Elcetric Power Engineer

Sincethe main target of this book is electrical power equipment, a change of title was agreed and so we now have the Newnes Electrical Power Engineer’s Handbook.. The opening chapter dea

Newnes Electrical Power Engineer’s

Handbook

Second Edition

This page intentionally left blank

Newnes Electrical Power Engineer’s

Handbook

Second Edition

D.F Warne

Newnes is an imprint of Elsevier

An imprint of Elsevier

Linacre House, Jordan Hill, Oxford OX2 8DP

30 Corporate Drive, Burlington, MA 01803

First published 2005

Copyright © 2005, D.F Warne All rights reserved

The right of D.F Warne 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 W1T 4LP Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publisher

Permissions may be sought directly from Elsevier’s Science and Technology Rights Department in Oxford, UK: phone: ( + 44) (0) 1865 843830; fax: ( + 44) (0) 1865 853333; e-mail: permissions@elsevier.co.uk You may also complete your request on-line via the Elsevier homepage

(http://www.elsevier.com), by selecting ‘Customer Support’ and

then ‘Obtaining Permissions’

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

Library of Congress Cataloguing in Publication Data

A catalogue record for this book is available from the Library of Congress ISBN 0 7506 6268 9

Printed and bound in Great Britain

For information on all Elsevier publications

visit our website at www.books.elsevier.com

3.3.1.3 Flexible insulating sleeving 42

3.3.1.4 Rigid fibrous reinforced laminates 42

vi Contents

3.3.1.6 Pressure-sensitive adhesive tapes 43

Contents vii

4.5.3 The linear variable differential transformer (LVDT) 82

5.3.6 Operating limits when in parallel with the mains 117

6.3.5 Transmission (or intertie) transformers 156

Contents ix

7.3.1 Switches, disconnectors, switch disconnectors and

7.3.1.1 Construction and operation 172

7.3.2 Air circuit breakers and moulded case circuit breakers 175

7.3.2.1 Construction and operation 175

7.5.3.1 Conventional or Air-Insulated Switchgear (AIS) 201

7.5.3.2 Gas-insulated metal-enclosed switchgear 201

x Contents

9.2.5 Low Smoke and Fume (LSF) and fire performance cables 252

9.3.1 Cables for the electricity supply industry 253

9.3.2.2 Polymeric cables for fixed installations 260

9.3.2.3 Polymeric cables for flexible connections 261

9.4.5 Symmetrical and earth fault capacity 266

Contents xi

10.10.2.1 AC to ac power converters with

10.10.2.2 General characteristics of a voltage

10.11.2.1 Machine rating: thermal effects 308

11.4.4 Sinusoidal Pulse Width Modulation (PWM) 330

12.3 Secondary cells based upon aqueous electrolytes 346

12.3.7 Lead acid – valve regulated sealed (VRSLA) 353

12.5.1 The Polymer Electrolyte Fuel Cell (PEFC) 357

Contents xiii

14.2.5 Design for EMC 406

14.2.5.3 Cable screens termination 408

15.4.1 Codes of practice for area classification 417

15.7.6.1 Cable and conduit entries 429

15.7.6.3 Wiring within enclosures 430

15.7.6.4 Thermal protection of electrical machines 430

15.8.3.3 Fault loop impedance or earth resistance 433

15.8.3.4 Insulation resistance measurements 434

16.2 Precautions against electric shock and contact burn injuries 440

16.2.2 Prevention of direct contact injuries 440

16.2.2.1 Insulation and enclosures 440

16.2.2.7 Earth leakage protection 442

16.2.3 Prevention of indirect contact injuries 44316.3 Precautions against arc and flashover burn injuries 444

16.6 Preventive maintenance and safe systems of work 445

16.6.2.1 Safe isolation procedures 445

This page intentionally left blank

When I was first asked to update the Newnes Electrical Engineer’s Handbook, it seemed

a relatively straightforward task But after studying the reviewer’s comments whichhad been assembled by the publisher it became clear that a number of changes

in emphasis would be worthwhile It was also evident that in North America, a clearerdistinction has to be made between electrical power engineering and electronics Sincethe main target of this book is electrical power equipment, a change of title was agreed

and so we now have the Newnes Electrical Power Engineer’s Handbook.

At the same time, some areas of the technology continue to advance apace, ularly in the structure and operation of power systems, and in emc and power quality

partic-So some chapters needed a substantial overhaul even though the Newnes Electrical

Engineer’s Handbook was published only five years ago.

