voltage

winding are illustrated in Figure 8-19. One testlead is connected to the earth (-) terminal ofthe megohmmeter and to the high voltage (H)terminal of the transformer. Another test lead is

connected to the line (+) terminal of the megohm-meter and to the low voltage (X) terminal of thetransformer. A lead is also connected between the

guard (G) terminal of the megohmmeter and atransformer case ground to divert current thatleaks to ground so that this leakage current is not

measured.

Connections for Testing the Insulation Resistance

Between the Transformer Core and Ground

A transformer core to ground test is a type ofinsulation resistance test that is typically performedafter a transformer has been moved or after any

work has been done inside a transformer. As illus-trated in Figure 8-20, a core ground connects thecore that the windings are wound around to the

Figure 8-18. Connections for testing insulation

resistance between the low voltage winding

and ground.

Figure 8-19. Connections for testing insulation

resistance between the low voltage winding

and the high voltage winding.

Figure 8-20. Transformer core and core ground.

Core ground

Core

Tank, or caseground


12/20

161

Circuit Breaker Operation

is no current flow. Circuit breakers are designed

to take advantage of these momentary absences ofcurrent flow to help extinguish arcs.

Classification of Circuit Breakers

Circuit breakers are generally classified accordingto the dielectric mediums they use to help extin-guish arcs. Four mediums that are commonly used

for this purpose are air, oil, vacuum and gas.

Figures 11-4 and 11-5 show two types of

breakers that use air as a dielectric medium. Theair-magnetic breaker (Figure 11-4) uses air and amagnetic field to help extinguish arcs.

The air-blast breaker (Figure 11-5) uses a high-pressure blast of air.

Figure 11-6 shows an oil breaker. In an oil breaker,the contacts are submerged in insulating oil, whichhelps extinguish the arc.

Figure 11-7 shows a vacuum breaker. A vacuumbreaker encloses its contacts in a vacuum, which

Figure 11-4. Air-magnetic breaker.

Figure 11-5. Air-blast breaker.

Figure 11-6. Oil breaker.

Figure 11-8. Gas-blast breaker.

Figure 11-7. Vacuum breaker.

Figure 11-9. Gas-puffer breaker.


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167

Circuit Breaker Operation

As illustrated in Figure 11-21, a gas-puffer breaker interruptor is enclosed in a pipe-like tank,

which is filled with low-pressure SF6 gas. Theinterruptor is an insulated tube that houses thebreakers interrupting mechanisms and insulates

them from the outer tank.

The interruptors main features (Figure 11-22)include a stationary contact assembly, a movingcontact assembly with a non-conducting nozzle,and a chamber where gas is compressed during

the operation of the breaker. Each of the contactassemblies includes main contact fingers andarcing contact fingers.

When the circuit breaker is closed, the currentpath is through the stationary contact assembly,the main contact fingers and the moving contact

assembly. When the breaker trips (Figure 11-23),the moving contact assembly moves away from thestationary assembly and the main contact fingers

separate. Arcing does not occur, however, becausethe circuit is still complete through the arcingcontacts.

As the moving contact assembly moves awayfrom the stationary assembly, the SF6 gas in the

compression chamber is compressed. Compressingthe gas increases its dielectric strength. Eventually,

the moving contact assembly moves so far that thearcing contact fingers separate, and an arc forms(Figure 11-24).

When the arcing fingers separate, the compres-

sion chamber opens, and thehigh-pressure gasflows through the arc to the low pressure areasof the interruptor. The dielectric strength of the

high-pressure gas weakens the arc. As the gas flowsthrough the arc, the arc is lengthened and cooled,until it eventually extinguishes at a current zero.

Figure 11-21. Gas-puffer breaker.

Bushings

Interruptor

TankLow pressure

SF6gas

Figure 11-23. Gas-puffer breaker interruptor

main contacts open.

Main contactsseparate

Gas

comnpressingin chamber

Arcing contactsstill meet

Figure 11-24. Gas-puffer breaker interruptor -

arcing contacts open.

Arc

Figure 11-22. Gas-puffer breaker interruptor

closed.

Main contactfingers

Moving contactassembly

Compressionchamber

Arcing contactfingers

Stationarycontact assembly

Nozzle


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211

New Circuit Breaker Inspections and Tests

rod travel velocity, and a variety of other circuit

breaker operating characteristics. Figure 13-27 isan illustration of typical time-travel traces.

