Table Of ContentElectrical Circuit Theory and Technology
John Bird
In Memory of Elizabeth
Electrical Circuit Theory and Technology
Revised second edition
John Bird, BSc(Hons), CEng, MIEE, FIEIE, CMath,
FIMA, FCollP
Newnes
OXFORD AMSTERDAM BOSTON LONDON NEWYORK PARIS
SANDIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO
Newnes
AnimprintofElsevierScience
LinacreHouse,JordanHill,OxfordOX28DP
200WheelerRd,Burlington,MA01803
Firstpublished1997
Secondedition2001
Reprinted2002
Revisedsecondedition2003
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Contents
Preface xvii
Part 1 Basic electrical engineering principles
1 Units associated with 1.1 SI units 3
basic electrical 1.2 Charge 4
quantities 1.3 Force 4
1.4 Work 5
1.5 Power 5
1.6 Electrical potential and e.m.f. 6
1.7 Resistance and conductance 6
1.8 Electrical power and energy 7
1.9 Summary of terms, units and their symbols 8
1.10 Further problems on units associated
with basic electrical quantities 9
2 An introduction to 2.1 Standard symbols for electrical components 10
electric circuits 2.2 Electric current and quantity of electricity 11
2.3 Potential difference and resistance 13
2.4 Basic electrical measuring instruments 13
2.5 Linear and non-linear devices 13
2.6 Ohm’s law 14
2.7 Multiples and sub-multiples 14
2.8 Conductors and insulators 16
2.9 Electrical power and energy 16
2.10 Main effects of electric current 20
2.11 Fuses 20
2.12 Further problems on the introduction to
electric circuits 21
3 Resistance variation 3.1 Resistance and resistivity 23
3.2 Temperature coefficient of resistance 26
3.3 Further problems on resistance variation 29
4 Chemical effects of 4.1 Introduction 31
electricity 4.2 Electrolysis 31
4.3 Electroplating 32
4.4 The simple cell 32
4.5 Corrosion 33
4.6 E.m.f. and internal resistance of a cell 34
4.7 Primary cells 36
vi Contents
4.8 Secondary cells 37
4.9 Cell capacity 39
4.10 Further problems on the chemical effects of electricity 39
Assignment 1 41
5 Series and parallel 5.1 Series circuits 42
networks 5.2 Potential divider 44
5.3 Parallel networks 45
5.4 Current division 48
5.5 Wiring lamps in series and in parallel 52
5.6 Further problems on series and parallel networks 53
6 Capacitors and 6.1 Electrostatic field 55
capacitance 6.2 Electric field strength 57
6.3 Capacitance 57
6.4 Capacitors 57
6.5 Electric flux density 59
6.6 Permittivity 59
6.7 The parallel plate capacitor 61
6.8 Capacitors connected in parallel and series 63
6.9 Dielectric strength 67
6.10 Energy stored 68
6.11 Practical types of capacitor 69
6.12 Discharging capacitors 70
6.13 Further problems on capacitors and capacitance 70
7 Magnetic circuits 7.1 Magnetic fields 74
7.2 Magnetic flux and flux density 75
7.3 Magnetomotive force and magnetic field strength 76
7.4 Permeability and B–H curves 77
7.5 Reluctance 80
7.6 Composite series magnetic circuits 81
7.7 Comparison between electrical and magnetic quantities 84
7.8 Hysteresis and hysteresis loss 84
7.9 Further problems on magnetic circuits 85
Assignment 2 87
8 Electromagnetism 8.1 Magnetic field due to an electric current 89
8.2 Electromagnets 91
8.3 Force on a current-carrying conductor 92
8.4 Principle of operation of a simple d.c. motor 96
8.5 Principle of operation of a moving coil instrument 97
8.6 Force on a charge 98
8.7 Further problems on electromagnetism 98
Contents vii
9 Electromagnetic 9.1 Introduction to electromagnetic induction 100
induction 9.2 Laws of electromagnetic induction 101
9.3 Inductance 104
9.4 Inductors 106
9.5 Energy stored 107
9.6 Inductance of a coil 107
9.7 Mutual inductance 108
9.8 Further problems on electromagnetic induction 109
10 Electrical measuring 10.1 Introduction 113
instruments and 10.2 Analogue instruments 113
measurements 10.3 Moving-iron instrument 113
10.4 The moving-coil rectifier instrument 114
10.5 Comparison of moving-coil, moving-iron and
moving-coil rectifier instruments 114
10.6 Shunts and multipliers 115
10.7 Electronic instruments 117
10.8 The ohmmeter 117
10.9 Multimeters 118
10.10 Wattmeters 118
10.11 Instrument ‘loading’ effect 118
