CONTENTS
Preface
1. Fundamental Concepts in Electrical Machines
1.1 Introduction 1.1
1.2 Classification of Electrical Machines and their Essential Features 1.2
1.3 Important Terminologies 1.8
1.4 Magnetic Circuit 1.13
1.5 Electromagnetic Induction 1.18
1.6 Induced emf 1.21
1.7 Fleming’s Rules 1.24
1.8 Force on a Current-carrying Conductor 1.25
1.9 Torque in a Current-carrying Coil 1.26
1.10 Fundamental Concepts of Generator and Motor Action 1.44
1.11 Steady-state Voltage Equations 1.48
1.12 Magnetic Hysteresis 1.54
1.13 Eddy Current 1.57
1.14 Efficiency of an Electrical Machine 1.60
1.15 Electromechanical Energy-conversion Principles 1.61
1.16 Energy in a Singly Excited Magnetic Field System 1.62
1.17 Forces and Torques in a Magnetic Field 1.63
1.18 Energy in a Doubly Excited Magnetic Field System 1.69
Review Questions 1.92
Problems 1.92
Multiple-Choice Questions 1.93
Answers 1.98
xvii
1.1–1.98
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2. Direct Current (dc) Machines
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
2.14
2.15
2.16
2.17
2.18
2.19
2.20
2.21
2.22
2.23
2.24
2.25
2.26
2.27
2.28
2.29
2.30
2.31
Introduction 2.1
Principle of Operation of a dc Machine 2.1
Construction of a dc Machine 2.4
Armature Winding 2.7
Magnetic Circuit and Flux Path in a dc Machine 2.17
Equivalent Circuit of a dc Machine 2.17
Classification of dc Machines with respect to Types of Excitation 2.18
Emf Equation of a dc Machine 2.19
Relationship between Voltages and Currents in a dc Machine 2.27
Armature Reaction 2.37
Commutation 2.44
Characteristics of dc Generators 2.50
Voltage Regulation 2.58
Parallel Operation of dc Generator 2.58
dc Generators in Series 2.62
Principle of Working of a dc Motor 2.70
Electromagnetic Torque Equation of a dc Motor 2.70
Torque–current Characteristic of a dc motor 2.89
Speed Equation of a dc Motor 2.91
Speed Regulation of a dc Motor 2.91
Speed vs Armature Current Characteristic of a dc Motor 2.92
Speed vs Torque Characteristic of a dc Motor 2.94
Dynamic Behaviour of a dc Motor on Loading and Unloading 2.95
Speed Control of a dc Motor 2.96
Dynamic Behaviour During Speed Adjustment 2.107
Efficiency of dc Machines 2.139
Starting of a dc Motor 2.164
dc Motor Starting Circuits 2.171
Electric Braking of dc Motors 2.175
Testing of dc Machines 2.176
Applications of dc Machines 2.181
Review Questions 2.187
Problems 2.188
Multiple-Choice Questions 2.194
Answers 2.198
2.1–2.198
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3. Single-phase Transformers
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
3.14
3.15
3.16
3.17
3.18
3.19
3.20
3.21
3.22
3.23
3.24
3.25
3.26
3.27
3.28
3.29
3.30
3.31
3.32
3.33
Introduction 3.1
Transformer as a Coupled Circuit 3.1
Principle of Operation 3.4
EMF Equation 3.4
Construction of a Single-phase Transformer 3.5
Ideal Transformer 3.7
Distribution and Power Transformer 3.8
Transformation Ratio 3.8
Impedance Transformation 3.9
No-load Operation of a Transformer 3.22
Concept of Leakage Reactance 3.23
Operation of a Transformer on Load 3.24
Transient Behaviour when Loading and Unloading 3.27
Equivalent Circuit of a Transformer 3.28
Approximate Equivalent Circuit of a Transformer 3.31
Magnetization Current in a Real Transformer 3.32
Voltage Regulation of a Transformer 3.63
Expression of Voltage Regulation 3.64
Per-unit Expression for Resistance, Leakage Reactance and
Impedance Voltage Drops 3.67
Approximate Per-unit Voltage Regulation 3.68
Condition for Zero Voltage Regulation 3.68
Condition for Maximum Voltage Regulation 3.68
Losses and Efficiency of Transformer 3.79
Condition for Maximum Efficiency 3.81
Testing of Transformers 3.104
All-day Efficiency 3.108
Parallel Operation of Two Single-phase Transformers 3.136
Auto-transformer 3.139
Step-down Auto-transformer 3.139
