Electrical_Circuit_Theory_and_Technology_2E.pdf

Electrical 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 NEW YORK PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Newnes An imprint of Elsevier Science Linacre House, Jordan Hill, Oxford OX2 8DP 200 Wheeler Rd, Burlington, MA 01803 First published 1997 Second edition 2001 Reprinted 2002 Revised second edition 2003 Copyright  1997, 2001, John Bird. All rights reserved The right of John Bird to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 4LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publisher British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0 7506 5784 7 For information on all Newnes publications visit our website at www.newnespress.com Typeset by Laser Words, Madras, India Printed and bound in Great Britain Part 1 Basic Electrical Engineering Principles.................................... 1 1 Units associated with basic electrical quantities........................................ 1 SI units.......................................................................................................................... 1 Charge........................................................................................................................... 4 Force............................................................................................................................. 4 Work.............................................................................................................................. 5 Power............................................................................................................................ 5 Electrical potential and e. m. f....................................................................................... 6 Resistance and conductance........................................................................................ 6 Electrical power and energy.......................................................................................... 7 Summary of terms, units and their symbols.................................................................. 8 Further problems on units associated with basic electrical quantities........................... 9 2 An introduction to electric circuits.............................................................. 10 Standard symbols for electrical components................................................................. 10 Electric current and quantity of electricity...................................................................... 11 Potential difference and resistance............................................................................... 13 Basic electrical measuring instruments......................................................................... 13 Linear and non- linear devices...................................................................................... 13 Ohms law..................................................................................................................... 14 Multiples and sub- multiples.......................................................................................... 14 Conductors and insulators............................................................................................. 16 Electrical power and energy.......................................................................................... 16 Main effects of electric current...................................................................................... 20 Fuses............................................................................................................................. 20 Further problems........................................................................................................... 13 3 Resistance variation.................................................................................. 23 Resistance and resistivity.............................................................................................. 23 Temperature coefficient of resistance........................................................................... 26 Further problems on resistance variation...................................................................... 29 4 Chemical effects of electricity.................................................................... 31 Introduction.................................................................................................................... 31 Electrolysis.................................................................................................................... 31 Electroplating................................................................................................................. 32 The simple cell.............................................................................................................. 32 Corrosion....................................................................................................................... 33 E.m.f. and internal resistance of a cell.......................................................................... 34 Primary cells.................................................................................................................. 36 Secondary cells............................................................................................................. 37 Cell capacity.................................................................................................................. 39 Further problems on the chemical effects of electricity................................................. 39 Assignment 1................................................................................................ 41 5 Series and parallel networks..................................................................... 42 Series circuits................................................................................................................ 42 Potential divider............................................................................................................. 44 Parallel networks........................................................................................................... 45 Current division............................................................................................................. 48 Wiring lamps in series and in parallel............................................................................ 52 Further problems on series and parallel networks........................................................ 53 6 Capacitors and capacitance...................................................................... 55 Electrostatic field........................................................................................................... 57 Electric field strength..................................................................................................... 57 Capacitance.................................................................................................................. 57 Capacitors..................................................................................................................... 57 Electric flux density........................................................................................................ 59 Permittivity..................................................................................................................... 59 The parallel plate capacitor........................................................................................... 61 Capacitors connected in parallel and series.................................................................. 63 Dielectric strength.......................................................................................................... 67 Energy stored................................................................................................................ 68 Practical types of capacitor........................................................................................... 69 Discharging capacitors.................................................................................................. 70 Further problems on capacitors and capacitance......................................................... 70 7 Magnetic circuits........................................................................................ 74 Magnetic fields.............................................................................................................. 74 Magnetic flux and flux density....................................................................................... 75 Magnetomotive force and magnetic field strength......................................................... 76 Permeability and B H curves....................................................................................... 77 Reluctance.................................................................................................................... 80 Composite series magnetic circuits............................................................................... 81 Comparison between electrical and magnetic quantities.............................................. 84 Hysteresis and hysteresis loss...................................................................................... 84 Further problems on magnetic circuits.......................................................................... 