The time-travel test is typically performed forseveral types of breaker operations. The traces for

each operation can be analyzed to determine howthe breaker is performing in comparison withthe manufacturers specifications. If the breakersperformance does not fall within acceptable ranges,

the breaker must be properly adjusted before it canbe put in service.

Contact Resistance Test

Resistance in the closed contacts of a circuitbreaker can have a number of causes, including

arcing deposits, a loose or incomplete connection,or pitting from repetitive arcing. Contact resistance

creates heat that can reduce the life of the contactsand possibly even lead to breaker failure.

The purpose of contact resistance testing is todetect unacceptably high contact resistance levelsbefore failure occurs.

In principle, the test is performed by passing adirect current through the closed contacts of the

breaker and measuring the voltage drop across the

contacts (Figure 13-28). The test instrument usesthe current and voltage values to calculate anddisplay the contact resistance.

If the contact resistance exceeds an acceptable limit,the contacts may have to be cleaned or replaced.

Insulation Resistance Test

When a circuit breakers contacts are open, thebreakers insulation should provide a high resis-

tance to prevent current from flowing.

The purpose of insulation resistance testing is to

detect unacceptably low levels of insulation resis-tance before poor or weakened insulation results infailure.

In principle, the test is performed by applying ahigh DC voltage to one of the breakers bushing

terminals with the breakers contacts open (Figure13-29). Then, leakage current is measured either to

Figure 13-28. Performing a contact resistance

test.

Figure 13-29. Performing an insulation resistance

test.

Figure 13-26. Transducer and timing rod on an oil

circuit breaker.

Transducer

Timing rod

Figure 13-27. Time-travel traces.


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294

the power factor in this case by using capacitor

banks, such as the one shown in Figure 20-8. Thecapacitor banks offset the excessive demand forinductive power, and thus bring the power factor

closer to unity.

Excessive demand for non-working capacitivepower also results in a lower power factor thandesirable. In this case, instead of increasing poweroutput to meet the demand for capacitive power,the utility can improve the power factor by using

shunt reactors. The shunt reactors offset theexcessive demand for capacitive power. Figure 20-9shows an example of a typical shunt reactor.

Clearing Capacitor Banks

The main steps for safely clearing a capacitor bankfor maintenance are similar to the steps taken to

clear any other device in a substation. These stepsinclude de-energizing, isolating, testing for dead,and grounding. However, a capacitor bank is

different from other devices in a substation in thatit stores an electrical charge even after the bank hasbeen separated from its source of energy. Because

of this ability to store a charge, some special safetyprecautions are required when clearing a capacitor

bank.

De-Energizing and Isolating a Capacitor Bank

A capacitor bank is de-energized by electricallyseparating the bank from its source of energy.

Figure 20-10 is a simplified illustration of a sectionof a substation that includes an energized three-phase bus, a three-phase circuit breaker, three

single-phase disconnect switches, and a three-phasecapacitor bank. In this example, the capacitor bankis de-energized by opening the circuit breaker.

A capacitor bank is isolated by physicallyseparating the bank from its source of energy. Asillustrated in Figure 20-11, the capacitor bank in

this example is isolated by opening the three single-phase disconnect switches. Opening these switchesprovides a visible break between the source of energy and the capacitor bank.

The actual switching devices that are operated and the sequence in which they are operatedvary with the design of the substation. In general, a capacitor bank is switched out only after

Figure 20-8. Capacitor bank.

Figure 20-9. Shunt reactor.

Figure 20-10. Substation capacitor bank.

Circuitbreaker

Disconnectswitches

Capacitorbank


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333

Voltage Regulators

Isolating the Regulator

After the bypass switch is closed, the regulatorcan be isolated from the circuit. This is done byopening the regulator source and load disconnect

switches. The disconnect switch that is opened

first depends on the design of the system and oncompany procedures.

The specific procedure for switching a regulatorout of service may vary. For example, the type of

switch shown in Figures 22-47 and 22-48 enablesthe regulator to be both bypassed and isolated inone switch operation. The switch in this exampleis made up of two bars. When the switch is closed,

one bar connects the source circuit to the sourcelead of the regulator. The other bar connects the

load lead of the regulator to the load circuit. Thetwo bars are separated by insulators.

By opening the switch, three switching operations

are completed in one action. The first operationis bypassing the regulator. When the switch isopened, a spring operated plate (Figure 21-48)

moves into the space where the switch was. Theplate connects the source circuit to the load circuit,and the regulator is bypassed.

