Electrical Machines (D.C. Machines, A.C. Machines and Polyphase Circuits) in [S.I. Units] for B.Tech./B.E. Courses, U.P.S.C., A.M.I.E. (India) Sec. B, and Competitive Examinations

This book on "Electrical Machines" has been written for students preparing for B.E./B.Tech, A.M.I.E. section B, U.P.S.C., and other Competitive Examinations. It consists of two parts: Part I ? deals with D.C. machines, and Part II ? deals with A.C. machines and Polyphase circuits. Besides this, "Additional Topics" and a "Questions Bank" on "Objective Type Questions" have been incorporated at the end of the book to make it a comprehensive Unit in all respects.

Solar Energy Society of India"R-K">R.K.href="../books/Jawahar-Lal" Title="Jawahar-Lal">Jawahar Laljput, born on 15th September, 1944 (coincident with Engineer?s Day) is a multi disciplinary engineer. He obtained his Master?s degree in Mechanical Engineering (with Hons.-Gold Medal) from Thapar Institute of Engineering and Technology, Patiala. He is also a Graduate Engineer in Electrical Engineering. Apart from this he holds memberships of various Professional bodies like Member Institution of Engineers (MIE); Member Indian Society of Technical Education (MISTE) and Member Solar Energy Society of India (MSESI). He is also Chartered Engineer (India). He has served for several years as Principal of "Punjab College of Information Technology", Patiala and "Thapar Polytechnic", Patiala.

He has more than 40 years of experience in Teaching different subjects of Mechanical and Electrical Engineering disciplines. He has published/presented a large number of technical papers. He is The Author of several Books on the important subjects of Mechanical as well as Electrical Engineering disciplines.

He has earned, by dint of hard work and devotion to duty, the following awards/honours :
Best Teacher (Academic) Award; Jawahar Lal Nehru Memorial Gold Medal for an outstanding Research Paper (Institution of Engineers); Distinguished Author Award; Man of Achievement Award.

Basic Concepts-Electromagnetism, Magnetic Circuits and Electromagnetic Induction

0. ELECTROMECHANICAL ENERGY CONVERSION :
1. Introduction
2. Principle of Energy Conversion
3. Faraday's Law of Electromagnetic Induction
4. Singly and Multiply-Excited Magnetic Field Systems
5. Torque Production in Rotating Machines
6. General Analysis of Electromechanical System
Worked Examples
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

Part A : B.C. MACHINES :
I. Direct Current Generators :
1. Basic Type of Direct Current (D.C.) Machine
2. Principle of a Generator
3. Elementary Generator
4. Construction of D.C. Machines :
i. Frame
ii. Field Poles
iii. Commutating Poles
iv. Armature
v. Commutator
vi. Brush Gear
vii. Armature Shaft Bearings
viii. Armature Windings :
a. Terminology
b. Types of Armature Windings
c. Lap and Wave Windings
d. Advantages/Uses of Lap and Wave Windings
e. Lap Winding
f. Wave Winding
g. Equiliser Rings
h. Dummy Coils

5. Ratings of Electrical Machines
6. Magnetic Circuit
7. E.M.F. Equation of a Generator
8. Types of D.C. Generators :
i. Classification :
a. Separately Excited Generators
b. Self-excited Generators

9. Power Division in a D.C. Generator
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

II. Armature Reaction and Commutation :
1. Armature Reaction :
i. Main Field of the Machine
ii. Armature Field
iii. Effect of Brush Shifting
iv. Distortion of Air Gap Flux in a Multipolar Machine

2. Remedies for Field Distortion (or Neutralising Armature Reaction)
3. Armature, Ampere-turns (AT)
4. Compensating Windings :
i. Number of Compensating Windings

5. Commutation :
i. Commutation Process :
a. Reactance Voltage
b. Determination of Co-efficient of Self-induction (L)

6. Methods of Improving Commutation :
i. Resistance Commutation
ii. E.M.F. Commutation

7. Equilizer Connections
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

III. Direct Current Generator Characteristics :
1. Characteristics of D.C. Generators
2. Separately Excited Generator :
i. No-load Saturation Characteristic (or O.C.C.)
ii. Internal and External Characteristics (or Load Characteristics)