85 Assignment 2................................................................................................ 87 8 Electromagnetism...................................................................................... 89 Magnetic field due to an electric current........................................................................ 89 Electromagnets............................................................................................................. 91 Force on a current- carrying conductor......................................................................... 92 Principle of operation of a simple d. c. motor................................................................ 96 Principle of operation of a moving coil instrument......................................................... 97 Force on a charge......................................................................................................... 98 Further problems on electromagnetism......................................................................... 98 9 Electromagnetic induction......................................................................... 100 Introduction to electromagnetic induction...................................................................... 100 Laws of electromagnetic induction................................................................................ 101 Inductance..................................................................................................................... 104 Inductors........................................................................................................................ 106 Energy stored................................................................................................................ 107 Inductance of a coil....................................................................................................... 107 Mutual inductance......................................................................................................... 108 Further problems on electromagnetic induction............................................................ 109 10 Electrical measuring instruments and measurements............................. 113 Introduction.................................................................................................................... 113 Analogue instruments.................................................................................................... 113 Moving-iron instrument.................................................................................................. 113 The moving-coil rectifier instrument.............................................................................. 114 Comparison of moving- coil, moving- iron and moving- coil rectifier instruments......... 114 Shunts and multipliers................................................................................................... 115 Electronic instruments................................................................................................... 117 The ohmmeter............................................................................................................... 117 Multimeters.................................................................................................................... 118 Wattmeters.................................................................................................................... 118 Instrument ˛ loading effect............................................................................................ 118 The cathode ray oscilloscope........................................................................................ 121 Waveform harmonics.................................................................................................... 124 Logarithmic ratios.......................................................................................................... 126 Null method of measurement........................................................................................ 129 Wheatstone bridge........................................................................................................ 129 D.c. potentiometer......................................................................................................... 130 A.c. bridges................................................................................................................... 130 Measurement errors...................................................................................................... 131 Further problems on electrical measuring instruments and measurements.................. 133 11 Semiconductor diodes............................................................................. 137 Types of materials......................................................................................................... 137 Silicon and germanium.................................................................................................. 138 n-type and p-type materials........................................................................................... 138 The p-n junction............................................................................................................. 139 Forward and reverse bias.............................................................................................. 140 Semiconductor diodes................................................................................................... 140 Rectification................................................................................................................... 143 Further problems on semiconductor diodes.................................................................. 143 12 Transistors............................................................................................... 145 The bipolar junction transistor....................................................................................... 145 Transistor action............................................................................................................ 147 Transistor symbols........................................................................................................ 149 Transistor connections.................................................................................................. 149 Transistor characteristics.............................................................................................. 150 The transistor as an amplifier........................................................................................ 152 The load line.................................................................................................................. 154 Current and voltage gains............................................................................................. 155 Thermal runaway........................................................................................................... 158 Further problems on transistors.................................................................................... 159 Assignment 3................................................................................................ 162 Main formulae for Part 1............................................................................... 164 General.......................................................................................................................... 164 Capacitors and capacitance.......................................................................................... 164 Magnetic circuits............................................................................................................ 164 Electromagnetism.......................................................................................................... 164 Electromagnetic induction............................................................................................. 164 Measurements............................................................................................................... 164 Part 2 Electrical Principles and Technology....................................... 165 13 D.c. circuit theory..................................................................................... 167 Introduction.................................................................................................................... 167 Kirchhoffs laws............................................................................................................. 167 The superposition theorem............................................................................................ 171 General d.c. circuit theory............................................................................................. 174 Th · evenins theorem.................................................................................................... 176 Constant-current source................................................................................................ 181 Nortons theorem........................................................................................................... 181 Th · evenin and Norton equivalent networks................................................................. 184 Maximum power transfer theorem................................................................................. 187 Further problems on d. c. circuit theory......................................................................... 