New contributors have been introduced to handle the various updates, partly because

of the retirement of former contributors and partly because of change of emphasis The co-operation of all the contributors during the preparation of material and through theinevitable differences of pace at which the different sections have been completed, isgratefully acknowledged

Every work of this type consumes a vast amount of time, with an inevitable fice of personal and social time Without the patience and understanding of my wifeGill, the completion of the project would have been much more difficult Her support

sacri-in this, as sacri-in all our ventures, is lovsacri-ingly acknowledged

D.F WarneOctober 2004

This page intentionally left blank

Chapter 1

Introduction

In many countries the public perception of more traditional aspects of engineeringremains at best indifferent and at worst quite negative Electrical engineering is per-haps seen as mature, unchanging and offering little scope for imagination, with poorprospects for any future career There is a serious risk in many parts of Europe andNorth America that substantial areas of knowledge are being lost as large numbers

of key experts are retiring without the opportunity to teach and train the specialists

of the future And yet the technology continues to move on, and the understanding ofthe basic mechanisms of circuits, electromagnetics and dielectrics continues to be aschallenging intellectually as it has ever been There have even been very prominentwarnings of the dangers of neglecting the importance of electrical power systems andplant, and of underestimating the value of the skilled engineers necessary to supportthis infrastructure The major power failures of the past few years, in the Easternseaboard of the USA, in Auckland, in Italy, in London and in parts of Scandinavia havehighlighted how dependent a modern society is on a reliable source of electricalenergy

So, the need has never been stronger for a basic understanding of principles and

a fundamental appreciation of how the major classes of electrical equipment operate

In a handbook, it is not possible to set out a comprehensive treatment but the aim is toprovide a balanced overview, and perhaps to engender the interest to pursue areas inmore depth A more complete coverage of all the subjects addressed here can be found

in the Newnes Electrical Engineer’s Reference Book.

The structure of the handbook is, as before, based around three groups of chapters

as follows:

• fundamentals and general material

• the design and operation of the main classes of electrical equipment

• special technologies which apply to a range of equipment

The first group covers the fundamentals and principles which run through all aspects

of electrical power technology

The opening chapter deals with the fundamentals of circuit theory and electric andmagnetic fields, together with a brief coverage of energy conversion principles.This is followed by a review of the materials which are crucial to the design andoperation of electrical equipment These are grouped under the headings of magnetic,insulating and conducting materials In each of these areas, technology continues tomove ahead Further improvement in the performance of permanent magnets is one ofthe key drivers behind the increasing use of electrical actuators and drives in cars andthe miniaturization of whole ranges of domestic and commercial equipment; and thechallenges in understanding the behaviour of soft magnetic materials, especially underconditions of distorted supply waveforms, are gradually being overcome Developments

in insulating materials mean that increased reliability can be achieved, and operation

at much higher temperatures can be considered Under the heading of conductors, thereare continuing advances in superconductors, which are now able to operate at liquidnitrogen temperatures, and of course semiconductor developments continue to trans-form the way in which equipment can be controlled.

Finally, in this opening group there is a chapter on measurement and tion Modern equipment and processes rely increasingly on sensors and instrumentationfor control and for condition assessment and diagnostics, so in this chapter there aresome changes in coverage, the emphasis now being on sensors and the way in whichsignals from sensors may be processed

instrumenta-The next group of eight chapters form the core of the book and they cover the tial groups of electrical equipment found today in commerce and industry

essen-The opening five chapters here cover generators, transformers, switchgear, fuses

and wires and cables These are the main technologies for the production and handling

of electrical power, from generation, transmission and distribution at high voltages andhigh powers down to the voltages found in factories, commercial premises and house-holds Exciting developments include the advances made in high-voltage switchgearusing SF6as an insulating and arc-extinguishing medium, the extension of polymerinsulation into high-voltage cables and the continuing compaction of miniature andmoulded-case circuit breakers A new section in the wires and cables chapter addressesthe growing technology of optical fibre cables Although the main use for this tech-nology is in telecommunications, which is outside the scope of the book, a chapter onwires and cables would not be complete without it and optical fibres have in any casefound a growing number of applications in electrical engineering

The following four chapters describe different groups of equipment which use or

store electrical energy Probably the most important here is electric motors and drives,

since these use almost two-thirds of all electrical energy generated Power electronics

is of growing importance not only in the conversion and conditioning of power, mostnotably in variable-speed motor drives, but also in static power supplies such as emer-gency standby, and in high-voltage applications in power systems The range of bat-teries now available for a variety of applications is extensive and a chapter is set asidefor this, including the techniques for battery charging and the emerging and relatedtechnology of fuel cells If fuel cells fulfil their promise and start to play a greater part

in the generation of electricity in the future then we can expect to see this area grow,perhaps influencing the generator and power systems chapters in future editions of thehandbook

