Information Circular 9258

Mine Power Systems

By Lloyd A. Morley

UNITED STATES DEPARTMENT OF THE INTERIOR Manuel Lujan, Jr., Secretary

BUREAU OF MINES T S Ary, Director

Library of Congress Cataloging in Publication Data:

Morley, Lloyd A. Mine power systems.

(Information circular: 9258)

Includes bibliographies.

Includes index.

Supt. of Docs. no.: 128.27:9258.

1. Electricity in mining. I. Title. 11. Series: Informalion circular (United States. Bureau of Mines); 9258.

TN295.U4 [TN343] 622 s [622'.48] 87-600213

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For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, DC 20402

The author is grateful to the several individuals and companies that supplied noncopyrighted material for use in this publication. This material is noted by the vari- ous courtesies given throughout the text. Its incorporation does not constitute an en- dorsement by the author, The Pennsylvania State University, the University of Ala- bama, or the Bureau of Mines.

Reference to specific products, equipment, or manufacturers does not imply endorsement by the Bureau of Mines.

The application of electricity to the mining industry is a distinctive area of both mining engineering and electrical engineering. The diEcult environment, the dynamic power loads, the cyclic and mobile operation and stringent safety requirements that characterize mining, all place unique demands on the mine power system. No other industry makes such extensive use of portable extensible equipment or has such com- plex grounding problems. Mine power systems can range from relatively simple in- stallations for small surface mines to complex underground systems where the harsh environment of dust, humidity, and cramped spaces stretches the ingenuity and crea- tivity of the engineer to provide reliable service.

At the present time there is no up-to-date engineering text available that deals specifically with mine power systems. This has created extensive difficulties for edu- cators, industry engineers, and regulatory agency personnel. The need for a suitable reference for students in mining engineering provided the main impetus for this book, since the technician-level material that was in existence proved unsuitable for teach- ing young engineers who have little practical experience.

The objective in preparing this manuscript was to assemble a single engineering reference on mine electrical power systems that is as comprehensive as possible. Ear- lier drafts of this material have been used successfully to instruct university students in courses ranging from basic electrical engineering through power-system design. It is felt, however, that the usefulness of this material extends beyond that of a student text. While not intended to replace other electrical or mining references, this publica- tion is also an indexed, reasonably comprehensive reference handbook for industry engineers and training personnel, and a source of material for electrical engineers who wish to expand their education into industrial power-system applications. Obviously, there will be some omissions; to include all aspects of mine electrical systems in one volume would approach an impossibility, but an attempt has been made to collect together the most significant information, thereby providing the tools needed to con- tinue a knowledgeable involvement in mine electricity.

This reference work is divided into three general content areas. Chapters 1 through 5 contain information considered elementary, chapters 6 through 11 deal with power- system components, and chapters 12 through 17 contain specifics on mine power sys- tems. A person familiar with electrical principals can use the earlier chapters as re- view material, but all chapters contain material relevant to mining and discuss the necessary combinations of equipment and components that should be contained in the mine power system. Emphasis throughout is placed on coal mining systems, although much of the material pertains to all mining operations. Both surface and underground power systems are discussed, the latter in more detail since these are the more com- plex systems and encounter the most problems.

This publication is a thoroughly upgraded and extensively revised edition of Bureau of Mines Open File Reports 178(1)-82 and 178(2)-82, prepared under Bureau contract 50155009 by The Pennsylvania State University. It contains new chapters, new illustra- tions, and example problems that were not included in the original report.

The assembly of this material has been a major undertaking. Many industry, academic, and Government agency personnel helped to review and critique practically every stage of draft preparation. The original report version was made available to students taking the mine power-systems courses a t The Pennsylvania State Univer- sity, and their involvement was critical input to manuscript -- preparation. --

The author is grateful to all the companies and individuals who contributed or cooperated in this effort; so much information could not have been gathered without their help. A special thanks is owed to the late Robert Stefanko. He originally perceived the need for this text and provided guidance and encouragement throughout the proj- ect that produced the original report version. Others deserving special mention are A. M. Christman, R. H. King, J. A. Kohler, G. W. Luxbacher, T. Novak, J. N. Tomlinson, F. C. Trutt and D. J. Tylavsky. Each contributed directly to the text while on the fac- ulty or staff a t The Pennsylvania State University; acknowledgements for their con- tributions are made in the individual chapters.

CONTENTS

Page Page

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Part l: Fundamentals

Chapter l.--Electrical power in mining . . . . . . Mine electrical history . . . . . . . . . . . . . . . . .

Underground mine history . . . . . . . . . . . . Surface mine history . . . . . . . . . . . . . . . .

Mine power equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Substations

Switchhouses . . . . . . . . . . . . . . . . . . . . . . Power centers . . . . . . . . . . . . . . . . . . . . . Distribution equipment . . . . . . . . . . . . . .

Basic distribution arrangements . . . . . . . . . . Radial system . . . . . . . . . . . . . . . . . . . . . Primary-selective system . . . . . . . . . . . . . Primary-loop system . . . . . . . . . . . . . . . . Secondary-selective system . . . . . . . . . . . . Secondary-spot network . . . . . . . . . . . . . .

Utility company power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surface mining

Power systems in surface mines . . . . . . . . . . Main substations and subtransmission . . . Surface mine distribution . . . . . . . . . . . . .

Underground coal mining . . . . . . . . . . . . . . Room-and-pillar mining . . . . . . . . . . . . . . Longwall mining . . . . . . . . . . . . . . . . . . .

Power systems in underground mines . . . . . . Regulations . . . . . . . . . . . . . . . . . . . . . . . Underground mine distribution . . . . . . . .

