Fundamentals of Electric Machines

This Book presents a comprehensive exposition of the theory, performance and analysis of electric machines. Transformers alongwith other machines including AC and DC, synchronous, 3 phase and single phase induction, commutator, special machines and Solid State control have all been explained in a simple and friendly style. A balance between the Mathematical and the qualitative aspects has been kept throughout the book.

A Large variety of solved examples are included to illustrate the basic concepts and techniques. Unsolved problems and objective questions have also been presented at the end of each chapter.

The Second Edition also includes :
1. Wide band transformers
2. Phase Groups of 3-phase transformers
3. Synchronous reactor and synchronous frequency changer
4. Speed control of 3-phase induction motor
5. Operation of 3-phase induction motor with unbalanced Supply voltages
6. Additional solved and unsolved problems

All these features make this book an ideal text for undergraduate electrical, Electronics and Computer Engineering students.

UPSC and AMIE candidates would also find the book extremely useful.

Dr. B.R. Gupta retired as Professor of Electrical Engineering, Punjab Engineering College, Chandigarh and is presently Visiting Professor and Consulting Engineer in Gurgaon, Haryana. He has over 38 years of teaching, Research and consultancy experience in electrical engineering. He has been the Principal Investigator of two research projects during 1973-86. He has authored over 75 research papers and 11 books. He has received Medals for Distinction in Engineering and Technology (1979 and 1992) and two research awards from the Institution of Engineers (India). Dr. Gupta is a Member of IE (India) and Senior Member Ieee (USA).

Vandana Singhal is Dupty Director in Central Electricity Authority, Department of Power, Government of India, New Delhi. She obtained her BE (Hons.) and ME (distinction) degree from Punjab University in 1986 and 1988 respectively. She has over 11 years experience in electrical power systems, electrical machines and allied subjects. She has co-authored the Books Electrical Science, Fundamentals of Electrical Networks and Power Electronics.

Preface to the Third Edition
Preface to the First Edition

I. BASIC PRINCIPLES :
1. Faraday's Law of Electromagnetic Induction
2. Lenz's Law
3. Methods of Linking Flux
4. Motional EMF (Dynamically Induced EMF or Speed EMF)
5. Statically Induced EMF (or Transformer EMF)
6. General Case of Induction
7. Coefficient of Self-Inductance
8. Coefficient of Mutual Inductance
9. Force on Current Carrying Conductor in a Magnetic Field
10. Torque on a Current Carrying Coil in a Magnetic Field
11. Fleming's Right-Hand Rule
12. Fleming's Left Hand Rule
13. Generator and Motor Action
14. Interaction of Magnetic Fields
15. Hysteresis Loss
16. Eddy Current Loss
17. Energy Balance
18. Losses and Efficiency
19. Load Types
20. Considerations Governing Machine Applications
21. Duty Cycles of Motors
22. Machine Ratings
23. Role of Electric Machines in Generation, Transmission and Distribution of Power
24. Classification of Electric Machines :
i. DC Machines
ii. AC Machines

Summary
Job Interview Questions
Review Questions
Problems

II. TRANSFORMERS :
1. Introduction
2. Principle of Operation
3. EMF Equation of Transformer
4. Types and Construction of Transformers
5. The Ideal Transformer
6. Effect of Iron-Losses
7. Effect of Leakage Flux
8. Phaser Diagram of Transformer
9. Equivalent Circuit of Transformer
10. Approximate Equivalent Circuit
11. Equivalent Resistance and Reactance
12. Transformer as a Coupled Circuit
13. Methods of Reducing Leakage Flux
14. Per Unit Values
15. Voltage Regulation
16. Losses in Transformer
17. Transformer Efficiency
18. Condition for Maximum Efficiency
19. All Day Efficiency (Energy Efficiency)
20. Polarity of Transformers
21. Test for Polarity
22. Open Circuit (or No Load) Test
23. Short Circuit Test
24. Back to Back Test (or Regenerative Test)
25. Separation of Core Losses
26. Principle of Auto-transformer
27. Saving in Copper in Auto-transformer
28. Phasor Diagram and Equivalent Circuit of Auto-transformer
29. Advantages Disadvantages and Applications of Auto-transformer
30. Introduction to Three-phase Transformers
31. Star-star Connection
32. Delta-Delta Connection
33. Star-Delta Connection
34. Delta-Star Connection
35. Zig Zag or Inter-Connected Star Connection
36. Phase Groups of Three Phase Transformers
37. Back-to-Back Test on 3-Phase Transformers
38. Per Unit System for Three-Phase Transformers
39. Open Delta (or V-V) Connection
40. Three-Phase to Two-Phase Conversion
41. Three Phase to Six-Phase Conversion
42. Three-Phase to Twelve-Phase Conversion
43. Conditions for Parallel Operation :
i. Polarity
ii. Voltage Ratio
iii. Impedance
iv. Phase Sequence and Phase Displacement

