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Electrical Machines
Introduction
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| Electrical Machines |
Electrical machines convert energy existing in one form to another, usable, form. These machines can broadly be divided into three categories: generators, motors and transformers. Generators convert mechanical energy into electrical energy, motors convert electrical energy to mechanical energy, and transformers change the voltage level in ac system and are considered to be the backbone of a power system.
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Electrical machines play an important role in domestic appliances, commercial devices and industrial applications. It is important for students of electrical and electronics engineering to learn the basic concepts of transformers, motors, generators and magnetic circuits. This book explains the design of transformers, decoding of generators and performance of electrical motors through descriptive illustrations, solved examples and mathematical derivations. Construction, working principles and applications of various electrical machines are discussed in detail. In addition, it offers an engrossing discussion on special purpose machines, which is useful from an industrial prospective in building customized machines. The text contains hundreds of worked examples and illustrations and more than a thousand self-assessment exercises. It is an ideal textbook for undergraduate students of electrical and electronics engineering.
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Table Of Contents
1. Electro Magnetic Circuits 1
Introduction 1
1.1 Magnetic Field and its Significance 2
1.2 Magnetic Circuit and its Analysis 3
1.3 Important Terms 3
1.4 Comparison between Magnetic and Electric Circuits 5
1.5 Ampere-turns Calculations 6
1.6 Series Magnetic Circuits 6
1.7 Parallel Magnetic Circuits 7
1.8 Leakage Flux 8
1.9 Magnetisation or B-H Curve 21
1.10 Magnetic Hysteresis 22
2. Single-Phase Transformers 79
Introduction 80
2.1 Transformer 80
2.2 Working Principle of a Transformer 82
2.3 Construction of Transformer 82
2.4 Simple Construction of Single-phase Small Rating (SAY 2 kVA) Transformers
2.5 An Ideal Transformer 94
2.6 Transformer on DC 95
2.7 emf Equation 96
Section Practice Problems 100
2.8 Transformer on No-load 103
2.9 Effect of Magnetisation on No-load (Exciting) Current 104
2.10 Inrush of Magnetising Current 106
3. Three-Phase Transformers 224
Introduction 224
3.1 Merits of Three-phase Transformer over Bank of Three Single-phase
Transformers 225
3.2 Construction of Three-phase Transformers 225
3.3 Determination of Relative Primary and Secondary Windings in Case of
Three-phase Transformer 227
3.4 Polarity of Transformer Windings 227
3.5 Phasor Representation of Alternating Quantities in Three-phase Transformer
Connections 228
3.6 Three-phase Transformer Connections 229
3.7 Selection of Transformer Connections
4. DC Generator 301
Introduction 301
4.1 DC Generator 302
4.2 Main Constructional Features 303
4.3 Simple Loop Generator and Function of Commutator 307
4.4 Connections of Armature Coils with Commutator Segments and Location
of Brushes 309
4.5 Armature Winding 311
4.6 Types of Armature Winding 314
4.7 Drum Winding 315
4.8 Lap Winding 316
4.9 Numbering of Coils and Commutator Segments in Developed Winding Diagram 318
4.10 Characteristics of a Simplex Lap Winding
5. DC Motors 395
Introduction 395
5.1 DC Motor 396
5.2 Working Principle of DC Motors 396
5.3 Back emf 397
5.4 Electro-magnetic Torque Developed in DC Motor 398
5.5 Shaft Torque 399
5.6 Comparison of Generator and Motor Action 399
5.7 Types of DC Motors 401
5.8 Characteristics of DC Motors 405
5.9 Characteristics of Shunt Motors 405
5.10 Characteristics of Series Motors
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Electrical Machines
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