3. Building Up the Voltage of Self-excited Shunt Generator
4. Shunt Generator Characteristics :
i. External Characteristics
ii. Effect of Varying Excitation
iii. Voltage Regulation
iv. Internal or Total Characteristic
v. External Characteristic and No-load Saturation Curve
vi. Voltage Control of Shunt Generators

5. Series Generator
6. Compound Wound Generator :
i. Characteristics of Cumulative Compound Generator
ii. Characteristic of Differential Compound Generator

7. Applications of D.C. Generators :
i. Separately Excited Generators
ii. Shunt Generators
iii. Series Generators
iv. Compound Generators

Worked Examples
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

IV. Parallel Operation of D.C. Generators :
1. Reasons for Paralleling D.C. Generators
2. Requirements of Paralleling D.C. Generators
3. Parallel Operation of Shunt Generators
4. Parallel Operation of Compound Generators
Worked Examples
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

V. Direct Current Motor :
1. General Aspects
2. Principle of Operation of D.C. Motor
3. Back or Counter E.M.F
4. Comparison between Motor and Generator Action
5. Torque Developed in a Motor
6. Mechanical Power Developed by Motor Armature
7. Types of D.C. Motors
8. Speed of a D.C. Motor
9. Speed Regulation
10. Armature Reaction and Commutation
11. Motor Characteristics :
i. Torque-current Characteristics
ii. Speed-current Characteristics
iii. Speed-torque (or Mechanical) Characteristics

12. Comparison of D.C. Motor Characteristics
13. Summary of Characteristics and Applications of D.C. Motors
14. D.C. Motor Reversing :
i. Reversing Circuit Connections of D.C. Motors

15. Starting of D.C. Motors :
i. Need for Starters
ii. Starters for Shunt and Compound Motors
iii. Determining the Steps of the Resistance for Shunt Motor Starter
iv. Starter for Series Motor
v. Automatic Starters

16. Self-governing Properties of D.C. Motors
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

VI. Speed Control of D.C. Motors :
1. Factors Controlling the Speed
2. Field Control Method
3. Rheostatic Control
4. Voltage Control
5. Thyristor Control of D.C. Motors :
i. General Aspects
ii. P-N Junction Diode :
a. Construction and Working
b. V/I Characteristic of a P-N Junction Diode
c. P-N Junction Diode as a Half Wave Rectifier
d. Full Wave Rectifier Circuit of two Junction Diodes

iii. Thyristor :
a. Introduction
b. Advantages of a Thyrister Over Thyratron (Gas Filled Triode)
c. Construction, Operation and Characteristics of a Thyristor
d. Thyristor Family
e. Comparison between Transistors and Thyristors
f. Applications of Thyristor

iv. Advantages of Thyristor Control over Ward-Leonard System of Speed Control
v. Speed Control of D.C. Motor with Thyristor
vi. Uncontrolled Rectifiers
vii. Controlled Rectifiers
viii. Thyristor Choppers
ix. Effects of Thyristor Power Supply on the D.C. Motor Performance
x. Special Features of Thyristor Drive Motors
xi. Types of Thyristor Drives

6. Electric Braking :
i. Electro-mechanical Brakes
ii. Electric Brakes :
a. Electric Braking of Shunt Motors
b. Electric Braking of Series Motor

Highlights
Objective Type Questions
Unsolved Examples

VII. Losses, Efficiency and Testing of D.C. Machines :
1. Losses and Efficiency :
i. Losses :
a. Copper (or Electrical) Losses
b. Iron Losses
c. Mechanical (or Friction) Losses

ii. Efficiency of D.C. Machines :
a. Condition for Maximum Efficiency

2. Testing of D.C. Machines :
i. Brake Test
ii. Swinburne's Test (or No-load Test or Losses Method)
iii. Hopkinson's Test
iv. Retardation (or Running Down) Test
v. Field's Test
vi. Temperature Rise Test

Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

VIII. Special Types of D.C. Machines :
1. Boosters :
i. Series Booster
ii. Shunt Booster
iii. Non-reversible (or Constant Current) Booster
iv. Reversible Booster

2. Armature Excited or Cross Field Rotating Machines :
i. The Rosenberg Generator
ii. The Amplidyne and Metadyn
iii. Rototrol and Regulex :
a. Rototrol
b. Regulex

3. Third-brush Generator
4. Three-wire Generator
5. Dynamotor
6. Electric Welding Generator
Highlights
Objective Type Questions
Theoretical Questions