For the second operation, the regulator is isolated

from the source circuit. When the switch is opened,there is a visible separation between the source

circuit and the regulator source lead.

For the third operation, the regulator is isolated

from the load circuit. When the switch is opened,there is a visible separation between the regulatorload lead and the load circuit.

Physically Disconnecting the Regulator

Generally, single-phase regulators in a substation

are grouped in three-phase banks, as shown inFigure 21-49. To remove one of the regulators,all three units must be taken out of service. Afterthe regulators have been switched out of service,

they are tagged, tested for dead, and groundedaccording to company procedures.

To remove the regulator, its conductors are discon-nected from the regulator terminals. In Figure21-50, one of the conductors has been marked Figure 21-49. Three single-phase regulators.

Figure 21-46. Regulator bypass switch closed.

Sourcedisconnect

switch

Loaddisconnect

switch

Bypass switch

Figure 21-47. Disconnect switch.

Regulatorload lead

Barsseparated by

insulators

Regulatorsource lead

Sourcecircuit

Loadcircuit

Figure 21-48. Disconnect switch opened.

Load circuitcontact

PlateSourcecircuitcontact


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365

Protective Relays, Transmission Systems

The specific voltage-to-current ratio setting for a

distance relay is affected by several considerations.For example, a distance relay in substation A can beset for a voltage-to-current ratio that would cause

the relay to operate for a fault anywhere on the

section of line between substations A and B. Withthis setting, however, the relay might trip for a fault

near substation B but between substations B andC (Figure 23-37). This type of relay operation isundesirable, because the basic approach to trans-

mission line protection is to isolate only the section of line in which a fault occurs. For a fault

between substations B and C,a relay in substation B should open a breaker in substation B, and,possibly by transfer tripping, also open a breaker in substation C to isolate the fault. If a distancerelay in substation A operates, it would isolate thesection of line between substations A and B, eventhough that section of line does not have to be

isolated to remove the fault from the system.

Zoned ProtectionTo prevent undesirable operations, a distance relayis generally set to protect approximately 90% of

a line section. This protected section is typicallyreferred to as Zone 1 (Figure 23-38).

To protect line sections between substations,additional Zone 1 sections can be set up (Figure

23-39). However, with this type of protection,approximately 10% of each line section is leftunprotected.

A common way to provide complete protection

for line sections is to use a distance relay in eachsubstation that provides Zone 1 protection in theopposite direction (Figure 23-40). This arrange-

ment provides overlapping protection for each linesection between substations.

In addition to Zone 1 protection, a distance relay

may also provide Zone 2 and Zone 3 protection.For example, as illustrated in Figure 23-41, Zone

2 protection from substation A covers the linesection between substations A and B, as well aspart of the line section between substations B andC. Zone 3 protection from substation A covers the

line sections between substations A and B, substa-tions B and C, and part of the line section beyondsubstation C.

Figure 23-37. Fault between substations B and C.

Figure 23-38. Zone 1 protection.

Figure 23-41. Zone 2 and Zone 3 protection fromsubstation A.

Figure 23-40. Overlapping Zone 1 protection.

= Overlapping protection

Figure 23-39. Multiple Zone 1 protection.

Unprotected linesections


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376

Sensing Equipment

Sensing equipment is equipment that changes a condition such as voltage or current to a valueor signal that can be measured. For example, potential transformers (Figure 24-1) change, ortransform, line voltage to a proportionally lower voltage for measurement.

Another example of sensing equipment is a current transformer. Current transformers (Figure24-2) transform line current to a proportionally lower current for measurement.

Measuring Equipment

The signals from sensing equipment are typically sent to measuring equipment and control-ling equipment. Measuring equipment measures the signal provided by sensing equipment andindicates the value of the condition being sensed. For example, a meter such as the ammetershown in Figure 24-3 indicates the value of current it receives from a current transformer.

Another example of measuring equipment is a recording meter, such as the one shown in Figure

24-4. A recording meter measures signals from sensing equipment and records the values of thesignals over a period of time.

Controlling Equipment

Controlling equipment detects the signals it gets from sensing equipment, and, if a signal isdifferent from a preset value, provides a signal that operates various other equipment. Anexample of controlling equipment is an overcurrent relay, such as the one shown in Figure 24-5.