189 14 Alternating voltages and currents............................................................ 193 Introduction.................................................................................................................... 193 The a.c. generator......................................................................................................... 194 Waveforms.................................................................................................................... 194 A.c. values..................................................................................................................... 195 The equation of a sinusoidal waveform......................................................................... 200 Combination of waveforms............................................................................................ 204 Rectification................................................................................................................... 208 Further problems on alternating voltages and currents................................................. 209 Assignment 4................................................................................................ 212 15 Single-phase series a.c. circuits.............................................................. 213 Purely resistive a.c. circuit............................................................................................. 214 Purely inductive a.c. circuit............................................................................................ 214 Purely capacitive a. c. circuit......................................................................................... 214 R L series a.c. circuit................................................................................................... 215 R C series a.c. circuit.................................................................................................. 220 R L C series a.c. circuit............................................................................................. 221 Series resonance.......................................................................................................... 225 Q-factor......................................................................................................................... 227 Bandwidth and selectivity.............................................................................................. 229 Power in a.c. circuits..................................................................................................... 230 Power triangle and power factor.................................................................................... 232 Further problems on single- phase series a. c. circuits................................................. 234 16 Single-phase parallel a. c. circuits........................................................... 238 Introduction.................................................................................................................... 238 R L parallel a.c. circuit................................................................................................. 238 R C parallel a.c. circuit................................................................................................ 240 L C parallel a.c. circuit................................................................................................. 241 LR C parallel a.c. circuit.............................................................................................. 243 Parallel resonance and Q- factor................................................................................... 247 Power factor improvement............................................................................................ 252 Further problems on single- phase parallel a. c. circuits............................................... 256 17 D.c. transients......................................................................................... 259 Introduction.................................................................................................................... 259 Charging a capacitor..................................................................................................... 260 Time constant for a C R circuit.................................................................................... 260 Transient curves for a C R circuit................................................................................ 261 Discharging a capacitor................................................................................................. 266 Current growth in an L R circuit................................................................................... 268 Time constant for an L R circuit................................................................................... 269 Transient curves for an L R circuit............................................................................... 269 Current decay in an L R circuit.................................................................................... 272 Switching inductive circuits............................................................................................ 275 The effects of time constant on a rectangular waveform............................................... 275 Further problems on d. c. transients.............................................................................. 276 18 Operational amplifiers............................................................................. 278 Introduction to operational amplifiers............................................................................ 278 Some op amp parameters............................................................................................. 280 Op amp inverting amplifier............................................................................................ 282 Op amp non- inverting amplifier.................................................................................... 285 Op amp voltage- follower.............................................................................................. 286 Op amp summing amplifier........................................................................................... 286 Op amp voltage comparator.......................................................................................... 288 Op amp integrator......................................................................................................... 288 Op amp differential amplifier......................................................................................... 289 Digital to analogue ( D/ A) conversion........................................................................... 291 Analogue to digital ( A/ D) conversion........................................................................... 293 Further problems on operational amplifiers................................................................... 294 Assignment 5................................................................................................ 296 19 Three phase systems.............................................................................. 297 Introduction.................................................................................................................... 297 Three-phase supply....................................................................................................... 298 Star connection............................................................................................................. 298 Delta connection............................................................................................................ 302 Power in three- phase systems..................................................................................... 303 Measurement of power in three- phase systems.......................................................... 306 Comparison of star and delta connections.................................................................... 312 Advantages of three- phase systems............................................................................ 312 Further problems on three- phase systems................................................................... 312 20 Transformers........................................................................................... 315 Introduction.................................................................................................................... 315 Transformer principle of operation................................................................................ 316 Transformer no- load phasor diagram........................................................................... 319 E.m.f. equation of a transformer.................................................................................... 320 Transformer on- load phasor diagram........................................................................... 324 Transformer construction.............................................................................................. 325 Equivalent circuit of a transformer................................................................................. 326 Regulation of a transformer........................................................................................... 329 Transformer losses and efficiency................................................................................. 