Surface facility power requirements . . . . . . . Basic design considerations . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 2.--Electrical fundamentals I . . . . . . . Basic electrical phenomena . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . Coulomb's law Voltage and current . . . . . . . . . . . . . . . .

System of units . . . . . . . . . . . . . . . . . . . . . . Experimental laws and paramcters . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . Ohm's law Kirchhoff's voltage law . . . . . . . . . . . . . . KirchofPs current law . . . . . . . . . . . . . . . Series circuits . . . . . . . . . . . . . . . . . . . . . Parallel circuits . . . . . . . . . . . . . . . . . . . . The magnctic field . . . . . . . . . . . . . . . . . Inductance . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . Capacitance Electric field . . . . . . . . . . . . . . . . . . . . . .

Instantaneous power . . . . . . . . . . . . . . . . Idealization and concentration . . . . . . . . .

. . . . . . . . . . . . . . . . . Direct current circuits Direct current and circuit elements ..... Series and parallel resistance ..........

. . . . . . . . . . . . Wye-delta transformations Circuit and loop equations . . . . . . . . . . . . Node equations . . . . . . . . . . . . . . . . . . . . Network theorems . . . . . . . . . . . . . . . . . .

Time-varying voltages and currents . . . . . . . . . . . . . . . . . . . . . Steady alternating current

. . . . . . . . . . . Effective alternating current Phasors . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . Phasors and complex quantities Impedance transforms . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . Steady-state analysis

. . . . . . . Chapter 3.-Electrical fundamentals I1 . . . . . . . . . Average power and power factor

. . . . . . . . . . . Complex and apparent power Resonance . . . . . . . . . . . . . . . . . . . . . . . . .

Series resonance . . . . . . . . . . . . . . . . . . . Parallel resonance . . . . . . . . . . . . . . . . . .

Transformers . . . . . . . . . . . . . . . . . . . . . . . Ideal transformer . . . . . . . . . . . . . . . . . . . . Actual transformers . . . . . . . . . . . . . . . . . .

Conductor loss . . . . . . . . . . . . . . . . . . . . Leakage reactance . . . . . . . . . . . . . . . . . .

. . . . . . . . Core losses and exciting current

. . . . . . . . Power-transformer construction Transformer models . . . . . . . . . . . . . . . . Determination of transformer

. . . . . . . . . . . . . . . . . . . . . parameters . . . Transformer efficiency and regulation

Autotransformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multivoltage transformers

. . . . . . . Current and potential transformers

Chapter 4.-Power.systcm concepts .... Basic power circuit . . . . . . . . . . . . . . Three-phase circuits . . . . . . . . . . . . . Balanced three-phase circuits . . . . . .

Three-phase system voltages . . . . . Load connections . . . . . . . . . . . . . Line and phase currents . . . . . . . . Equivalent delta and wye loads . . . Three-phase power . . . . . . . . . . . .

Three-phase transformers . . . . . . . . . Balanced three-phase circuit analysis .

One-line and three-line diagrams . .

Page Page

. . . . . . . . Circuits containing transformers Per-unit system . . . . . . . . . . . . . . . . . . . . . .

Transformer impcdancc . . . . . . . . . . . . . . . . . . . . . . . . . Three-winding transformers

. . . . . . Per-unit method in system analysis . . . . . . . . . Unbalanced three-phase circuits

Fault types . . . . . . . . . . . . . . . . . . . . . . . Fault analysis . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . Symmetrical componcnts Sequence components . . . . . . . . . . . . . . .

. . . . . . . . Sequence-quantity combinations . . . . Symmetrical-component relationship

Symmetrical-component impedance . . . . . .................. Fault calculations

. . . . . . . . . . . . . . . . . . . Power terminology References . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 5.-Basic solid-state devices and instrumentation . . . . . . . . . . . . . . . . . . . . . . 104 Semiconductors . . . . . . . . . . . . . . . . . . . . . . 104 Diodes and rectifiers . . . . . . . . . . . . . . . . . . 104

Diodc equations . . . . . . . . . . . . . . . . . . . 105 Rectifier circuits . . . . . . . . . . . . . . . . . . . 105 Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Overloads . . . . . . . . . . . . . . . . . . . . . . . . 107

Three-phase rectification . . . . . . . . . . . . . . . 107 Rectifier circuits . . . . . . . . . . . . . . . . . . . 108 Parallel rectifier operation . . . . . . . . . . . . 109

Transistors . . . . . . . . . . . . . . . . . . . . . . . . . 109 Transistor operation . . . . . . . . . . . . . . . . 109 Bipolar-transistor amplifiers . . . . . . . . . . . 110 Field-effect transistors . . . . . . . . . . . . . . . 112

Silicon-controllcd rcctifiers . . . . . . . . . . . . . 113 Integrated circuits . . . . . . . . . . . . . . . . . . . . 114 Basic instrumentation . . . . . . . . . . . . . . . . . 114 Basic meter movements . . . . . . . . . . . . . . . 115

Meter-movement applications . . . . . . . . . 116 Wattmeters . . . . . . . . . . . . . . . . . . . . . . . 117 Varmeters . . . . . . . . . . . . . . . . . . . . . . . . 118 Power-factor meters . . . . . . . . . . . . . . . . 118

Power-system instrumentation . . . . . . . . . . . 118 Instrument transformers . . . . . . . . . . . . . 118 Single-phase connections . . . . . . . . . . . . . 119 Three-phase connections . . . . . . . . . . . . . 120

Special instruments . . . . . . . . . . . . . . . . . . . 122 Watthour meters . . . . . . . . . . . . . . . . . . . 122 Demand meters . . . . . . . . . . . . . . . . . . . 122 Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Megohmmeters . . . . . . . . . . . . . . . . . . . . 123 Phase-sequence indicators . . . . . . . . . . . . 124