IX. Miscellany :
1. Rating and Heating of D.C. Machines :
i. Rating
ii. Heating

2. Selection of D.C. Generators and Motors
3. Types of D.C. Machine Enclosures
4. Heating and Cooling Curves of D.C. Machines
5. Applications of D.C. Machines
Worked Examples
Highlights
Objective Type Questions
Unsolved Examples

Part B : A.C. MACHINES :
I. Polyphase Circuits :
1. Introduction
2. Advantages of Polyphase Systems
3. Generation of Three-phase Voltages
4. Phase Sequence and Numbering of Phases
5. Inter-connection of Three-phases
6. Star or Wye (Y) Connection
7. Delta (Δ) or Mesh Connection
8. Comparison between Star and Delta Systems
9. Measurement of Power in 3-phase Circuit :
i. Three Wattmeters Method
ii. Two Wattmeters Method
iii. One Wattmeter Method

10. Measurement of Reactive Volt-amperes
11. Unbalanced Star-connected Load :
i. Three-phase Four-wire System
ii. Three-phase Three-wire System

12. Unbalanced Delta-connected Load
13. Power Factor Improvement
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

II. Transformers :
1. General Aspects
2. Basic Definitions
3. Working Principle of a Transformer
4. Transformer Ratings
5. Kinds of Transformers
6. Transformer Construction :
i. Core-type Transformer
ii. Shell-type Transformer
iii. Spiral-core Transformer

7. Transformer Windings, Terminals, Tappings and Bushings :
i. Transformer Windings
ii. Terminals and Leads
iii. Tappings
iv. Bushings

8. Transformer Cooling :
i. Cooling Methods
ii. Transformer Oil
iii. Conservator and Breather

9. Single-phase Transformer :
i. Elementary Theory of an Ideal Transformer
ii. E.M.F. Equation of a Transformer
iii. Voltage Transformation Ratio (K)
iv. Transformer with Losses But No Magnetic Leakage :
a. Transformer on No-load
b. Transformer on Load

v. Resistance and Magnetic Leakage
vi. Transformer with Resistance and Leakage Reactance
vii. Equivalent Resistance and Reactance
viii. Total Voltage Drop in a Transformer
ix. Equivalent Circuit
x. Transformer Tests :
a. Open-circuit or No-load Test (O.C. Test)
b. Short-circuit or Impedance Test (S.C. Test)

xi. Regulation of a Transformer
xii. Percentage Resistance and Reactance
xiii. Kapp Regulation Diagram
xiv. Sumpner's or Back-to-back Test
xv. Transformer Losses
xvi. Transformer Efficiency
xvii. All-day Efficiency
xviii. Transformer Noise
xix. Auto-transformer
xx. Polarity of Transformers
xxi. Parallel Operation of Single-phase Transformers

10. Three-phase Transformer :
i. Three-phase Transformer Connections :
a. The Y-Y Connection
b. The Δ-Δ Connection
c. The Y-Δ Connection
d. The Δ-Y Connection
e. The V-V (Open-Δ) Connections
f. Scott or T-T Connection

ii. Three-phase Transformer Construction
iii. Parallel Operation of 3-phase Transformers

11. Instrument Transformers :
i. Potential Transformers (P.T.)
ii. Current Transformers (C.T.)

12. Constant-current Transformers
13. Induction Regulators
14. Grounding Transformers
15. Furnace Transformers
16. High Frequency Transformers
17. Transformer Specifications
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Examples

III. Polyphase Induction Motors :
1. General Aspects
2. Classification of A.C. Motors
3. Constructional Details :
i. The Stator
ii. The Rotor
iii. Slip-rings
iv. Shaft and Bearings

4. Production of Rotating Magnetic Field
5. Theory of Operation of an Induction Motor
6. Slip
7. Frequency of Rotor Current
8. Rotor E.M.F. and Rotor Current
9. Torque :
i. Starting Torque
ii. Condition for Maximum Torque
iii. Starting Torque of a Squirrel-cage Motor
iv. Starting Torque of a Slip-ring Motor
v. Power

10. Effect of Change in Supply Voltage on Starting Torque
11. Effect of Change in Supply Voltage on Torque and Slip
12. Full-load Torque and Maximum Torque
13. Starting Torque and Maximum Torque
14. Torque-slip and Torque-speed Curves
15. Operating Characteristics of a 3-phase Squirrel-cage Induction Motor
16. Operating Characteristics of a Wound-rotor (Slip-ring) Induction Motor
17. Power Stages in an Induction Motor :
i. Rotor Output
ii. Synchronous Watt
iii. Factor Determining Torque