330 Resistance matching..................................................................................................... 334 Auto transformers.......................................................................................................... 337 Isolating transformers.................................................................................................... 340 Three-phase transformers............................................................................................. 340 Current transformers..................................................................................................... 342 Voltage transformers..................................................................................................... 343 Further problems on transformers................................................................................. 344 Assignment 6................................................................................................ 349 21 D.c. machines.......................................................................................... 350 Introduction.................................................................................................................... 350 The action of a commutator........................................................................................... 351 D.c. machine construction............................................................................................. 352 Shunt, series and compound windings.......................................................................... 353 E.m.f. generated in an armature winding...................................................................... 353 D.c. generators.............................................................................................................. 356 Types of d.c. generator and their characteristics.......................................................... 356 D.c. machine losses...................................................................................................... 362 Efficiency of a d.c. generator......................................................................................... 363 D.c. motors.................................................................................................................... 364 Torque of a d.c. machine............................................................................................... 365 Types of d.c. motor and their characteristics................................................................. 368 The efficiency of a d. c. motor....................................................................................... 373 D.c. motor starter........................................................................................................... 376 Speed control of d. c. motors........................................................................................ 377 Motor cooling................................................................................................................. 381 Further problems on d. c. machines.............................................................................. 381 22 Three-phase induction motors................................................................. 386 Introduction.................................................................................................................... 386 Production of a rotating magnetic field.......................................................................... 387 Synchronous speed....................................................................................................... 388 Construction of a three- phase induction motor............................................................ 390 Principle of operation of a three- phase induction motor............................................... 390 Slip................................................................................................................................ 391 Rotor e.m.f. and frequency............................................................................................ 393 Rotor impedance and current........................................................................................ 394 Rotor copper loss.......................................................................................................... 395 Induction motor losses and efficiency........................................................................... 395 Torque equation for an induction motor........................................................................ 397 Induction motor torque - speed characteristics............................................................. 401 Starting methods for induction motors........................................................................... 403 Advantages of squirrel- cage induction motors............................................................. 404 Advantages of wound rotor induction motor.................................................................. 405 Double cage induction motor......................................................................................... 405 Uses of three-phase induction motors........................................................................... 405 Further problems on three- phase induction motors..................................................... 406 Assignment 7................................................................................................ 408 Main formulae for Part 2............................................................................... 409 A.c. theory:.................................................................................................................... 409 Single-phase circuits:.................................................................................................... 410 D.c. transients:.............................................................................................................. 410 Operational amplifiers.................................................................................................. 411 Three-phase systems:................................................................................................... 411 Transformers:................................................................................................................ 411 D.c. machines:............................................................................................................... 411 Three-phase induction motors:...................................................................................... 411 Part 3 Advanced Circuit Theory and Technology............................... 413 23 Revision of complex numbers................................................................. 415 Introduction.................................................................................................................... 415 Operations involving Cartesian complex numbers........................................................ 417 Complex equations........................................................................................................ 419 The polar form of a complex number............................................................................ 421 Multiplication and division using complex numbers in polar form.................................. 421 De Moivres theorem powers and roots of complex numbers..................................... 423 Further problems on complex numbers......................................................................... 424 24 Application of complex numbers to series a. c. circuits........................... 429 Introduction.................................................................................................................... 429 Series a.c. circuits......................................................................................................... 429 Further problems on series a. c. circuits....................................................................... 440 25 Application of complex numbers to parallel a. c. networks...................... 25 Introduction.................................................................................................................... 25 Admittance, conductance and susceptance.................................................................. 25 Parallel a.c. networks.................................................................................................... 448 Further problems on parallel a. c. networks.................................................................. 454 26 Power in a.c. circuits............................................................................... 459 Introduction.................................................................................................................... 459 Determination of power in a. c. circuits......................................................................... 459 Power triangle and power factor.................................................................................... 464 Use of complex numbers for determination of power.................................................... 465 Power factor improvement............................................................................................ 470 Further problems on power in a. c. circuits................................................................... 