The final group of four chapters covers subjects which embrace a range of nologies and equipment There is a chapter on power systems which describes the way

tech-in which generators, switchgear, transformers, ltech-ines and cables are connected and trolled to transmit and distribute our electrical energy The privatization of electricitysupply in countries across the world continues to bring great changes in the way thepower systems are operated, and these are touched upon here, as is the growing impact

con-of distributed generation The second chapter in this group covers the connected jects of electromagnetic compatibility and power quality With the growing number ofelectronically controlled equipment in use today, it is imperative that precautions aretaken to prevent interference and it is also important to understand the issues which areraised by the resulting disturbances in power supply, such as harmonics, unbalance, dipsand sags The next chapter describes the certification and use of equipment for opera-tion in hazardous and explosive environments; this covers a wide range of equipmentand several different classes of protection And finally, but perhaps most importantly,

sub-a chsub-apter on hesub-alth sub-and ssub-afety hsub-as been sub-added for this edition; this issue rightly pervsub-ades

most areas of the use of electrical power and this topic is a valuable addition to thehandbook.

In most chapters there is a closing section on standards, which influence all aspects

of design, specification, procurement and operation of the equipment At the highestlevel are the recommendations published by the International ElectrotechnicalCommission (IEC), which are performance standards, but they are not mandatoryunless referred to in a contract Regional standards in Europe are Euro-Norms (ENs)

or Harmonized Documents (HDs) published by the European Committee forElectrotechnical Standardization (CENELEC) CENELEC standards are part ofEuropean law and ENs must be transposed into national standards and no nationalstandard may conflict with an HD Many ENs and HDs are based on IEC recommen-dations, but some have been specifically prepared to match European legislationrequirements such as EU Directives National standards in the UK are published by the British Standards Institution (BSI) BSI standards are generally identical to IEC

or CENELEC standards, but some of them address issues not covered by IEC or CENELEC In North America, the main regional standards are published by theAmerican National Standards Institute (ANSI) in conjunction with the Institute ofElectrical and Electronics Engineers (IEEE) The ANSI/IEEE standards are generallydifferent from IEC recommendations, but the two are becoming closer as a result ofinternational harmonization following GATT treaties on international trade Coverage

of all these groups is attempted in the tables listing the key standards

This page intentionally left blank

Chapter 2

Principles of electrical engineering

Dr D.W Shimmin

University of Liverpool

2.1 Nomenclature and units

This book uses notation in accordance with the current British and InternationalStandards Units for engineering quantities are printed in upright roman characters, with

a space between the numerical value and the unit, but no space between the decimalprefix and the unit, e.g 275 kV Compound units have a space, dot or solidus betweenthe unit elements as appropriate, e.g 1.5 N m, 9.81 m.s−2, or 300 m/s Variable symbols

are printed in italic typeface, e.g V For ac quantities, the instantaneous value is printed

in lower case italic, peak value in lower case italic with caret (^), and rms value in upper

case, e.g i, î, I Symbols for the important electrical quantities with their units are given

in Table 2.1, and decimal prefix symbols are shown in Table 2.2 Graphical symbols forbasic electrical engineering components are shown in Fig 2.1

2.2 Electromagnetic fields

2.2.1 Electric fields

Any object can take an electric or electrostatic charge When the object is charged

positively, it has a deficit of electrons, and when charged negatively it has an excess ofelectrons The electron has the smallest known charge, –1.602 × 10−19C

Charged objects produce an electric field The electric field strength E (V/m) at a distance d (m) from an isolated point charge Q (C) in air or a vacuum is given by

(2.1)

where the permittivity of free spaceεο=8.854 ×10−12 F/m If the charge is inside an

insulating material with relative permittivityεr, the electric field strength becomes

(2.2)

Any charged object or particle experiences a force when inside an electric field The force

F (N) experienced by a charge Q (C) in an electric field strength E (V/m) is given by

6 Principles of electrical engineering

Table 2.1 Symbols for standard quantities and units

p Number of machine pole pairs

angular frequency

Electric field strength is a vector quantity The direction of the force on one charge due

to the electric field of another is repulsive or attractive Charges with the same ity repel; charges with opposite polarities attract

polar-Work must be done to move charges of the same polarity together The effort

required is described by a voltage or electrostatic potential The voltage at a point

is defined as the work required to move a unit charge from infinity or from earth (It is normally assumed that the earth is at zero potential.) Positively charged objectshave a positive potential relative to the earth