18. Measurement of Slip :
i. Electromechanical Counter
ii. Mechanical-differential Counter
iii. Stroboscopic Method

19. Induction Motor as Transformer :
i. Rotor Output
ii. Equivalent Circuit of the Rotor

20. Equivalent Circuit of an Induction Motor
21. Induction Motor Losses and Efficiency
22. Circle Diagram
23. Starting of Induction Motors :
i. Squirrel-cage Motors :
a. Stator Rheostat Starter
b. Auto-transformer
c. Star-delta Starter

ii. Slip-ring Induction Motors-starting of

24. Resistance Steps for 3-phase Slip-ring Induction Motor Starter
25. Crawling
26. Cogging
27. Double Squirrel-cage Motor
28. Speed Control of Induction Motors
29. Electrical Braking of Polyphase Induction Motors
30. Factors Governing Performance of Induction Motors
31. Effects of Opera ting Conditions
32. Ratings of 3-phase Induction Motors
33. Squirrel-cage Motors-Advantages, Disadvantages and Applications
34. Wound Rotor (or Slip-ring) Induction Motors-Advantages, Disadvantages and Applications
35. Comparison of a Squirrel-cage and a Slip-ring (or Phase Wound) Induction Motor
36. Comparison between Induction and Synchronous Motors
37. Schrage Motor
38. Induction Generator
39. Linear Induction Motor :
i. Introduction
ii. Construction and Working

Highlights
Objective Type Questions
Theoretical Questions
Unsolved Problems

IV. Single-Phase Motors :
1. General
2. Types of Single-phase Motor
3. Single-phase Induction Motors :
i. Applications and Disadvantages
ii. Construction and Working
iii. Equivalent Circuit and Performance Characteristics

4. Split-phase Motors :
i. Split-phase Resistance-start Induction Motor
ii. Split-phase Capacitor-start Induction Motor
iii. Permanent-split Capacitor Induction Motor
iv. Two-value Capacitor Induction Motor
v. Shaded-pole Induction Motor
vi. Reluctance-start Induction Motor

5. Single-phase Commutator Motors :
i. Repulsion Motor
ii. Repulsion-start Induction Motor
iii. Repulsion-induction Motor
iv. A.C. Series Motor
v. Universal Motor

6. Single Phase Synchronous Motors :
i. Reluctance Motor
ii. Hysteresis Motor
iii. Sub-synchronous Motor

7. Stepper Motors :
i. Introduction
ii. Advantage and Applications
iii. Construction and Working

Highlights
Objective Type Questions
Theoretical Questions
Unsolved Problems

V. Synchronous Generators or Alternators :
1. Introduction
2. Classification and Operating Principle
3. Constructional Details :
i. Stator
ii. Rotor
iii. Bearings

4. Frequency
5. Armature Windings :
i. Winding Types
ii. Number of Coils
iii. Conductor Design
iv. Skewing
v. Dead Coils
vi. Coil Pitch
vii. Single-phase Windings
viii. Two-phase Windings
ix. Double Windings
x. Multispeed Windings

6. Chording of Windings
7. Pitch Factor
8. Distribution or Breadth or Winding Factor
9. E.M.F. Equation
10. Shape of the E.M.F. Wave
11. Rating of Alternators
12. Alternator on Load
13. Voltage Regulation :
i. Determination of Voltage Regulation :
a. Synchronous Impedance Method
b. The Ampere-turn or M.M.F. Method
c. Zero Power Factor or Potier Method

14. Two Reactance Concept for Salient Pole Synchronous Machines :
i. General Aspects
ii. Construction of Two-reaction Diagram for Test Data
iii. Power Developed by a Synchronous Generator

15. Losses and Efficiency
16. Parallel Operation of Alternators :
i. Necessity
ii. Requirements for Paralleling
iii. Alternator Synchronising Procedure
iv. Synchronising Current, Power and Torque
v. Effect of Reactance
vi. Effect of Increasing the Excitation of One of the Alternators
vii. Effect of Increasing the Driving Torque of One of the Alternators
viii. Effect of Changes in Speed of One of the Alternators
ix. Effect of Unequal Voltages
x. Distribution of Load
xi. Load Sharing between Two Alternators