472 Assignment 8................................................................................................ 475 27 A.c. bridges............................................................................................. 476 Introduction.................................................................................................................... 476 Balance conditions for an a. c. bridge........................................................................... 476 Types of a.c. bridge circuit............................................................................................ 478 Further problems on a. c. bridges................................................................................. 488 28 Series resonance and Q- factor.............................................................. 491 Introduction.................................................................................................................... 491 Series resonance.......................................................................................................... 491 Q-factor......................................................................................................................... 495 Voltage magnification.................................................................................................... 498 Q-factors in series......................................................................................................... 502 Bandwidth...................................................................................................................... 504 Small deviations from the resonant frequency.............................................................. 509 Further problems on series resonance and Q- factor.................................................... 512 29 Parallel resonance and Q- factor............................................................. 515 Introduction.................................................................................................................... 516 The LR C parallel network........................................................................................... 516 Dynamic resistance....................................................................................................... 517 The LR CR parallel network........................................................................................ 517 Q-factor in a parallel network........................................................................................ 519 Further problems on parallel resonance and Q- factor.................................................. 527 Assignment 9................................................................................................ 530 30 Introduction to network analysis.............................................................. 531 Introduction.................................................................................................................... 531 Solution of simultaneous equations using determinants............................................... 532 Network analysis using Kirchhoffs laws....................................................................... 535 Further problems on Kirchhoffs laws............................................................................ 542 31 Mesh-current and nodal analysis............................................................ 545 Mesh-current analysis................................................................................................... 545 Nodal analysis............................................................................................................... 550 Further problems on mesh- current and nodal analysis................................................ 559 32 The superposition theorem...................................................................... 562 Introduction.................................................................................................................... 562 Using the superposition theorem................................................................................... 562 Further problems on the superposition theorem........................................................... 573 33 Thevenins and Nortons theorems......................................................... 5755 Introduction.................................................................................................................... 575 Thevenins theorem....................................................................................................... 575 Nortons theorem........................................................................................................... 587 Thevenin and Norton equivalent networks.................................................................... 593 Further problems on Thevenins and Nortons theorem................................................ 598 Assignment 10.............................................................................................. 602 34 Delta-star and star-delta transformations................................................ 603 Introduction.................................................................................................................... 603 Delta and star connections............................................................................................ 603 Delta-star transformation............................................................................................... 603 Star-delta transformation............................................................................................... 611 Further problems on delta-star and star-delta transformations..................................... 614 35 Maximum power transfer theorems and impedance matching................ 617 Maximum power transfer theorems............................................................................... 617 Impedance matching..................................................................................................... 623 Further problems on maximum power transfer theorems and impedance matching.... 626 Assignment 11.............................................................................................. 629 36 Complex Waveforms............................................................................... 631 Introduction.................................................................................................................... 631 The general equation for a complex waveform............................................................. 632 Harmonic synthesis....................................................................................................... 633 Rms value, mean value and the form factor of a complex wave................................... 645 Power associated with complex waves......................................................................... 650 Harmonics in single- phase circuits............................................................................... 653 Resonance due to harmonics........................................................................................ 664 Sources of harmonics.................................................................................................... 666 Further problems on complex waveforms..................................................................... 671 37 A numerical method of harmonic analysis............................................... 678 Introduction.................................................................................................................... 678 Harmonic analysis on data given in tabular or graphical form....................................... 683 Complex waveform considerations............................................................................... 683 Further problems on a numerical method of harmonic analysis.................................... 685 38 Magnetic materials.................................................................................. 688 Revision of terms and units used with magnetic circuits............................................... 688 Magnetic properties of materials................................................................................... 690 Hysteresis and hysteresis loss...................................................................................... 692 Eddy current loss........................................................................................................... 696 Separation of hysteresis and eddy current losses......................................................... 701 Nonpermanent magnetic materials............................................................................... 704 Permanent magnetic materials...................................................................................... 706 Further problems on magnetic materials....................................................................... 707 Assignment 12.............................................................................................. 710 39 Dielectrics and dielectric loss.................................................................. 711 Electric fields, capacitance and permittivity................................................................... 711 Polarization.................................................................................................................... 