10.12 The cathode ray oscilloscope 121
10.13 Waveform harmonics 124
10.14 Logarithmic ratios 126
10.15 Null method of measurement 129
10.16 Wheatstone bridge 129
10.17 D.c. potentiometer 130
10.18 A.c. bridges 130
10.19 Measurement errors 131
10.20 Further problems on electrical measuring
instruments and measurements 133
11 Semiconductor 11.1 Types of materials 137
diodes 11.2 Silicon and germanium 138
11.3 n-type and p-type materials 138
11.4 The p-n junction 139
11.5 Forward and reverse bias 140
11.6 Semiconductor diodes 140
11.7 Rectification 143
11.8 Further problems on semiconductor diodes 143
12 Transistors 12.1 The bipolar junction transistor 145
12.2 Transistor action 147
12.3 Transistor symbols 149
12.4 Transistor connections 149
12.5 Transistor characteristics 150
12.6 The transistor as an amplifier 152
12.7 The load line 154
12.8 Current and voltage gains 155
viii Contents
12.9 Thermal runaway 158
12.10 Further problems on transistors 159
Assignment 3 162
Main formulae for Part 1 164
Part 2 Electrical principles and technology
13 D.c. circuit theory 13.1 Introduction 167
13.2 Kirchhoff’s laws 167
13.3 The superposition theorem 171
13.4 General d.c. circuit theory 174
13.5 The´venin’s theorem 176
13.6 Constant-current source 181
13.7 Norton’s theorem 181
13.8 The´venin and Norton equivalent networks 184
13.9 Maximum power transfer theorem 187
13.10 Further problems on d.c. circuit theory 189
14 Alternating voltages 14.1 Introduction 193
and currents 14.2 The a.c. generator 193
14.3 Waveforms 194
14.4 A.c. values 195
14.5 The equation of a sinusoidal waveform 200
14.6 Combination of waveforms 204
14.7 Rectification 208
14.8 Further problems on alternating voltages and currents 209
Assignment 4 212
15 Single-phase series 15.1 Purely resistive a.c. circuit 213
a.c. circuits 15.2 Purely inductive a.c. circuit 214
15.3 Purely capacitive a.c. circuit 214
15.4 R–L series a.c. circuit 215
15.5 R–C series a.c. circuit 220
15.6 R–L–C series a.c. circuit 221
15.7 Series resonance 225
15.8 Q-factor 227
15.9 Bandwidth and selectivity 229
15.10 Power in a.c. circuits 230
15.11 Power triangle and power factor 232
15.12 Further problems on single-phase series a.c. circuits 234
16 Single-phase parallel 16.1 Introduction 238
a.c. circuits 16.2 R–L parallel a.c. circuit 238
16.3 R–C parallel a.c. circuit 240
Contents ix
16.4 L–C parallel a.c. circuit 241
16.5 LR–C parallel a.c. circuit 243
16.6 Parallel resonance and Q-factor 247
16.7 Power factor improvement 252
16.8 Further problems on single-phase parallel a.c. circuits 256
17 D.c. transients 17.1 Introduction 259
17.2 Charging a capacitor 260
17.3 Time constant for a C–R circuit 260
17.4 Transient curves for a C–R circuit 261
17.5 Discharging a capacitor 266
17.6 Current growth in an L–R circuit 268
17.7 Time constant for an L–R circuit 269
17.8 Transient curves for an L–R circuit 269
17.9 Current decay in an L–R circuit 272
17.10 Switching inductive circuits 275
17.11 The effectsoftime constanton arectangularwaveform 275
17.12 Further problems on d.c. transients 276
18 Operational 18.1 Introduction to operational amplifiers 278
amplifiers 18.2 Some op amp parameters 280
18.3 Op amp inverting amplifier 282
18.4 Op amp non-inverting amplifier 285
18.5 Op amp voltage-follower 286
18.6 Op amp summing amplifier 286
18.7 Op amp voltage comparator 288
18.8 Op amp integrator 288
18.9 Op amp differential amplifier 289
18.10 Digital to analogue (D/A) conversion 291
18.11 Analogue to digital (A/D) conversion 293
18.12 Further problems on operational amplifiers 294
Assignment 5 296
19 Three phase systems 19.1 Introduction 297
19.2 Three-phase supply 297
19.3 Star connection 298
19.4 Delta connection 302
19.5 Power in three-phase systems 303
19.6 Measurement of power in three-phase systems 306
19.7 Comparison of star and delta connections 312
19.8 Advantages of three-phase systems 312
19.9 Further problems on three-phase systems 312
20 Transformers 20.1 Introduction 315
20.2 Transformer principle of operation 316
20.3 Transformer no-load phasor diagram 319
20.4 E.m.f. equation of a transformer 320