Recording instruments . . . . . . . . . . . . . . . . 124 Electronic instruments . . . . . . . . . . . . . . . . 125

Electronic meters . . . . . . . . . . . . . . . . . . 125 . . . . . . . . . . . . . . . . . . . . . Oscilloswpes 125 .................... Tape recorders 126

Transducers . . . . . . . . . . . . . . . . . . . . . . 126 ................ Instrument installations 127

Part 11: Power-System Components

Chapter 6.--Motors and motor control ...... 129 Alternating current generation . . . . . . . . . . . 129

Principle of generator operation . . . . . . . . 129 . . . . . . . . . . . . . . Generator construction 129

Three-phase generation . . . . . . . . . . . . . . 131 Direct current generators .............. 131 Motor basics . . . . . . . . . . . . . . . . . . . . . . . . 133

Torque . . . . . . . . . . . . . . . . . . . . . . . . . . 133 . . . . . . . . . . . . Speed-torque relationships 133

. . . . . . . . . . . . . . . . . . . . Standardization 134 Motor type . . . . . . . . . . . . . . . . . . . . . . . 135

Three-phase squirrel-cage induction motors . . . . . . . . . . . . . . . . . . . . . . . . . . 136

. . . . . . . . . Elementary three-phase motor 136 . . . . . . . . . . . . . . . . . Motor conslruction 138

Motor behavior . . . . . . . . . . . . . . . . . . . . 138 Insulation . . . . . . . . . . . . . . . . . . . . . . . . 139

. . . . . . . . . . . . . . . Design characteristics 139 . . . . . . . . . . . . . Induction-motor starting 141

. . . . . . . . . . Wound-rotor induction motors 142 Three-phase synchronous motors . . . . . . . . . 143

........... Synchronous-motor starting 144 . . . . . . . . . . . . Synchronous-motor torque 145

Generated voltage . . . . . . . . . . . . . . . . . . 146 Power factor . . . . . . . . . . . . . . . . . . . . . . 146 Applications . . . . . . . . . . . . . . . . . . . . . . 147

Direct current motors . . . . . . . . . . . . . . . . . 147 Elementary motor . . . . . . . . . . . . . . . . . . 147

. . . . . . . . . . . . Actual motor construction 148 Torque . . . . . . . . . . . . . . . . . . . . . . . . . . 148

.... Motor connections and performance 148 ............... Ward-Leonard system 152

Mine motors . . . . . . . . . . . . . . . . . . . . . . . . 153 Applications . . . . . . . . . . . . . . . . . . . . . . 153

........... Actual equipment operation 153 Single-phase motors . . . . . . . . . . . . . . . . . . 156

. . . . . . . . . . . . . . . . Rotating stator lield 156 . . . . . . . . . . . . . . . . . Split-phase starting 157

. . . . . . . . . . . . . . . Capacitor-start motors 157 References . . . . . . . . . . . . . . . . . . . . . . . . . 158

Chapter 7..-Grounding . . . . . . . . . . . . . . . . . . 159 Grounding systems . . . . . . . . . . . . . . . . . . . 160 Ungrounded neutral . . . . . . . . . . . . . . . . . . 160

............... Solidly grounded neutral ....... Low-resistance grounded neutral

High-resistance grounded neutral . . . . . . . Electric shock . . . . . . . . . . . . . . . . . . . . . . . Characteristics of mine grounding systems . .

Ground beds . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grounding in underground mining

........... Grounding in surface mines ............... Ground-bed construction

. . . . . . . . . . . . . . . . . . Ground resistance . . . . . . . Electrode c o ~ g w a t i o n formulas

. . . . . . . . . . . . Two-layer earth structures ................. Soil-heating effects

. . . . . . . . . Control of potential gradients . . . . . . Ground-bed resistance measurement

Measurement method . . . . . . . . . . . . . . . Ground test instruments . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . Ground-bed resistivity Factors affecting resistivity . . . . . . . . . . . . Resistivity measurements . . . . . . . . . . . . . Effect of chemical treatment of soils . . . .

. ................ Ground-bed corrosion General ground-bed guidelines . . . . . . . . . . Grounding equipment . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . Grounding resistor Grounding transformers . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . Summary References . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 8.--Distribution . . . . . . . . . . . . . . . . . Nature of cable distribution . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . Cable components . . . . . . . . . . . . . . . . . . . . . . . Conductors

Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cable jacket

.................... Cable shielding Cable types . . . . . . . . . . . . . . . . . . . . . . . . . Cable terminations . . . . . . . . . . . . . . . . . . . Cable couplers . . . . . . . . . . . . . . . . . . . . . .

Coupler contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coupler insulation

. . . . . . . . . . . . . . . . . . . Coupler housing High-voltage couplers . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . Low-voltage couplers . . . . . . . . . . . . . . . . . . . . . . Cable selection

Cable length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conductor selection

Cable installation and handling .......... . . . . . . . . . . . . . . . . . . . . Borehole cables

Feeder cable installation . . . . . . . . . . . . . Recommended handling practices . . . . . .

Cable failures and repairs . . . . . . . . . . . . . .

Cable testing . . . . . . . . . . . . . . . . . . . . . . . ................... Failure location

Splicing . . . . . . . . . . . . . . . . . . . . . . . . . . Trolley systems . . . . . . . . . . . . . . . . . . . . . .

Trolley wire . . . . . . . . . . . . . . . . . . . . . . Trolley feeder . . . . . . . . . . . . . . . . . . . . .

. . . . . Supports. lubrications. and turnouts . . . . . . . . . . . . . . . . . . . Rails and bonds

Overhead lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Overhead-line design

Overhead-line electrocutions . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 9.-Protective equipment and relaying . . . . . . . . . . . . . . . . . . . . . . . . . . . Switching apparatus . . . . . . . . . . . . . . . . . .