If a positively charged object is held some distance above the ground, then the age at points between the earth and the object rises with distance from the ground, so

volt-that there is a potential gradient between the earth and the charged object There is also

an electric field pointing away from the object, towards the ground The electric fieldstrength is equal to the potential gradient, and opposite in direction

(2.4)

2.2.2 Electric currents

Electric charges are static if they are separated by an insulator If charges are separated

by a conductor, they can move giving an electric current A current of one ampereflows if one coulomb passes along the conductor every second

(2.5)

A given current flowing through a thin wire represents a greater density of current than

if it flowed through a thicker wire The current density J (A/m2) in a wire with cross

section area A (m2) carrying a current I (A) is given by

(2.6)

For wires made from most conducting materials, the current flowing through the wire

is directly related to the difference in potential between the ends of the wire

J I A

=

I Q t

=

E= −ddV x

Table 2.2 Standard decimal prefix symbols

8 Principles of electrical engineering

Fixed

Fixed

Variable

Variable Polarized

X = 0

+

Fig 2.1 Standard graphical symbols

Ohm’s law gives this relationship between the potential difference V (V) and the

current I (A) as

(2.7)

where R (Ω) is the resistance, and G (S) = 1/R is the conductance (Fig 2.2) For a wire

of length l and cross section area A, these quantities depend on the resistivity ρ(Ω.m)

and conductivity σ(S/m) of the material

(2.8)

For materials normally described as conductors ρ is small, while for insulators ρ is

large Semiconductors have resistivity in between these extremes, and their properties

are usually very dependent on purity and temperature

In metal conductors, the resistivity increases with temperature approximately linearly:

(2.9)

for a conductor with resistance RTo at reference temperature To This is explained inmore detail in section 3.4.1

Charges can be stored on conducting objects if the charge is prevented from

mov-ing by an insulator The potential of the charged conductor depends on the capacitance

C (F) of the metal/insulator object, which is a function of its geometry The charge is

related to the potential by

(2.10)

A simple parallel-plate capacitor, with plate area A, insulator thickness d and relative

permittivity εrhas capacitance

(2.11)

2.2.3 Magnetic fields

A flow of current through a wire produces a magnetic field in a circular path aroundthe wire For a current flowing forwards, the magnetic field follows a clockwise path, as given by the right-hand corkscrew rule (Fig 2.3) The magnetic field strength

Fig 2.2 Ohm’s law

H (A m–1) is a vector quantity whose magnitude at a distance d from a current I is

given by

(2.12)

For a more complicated geometry, Ampère’s law relates the number of turns N in

a coil, each carrying a current I, to the magnetic field strength H and the distance around the lines of magnetic field l.

sur-by the presence of ferromagnetic materials, such as iron or steel The magnetic field

produces a magnetic flux density B (T) in air or vacuum

(2.14)

where the permeability of free space µo = 4π ×10–7H/m In a ferromagnetic material

with relative permeability µr

(2.15)

A second conductor of length l carrying an electric current I will experience a force F

in a magnetic flux density B

(2.16)The force is at right angles to both the wire and the magnetic field Its direction is

given by Fleming’s left-hand rule (Fig 2.4) If the magnetic field is not itself dicular to the wire, then the force is reduced; only the component of B at right angles

perpen-to the wire should be used

F=BIl

B=µ µo rH

B=µoH

Hl NI F

A magnetic fluxΦ(Wb) corresponding to the flux density in a given cross-section

(2.19)

In ideal materials, the flux density B is directly proportional to the magnetic field strength H In ferromagnetic materials the relation between B and H is non-linear

(Fig 2.5(a)), and also depends on the previous magnetic history of the sample The

magnetization or hysteresis or BH loop of the material is followed as the applied

mag-netic field is changed (Fig 2.5(b)) Energy is dissipated as heat in the material as the

operating point is forced around the loop, giving hysteresis loss in the material These

concepts are developed further in section 3.2

2.2.4 Electromagnetism

Any change in the magnetic field near a wire generates a voltage in the wire by

elec-tromagnetic induction The changing field can be caused by moving the wire in the

magnetic field For a length l of wire moving sideways at speed ν(m/s) across a

mag-netic flux density B, the induced voltage or electromotive force (emf) is given by

(2.20)

The direction of the induced voltage is given by Fleming’s right-hand rule (Fig 2.6).