44. Load Sharing by Transformers in Parallel :
i. Equal Voltage Ratios
ii. Unequal Voltage Ratios

45. Parallel-Generator Theorem
46. Parallel Operation of Three-Phase Transformers
47. Applications
48. Equivalent Circuit
49. Determination of Parameters
50. Magnetising Current :
i. Wave Shape of Magnetising Current
ii. Inrush of Magnetising Current

51. Magnetising Current in 3-Phase Transformers :
i. Delta Connected Primaries
ii. Y-Connected Primaries

52. Transformer Taps :
i. Off-Load Tap Changing
ii. Tap Changing Under Load (TCUL)

53. Induction Regulators :
i. Single-Phase Induction Regulator
ii. Three-Phase Induction Regulator

54. Moving Coil Voltage Regulator
55. Instrument Transformers :
i. Potential Transformer
ii. Current Transformer

56. Transformer Cooling :
i. Oil Immersed Self-cooled Transformer
ii. Oil Immersed Forced Air Cooled Transformer
iii. Oil Immersed Water Cooled Transformer
iv. Oil Immersed Forced Oil Cooled Transformer

57. Transformer Oil
58. Conservator and Breather
59. Transformer Noise
60. Name Plate and Ratings
61. Wide-Band Transformer :
i. Classification
ii. Equivalent Circuit
iii. Frequency Response
iv. Special Design Features

62. Pulse Transformer
63. Audio-Frequency Transformer
64. Grounding Transformer
65. Amorphous Metal Core Transformer
66. Cast Resin Dry Type Transformers
Summary
Job Interview Questions
Review Questions
Problems

III. DC MACHINES :
1. Construction :
i. Field Poles
ii. Yoke
iii. Armature
iv. Commutator
v. Brushes
vi. Interpoles

2. Armature Winding :
i. Armature Coils
ii. Coil Span
iii. Single-Layer and Multi-Layer Windings
iv. Simplex and Multiplex Windings
v. Back Pitch and Front Pitch
vi. Commutator Pitch
vii. Progressive and Retrogressive Winding
viii. Types of Windings

3. Lap and Wave Windings :
i. Lap Winding
ii. Wave Winding
iii. Comparison of Lap and Wave Windings

4. Dummy Coil
5. Equaliser Rings
6. Magnetic Circuit and Flux Path
7. EMF Equation
8. Commutator Action : Conversion of AC into DC :
i. Commutation Process, Reactance Voltage

9. Armature Reaction in DC Generators :
i. Cross-Magnetising Effect
ii. Demagnetising Effect
iii. Cross Magnetising and Demagnetising Ampere Turns

10. Solution of Commutation Problems
11. Flux Density Wave Forms
12. Classification of DC Generators
13. Magnetisation Characteristics
14. Terminal Characteristics of Separately Excited Generator
15. Voltage Build up in Self-excited Generator
16. Terminal Characteristics of Shunt Generator
17. Series Generator :
i. Terminal Characteristics
ii. Applications

18. Compound Generator
19. Parallel Operation of DC Generators :
i. Shunt Generators in Parallel
ii. Compound Generators in Parallel

20. Principle of DC Motor
21. Electromagnetic Torque
22. Driving and Retarding Torques, Back EMF
23. Relation between Torque and Voltage
24. Commutation in DC Motors
25. Armature Reaction in DC Motors
26. Classification and Characteristics of DC Motors :
i. Characteristics of Shunt Motor
ii. Series Motor Characteristics
iii. Compound Motor Characteristics

27. Speed Control of Shunt Motors :
i. Field Control
ii. Armature Control

28. Speed Control of Series Motors :
i. Field Control
ii. Armature Control

29. Ward Leonard Control
30. DC Motor Starter :
i. Problem at Starting
ii. Functions of Starter
iii. Construction
iv. Calculation of Resistance Elements

31. Modern DC Motor Starters :
i. Starter Using Time Delay Relays
ii. Starter Using Back-emf Sensing Relays

32. Electric Braking :
i. Plugging
ii. Dynamic Braking
iii. Regenerative Braking

33. Permanent Magnet DC Motors
34. Losses and Power Flow in DC Machines :
i. Losses

35. Efficiency
36. Brake Test
37. Swinburne Test
38. Hopkinson Test :
i. Circuit
ii. Test Procedure
iii. Advantages
iv. Disadvantages

39. Metadyne
40. Amplidyne :
i. Characteristics
iii. Voltage Equation

41. Separately Excited Motor
42. Separately Excited Generator
43. Applications of DC Machines :
i. DC Generators
ii. DC Shunt Motor
iii. DC Series Motor
iv. Compound Motors