............ Arcs and circuit interruption Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuit breakers ..................... Circuit breakers for low and medium

voltage . . . . . . . . . . . . . . . . . . . . . . . . . . Molded case circuit breakers . . . . . . . . . .

. . . . . . . . . . . . . . . Power circuit breakers High-voltage circuit breakers . . . . . . . . . . . .

Typical ratings . . . . . . . . . . . . . . . . . . . . . Oil circuit breakers . . . . . . . . . . . . . . . . . Minimum-oil circuit breakers . . . . . . . . . . Vacuum circuit breakers . . . . . . . . . . . . .

Fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Low-voltage fuses . . . . . . . . . . . . . . . . . . . .

Non-time-delay fuses . . . . . . . . . . . . . . . . Time-delay fuses . . . . . . . . . . . . . . . . . . . Dual-element fuse . . . . . . . . . . . . . . . . . . Current-limiting fuses . . . . . . . . . . . . . . . Standard fuses . . . . . . . . . . . . . . . . . . . . . Nonstandard fuses . . . . . . . . . . . . . . . . . .

High-voltage fuses . . . . . . . . . . . . . . . . . . . . Expulsion types . . . . . . . . . . . . . . . . . . . . Current-limiting high-voltage fuses . . . . . . Load-break switches . . . . . . . . . . . . . . . .

Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relay terminology and types . . . . . . . . . . Thermal relays . . . . . . . . . . . . . . . . . . . . Electromagnetic-attraction relays . . . . . . . Electromagnetic-induction relays .......

Basic relay connections . . . . . . . . . . . . . . . . Alternating current direct relaying ...... Alternating current potential relaying . . . . Alternating current differential relaying . . Direct current connections . . . . . . . . . . . .

Kinds of protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control wiring

Page

206 207 207 211 211 211 211 215 216 217 218 222

224 224 225 226 226

227 228 232 232 232 232 233 234 235 235 236 236 236 236 236 237 237 237 238 239 240 240 240 241 242 244 244 246 247 247 248 248

Page Page

Phase protection . . . . . . . . . . . . . . . . . . . Ground overcurrent . . . . . . . . . . . . . . . . . Ground-check monitoring . . . . . . . . . . . .

. . . . . . . . . Advantages and disadvantages Arrangements for mining . . . . . . . . . . . . . .

Zones of protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coordination

. . . . . . . . . . . . . . Ground-fault protection Overloads and short circuits . . . . . . . . . . . Surface mines . . . . . . . . . . . . . . . . . . . . . Underground mines .................

. . . . . . . . . . . . . . . . . . . . . . . . . References

. . . . . . . Chapter 10.Suing protective devices . . . . . . . . . . . . . . . . . . . . . . . Fault current

Fault-current sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Source equivalent circuit

Fault calculations for three-phase systems . . Short-circuit calculation procedures ..... Three-phase calculation example . . . . . . . Computer fault analysis . . . . . . . . . . . . . . Ground-fault current calculations . . . . . . .

Direct current system faults . . . . . . . . . . . . . Device settings . . . . . . . . . . . . . . . . . . . . . . Relay pickup settings . . . . . . . . . . . . . . . . .

Short-circuit protection . . . . . . . . . . . . . . Overload protection . . . . . . . . . . . . . . . . . Ground-fault protection . . . . . . . . . . . . . .

Current transformer matching . . . . . . . . . . . Current transformer accuracy ......... Accuracy calculations . . . . . . . . . . . . . . . .

Low-voltage circuit breaker trips . . . . . . . . . Overload protection . . . . . . . . . . . . . . . . . Short-circuit protection . . . . . . . . . . . . . . Low-voltage power circuit breakers . . . . .

Fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coordination

. . . . . . . . . . . . . . . . . . . . . . . . . References

Chapter ll.--Transients and overvoltages . . . . . Transient sources . . . . . . . . . . . . . . . . . . . . Lightning phenomena . . . . . . . . . . . . . . . . . Switching transients . . . . . . . . . . . . . . . . . . .

............... Capacitance switching . . . . . . . . . . . . . . . . . . Current chopping

Prestrike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Direct current interruption

General switching transients .......... Other transient phenomena . . . . . . . . . . . . . Traveling waves . . . . . . . . . . . . . . . . . . . . . Electromagnetic phenomena . . . . . . . . . . . . Transient-induced failures . . . . . . . . . . . . . .

Winding response . . . . . . . . . . . . . . . . . . . . . . . . . . Coupling through transformers

Transient protection . . . . . . . . . . . . . . . . . . Surge arresters ....................

. . . . . . . . . . . . Surge arrester applications Capacitors and system capacitance . . . . . .

. . . . . . . . . . . . Other suppression devices Faraday shields . . . . . . . . . . . . . . . . . . . .

................ Circuit arrangements . . . . . . . . . . . Protection of overhead lines

Impulse performance of ground beds .... References . . . . . . . . . . . . . . . . . . . . . . . . .

Part 111: Mine Power Systems

.......... Chapter 12.-Mine power centers . . . . . . . . . . . . . . . Equipment specifications

Mine power centers . . . . . . . . . . . . . . . . . . High-voltage cable coupler . . . . . . . . . . . . . Interlock switches . . . . . . . . . . . . . . . . . . . . Disconnect switch . . . . . . . . . . . . . . . . . . . . High-voltage fuses .................... Surge arrestors . . . . . . . . . . . . . . . . . . . . . . Transformers . . . . . . . . . . . . . . . . . . . . . . .

SpeciF~cations . . . . . . . . . . . . . . . . . . . . . Transformer construction ............. Faraday shields . . . . . . . . . . . . . . . . . . . .