Power Relation in an Auto-transformer 3.141
Step-up Auto-transformer 3.143
Saving in Conductor Material in Auto-transformer 3.144
Advantages and Disadvantages of an Auto-transformer 3.145
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3.1–3.199
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3.34
3.35
3.36
3.37
3.38
3.39
3.40
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Application of an Auto-transformer 3.146
Pulse Transformer 3.146
Welding Transformer 3.147
Instrument Transformer 3.150
Transformer Cooling 3.152
Conservators and Breathers 3.153
Nameplate and Rating of a Single-phase Transformer 3.153
Review Questions 3.173
Problems 3.174
Multiple-Choice Questions 3.195
Answers 3.199
4. Three-phase Transformers
4.1 Introduction 4.1
4.2 Three Single-phase Transformer Banks to Form
One Three-phase Transformer 4.1
4.3 Three-phase Transformer as a Single Unit 4.2
4.4 Three-phase Transformer Connections 4.3
4.5 Salient Features of Commonly Used Transformer Connections 4.9
4.6 Open-delta or V–V Connection 4.10
4.7 Scott Connection or T-connection 4.12
4.8 Three-phase to Six-phase Conversion 4.19
4.9 Three-phase to Twelve-phase Conversion 4.22
4.10 Parallel Operation of Three-phase Transformers 4.40
4.11 Harmonic Phenomena in a Three-phase Transformer 4.40
4.12 Inrush Current 4.42
4.13 Transformer Tappings 4.43
4.14 Induction Regulator 4.45
4.15 Three-phase Auto-transformers 4.47
4.16 Three-winding Transformers 4.48
4.17 Audio Frequency Transformer 4.52
4.18 Rectifier Transformer 4.53
4.19 Grounding Transformer 4.53
4.20 Transformer Nameplate 4.53
4.1–4.91
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Review Questions 4.86
Problems 4.87
Multiple-Choice Questions
Answers 4.91
4.87
5. Fundamentals of ac Rotating Machines
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.1–5.47
Introduction 5.1
ac Windings 5.1
Concept of Electrical and Mechanical Degrees 5.6
Breadth Factor 5.7
Pitch Factor 5.9
Mmf of ac Windings 5.15
Emf Generated in Electrical Machines 5.21
Torque in ac Machines 5.25
Slot or Tooth Harmonics 5.33
Review Questions 5.40
Problems 5.41
Multiple-Choice Questions 5.41
Answers 5.47
6. Synchronous Generator
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
6.11
6.12
6.13
6.14
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Introduction 6.1
Principle of Operation 6.1
Construction 6.2
Different Types of Excitation Systems 6.5
Cooling 6.9
Emf Equation in a Synchronous Generator 6.10
Flux and mmf Diagram of Cylindrical-rotor Synchronous Generator
6.17
Concept of Synchronous Impedance 6.19
Voltage Regulation 6.20
Short-circuit Ratio 6.27
External Characteristic of a Synchronous Generator 6.45
Power-angle Characteristic of Cylindrical-rotor Synchronous Generator 6.47
Parallel Operation of Two Synchronous Generators 6.58
Synchronous Generator Connected to Infinite Bus 6.67
6.1–6.123
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6.15
6.16
6.17
6.18
6.19
6.20
6.21
6.22
6.23
6.24
6.25
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V Curves 6.72
Inverted V Curves 6.74
Operational Aspects 6.74
Salient-pole Synchronous Generator 6.77
Two-reaction Theory and Phasor Diagram of a
Salient-pole Synchronous Generator 6.77
Methods of Determining Xd and Xq 6.79
Power-angle Characteristic of Salient-pole Synchronous Generator
Synchronizing Power and Synchronizing Torque 6.84
Role of Damper Winding 6.91
Symmetrical and Unsymetrical Short Circuit in a
Three-phase Synchronous Generator 6.91
Losses and Efficiency 6.94
Review Questions 6.109
Problems 6.110
Multiple-Choice Questions 6.118
Answers 6.123
6.82
7. Synchronous Motor
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
7.11
7.12
7.13
Introduction 7.1
Principle of Operation 7.1
Equivalent Circuit and Phasor Diagram of a Synchronous Motor 7.2
Starting of Synchronous Motors 7.5