Summary
Job Interview Questions
Review Questions
Problems

IV. AC MACHINE FUNDAMENTALS :
1. Introduction
2. AC Windings :
i. Single and Double Layer Winding
ii. Phase Spread
iii. Multiturn Coil Windings
iv. Full-Pitch and Fractional Pitch Windings
v. Integral Slot Windings
vi. Fractional Slot Windings

3. EMF Equation :
i. Breadth Factor
ii. Pitch Factor

4. MMF of AC Windings :
i. MMF Space Wave of Concentrated Coil
ii. MMF of Distributed Single-Phase Winding

5. MMF of 3-Phase Windings, Rotating Magnetic Field
6. Reversal of Direction of Rotating Field
7. Torque in AC Machines
8. Losses :
i. Copper-Losses
ii. Core-Losses
iii. Mechanical Losses
iv. Stray Load Losses

9. Slot or Tooth Harmonics
Summary
Job Interview Questions
Review Questions
Problems

V. SYNCHRONOUS GENERATORS :
1. Introduction
2. Frequency
3. Construction :
i. Cylindrical Rotor Machines
ii. Salient Pole Machines

4. Cooling
5. Excitation System :
i. Brushless Excitation System
ii. Static Excitation System

6. Phaser Diagram of Cylindrical Rotor Alternator :
i. No-Load Condition
ii. Effect of Armature Reaction
iii. Effect of Armature Resistance and Leakage Reactance

7. Voltage Regulation
8. Synchronous Impedance Method
9. Experimental Determination of Synchronous Impedance
10. MMF Method
11. Saturated Synchronous Impedance Method
12. Zero Power Factor (Potier Reactance) Method
13. Effect of Power Factor on Characteristics
14. Short Circuit Ratio (SCR)
15. Power Angle Characteristics of Cylindrical Rotor Alternator :
i. Power Output
ii. Power Input

16. Salient Pole Machines : Two-Reaction Theory
17. Power Angle Characteristics of Salient Pole Generator
18. Measurement of xd and xq : Slip Test
19. Operating Limits on Alternators
20. MW-Frequency and MV Ar-Voltage Characteristics of Alternators
21. Parallel Operation of Alternators :
i. Need for Parallel Operation
ii. Conditions for Parallel Operation
iii. Synchronising

22. Synchronizing Power, Torque
23. Two Alternators in Parallel :
i. Effect of Change in Excitation
ii. Effect of Change in Mechanical Power Input (Steam Supply)
iii. Sharing of Load Currents

24. Operation of Alternator on Infinite Bus Bars
25. Symmetrical Short Circuit Transient
26. Equivalent Circuit for Alternator Transient Conditions
27. Synchronous Machine Reactance :
i. Direct Axis Synchronous Reactance xd
ii. Direct Axis Transient Reactance xd
iii. Direct Axis Sub-Transient Reactance xd”
iv. Potier Reactance
v. Quadrature Axis Synchronous Reactance
vi. Quadrature Axis Transient Reactance x’q and Sub-Transient Reactance xq”
vii. Negative Sequence Reactance x2
viii. Zero Sequence Reactance x0

28. Synchronous Machine Time Constants :
i. Direct Axis Transient Open Circuit Time Constant Tdo
ii. Direct Axis Transient Short Circuit Time Constant Td
iii. Armature Short Circuit Time Constant Ta
iv. Direct Axis Sub-Transient Time Constants T”do and T”d

29. Electro-Mechanical Transients, Hunting
30. Damper Winding
Summary
Job Interview Questions
Review Questions
Problems

VI. SYNCHRONOUS MOTORS :
1. Principle of Operation
2. Steady State Constant Speed Operation
3. Construction
4. Equivalent Circuit and Phasor Diagram : Cylindrical Rotor Theory
5. Phasor Diagram : Two-Reaction Theory
6. Power and Torque :
i. Cylindrical Rotor Theory
ii. Two-Reaction Theory

7. Change in Load
8. Speed-Torque Characteristics
9. Power Factor Control : Effect of Change of Excitation
10. Armature Current Locus
i. Constant Power
ii. Constant Excitation

11. Curves
12. Synchronous Condenser :
i. Capacity of Synchronous Condenser Running at No-Load
ii. Capacity of Synchronous Condenser Supplying Mechanical Load

13. Synchronous Reactor
14. Synchronous Frequency Changer
15. Starting of Synchronous Motor :
i. Auxiliary Motor Starting
ii. Induction Motor Starting

16. Hunting
17. Applications
18. Synchronous Induction Motor
19. Permanent Magnet Synchronous Motor
Summary
Job Interview Questions
Review Questions
Problems