Grounding resistor . . . . . . . . . . . . . . . . . . . Busway . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . Outgoing circuit breaker Ground-fault protection . . . . . . . . . . . . . . .

.............. Single-phase transformers Metering circuits . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . Outgoing cable couplers . . . . . . . . . . . . . . . . Ground-check monitors ................ Power-factor correction . . . . . . . . . . . . . . . Direct current utilization

Rectifier transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rectifier

Direct current ground-fault protection schemes . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . Direct current control circuitry ........ Direct current interrupting devices

References . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 13.Switchhouses and substations ... Switchhouses . . . . . . . . . . . . . . . . . . . . . . . Switchhouse internal components ......... Switchhouse protective relaying .......... Power circuit breakers . . . . . . . . . . . . . . . . Switchhouse control circuits . . . . . . . . . . . . . Switchhouse design . . . . . . . . . . . . . . . . . . .

Page Page

Substations ......................... Basic substation arrangements . . . . . . . . . . .

Single-ended substations . . . . . . . . . . . . . Double-ended substations . . . . . . . . . . . .

Substation transformers . . . . . . . . . . . . . . . . Substation switching apparatus . . . . . . . . . .

........................ Reclosers Disconnect switches and fuses .........

Protective relaying in substations . . . . . . . . . Lightning and surge protection in

substations . . . . . . . . . . . . . . . . . . . . . . . .................. Substation grounding

Substation ground mat ............... . . . . . . . . . . . . . . Ground-fault protection

Additional mine substation loads . . . . . . . . . Portable substations . . . . . . . . . . . . . . . . . .

. . . . . . . Utility voltage as mine distribution Additional substation design

. . . . . . . . . . . . . . . . . . . . . considerations References . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 14.4olid-state control and relaying . . . . . . . . . . . . . . . . . . . . . . . . . Motor control

. . . . . . . . . . . . . . . . Simple motor control Control systems ....................

. . . . . Physical characteristics of thyristors Direct current applications . . . . . . . . . . . . .

. . . . . . . . . . Alternating current applications . . . . . . . . . . . . . . . Static protective relaying

Operation of simpwed solid-state and hybrid relays . . . . . . . . . . . . . . . . . . . . . .

Static and electromechanical relay ....................... comparison

Static relay mining applications . . . . . . . . . . Sensitive earth-leakage system . . . . . . . . . Phase-sensitive short-circuit protection . . .

Solid-state relays in the future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary

References . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter IS.--Batteries and battery charging . . . . . . Basic battery and battery-charging theory

Battery maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chargers

Charging stations . . . . . . . . . . . . . . . . . . . . Battery-box ventilation . . . . . . . . . . . . . . . .

1.1. Simple mine electrical system arrangement . 1.2. Simple radial distribution system . . . . . . . . 1.3. Power-center type of radial distribution . . .

332 Battery surface leakage and faults . . . . . . . . 375 . . . . . . . . . . . . . . . 332 Battery-charging hazards 377

. . . . . . . . . . . . . . . . . . . . . . . . . 333 References 381 Chapter 16.-Permissibility and hazard

.......................... reduction . . . . . . . . . . . . . . . . . . . . . . . . Terminology

. . . . . . . . . . . . . Hazard-reduction methods Explosion-proof enclosures .............

Explosion transmission .............. ... . . . . . . . . . . . . . . . . Enclosure joints

Enclosure mechanical strength and internal pressures . . . . . . . . . . . . . . . . . . . . . . .

Enclosure hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Permissible equipment

. . . . . . . . Permissible equipment schedule . . . Maintenance of permissible equipment

. . . . . . . . . . . . . . . . . . . . Coal dust hazards . . . . . . . . Classifications of dust locations

. . . . . . . . . . . . . . . Reducing dust hazards Hazardous locations in preparation

plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References

. . . . . . . . . . . . . . . . Chapter 17.-Maintenance . . . . . . . . . . . . . Mine maintenance program

. . . . . . . . . . . . . . . Economic justification Preventive maintenance program

. . . . . . . . . . . . . . . . . . implementation . . . . . Techniques of preventive maintenance

. . . . . . . . . Basic electrical measurements . . . . . . . . . . . . . Insulation measurements

. . . . . . . . . . . . . . . . . Megohmmeter tests . . . . . . . . . . . . . . Mechanical measurements

. . . . . . . . . . Continuous-monitoring systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corona 406

. . . . . . . . . . . . . . . . . . . Corona behavior 408

. . . . . . . . . . . . . . . . . . . Corona detection 409 . . . . Partial-discharge problems in mining 410

. . . . . . . . . . . . . . . . . . Intermachiue arcing 411 . . . . . . . . . . . Ground direct current offsets 412

. . . . . . . . . . . . . . . . . . . . . . . . . . Summary 413 . . . . . . . . . . . . . . . . . . . . . . . . . References 414

. . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography 415 . . . . . . Appendix.-Abbreviations and symbols 416

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index 420

ILLUSTRATIONS

Page

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary-selective distribution system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary-loop distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Secondary-selective system

.................................................... Secondary-spot network technique ........................................ Representative utility transmission and distribution

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Subtransmission for surface mine Radial strip mine distribution system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Secondary-selective distribution in strip mining Primary-loop design for strip mining .................................................. Radial distribution for strip mine with overhead poleline base line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radial distribution for strip mine with all-cable distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surface mine distribution system using two base lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Openpitpowersystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..................................................... Layout of underground coal mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plan view of retreating longwall

Subtransmission for underground mine ................................................. Radially distributed underground power system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Secondary-selective distribution in underground mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Utilization in continuous mining section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Power-system segment with longwall equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram of electrical-system segment for longwall Parallel-feed haulage system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Representative expanded radial distribution for preparation plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Representative secondary-selective distribution for preparation plant . . . . . . . . . . . . . . . . . . . . . . . . . . .

