Basic Electrical Engineering S.N. Singh
Basic Electrical Engineering S.N. Singh Professor Department of Electrical Engineering Indian Institute of Technology Kanpur PHI Learning Private Limited New Delhi-110001 2011
BASIC ELECTRICAL ENGINEERING S.N. Singh 2011 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN-978-81-203-4188-3 The export rights of this book are vested solely with the publisher. Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus, New Delhi-110001 and Printed by Baba Barkha Nath Printers, Bahadurgarh, Haryana-124507.
To My Mother
Contents Preface... xv 1. INTRODUCTION...1 10 1.1 General 1 1.2 SI Units and Power of 10 3 1.3 Structure of Modern Electric Supply System 5 1.4 Energy Management System 7 1.5 Network Analysis Approaches 9 1.6 Outline of the Book 9 2. CIRCUIT ELEMENTS...11 27 2.1 Introduction 11 2.2 Energy Sources (Active Elements) 12 2.2.1 Independent Sources 12 2.2.2 Dependent or Controlled Sources 13 2.2.3 Practical (Real) Energy Sources 14 2.3 Passive Elements 15 2.3.1 Ideal Resistor 15 2.3.2 Ideal Capacitor 18 2.3.3 Ideal Inductor 20 2.4 Important Properties of Ideal Passive Elements 23 2.5 Network/Circuit Properties 23 2.5.1 Linear and Non-linear Networks 24 v
vi Contents 2.5.2 Bilateral and Unilateral Networks 24 2.5.3 Lumped and Distributed Parameters Networks 24 2.6 Source Transformation 24 Problems 26 3. ANALYSIS OF DC CIRCUITS...28 69 3.1 Introduction 28 3.2 Circuit Laws 29 3.2.1 Kirchhoff s Current Law (KCL) 29 3.2.2 Kirchhoff s Voltage Law (KVL) 30 3.3 Applications of KCL and KVL 31 3.3.1 Voltage and Current Dividers 31 3.3.2 Series and Parallel Combinations 33 3.4 Star-Delta or Delta-Star Transformation 36 3.4.1 Delta-Star Transformation 36 3.4.2 Star-Delta Transformation 38 3.5 Mesh Current (Loop Current) Method 42 3.6 Node Voltage (or Node Pair Voltage) Method 47 3.7 Linearity and Superposition Theorem 51 3.7.1 Superposition Theorem 51 3.8 Thevenin s Theorem 53 3.9 Norton s Theorem 58 3.10 Maximum Power Transfer Theorem 61 3.11 Reciprocity Theorem 63 3.12 Millman s Theorem 64 3.13 Two-Port (4-Terminal) Network 64 Problems 65 4. STEADY-STATE ANALYSIS OF AC CIRCUITS...70 112 4.1 Introduction 70 4.2 Sinusoidal Signal 70 4.2.1 Effective (or RMS) Value 72 4.2.2 Average Value 73 4.3 Phasor Representation 74 4.4 Applications of Kirchhoff s Laws 80 4.4.1 Series and Parallel Combinations of Inductors and Capacitors 81 4.5 Definition of Impedance and Admittance 84 4.6 Star-Delta or Delta-Star Transformation 87 4.6.1 Delta-Star Transformation 88 4.6.2 Star-Delta Transformation 89 4.7 Network Theorems 90 4.7.1 Mesh Current (or Loop Current) Method 90 4.7.2 Node Voltage Method 91
Contents vii 4.7.3 Thevenin s Theorem 92 4.7.4 Norton s Theorem 96 4.7.5 Maximum Power Transfer Theorem 98 4.8 Power Calculation in AC Circuit 100 4.8.1 Reactive Power 102 4.8.2 Using Phasor Concept 103 4.8.3 Apparent Power 103 4.9 Superposition and Conservation of Power 107 Problems 108 5. TRANSIENT ANALYSIS OF AC/DC CIRCUITS...113 141 5.1 Introduction 113 5.2 Transient Response of First-Order Circuits with DC Source 113 5.2.1 Current through an Ideal Inductor 113 5.2.2 Transient in RL Circuit 114 5.2.3 Transient in Series RC Circuit 117 5.2.4 Natural and Forced Response of First-Order Circuit 120 5.2.5 Discharge Transients 122 5.2.6 Decay Transients 123 5.3 Transient Response of Second-Order Circuits 126 5.4 Transients Response in Series RLC circuit 127 5.5 Laplace Transform 133 