SPECIAL ELECTRICALB.E. (Electrical Engineering) Jabalpur (Govt.) Engineering College, Jabalpur M.Tech. (Persuing), GBTU Lucknow Power System and Energy S.K. KATARIA & SONS® Publisher

SPECIAL ELECTRICALMACHINES

SIMMI P. BURMAN

B.E. (Electrical Engineering)Jabalpur (Govt.) Engineering College, Jabalpur

M.Tech. (Persuing), GBTU LucknowPower System and Energy

S.K. KATARIA & SONS®Publisher of Engineering and Computer Books

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PrefaceP

The primary aim of presenting this book is to meet the needs of B.Tech (ElectricalEngineering and Electrical and Electronics Engineering) students of UP TechnicalUniversity for the subject of Special Electrical Machines. The subject matter has beenpresented in an easy comprehensive manner, logical sequence using simple languageand to provide a detailed exposition of the fundamental.

The book consists of 5 divided units providing a comprehensive coverage of coursesprescribed by UP Technical University for the subject of Special Electrical Machines.A large number of worked out examples, theoretical exercises and numerical problems,all of Degree standard, have been included in the text. The solution to illustrativeexamples covering almost all topics makes the entire presentation easy to follow.

Every care has been taken to eliminate misprints, omissions and errors but it is toomuch to expect that no in accuracy misprint/error has crept in and the author would begrateful to the readers for bringing to his notice any such errors/misprints/omissions,they may come across while going through the book.

The author shall feel satisfied that, if the book meets the needs of the students forwhom it is meant. Suggestions and criticism for the improvement of the book shall bewelcomed.

The author will like to thank all the scientists, Engineers. Authors and publishers,whose works and text have been the source of enlightenment, inspiration and guidanceto me in the presentation.

Lastly, but not the least, the author is thankful to her publisher for bringing out thebook in such a short time and for pricing it moderately deposit heavy cost of paper inprinting.

January, 2013 Simmi P. Burman

AcknowledgementA

The author expresses her kind gratitude to, Dr. Raghuvir Kumar, Director of BabuBanarasi Das National Institute of Technology and Management and, Dr. Seethalekshmi.K, Director of BBDNITM, HoD EE Dept, Lucknow.

The author places on record his heart felt thanks to Mr. Bipin Singh, SeniorLecturer, BBDNITM for the encouragement extended to her.

The author also wishes to thank Mr. Jegan Raj. S, Senior Lecturer, Department ofElectrical Engineering, BBDNITM and her colleagues for their consistent co-operationdirectly or indirectly in bringing out this book.

The author likes to remember the motivation initiated by her husband Mr. AvnishBurman, Deputy Manager, Hindustan Aeronautics Limited.

Simmi P Burman

To My Loving SonSAUBHAGYA BURMAN

(JOY)