711 Dielectric strength.......................................................................................................... 712 Thermal effects.............................................................................................................. 714 Mechanical properties................................................................................................... 714 Types of practical capacitor........................................................................................... 715 Liquid dielectrics and gas insulation.............................................................................. 715 Dielectric loss and loss angle........................................................................................ 715 Further problems on dielectric loss and loss angle....................................................... 719 40 Field theory.............................................................................................. 720 Field plotting by curvilinear squares.............................................................................. 720 Capacitance between concentric cylinders................................................................... 725 Capacitance of an isolated twin line.............................................................................. 733 Energy stored in an electric field................................................................................... 737 Induced e.m.f. and inductance...................................................................................... 741 Inductance of a concentric cylinder ( or coaxial cable).................................................. 741 Inductance of an isolated twin line................................................................................ 746 Energy stored in an electromagnetic field..................................................................... 750 Further problems on field theory................................................................................... 753 41 Attenuators.............................................................................................. 758 Introduction.................................................................................................................... 758 Characteristic impedance.............................................................................................. 759 Logarithmic ratios.......................................................................................................... 761 Symmetrical T-and p- attenuators................................................................................. 764 Insertion loss................................................................................................................. 772 Asymmetrical Tand p- sections..................................................................................... 775 The L-section attenuator............................................................................................... 779 Two-port networks in cascade....................................................................................... 782 Further problems on attenuators................................................................................... 785 Assignment 13.............................................................................................. 789 42 Filter networks......................................................................................... 790 Introduction.................................................................................................................... 791 Basic types of filter sections.......................................................................................... 791 The characteristic impedance and the attenuation of filter sections.............................. 792 Ladder networks............................................................................................................ 795 Low-pass filter sections................................................................................................. 797 High-pass filter sections................................................................................................ 807 Propagation coefficient and time delay in filter sections................................................ 815 ˛m-derived filter sections.............................................................................................. 825 Practical composite filters.............................................................................................. 833 Further problems on filter networks............................................................................... 837 43 Magnetically coupled circuits................................................................... 841 Introduction.................................................................................................................... 841 Self-inductance.............................................................................................................. 841 Mutual inductance......................................................................................................... 842 Coupling coefficient....................................................................................................... 843 Coils connected in series.............................................................................................. 845 Coupled circuits............................................................................................................. 849 Dot rule for coupled circuits........................................................................................... 857 Further problems on magnetically coupled circuits....................................................... 864 44 Transmission lines................................................................................... 869 Introduction.................................................................................................................... 869 Transmission line primary constants............................................................................. 869 Phase delay, wavelength and velocity of propagation.................................................. 871 Current and voltage relationships.................................................................................. 873 Characteristic impedance and propagation coefficient in terms of the primary constants....................................................................................................................... 875 Distortion on transmission lines..................................................................................... 882 Wave reflection and the reflection coefficient................................................................ 885 Standing waves and the standing wave ratio................................................................ 890 Further problems on transmission lines........................................................................ 897 45 Transients and Laplace transforms......................................................... 901 Introduction.................................................................................................................... 901 Response of R C series circuit to a step input............................................................ 901 Response of R L series circuit to a step input............................................................. 906 L R C series circuit response.................................................................................... 910 Introduction to Laplace transforms................................................................................ 914 Inverse Laplace transforms and the solution of differential equations.......................... 921 Laplace transform analysis directly from the circuit diagram......................................... 930 L R C series circuit using Laplace transforms........................................................... 944 Initial conditions............................................................................................................. 949 Further problems on transients and Laplace transforms............................................... 952 Assignment 14.............................................................................................. 958 Main formulae for part 3 advanced circuit theory and technology................ 960 Complex numbers:........................................................................................................ 960 General:......................................................................................................................... 960 R L C series circuit:................................................................................................... 9600 LR C network:.............................................................................................................. 961 LR CR network:........................................................................................................... 961 Determinants:................................................................................................................ 961 Delta-star:...................................................................................................................... 