Circuit element illustrating voltage polarity and current flow direction . . . . . . . . . . . . . . . . . . . . . . . . . . Simpleseriescircuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ideal and actual voltage sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuit for example 2.1 ............................................................. Demonstration of Kirchhoffs current law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simple parallel circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ideal and actual current sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parallel circuit for example 2.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simple series circuit and equivalent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simpleparallelcircuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Series-parallel circuit for example 2.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Series-parallel circuit for example 2.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Magnetic flux in a straight conductor and in a long coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Demonstration of induced current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Two coils demonstrating mutual inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Long-coil inductance and inductor symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Toroidalcoil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Charge. voltage. and current relationships of capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electric lines of force between two parallel charged plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resistor used to demonstrate instantaneous power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simple example of idealization and concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modeling of load center. trailing cable. and shuttle car . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic elements of resistance. inductance. and capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sirnplilicalion of dc circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.25. Simple circuit reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Page

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cicuitforexample2.5

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuitforexample2.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Series-parallel conductances for example 2.7

Series-parallel circuit for example 2.8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Two-terminal and three-terminal networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

................................................... Wye and delta circuit configuration "T" and "nu circuit configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Commonbridgecircuit ..................................................... Circuit reduction of bridge circuit

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Partsofcircuit Circuit demonstrating two independent loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Two-loop circuit for example 2.11 Bridge circuit demonstrating loop analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-loop circuit for example 2.12 ................................................... Simple two-node circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-junction circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-junction circuit with grounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Voltage-source circuit demonstrating node analysis Circuit for examples 2.13, 2.15, and 2.16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuit for example 2.14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuit for demonstrating superposition theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuit in figure 2.44 with sources turned off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Demonstration of reciprocity theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Practical voltage-source model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Practical current-source model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Source transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . Circuit in figure 2.44 with current sources transformed to voltage sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thevenin'stheorem

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Norton'stheorem Comparison of Thevenin's and Norton's circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuit for example 2.17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Active circuit for example 2.18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuits illustrating solution steps to example 2.18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Some time-varying electrical waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sinusoidal ac waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steady ac showing phase shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steady ac through resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steady ac through inductance Steady ac through capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simple series RL circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simple series RC circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simple series RLC circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Graphical representation of complex number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trigonometric or polar representation of complex number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sinusoid versus time and as phasor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phasor representation of current and voltage Other expressions for phasors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Voltage-current phasor relationships for circuit elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steady sinusoid analysis of simple RL series circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steady sinusoid analysis of simple RC series circuit

Page

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.76. Steady sinusoid analysis of simple RLC series circuit 2.77. Circuit for example 2.21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.78. Circuit for example 2.22 ............................................................

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.79. Two-loop circuit for example 2.23 2.80. Activecircuitforexample2.24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

...................................... Power represented as real and imaginary components Illustration of leading and lagging power factors ..........................................

........................................... Circuit demonstrating sum of complex powers ................................................ Simple series RLC circuit for resonance

Plot of impedance magnitude versus frequency for series RLC illustrating resonance . . . . . . . . . . . . . . . Circuits that exhibit parallel resonance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Magnetic coupling between two conductors Magneticcouplingbetweentwocoils .................................................. Demonstration of coil winding sense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dot convention for mutal inductance sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Demonstration of impedance transfer in transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ideal transformer with winding resistance included ........................................ Accounting for transformer leakage flux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transformer magnetizing current ..................................................... Eddy current and magnetic hysteresis creating power loss in core . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equivalent circuit of practical transformer Common power-transformer construction techniques ...................................... Movement of exciting components to input ..............................................

.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transferring secondary components to primary Final simplification of pratical circuit model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transformer parameter test series ....................................................

............................................................ Circuit for example 3.8 Comparison of two-winding transformer and autotransformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Two-winding transformer as an autotransformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of transformers for multivoltage applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TwotypesofCT's . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of CT and PT placement in circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basicpowercircuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Applications of basic power circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elementary three-phase generation .................................................... Three-phase voltage sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wye-connected source demonstrating line-to-line and line-to-neutral voltages . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Balanced three-phase load connections Four-wire wye-to-delta system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Balanced delta load illustrating phase and line currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of equivalent delta and wye loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-single-phase transformers connected for three-phase operation . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-phase diagrams for the transformers of figure 4.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Open-delta three-phase transformer operation

Per-phase reduction of wye-to-wye system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Per-phase reduction of delta-to-delta system .............................................

............................................................... Three-linediagram One-line diagram of circuit shown in figure 4.15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Page

.................................... Commonly used symbols for one-line electrical diagrams ......................................................... Symbolsforrelayfunctions

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One-line diagram for example 4.7 Three-phase diagram of figure 4.19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Per-phase diagram of figure 4.19 One-line diagram with delta-delta transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Per-phase diagram of figure 4.22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One-line diagram with delta-wye transformer

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One leg of three-phase transformer from figure 4.24 Approximate per-phase equivalent circuit for 750-kVA load-center transformer; impedance referred

................................................................... tohighside Transformer of figure 4.26 with impedance referred to low side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simplified equivalent circuit of transformer expressed in per-unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Approximate equivalent circuit of three-winding transformer expressed in per-unit . . . . . . . . . . . . . . . . .