An over current relay detects current that it receives from a current transformer. If the current

Figure 24-1. Potential transformer. Figure 24-2. Current transformer.

Figure 24-4. Recording meter.Figure 24-3. Ammeter.


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396

If alternating current to the charger is interrupted for any reason, the battery will instantlyprovide direct current to the steady, continuous loads and, as required, to the intermittent loads.It will continue to supply the loads until alternating current is restored or until the battery is

fully discharged.

Cell Components and Electrochemical ActionSubstation battery maintenance and testing are more likely to be performed properly when theworker knows the construction of the battery cells, how the cells work, and what can go wrong

with the cells and why. This section describes the components and electrochemical action of atypical lead-acid substation battery cell.

Components of a Lead-Acid Cell

Battery cells used in substations are typicallylead-acid cells. The external components of atypical lead-acid cell (Figure 25-10) include a

container, which is often called a jar, positive andnegative terminal posts, and a vent with a flamearrestor. The flame arrestor shields explosivegases at the vent from external sparks or flames.

The internal components include a liquid calledan electrolyte, conductive lead-based plates, andnon-conductive separators. The electrolyte is

composed of sulfuric acid and water.

Figure 25-11 shows a cell that has been disas-

sembled so that the plates and separators can be

seen. The plates are arranged so that the negativeplates and the positive plates alternate. A cell always

has one more negative plate than positive, and theplates at each end of the cell are negative. This isbecause each positive plate needs a negative plate

on each side of it in order to function efficiently.All the positive plates are mechanically and electri-cally linked together by a bus bar and connected toone of the terminal posts. The negative plates are

also linked together, and they are connected to theother terminal post. The non-conductive separa-

tors insulate the negative and positive plates fromeach other.

The most widely used cell plate design is a type

called the pasted plate, although there is a varietyof other designs. The pasted plate uses porous leadcompounds for the chemically active portions of

the plate. This material is too soft to hold togetherby itself, so it is typically pasted onto a metal grid(Figure 25-12).

Figure 25-10. Components of a lead-acid cell.

Figure 25-11. Disassembled lead-acid cell.

Figure 25-12. Plate grid and lead.


20/20


terminal of cell 7 is connected to the positive

terminal of cell 8.

To begin the cell replacement procedure, the

jumpers are connected to cells 6 and 8 and tothe new cell (Figure 28-3). One end of a jumper

is connected to the negative terminal of cell 6,and the other end of the jumper is connected tothe positive terminal of the new cell. One endof a second jumper is connected to the positiveterminal of cell 8, and the other end of that jumper

is connected to the negative terminal of the newcell. The jumpers are connected to the terminal sothat they will not interfere with the removal and

reinstallation of the intercell connecting straps.

With the jumpers in place, the bad cell is then

disconnected from the battery by removing theintercell connecting straps between cells 6 and 7and between cells 7 and 8. Because the new cell is

connected in parallel, no arcing occurs when theintercell connecting straps are disconnected fromthe bad cell.

Next, the bad cell is removed from the battery rack,and the new cell is put in its place (Figure 28-4).

Once the new cell is in place, it is connected tothe adjacent cells in the battery. The intercell

connecting straps are reinstalled, connecting thenegative terminal of cell 6 to the positive terminalof the new cell, and the positive terminal of cell 8to the negative terminal of the new cell. Then, both

jumper cables are removed. Connecting a new cellin parallel with the old cell makes it possible toremove and replace a bad cell on a battery that is

still in service.

Bypassing a Cell Using a Diode and Jumpers

As shown in Figure 28-5, the equipment required

for bypassing a cell using a diode and jumpersincludes a jumper with a diode that is connectedin line with the jumper, and two jumpers without

diodes. Also shown in Figure 28-5 are a combus-tible gas detector, an ohmmeter, and the new cell tobe installed in place of the bad cell.

Some companies require that a combustible gasdetector be used whenever work is performed on

Figure 28-4. New cell installed between cells 6

and 8 with temporary jumper connections only.

Figure 28-2. Typical cell arrangement - one bad

cell.

Negative terminals Positive terminals

Bad cell

Figure 28-3. Jumper connections to bypass bad

cell.

New cell

PositiveNegative

Figure 28-5. Equipment for bypassing a cell using

a diode and jumpers.

New cell

Jumber withdiode

Jumperswithoutdiodes

Diode

Combustiblegas detector

Ohmmeter

Substation Operation Aand Maintenance Mannuals

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