ContentsC

1. POLY-PHASE AC MACHINES 1–1111.1 Introduction 1

1.2 Construction 1

1.2.1 Slip Ring Induction Motor 1

1.2.2 Squirrel-Cage Rotor 2

1.3 Flux and MMF Waves in Induction Motor 3

1.4 Development of Circuit Model (Equivalent Circuit) 3

1.5 Torque Slip Characteristics 14

1.6 Deep-Bar/Double-Cage Rotor 20

1.6.1 Deep-Bar Rotor 20

1.6.2 Double-Cage Rotor 22

1.7 Emf Injection in Rotor Circuit of Slip Ring Induction Motor 30

1.7.1 Rating of the Auxiliary Equipment 34

1.7.2 Torque-speed Characteristic 34

1.8 Comparison between Single-cage and Double Cage Motors 36

1.9 Constant Torque 37

1.10 Constant Power 37

1.10.1 Static Slip Power Recovery Control Schemes 38

1.10.2 Mechanical Recovery 39

1.10.3 Electrical Recovery 39

Solved Numericals 41

Solved Problems 97

2. SINGLE PHASE INDUCTION MOTORS 112–141

2.1 Single Phase Motors 112

2.2 Production of Rotating Field 112

2.2.1 Single Phase Induction Motor Principle 113

2.2.2 Double Revolving Field Theory of Single Phase Induction Motor 113

2.2.3 Rotor Slip w.r.t. Two Relating Field 114

xii Contents

2.2.4 Equivalent Circuit of Single Phase Induction Motor 115

2.2.5 Performance Calculation of a Single Phase Single

Winding Induction Motor 117

2.3 Determination of Equivalent Parameters 118

2.3.1 Blocked Rotor Test 118

2.3.2 No Load Test 119

2.4 Starting Methods and Types of Single Phase than Motor 120

2.4.1 Split Phase Induction Motor 120

2.4.2 Capacitor Motors 122

2.4.3 Permanent Split Capacitor Motor 125

2.4.4 Shaded Pole Motor 126

2.5 Comparison between 1-φ and 3-φ Induction Motor 127

2.6 Single Phase Series (Universal) Motor 127

2.7 Two Phase AC Servomotors 131

2.7.1 AC Servomotors 132

Solved Problems 134

3. STEPPER MOTORS AND SWITCHED RELUCTANCE MOTORS 142–200

3.1 Stepper Motors 142

3.2 Step Angle 142

3.2.1 Resolution 143

3.2.2 Slewing 143

3.2.3 Stepper Motor Application 143

3.3 Classifications of Stepper Motors 144

3.3.1 Variable Reluctance Stepper Motor 144

3.3.2 Permanent Magnet Stepper Motor 152

3.4 Hybrid Stepping Motors 158

3.5 Theory Torque Production in VR Stepping Motor 160

3.5.1 The Case of Infinitely Permeable Cores 160

3.5.2 The Case Constant Permeabilities 162

3.6 Effects of Mutual Induction 164

3.7 Characteristics of Stepper Motor 165

3.7.1 Static Characteristics 165

3.7.2 Dynamic Characteristics 166

3.8 Power Drive Circuits 168

3.8.1 Simple Power Drive Circuit 169

3.8.2 Dual Voltage Drive 170

3.8.3 Chopper Drive 172

3.8.4 Bipolar Drives for Stepper Motors 173

Contents xiii

3.9 Switched Reluctance Motor (SRM) 177

3.9.1 Introduction 177

3.9.2 Principle of Operation 179

3.9.3 Voltage and Torque Equation of a SRM 181

3.9.4 Operating Modes 182

3.10 Power Semiconductor Switching Circuits for SRM(Power Controller Switching Circuits) 185

3.10.1 Clamic Converter 185

3.10.2 (n + 1) Power Semiconductor Switches and (n + 1)

Diodes per Phase, where ‘n’ is Number of Phase Windings 187

3.10.3 Phase Winding using Bipolar Wires 188

3.10.4 Split Power Supply Converter 188

3.10.5 Dump ‘C’ Converter 190

Solved Numericals 191

Solved Problems 196

Review Questions 198

4. PERMANENT MAGNET GENERATORS 201–223

4.1 Introduction to Permanent Magnet Generators 2014.2 Brushless DC Motors 202

4.2.1 Schematic and Operation 2034.3 Permanent Magnet DC Motors 2054.4 Reluctance Motor 205

4.4.1 Operating Principle 2064.4.2 Torque – δ Characteristics 207

4.5 Hysteresis Motor 2084.6 Permanent Magnet Synchronous Motors 209

4.6.1 Sinusoidal PMAC Motors 2104.7 Permanent Magnets 212

4.7.1 Types of Permanent Magnets 2124.7.2 Permanent Magnets: (Materials Used for Permanent Magnets) 2124.7.3 Magnetization Methods 2134.7.4 Magnetization Characteristics 213