5.6 Transient Response in AC Circuits 134 5.7 Initial and Steady-State Values 136 Problems 138 6. ELECTRICAL MEASURING INSTRUMENTS AND MEASUREMENTS...142 163 6.1 Introduction 142 6.2 Types of Electrical Measuring Instruments 143 6.2.1 AC and DC Instruments 143 6.2.2 Absolute and Secondary Instruments 143 6.2.3 Deflection and Null Type Instruments 143 6.2.4 Analog and Digital Instruments 143 6.2.5 Indicating, Recording and Integrating Instruments 143 6.2.6 Direct Measuring and Comparison Instruments 144 6.3 Main Components of Indicating Instruments 144 6.4 Principle of Operation of Indicating Instruments 145 6.4.1 Magnetic Effect 145 6.4.2 Thermal Effect 145 6.4.3 Electrostatic Effect 145 6.4.4 Electromagnetic Effect 146 6.4.5 Hall Effect 146
viii Contents 6.5 Controlling Mechanism 146 6.5.1 Gravity Control 146 6.5.2 Spring Control 147 6.6 Damping Mechanism 147 6.6.1 Friction Damping 148 6.6.2 Electromagnetic Damping 148 6.7 Permanent Magnet Moving Coil Instruments 149 6.8 Moving-Iron Instruments 151 6.8.1 Attraction Type 151 6.8.2 Repulsion Type 151 6.9 Electrodynamic or Dynamometer Instruments 153 6.10 Ammeter Design 153 6.11 Voltmeter Design 155 6.12 Wattmeter or Power Meter 157 6.12.1 Measurement of Three-Phase Power with Single-Phase Wattmeters 159 6.12.2 Three-Phase Wattmeters 159 6.13 Energy Meter 159 6.14 Performance of Indicating Instruments 160 6.14.1 Errors 160 6.14.2 Loading Effect 161 6.14.3 Sensitivity and Efficiency 161 6.14.4 Precautions 162 Problems 162 7. THREE-PHASE AC CIRCUITS...164 190 7.1 Introduction 164 7.2 Generation of Three-Phase Voltage 165 7.3 Star and Delta Connections 166 7.3.1 Star Connection 166 7.3.2 Delta Connection 168 7.4 Power in Three-Phase Circuit 169 7.5 Three-Phase Load Circuit 171 7.5.1 Star Connected Three-Phase Load 171 7.5.2 Delta-Connected Three-Phase Load 173 7.6 Measurement of Real Power 175 7.6.1 One-Wattmeter Method 175 7.6.2 Three-Wattmeter Method 175 7.6.3 Two-Wattmeter Method 177 7.6.4 Power Factor Determination for Three-Phase Balanced Load 178 7.7 Single-Phase Analysis of 3j Circuit 178 7.7.1 Star-Connected Balanced Load 178 7.7.2 Delta-Connected Balanced Load 179 7.8 Unbalance Loads 180
Contents ix 7.8.1 Delta-Connected Unbalanced Load 181 7.8.2 Star-Connected Unbalanced Load 181 Problems 187 8. RESONANCE...191 202 8.1 Introduction 191 8.2 Series RLC Resonance 191 8.2.1 Quality Factor 193 8.2.2 Bandwidth and Selectivity 194 8.3 Parallel RLC Resonance 196 8.3.1 Quality Factor 198 8.3.2 Selectivity and Bandwidth 199 8.4 Practical Parallel Resonant Circuits 200 8.5 Applications of Resonant Circuits 201 Problems 202 9. MAGNETIC CIRCUIT...203 226 9.1 Introduction 203 9.2 Ampere s Law 204 9.3 Magnetic Resistance or Reluctance 206 9.4 Magnetic Circuit Analysis 206 9.5 Inductance 211 9.6 Mutual Inductance 212 9.6.1 Sign Convention of Mutually Induced Voltages 215 9.6.2 Induced Voltage Phasor 215 9.6.3 Two-Port Representation 216 9.6.4 Computation of Inductances 219 Problems 222 10. TRANSFORMERS...227 278 10.1 Introduction 227 10.2 Constructional Features 228 10.3 Principle of Transformer Action 230 10.3.1 Ideal Transformer Case 230 10.3.2 Induced emf Flux Relationship 232 10.3.3 Impedance Transformation 233 10.4 Transformer Rating 236 10.5 Losses in Transformer 236 10.5.1 Hysteresis Loss 237 10.5.2 Eddy Current Loss 238 10.5.3 Core Loss 239 10.5.4 Copper Loss 240 10.6 Practical Transformer 240
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