961 Star-delta:...................................................................................................................... 961 Impedance matching:.................................................................................................... 961 Complex waveforms:..................................................................................................... 961 Harmonic analysis:........................................................................................................ 961 Hysteresis and Eddy current:........................................................................................ 961 Dielectric loss:............................................................................................................... 962 Field theory:................................................................................................................... 962 Attenuators:................................................................................................................... 962 Filter networks............................................................................................................... 963 Magnetically coupled circuits......................................................................................... 963 Transmission lines:........................................................................................................ 964 Transients:..................................................................................................................... 964 Part 4 General Reference...................................................................... 966 Standard electrical quantities their symbols and units............................... 968 Greek alphabet............................................................................................. 971 Common prefixes......................................................................................... 972 Resistor colour coding and ohmic values..................................................... 973 Colour code for fixed resistors....................................................................................... 973 Letter and digit code for resistors.................................................................................. 973 Index............................................................................................................. 975 Preface ‘Electrical Circuit Theory and Technology, Revised second Edition’ provides coverage for a wide range of courses that contain electrical principles, circuit theory and technology in their syllabuses, from introductory to degree level. The chapter ‘Transients and Laplace transforms’, which had been removed from the second edition due to page restraints, has been included in this edition in response to popular demand. The text is set out in four parts as follows: PART 1, involving chapters 1 to 12, contains ‘Basic Electrical Engineering Principles’ which any student wishing to progress in electrical engineering would need to know. An introduction to electrical circuits, resistance variation, chemical effects of electricity, series and parallel circuits, capacitors and capacitance, magnetic circuits, electromagnetism, electromagnetic induction, electrical measuring instruments and measurements, semiconductor diodes and transistors are all included in this section. PART 2, involving chapters 13 to 22, contains ‘Electrical Principles and Technology’ suitable for Advanced GNVQ, National Certificate, National Diploma and City and Guilds courses in electrical and electronic engineering. D.c. circuit theory, alternating voltages and currents, single-phase series and parallel circuits, d.c. transients, operational amplifiers, three-phase systems, transformers, d.c. machines and three- phase induction motors are all included in this section. PART 3, involving chapters 23 to 45, contains ‘Advanced Circuit Theory and Technology’ suitable for Degree, Higher National Certificate/Diploma and City and Guilds courses in electrical and electronic/telecommunications engineering. The two earlier sections of the book will provide a valuable reference/revision for students at this level. Complex numbers and their application to series and parallel networks, power in a.c. circuits, a.c. bridges, series and parallel resonance and Q-factor, network analysis involving Kirchhoff’s laws, mesh and nodal analysis, the superposition theorem, Thévenin’s and Norton’s theorems, delta-star and star-delta transforms, maximum power transfer theorems and impedance matching, complex waveforms, harmonic analysis, magnetic materials, dielectrics and dielectric loss, field theory, attenuators, filter networks, magnetically coupled circuits, transmission line theory and transients and Laplace transforms are all included in this section. PART 4 provides a short, ‘General Reference’ for standard electrical quantities — their symbols and units, the Greek alphabet, common prefixes and resistor colour coding and ohmic values. At the beginning of each of the 45 chapters learning objectives are listed. At the end of each of the first three parts of the text is a handy reference of the main formulae used. xviii Electrical Circuit Theory and Technology It is not possible to acquire a thorough understanding of electrical principles, circuit theory and technology without working through a large number of numerical problems. It is for this reason that ‘Electrical Circuit Theory and Technology, Revised second Edition’ contains some 740 detailed worked problems, together with over 1100 further problems, all with answers in brackets immediately following each question. Over 1100 line diagrams further enhance the understanding of the theory. Fourteen Assignments have been included, interspersed within the text every few chapters. For example, Assignment 1 tests understanding of chapters 1 to 4, Assignment 2 tests understanding of chapters 5 to 7, Assignment 3 tests understanding of chapters 8 to 12, and so on. These Assignments do not have answers given since it is envisaged that lecturers could set the Assignments for students to attempt as part of their course structure. Lecturers’ may obtain a complimentary set of solutions of the Assignments in an Instructor’s Manual available from the publishers via the internet — see below. ‘Learning by Example’ is at the heart of ‘Electrical Circuit Theory and Technology, Revised second Edition’. JOHN BIRD University of Portsmouth Free web downloads Instructor’s Manual Full worked solutions and mark scheme for all the Assignments in this book. This material is available to lecturers only. To obtain a password please e-mail [email protected] with the following details: course title, number of students, your job title and work postal address. To download the Instructor’s Manual visit http://www.newnespress.com and enter the book title in the search box, or use the following direct URL: http://www.bh.com/manuals/0750657847/ For up-to-date information on all Newnes textbooks visit our websites: www.newnespress.com www.bh.com/engineering Register as a user to receive regular e-mail bulletins. If you have any suggestions for how we could improve this book in future editions, corrections, or ideas for our future publishing programme please e-mail Newnes at: [email protected] Part 1 Basic Electrical Engineering Principles 1 Units associated with basic electrical quantities At the end of this chapter you should be able to: ž state the basic SI units ž recognize derived SI units ž understand prefixes denoting multiplication and division ž state the units of charge, force, work and power and perform simple calculations involving these units ž state the units of electrical potential, e.m.f., resistance, conductance, power and energy and perform simple calculations involving these units 1.1 SI units The system of units used in engineering and science is the Système Inter- nationale d’Unités (International system of units), usually abbreviated to SI units, and is based on the metric system. This was introduced in 1960 and is now adopted by the majority of countries as the official system of measurement. The basic units in the SI system are listed with their symbols, in Table 1.1. TABLE 1.1 Basic SI Units Quantity Unit length metre, m mass kilogram, kg time second, s electric current ampere, A thermodynamic temperature kelvin, K luminous intensity candela, cd amount of substance mole, mol Derived SI units use combinations of basic units and there are many of them. Two examples are: ž Velocity — metres per second (m/s) ž Acceleration — metres per second squared (m/s2 ) 4 Electrical Circuit Theory and Technology SI units may be made larger or smaller by using prefixes which denote multiplication or division by a particular amount. The six most common multiples, with their meaning, are listed in Table 1.2. TABLE 1.2 Prefix Name Meaning M mega multiply by 1 000 000 (i.e. ð106 ) k kilo multiply by 1000 (i.e. ð103 ) m milli divide by 1000 (i.e. ð103 ) micro divide by 1 000 000 (i.e. ð106 ) n nano divide by 1 000 000 000 (i.e. ð109 ) p pico divide by 1 000 000 000 000 (i.e. ð1012 ) 1.2 Charge The unit of charge is the coulomb (C) where one coulomb is one ampere second. (1 coulomb D 6.24 ð 1018 electrons). The coulomb is defined as the quantity of electricity which flows past a given point in an electric circuit when a current of one ampere is maintained for one second. Thus, charge, in coulombs Q = It where I is the current in amperes and t is the time