4.8 PCB Motor 215Solved Problems 216Review Questions 223

5. SINGLE PHASE COMMUTATOR MOTORS 224–233

5.1 Single Phase Commutator Motors 2245.2 Basic Connection are Two Types 224

xiv Contents

5.3 Repulsion Motors 2285.4 Linear Induction Motors 229

5.4.1 Introduction 2295.4.2 Construction of Linear Induction Motor 2295.4.3 Principle of Operation 2305.4.4 Phenomena Peculiar to LEM 2325.4.5 End Effects 232

MODEL PAPERS 234–241

EXAMINATION PAPER 242–243

INDEX 244–245

Poly-phase AC Machines1

ChapterChapterChapterChapterChapter

1.1 INTRODUCTION

The induction machine is an important clam of electric machines, which finds wideapplicability as a motor in industry and in its single-phase form in several domesticapplication. More than 85% of industrial motors in use today are infact inductionmotors.

It is substantially a constant-speed motor with a shunt characteristic, a few percentspeed drop from no load to full load.

The torque developed in this motor has its origin in current induction in the rotorwhich is only possible at non-synchronous speed, hence the name asynchronous machine.On the other hand the torque in a synchronous machine is developed only at synchronousspeed when the locking of the two field takes place. Therefore, the induction motor isnot plagued by the stability problem inherent in the synchronous motor. As a consequenceit inherently has a power factor less then unity which usually must be corrected bymeans of shunt capacitors at motor terminals. There is no simple and in expensivemethod of controlling the induction motor speed as is possible in a dc shunt motor.

A wide range of speed control is possible only by expensive circuit using (SCRs).

1.2 CONSTRUCTION

The stator of an induction motor is similar to that of a synchronous machine and iswound for three phases. Two types of construction are employed for the rotor-wound-rotor and squirrel-cage-rotor.

The rotor core is of laminated construction with slots suitably punched in foraccommodating the rotor winding/rotor bars. The punched laminated are slacked andfitted directly on to a shaft in the case of small machines while in the case of largemachines a stuck of annular punching of a suitable cross-sectional area are fitted on toa spider-web arrangement on the shaft.

1.2.1 Slip Ring Induction Motor

The winding of a wound-rotor is polyphase with coils placed in the slots of this rotorcore. It is similar to that of the stator except that the number of slots is smaller andfewer turns per phase of a heavier conductor are used. The rotor is wound and connectedin star with three leads brought out of the machine via slip-rings placed on the shaft.The slip-rings are tapped by means of copper-carbon brushes. Wound rotor construction

1

2 Special Electrical Machines

is generally employed for large size machines to be used where the starting torquerequirements are stringent, external resistance can be induced in the rotor circuit throughslip-ring for reducing the starting current and simultaneously improving the startingtorque.

Fig. 1.1(a) Wound rotor for induction motor

1.2.2 Squirrel-Cage rotorThe squirrel-cage rotor has solid bars of conducting material placed in rotor slots andshorted through end rings on each side. In large machines alloyed copper bars aredriven in the slots and are brazed onto copper end rings. Rotors up to 50 cm diameterusually have diecast aluminium bars wherein the end-rings are also cast simultaneouslywith the same material by using a suitable mould. This is an economical process and isgenerally employed in mass production of small size induction motors.

Fig. 1.1(b) Squirrel-cage rotor showing cast aluminium bars and end rings

The rotor circuit of a squirrel-cage machine cannot be tempered with and themachine have a low starting torque. While it has excellent running performance thereforeit cannot be used where a high starting torque is required. The starting torque of asquirrel-cage motor can be improved by employing either a double-cage rotor or adeep-bar rotor. Such type of construction serves the purpose of a medium startingtorque requirement. The rotor has a smaller number of slots than the stator and theremust be a nonintegral multiple of stator slots so as to prevent magnetic locking of rotorand stator teeth of the time of starting. The slots in the induction machine are semi-

Special Electrical Machines

Publisher : S K Kataria and Sons( KATSON ) ISBN : 9789350142622 Author : Simmi P. Burman

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