An emf can also be produced by keeping the wire stationary and changing the

Field (Forefinger)

resulting Motion (thuMb)

Fig 2.4 Fleming’s left-hand rule

magnetic field In either case the induced voltage can be found using Faraday’s law If a

magnetic flux Φpasses through a coil of N turns, the magnetic flux linkageψ(Wb t) is

(2.21)Faraday’s law says that the induced emf is given by

(2.22)

The direction of the induced emf is given by Lenz’s law, which says that the induced

voltage is in the direction such that, if the voltage caused a current to flow in the wire,the magnetic field produced by this current would oppose the change in ψ The nega-

tive sign indicates the opposing nature of the emf

V t

Motion (thuMb)

Field (Forefinge

r)

Fig 2.6 Fleming’s right-hand rule

A current flowing in a simple coil produces a magnetic field Any change in the

cur-rent will change the magnetic field, which will in turn induce a back-emf in the coil The self-inductance or just inductance L (H) of the coil relates the induced voltage

to the rate of change of current

is described in detail in section 6.1

Power in a resistor is converted directly into heat

When two or more resistors are connected in series, they carry the same current but

their voltages must be added together (Fig 2.7)

(2.28)

As a result, the total resistance is given by

(2.29)

When two or more resistors are connected in parallel, they have the same voltage but

their currents must be added together (Fig 2.8)

N N

1 2 2 1

=

V V

N N

1 2 1 2

=

V2=MddI t1

V L I t

= d

d

(2.30)The total resistance is given by

(2.31)

A complicated circuit is made of several components of branches connected together

at nodes forming one or more complete circuits, loops or meshes At each node,

Kirchhoff ’s current law (Fig 2.9(a)) says that the total current flowing into the node

must be balanced by the total current flowing out of the node In each loop, the sum of

all the voltages taken in order around the loop must add to zero, by Kirchhoff’s voltage

law (Fig 2.9(b)) Neither voltage nor current can be lost in a circuit.

DC circuits are made of resistors and voltage or current sources A circuit with onlytwo connections to the outside world may be internally complicated However, to theoutside world it will behave as if it contains some resistance and possibly a source of

voltage or current The Thévenin equivalent circuit consists of a voltage source and a resistor (Fig 2.10 (a)), while the Norton equivalent circuit consists of a current source

and a resistor (Fig 2.10(b)) The resistor equals the internal resistance of the circuit,the The´venin voltage source equals the open-circuit voltage, and the Norton currentsource is equal to the short-circuit current

Many circuits contain more than one source of voltage or current The current ing in each branch, or the voltage at each node, can be found by considering each

flow-source separately and adding the results During this calculation by superposition, all

sources except the one being studied must be disabled: voltage sources are circuited and current sources are open-circuited In Fig 2.11, each of the loop currents

short-I1and I2can be found by considering each voltage source separately and adding the

results, so that I1=I1a+I1band I2=I2a+I2b

Fig 2.9 Kirchhoff’s laws

+

R

G

(a) Thévenin equivalent circuit (b) Norton equivalent circuit

Fig 2.10 Equivalent circuits

16 Principles of electrical engineering

2.3.2 AC circuits

AC is supplied through a power system from large ac generators or alternators, by

a local alternator, or by an electronic synthesis AC supplies are normally sinusoidal,

so that at any instant the voltage is given by

(2.32)

Vmaxis the peak voltage or amplitude, ωis the angular frequency (rad s−1) and φthe

phase angle (rad) The angular frequency is related to the ordinary frequency f (Hz) by

(2.33)

and the period is 1/f The peak-to-peak or pk–pk voltage is 2Vmax, and the root mean

square or rms voltage is It is conventional for the symbols V and I in ac circuits

to refer to the rms values, unless indicated otherwise AC voltages and currents are

shown diagrammatically on a phasor diagram (Fig 2.12).

It is convenient to represent ac voltages using complex numbers A sinusoidal voltagecan be written

The current in an inductor lags the voltage across it by 90°(π/2 rad) (Fig 2.14)

The ac resistance or reactance X of an inductor increases with frequency

c= 1ω

(2.42)The direction of the phase shift in inductors and capacitors is easily remembered bythe mnemonic CIVIL (i.e C-IV, VI-L) Imperfect inductors and capacitors have someinherent resistance, and the phase lead or lag is less than 90° The difference between

the ideal phase angle and the actual angle is called the loss angleδ For a component

of reactance X having a series resistance R

An important filter is the resonant circuit A series combination of inductor and

capacitor has zero impedance (infinite admittance) at its resonant frequency

(2.45)

A parallel combination of inductor and capacitor has infinite impedance (zero tance) at the same frequency

admit-In practice a circuit will have some resistance (Fig 2.16), which makes the resonant

circuit imperfect The quality factor Q of a series resonant circuit with series resistance