in seconds. Problem 1. If a current of 5 A flows for 2 minutes, find the quan- tity of electricity transferred. Quantity of electricity Q D It coulombs I D 5 A, t D 2 ð 60 D 120 s Hence Q D 5 ð 120 D 600 C 1.3 Force The unit of force is the newton (N) where one newton is one kilogram metre per second squared. The newton is defined as the force which, when applied to a mass of one kilogram, gives it an acceleration of one metre per second squared. Thus, force, in newtons F = ma where m is the mass in kilograms and a is the acceleration in metres per second squared. Gravitational force, or weight, is mg, where g D 9.81 m/s2 Units associated with basic electrical quantities 5 Problem 2. A mass of 5000 g is accelerated at 2 m/s2 by a force. Determine the force needed. Force D mass ð acceleration kg m D 5 kg ð 2 m/s2 D 10 D 10 N s2 Problem 3. Find the force acting vertically downwards on a mass of 200 g attached to a wire. Mass D 200 g D 0.2 kg and acceleration due to gravity, g D 9.81 m/s2 Force acting downwards D weight D mass ð acceleration D 0.2 kg ð 9.81 m/s2 D 1.962 N 1.4 Work The unit of work or energy is the joule (J) where one joule is one newton metre. The joule is defined as the work done or energy transferred when a force of one newton is exerted through a distance of one metre in the direction of the force. Thus work done on a body, in joules W = Fs where F is the force in newtons and s is the distance in metres moved by the body in the direction of the force. Energy is the capacity for doing work. 1.5 Power The unit of power is the watt (W) where one watt is one joule per second. Power is defined as the rate of doing work or transferring energy. Thus, W power in watts, P= t where W is the work done or energy transferred in joules and t is the time in seconds. Thus energy, in joules, W = Pt 6 Electrical Circuit Theory and Technology Problem 4. A portable machine requires a force of 200 N to move it. How much work is done if the machine is moved 20 m and what average power is utilized if the movement takes 25 s? Work done D force ð distance D 200 N ð 20 m D 4000 Nm or 4 kJ work done 4000 J Power D D D 160 J=s = 160 W time taken 25 s Problem 5. A mass of 1000 kg is raised through a height of 10 m in 20 s. What is (a) the work done and (b) the power developed? (a) Work done D force ð distance and force D mass ð acceleration Hence, work done D 1000 kg ð 9.81 m/s2 ð 10 m D 98 100 Nm D 98.1 kNm or 98.1 kJ work done 98100 J (b) Power D D D 4905 J/s time taken 20 s D 4905 W or 4.905 kW 1.6 Electrical potential The unit of electric potential is the volt (V) where one volt is one joule and e.m.f. per coulomb. One volt is defined as the difference in potential between two points in a conductor which, when carrying a current of one ampere, dissipates a power of one watt, i.e. watts joules/second joules joules volts D D D D amperes amperes ampere seconds coulombs A change in electric potential between two points in an electric circuit is called a potential difference. The electromotive force (e.m.f.) provided by a source of energy such as a battery or a generator is measured in volts. 1.7 Resistance and The unit of electric resistance is the ohm (Z) where one ohm is one conductance volt per ampere. It is defined as the resistance between two points in a conductor when a constant electric potential of one volt applied at the two points produces a current flow of one ampere in the conductor. Thus, V resistance, in ohms R = I Units associated with basic electrical quantities 7 where V is the potential difference across the two points in volts and I is the current flowing between the two points in amperes. The reciprocal of resistance is called conductance and is measured in siemens (S). Thus, 1 conductance, in siemens G= R where R is the resistance in ohms. Problem 6. Find the conductance of a conductor of resistance (a) 10 , (b) 5 k and (c) 100 m 1 1 (a) Conductance G D D siemen D 0.1 s R 10 1 1 (b) GD D S D 0.2 ð 103 S D 0.2 mS R 5 ð 103 1 1 103 (c) GD D S D S D 10 S R 100 ð 103 100 1.8 Electrical power and When a direct current of I amperes is flowing in an electric circuit and energy the voltage across the circuit is V volts, then power, in watts P = VI Electrical energy D Power ð time D VIt Joules Although the unit of energy is the joule, when dealing with large amounts of energy, the unit used is the kilowatt hour (kWh) where 1 kWh D 1000 watt hour D 1000 ð 3600 watt seconds or joules D 3 600 000 J Problem 7. A source e.m.f. of 5 V supplies a current of 3 A for 10 minutes. How much energy is provided in this time? Energy D power ð time and power D voltage ð current. Hence 8 Electrical Circuit Theory and Technology Energy D VIt D 5 ð 3 ð 10 ð 60 D 9000 Ws or J D 9 kJ Problem 8. An electric heater consumes 1.8 MJ when connected to a 250 V supply for 30 minutes. Find the power rating of the heater and the current taken from the supply. i.e. Power rating of heater = 1 kW P 1000 Power P D VI, thus I D D D4A V 250 Hence the current taken from the supply is 4 A 1.9 Summary of terms, units and their symbols Quantity Quantity Unit Unit symbol Symbol Length l metre m Mass m kilogram kg Time t second s Velocity v metres per second m/s or m s1 Acceleration a metres per second squared m/s2 or m s2 Force F newton N Electrical charge coulomb C or quantity Q Electric current I ampere A Resistance R ohm Conductance G siemen S Electromotive volt V force E Potential volt V difference V Work W joule J Energy E (or W) joule J Power P watt W As progress is made through Electrical Circuit Theory and Technology many more terms will be met. A full list of electrical quantities, together with their symbols and units are given in Part 4, page 968. Units associated with basic electrical quantities 9 1.10 Further problems 1 What force is required to give a mass of 20 kg an acceleration of on units associated with 30 m/s2 ? [600 N] basic electrical quantities 2 Find the accelerating force when a car having a mass of 1.7 Mg (Take g = 9.81 m/s2 where increases its speed with a constant acceleration of 3 m/s2 [5.1 kN] appropriate) 3 A force of 40 N accelerates a mass at 5 m/s2. Determine the mass. [8 kg] 4 Determine the force acting downwards on a mass of 1500 g suspended on a string. [14.72 N] 5 A force of 4 N moves an object 200 cm in the direction of the force. What amount of work is done? [8 J] 6 A force of 2.5 kN is required to lift a load. How much work is done if the load is lifted through 500 cm? [12.5 kJ] 7 An electromagnet exerts a force of 12 N and moves a soft iron armature through a distance of 1.5 cm in 40 ms. Find the power consumed. [4.5 W] 8 A mass of 500 kg is raised to a height of 6 m in 30 s. Find (a) the work done and (b) the power developed. [(a) 29.43 kNm (b) 981 W] 9f 3 What A flows for 5 minutes. quantity Whatischarge of electricity carriedisby 6.24 ð 1021 electrons? transferred? [1000 C] 10 In what time would a current of 1 A transfer a charge of 30 C? [30 s] 11 A current o [900 C] 12 How long must a current of 0.1 A flow so as to transfer a charge of 30 C? [5 minutes] 13 Find the conductance of a resistor of resistance (a) 10Z (b) 2 kZ (c) 2 mZ [(a) 0.1 S (b) 0.5 mS (c) 500 S] 14 A conductor has a conductance of 50 µS. What is its resistance? [20 k] 15 An e.m.f. of 250 V is connected across a resistance and the current flowing through the resistance is 4 A. What is the power developed? [1 kW] 16 450 J of energy are converted into heat in 1 minute. What power is dissipated? [7.5 W] 17 A current of 10 A flows through a conductor and 10 W is dissipated. What p.d. exists across the ends of the conductor? [1 V] 18 A battery of e.m.f. 12 V supplies a current of 5 A for 2 minutes. How much energy is supplied in this time? [7.2 kJ] 19 A dc electric motor consumes 36 MJ when connected to a 250 V supply for 1 hour. Find the power rating of the motor and the current taken from the supply. [10 kW, 40 A] 2 An introduction to electric circuits At the end of this chapter you should be able to: ž recognize common electrical circuit diagram symbols ž understand that electric current is the rate of movement of charge and is measured in amperes ž appreciate that the unit of charge is the coulomb ž calculate charge or quantity of electricity Q from Q D It ž understand that a potential difference between two points in a circuit is required for current to flow ž appreciate that the unit of p.d. is the volt ž understand that resistance opposes current flow and is measured in ohms ž appreciate what an ammeter, a voltmeter, an ohmmeter, a multimeter and a C.R.O. measure ž distinguish between linear and non-linear devices V V ž state Ohm’s law as V D IR or I D or R D R I ž use Ohm’s law in calculations, including multiples and sub-multiples of units ž describe a conductor and an insulator, giving examples of each ž appreciate that electrical power P is given by V2 P D VI D I2 R D watts R ž calculate electrical power ž define electrical energy and state its unit ž calculate electrical energy ž state the three main effects of an electric current, giving practical examples of each ž explain the importance of fuses in electrical circuits 2.1 Standard symbols for Symbols are used for components in electrical circuit diagrams and some electrical components of the more common ones are shown in Figure 2.1. An introduction to electric circuits 11 Figure 2.1 2.2 Electric current and All atoms consist of protons, neu

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