........................................... One-line diagram of small mine power system Impedance diagram of system in figure 4.30, expressed in per-unit on a 1.00 0.kVA base . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basicfaultdescriptions Positive.sequence. negative.sequence. and zero-sequence vector sets . . . . . . . . . . . . . . . . . . . . . . . . . . . Symmetrical component addition to obtain unbalanced three-phase set . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equivalent delta-connected and wye-connected loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-phase system with line-to-neutral fault

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Symbol and operation of a p-n junction device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bias conditions and current flow for a diode

Diode or rectifier characteristic curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Half-wave rectifier circuit and waveforms

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single-way full-wave rectifier waveforms Bridge rectifier circuit and waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of filtering a rectifier output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heatsinkcooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heat sink thermal relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-phase half-wave rectifier circuit and output voltage waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-phase full-wave rectifier circuit with input and output voltage waveforms . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parallel operation of rectifiers using paralleling reactors An n-pn junction transistor .........................................................

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A p-n-p junction transistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Current relationships for p-n-p and n-p-n devices

Common-baseamplifiers ........................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common-emitter amplifier

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common-emitter characteristic curves Bias techniques for common-emitter amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common-collector amplifier arrangment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Model and symbols for junction FET's . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of a junction-FET application

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Model and symbols for MOS-FET devices SCRmodelandsymbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SCR equivalent model and circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General characteristic curve for SCR

............................................. Sketch of simple monolithic IC cross section TopviewofanactualIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Page

................................................ Examples of symbols employed for IC's . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Permanent-magnet moving coil movements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shunting d'Arsonval meter for high-current tests

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D'Arsonval meter used to measure dc potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . External shunts used for high-current measurements

Simpleohmmetercircuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rectifier ammeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dynamometer connected as wattmeter Power-factor movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.............................................. Simple instrument-transformer connections . . . . . . . . . . . . . . . . . . . . . . . . . . . Voltmeter. ammeter. and wattmeter arranged as single-phase system

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of transducers with standard d'Arsonval movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-phase wattmeter connections

Two-wattmetermethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-phase power measurement with transducer

. . . . . . . . . . . . . . . . . . . . . . Balanced three-phase measurement of voltage. current. and average power Line current measurements with two or three CT's ........................................

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Line-to-line voltage measurements with three or two PT's

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simplified sketch of watthour meter induction mechanism Wheatstonebridgecircuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kelvindoublebridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Megohmmeter testing insulation resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Internal components of megohmmeter

Phase-sequenceindicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strip-chart recorder

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Input circuits on electronic voltmeter Digitaldisplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cathode-raytube .................................................................

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Semiconductor illustrating Hall effect

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Production of voltage from magnetic field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Demonstration of ac generation

. . . . . . . . . . . . . . . . Cross section of machine with salient poles on stator and nonsalient poles on rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross section of machine with nonsalient poles on stator and rotor

. . . . . . . . . . . . . . . . . . Simplified sketch of electromechanical machine illustrating physical components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elementary four.pole. single-phase ac generator

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elementary two.pole. three-phase generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elementary four.pole. three-phase generator

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Demonstration of dc generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dc generator with two armature windings at right angles

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Separately excited dc generator Seriesdcgenerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shuntdcgenerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Compounddcgenerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Current-carrying conductor in a magnetic field .............................................. General speed-torque motor characteristic

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of three frame number dimensions

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Demonstration of induction-motor operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elementary three-phase induction motor

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Squirrel-cage rotor winding

. . . . . . . . . . . . . . . . . . . . . Rotating magnetic field in elementary three.phase. two-pole induction motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Induced rotor potential by rotating flux

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lapped windings of three-phase motor stator Characteristic curves of three-phase induction motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . Typical torque-speed characteristic for general-purpose induction motor . . . . . . . . . . . . . . . . . . . . . . . . . . . Phasor diagrams of rotor and stator flux density for induction motor

Typical torque-speed characteristics for NEMA-design three-phase squirrel-cage motors . . . . . . . . . . . . Other rotor-conductor designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

...................................................... Across-the-line magnetic starter Starting methods for induction motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . Schematic of wound-rotor induction motor showing external resistance controller . . . . . . . . . . . . . . Torque-speed characteristics for wound-rotor motor with stepped-resistance controller

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simplified step starter using individually timed magnetic relays

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sketch showing construction of salient-pole synchronous motor . . . . . . . . . . . . . . . . . . . . . Simplified diagram of synchronous motor using generator for field excitation

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . External solid-state supply used to provide field excitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Schematic of low-speed cylindrical-rotor synchronous motor

. . . . . . . . . . . . . . . . . . . Controller used to demonstrate general starting method for synchronous motor . . . . . . . . . . . . . . . . . . Typical torque-speed characteristic for synchronous motor with damper winding

Effect of load on rotor position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equivalent per-phase circuit of a synchronous motor and phasor diagrams for underexcited and

overexcited field winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-curves for synchronous motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plan view of typical mining shovel showing m-g set Elementary two-pole dc motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elementary four-pole dc motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . Cross-sectional sketch of dc motor showing interpole and compensating windings . . . . . . . . . . . . . . . . . Interaction between armature and main-field flux to produce main-field distortion

Four connections for dc motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical characteristics for shunt. series. and compound motors of equal horsepower and speed

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simplified dc motor schematics with starting resistances

Faceplate manual starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple-switch starting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drum-typestarter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simplified diagram of dynamic braking applied to shunt motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Two-step resistance starting of series-wound motor

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forward-reverse switching of series-wound motor Dynamic braking applied to series-wound motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One-step starting of compound-wound motor Basic WardLeonard system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical characteristic curves for each motor in traction locomotive Stator field of two.pole. single-phase induction motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rotor field of stationary two.pole. single-phase induction motor Phase relationships between stator and turning rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Starting and running stator windings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Centrifugal switch to remove starting winding Capacitor-start motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Illustration of electrical shock hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Capacitance coupling in ungrounded system