17. Hunting of Alternators
18. Time Period of Oscillation
19. Maximum Power Output
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Problems

VI. Synchronous Motors :
1. Introduction
2. Characteristic Features, Advantages and Disadvantages
3. Applications
4. Construction
5. Principle of Operation
6. Synchronous Motors-Starting
7. Effect of Load on a Synchronous Motor
8. Torque Developed by the Motor
9. Two Reactance Concept for Salient Pole Synchronous Motors
10. Effect of Excitation on Armature Current and Power Factor (V-curves)
11. Synchronous Condensers
12. Synchronous Motor Ratings
13. Hunting of Synchronous Motors
14. Comparison between Synchronous and Induction Motors
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Problems

VII. Converters and Rectifiers :
1. General
2. Motor-generator Set
3. Motor Converter
4. Synchronous or Rotary Converter :
i. Construction and Working
ii. Voltage and Current Relations-General Case
iii. Armature Current and Heating
iv. Necessity of Transformers for Converters
v. Transformer Connections for Six-phase Rotary Converter
vi. Starting of Rotary Converters :
a. Starting of Rotary Converter from A.C. Side
b. Starting of Rotary Converter from D.C. Side

vii. Hunting
viii. Power Factor
ix. Armature Reaction
x. Inverted Running
xi. Speed-limiting Device
xii. Parallel Operation
xiii. Voltage Control :
a. By Using Tap-changing Transformer
b. Reactance Control Method
c. Induction Regulator Method
d. Synchronous Booster Control Method

5. Rectifiers :
i. Introduction
ii. Types of Rectifiers
iii. Mercury Arc Rectifiers :
a. Mercury Arc Rectifier (Simplest Form)
b. Merits of a Mercury Arc Rectifier
c. Single-phase Mercury Arc Rectifier
d. Poly-phase Mercury Arc Rectifiers
e. Voltage Relation
f. Current Relations
g. Utility Factor
h. Effect of Transformer Reactance
i. Regulation
j. Inter-phase Transformer
k. Grid Control of Mercury Arc Rectifiers
l. Output Voltage with Grid Control

iv. Metal Rectifiers :
a. Copper Oxide Rectifiers
b. Selenium Rectifiers
c. Methods of Representation of Rectifiers
d. Half-wave Rectifier
e. Full-wave rectifier

v. Mechanical Rectifiers :
a. Commutating Type Rectifier
b. Vibrating Rectifier

vi. Electrolytic Rectifiers
Highlights
Objective Type Questions
Theoretical Questions
Unsolved Problems

ADDITIONAL Topics :
I. Special Types of D.C. Motors :
1. Permanent Magnet D.C. Motors
2. D.C. Servomotors
3. Moving Coil Motors
4. Torque Motors
5. Brushless D.C. (or Trapezoidal PMAC) Motors

II. Electronic Control of D.C. Motors :
1. Introduction
2. Advantages of Electronic Control Systems
3. D.C. Motor Speed Control

III. Eddy Current Drives
IV. Electronic Control of A.C. (Induction) Motors :
1. Introduction
2. Speed Control of a Single-phase Induction Motor
3. Speed Control of Three-phase Induction Motors
4. Braking of Single-phase Motors
5. Dynamic Braking of a 3-phase Induction Motor

V. Synchronous Motors Types, Starting, Speed Control and Braking :
1. Types of Synchronous Motors
2. Starting of Synchronous Motor
3. Braking of Synchronous Motors
4. Speed Control of Synchronous Motors

VI. Digital Control of Electric Motors
VII. Transient Conditions in Electrical Drives :
1. Introduction
2. Acceleration Time
3. Energy Losses During Starting
4. Energy Losses During Braking
5. Braking of Motors During Lowering of Loads
6. Dynamics of Braking

VIII. Size and Rating of Motors :
1. Standard Rating of Motors
2. Classes of Duty
3. Ambient Temperature Ratings
4. Overload Capacity of Motors
5. Determination of Power Rating of Electric Motors for Different Applications
6. Temperature Use with Short Time Ratings
7. Load Equalisation

IX. Enclosures for Rotating Electrical Machines
X. Selection of Electric Motor for Any Application
XI. Motors for Particular Applications
XII. Energy Conservation in Electrical Drives

Questions Bank