Power and Torque Developed in a Cylindrical Rotor Motor 7.11
Power and Torque Developed in a Salient-pole Motor 7.13
Effect of Change in Load 7.22
Effect of Change in Excitation 7.23
V Curves of a Synchronous Motor 7.24
Hunting of a Synchronous Machine 7.25
Methods of Reducing Hunting 7.26
Comparison between Synchronous and Induction Motors 7.26
Applications of Synchronous Motor 7.26
Review Questions 7.40
Problems 7.40
Multiple-Choice Questions 7.45
Answers 7.47
7.1–7.47
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8. Three-Phase Induction Motor
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
8.10
8.11
8.12
8.13
8.14
8.15
8.16
8.17
8.18
8.19
8.20
8.21
8.22
8.23
8.24
8.25
8.26
8.27
8.28
8.29
8.30
8.31
8.32
Introduction 8.1
Construction of Induction Machines 8.1
Comparison of Squirrel-cage and Wound Rotors 8.4
Advantages and Disadvantages of a Three-phase Induction Motor 8.5
Principle of Operation 8.5
Induction Machine as a Generalized Transformer 8.6
Concept of Slip 8.7
Frequency of Rotor Voltage and Current 8.9
Emfs in Windings of Induction Motor 8.10
Equivalent Circuit of an Induction Motor 8.15
Power Relations in a Three-phase Induction Motor 8.20
Losses and Efficiency of Induction Motor 8.21
Torque Expression of Induction Motor 8.51
Torque–slip Characteristics of a Three-phase Induction Motor 8.55
Torque Condition During Loading, Breakdown and No-load 8.57
Determination of Motor Efficiency 8.83
Starting of a Three-phase Induction Motor 8.87
Reversal of Rotation 8.93
Speed Control of a Three-phase Induction Motor 8.102
Power Factor at Different Loading 8.107
Operation of an Induction Motor at Different Frequencies 8.108
Crawling and Cogging of Induction Motor 8.108
Skewing of Rotor Slots in a Three-phase Induction Motor 8.109
Operation on Unbalanced Voltage and Single Phasing 8.110
Circle Diagram 8.110
High-torque Induction Motors 8.114
Different Operating Zones of an Induction Machine 8.120
Induction Regulator 8.121
Frequency Changer 8.122
Induction Generator 8.123
Comparison of Induction Motor and Synchronous Motor 8.125
Application of Induction Motors 8.126
Review Questions 8.135
Problems 8.136
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8.1–8.149
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Multiple-Choice Question
Answers 8.149
8.146
9. Single-phase Induction Motors
9.1
9.2
9.3
9.4
9.5
9.6
9.7
9.8
9.9
9.10
9.11
9.1–9.32
Introduction 9.1
Production of Torque 9.1
Equivalent Circuit 9.5
Determination of Parameters of Equivalent Circuit 9.10
Starting of Single-phase Induction Motors 9.14
Split-phase Induction Motors 9.15
Capacitor-start Motor 9.16
Capacitor-start Capacitor-run Motor 9.17
Shaded-pole Motors 9.19
Speed Control of a Single-phase Induction Motor 9.21
Comparison between Single-phase and Three-phase Induction Motors 9.22
Review Questions 9.27
Problems 9.27
Multiple-Choice Questions 9.28
Answers 9.32
10. Special Machines
10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9
10.10
10.11
10.12
10.13
10.14
10.15
Universal Motors 10.1
Repulsion Motor 10.5
Single-phase Series Motor 10.7
Single-phase Synchronous Motors 10.9
Synchronous Induction Motor 10.10
Linear Induction Motor 10.11
Reluctance Motor 10.13
Switched Reluctance Motor 10.14
Servomotor 10.15
Tachometer 10.16
Hysteresis Motor 10.17
Brushless DC Motors 10.19
Stepper Motors 10.22
Permanent Magnet DC (PMDC) Motors 10.26
Permanent Magnet Generators 10.27
10.1–10.33
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Review Questions 10.30
Multiple-Choice Questions
Answers 10.33
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10.31
11. Review Problems (MCQs) with Solutions
11.1–11.108
Section A: DC Machines 11.1
Section B: Transformers 11.35
Section C: Induction Motors 11.67
Section D: Synchronous Generator 11.93
Index
I.1–I.7