Page

Solidlygroundedsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Resistance-grounded systcm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Effect of frequency on let-go current for men . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simplified one-line diagram of substation 163 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Step potentials near grounded structure 163

Touch potentials ncar grounded structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 ~ine-to-earth fault resulting in current flow through safety ground bed . . . . . . . . . . . . . . . . . . . . . . . . . 163 Lightning stroke to equipment causing current flow through safety ground bed . . . . . . . . . . . . . . . . . . . 164 Lightning stroke current through system ground bed causing elevation of safety ground bed . . . . . . . . . . 164 One-line diagram of simplified mine power system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Mied ac-dc mine power system; dc load energized from trolley system . . . . . . . . . . . . . . . . . . . . . . . . . 165 System grounding with current-limiting resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Diode grounding of machine frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Resistance of earth surrounding electrode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Decrease in earth resistance as electrode penetrates deeper soil horizons . . . . . . . . . . . . . . . . . . . . . . . . 167 Calculated values of resistance and conductance for 314-in rod driven to depth of 25 it . . . . . . . . . . . . . 167 Calculated values of resistance and conductance for 314411 rod driven to depth of 100 ft . . . . . . . . . . . . 167 Nomogram to provide resistance of driven rod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resistance of one ground rod. 314411 diameter 168 Resistance of parallel rods when arranged in straight line or circle with spacing equal to rod

length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Variation of earth resistance as numbcr of ground rods is increased for various spacings between

rods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Values of coefficient kl as function of length-to-width ratio of area . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Values of coefficient k2 as function of length-to-width ratio of area . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Influence of first-layer height of potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 Potential on ground surface due to rod 6 ft long and 1-in diameter buried vertically at various

depths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Potential on ground surface due to strips. 1 in by 0.1 in. of various lengths buried horizontally at

depthof2ft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Measuring resistance of grounding system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Concentric earth shells around ground connection being tested and around current electrode . . . . . . . . . 173 Correct spacing of auxiliary electrodes to give true resistance within 2.0% . . . . . . . . . . . . . . . . . . . . . . . 173 Resistivity range of some rocks. minerals. and metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Variation in soil resistivity with moisture content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Typical resistivity curves of solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Diagram for four-electrode resistivity survey showing lines of current flow in two-layer earth . . . . . . . . . 176 Connections for Wenner four-terminal resistivity test using megohmmeter . . . . . . . . . . . . . . . . . . . . . . . 176 Typical curve of resistivity versus elcctrodc separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

~ .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reduction in ground mat resistance by soil treatment 177 Seasonal resistance variations attenuated by soil treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Trench model of soil treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Voltage gradients in earth during ground-fault conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

. .

Delta secondary with rig-zag grounding ................................................ 180 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Delta secondary with wye-delta grounding transformer 180

Cable distribution in underground coal mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cable distribution in surface coal mines 183

Shieldtypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross sections of round unshicldcd mining cablcs 188

Page

Cross sections of flat unshielded mining cables ........................................... Cross sections of some shielded mining cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Round unshielded mining cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flat unshielded mining cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Round shielded mining cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cable types for typical distribution systems in underground coal mines . . . . . . . . . . . . . . . . . . . . . . . . . Cable types for typical distribution systems in surface coal mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cable terminations for applications up to 15 kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Couplercomponents Simplified one-line diagram for situation described in example 8.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable short-circuit currents for insulated copper conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Representative end-suspension termination for borehole cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Messenger wire supports for mine power-feeder cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Splice layout using template for staggered connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effective method for removing unwanted insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Staggering splice connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of popular connectors and connections used in splices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinsulating power conductors with soft rubber tape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical taped splice in high-voltage shielded cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trolley-wire cross sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical trolley-wire and feeder-cable supports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trolley-wire semicatenary suspension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trolley system accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Theoretical resistance of bonded joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pole strength calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Guy and log-anchor calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical arrangements and pin-insulator spacings on wooded poles

Typical system fault current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steps in circuit interruption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Arc between two contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load-breakswitch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extinguishing arc by increasing the length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metal-barrier arc chute assists in arc deionization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Insulated-barrier arc chute used with mametic field - Molded-case circuit breaker components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Magnetic-trip relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Adjustable instantaneous setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermal-magnetic action of molded-case circuit brcakcr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Time-current characteristics for thermal-magnetic circuit breakers Shunt-trip and undervoltage-release accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction and operation of dead-tank OCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Turboaction are chamber for OCB's . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross section of minimum-oil breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CrosssectionofVCB Operating mechanism for vacuum interrupter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VCB assembly incorporating a load-break switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common cartridge fuses Inside view of dual-element fuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Current-limiting action of fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Energy-limitingactionoffuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High-voltage power fuse and support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fusible element under spring tension in high-voltage fuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

............................................. Cross section of boric acid power fuse refill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disassembled refill unit for boric acid fuse

Load-break switch with interlocked high-voltage fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relay contact symbols

Temperature-monitoring protector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electromechanical-thermal relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solenoid and clapper relays Polarrelay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common induction-disk relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Front view of induction-disk relay removed from case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inverse-time curve compared with definite-time curve

Various time characteristics of induction units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Family of inverse-time characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cylinder directional relay Directional overcurrent relay using induction-disk relay and cylinder relay . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Direct relaying in ac system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potential-relaying connections

Differential-relaying connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dc dircct-relaying connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical control wiring for UVR

Typical control wiriig for shunt-tripping element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Three-phase overcurrent and short-circuit connections

TwoCTapproaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Neutral-resistor current-relaying scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Neutral-resistor potential-relaying scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zero-sequence ground relay connections

Ground relay in residual connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Broke