VII. POLYPHASE INDUCTION MOTORS :
1. Construction :
i. Stator
ii. Rotor
iii. Frame

2. Principle of Operation
3. Slip
4. Production of Torque
5. EMF and Current
6. Induction Motor as Transformer
7. Phasor Diagram
8. Equivalent Circuit :
i. Stator Circuit Model
ii. Rotor Circuit Model
iii. Exact Equivalent Circuit
iv. Approximate Equivalent Circuit

9. Losses, Power Output
10. Torque
11. Torque-slip Curve
12. Starting of Induction Motor :
i. Wound Rotor Induction Motor
ii. Cage Rotor Induction Motor

13. No-Load Test
14. Blocked Rotor Test
15. Brake Test
16. Computation of Performance by Circle Diagram :
i. Theory
ii. Construction
iii. Computation of Performance
iv. Assumptions

17. Deep Bar Rotor
18. Double Cage Rotor
19. Cogging and Crawling
20. Speed Control :
i. Frequency Control
ii. Pole Changing
iii. Line Voltage Control
iv. Rotor Resistance Control
v. Voltage Injection in Rotor Circuit
vi. Cascade Connection

21. Operation with Unbalanced Supply Voltage :
i. Symmetrical Components in Three Phase Systems
ii. Positive Sequence Equivalent Circuit
iii. Negative Sequence Equivalent Circuit
iv. Single Phasing

22. Induction Generator :
i. Induction Generator in Parallel with Capacitor Bank

23. Induction Frequency Changer
24. Comparison of Induction Motor and Synchronous Motor
25. Applications of Induction Motors
Summary
Job Interview Questions
Review Question
Problem

VIII. SINGLE-PHASE INDUCTION MOTOR :
1. Introduction
2. Construction
3. Conditions at Starting
4. Double Revolving Field Theory
5. Equivalent Circuit (Circuit Model)
6. Analysis
7. Determination of Parameters :
i. Blocked Rotor Test
ii. No-Load Test

8. Symmetrical Components
9. Analysis of Single Phase Induction Motor Using Symmetrical Components
10. Cross-Field Theory :
i. Motor at Standstill
ii. Motor Running

11. Starting of Single-Phase Induction Motors :
i. Split Phase Motor
ii. Capacitor Start Motor
iii. Capacitor Start Capacitor Run Motor
iv. Permanent Split Capacitor Motor
v. Shaded Pole Motor

12. Speed Control
Summary!
Job Interview Questions
Review Questions
Problems

IX. AC COMMUTATOR MOTORS :
1. Schrage Motor :
i. Construction
ii. Operation
iii. Advantages
iv. Disadvantages
v. Application

2. Single-Phase Series Motor :
i. Construction
ii. Phaser Diagram
iii. Analysis
iv. Application

3. Universal Motor :
i. Applications
ii. Phasor Diagram
iii. Analysis

4. Repulsion Motor
5. Repulsion Start-Induction Motor
6. Repulsion-Induction Motor
Summary
Job Interview Questions
Review Questions
Problems

X. SPECIAL MACHINES :
1. Reluctance Motor
2. Hysteresis Motor
3. Two-Phase Servo Motor :
i. Construction
ii. Analysis Using Symmetrical Components
iii. Torque-Speed Curve
iv. Transfer Function
v. Drag Cup Rotor
vi. Special Features

4. Stepper Motor :
i. Single Stack Variable Reluctance Stepper Motor
ii. Multistack Variable Reluctance Stepper Motor
iii. Hybrid Stepper Motor

5. DC Tachometer
6. AC Tachometer
7. Synchros and Control Transformers
Summary
Job Interview Questions
Review Questions
Problems

XI. Solid STATE MOTOR CONTROL :
1. Introduction
2. DC Motor Control Using Converters :
i. Single-Phase Two Quadrant Bridge Converter (Fully Controlled)
ii. 3-Phase, Six-Pulse Two-Quadrant Bridge Converter (Fully Controlled)
iii. Single-Phase, One-Quadrant Bridge Converter
iv. 3-Phase, One Quadrant Bridge Converter

3. DC Motor Control Using Choppers :
i. Basic Chopper Circuit
ii. DC Chopper Commutation
iii. Step-Up Chopper

4. AC Motor Control Using Inverters :
i. Single-Phase Bridge Inverter
ii. 3-Phase Bridge Inverter

5. Speed Control of Induction Motor Using AC Regulator
6. Static Kramer Drive (Slip Power Recovery Scheme)
7. Static Scherbius Drive (Slip Power Recovery Scheme)
8. Integrated Motors
9. Speed Control of Single Phase Induction Motor Using Triac (Fan Regulator)
Summary
Job Interview Questions
Review Questions
Problems