Arc Flash Hazard Analysis and Mitigation

638 Pages·2012·5.26 MB·English

by  J. C. Das(auth.)

ARC FLASH HAZARD
ANALYSIS AND
MITIGATION
IEEE Press
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A complete list of titles in the IEEE Press Series on Power Engineering appears at
the end of this book.
ARC FLASH HAZARD
ANALYSIS AND
MITIGATION
J.C. Das
IEEE PRESS
A JOHN WILEY & SONS, INC., PUBLICATION
Cover Image: Powerline © Corbis Premium RF/ Alamy; Arcing fault in a non arc resistant switchboard.
Courtesy of ABB.
Copyright © 2012 by The Institute of Electrical and Electronics Engineers, Inc.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey. All rights reserved
Published simultaneously in Canada
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ISBN 978-1-118-16381-8
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
CONTENTS
Foreword xix
Preface xxi
About the Author xxiii
1
ARC FLASH HAZARDS AND THEIR ANALYSES 1
1.1 Electrical Arcs 2
1.1.1 Arc as a Heat Source 3
1.1.2 Arcing Phenomena in a Cubicle 3
1.2 Arc Flash Hazard and Personal Safety 4
1.3 Time Motion Studies 5
1.4 Arc Flash Hazards 6
1.5 Arc Blast 6
1.6 Electrical Shock Hazard 9
1.6.1 Resistance of Human Body 11
1.7 Fire Hazard 14
1.8 Arc Flash Hazard Analysis 15
1.8.1 Ralph Lee’s and NFPA Equations 17
1.8.2 IEEE 1584 Guide Equations 18
1.9 Personal Protective Equipment 23
1.10 Hazard Boundaries 24
1.10.1 Working Distance 25
1.10.2 Arc Flash Labels 25
1.11 Maximum Duration of an Arc Flash Event and Arc
Flash Boundary 26
1.11.1 Arc Flash Hazard with Equipment Doors Closed 28
1.12 Reasons for Internal Arcing Faults 29
1.13 Arc Flash Hazard Calculation Steps 30
1.13.1 NFPA Table 130.7(C)(15)(a) 32
v
vi CONTENTS
1.14 Examples of Calculations 32
1.15 Reducing Arc Flash Hazard 36
Review Questions 37
References 37
2
SAFETY AND PREVENTION THROUGH DESIGN: A NEW FRONTIER 40
2.1 Electrical Standards and Codes 41
2.2 Prevention through Design 43
2.3 Limitations of Existing Codes, Regulations, and Standards 44
2.4 Electrical Hazards 45
2.5 Changing the Safety Culture 48
2.6 Risk Analysis for Critical Operation Power Systems 48
2.6.1 Existing Systems 49
2.6.2 New Facilities 49
2.7 Reliability Analysis 50
2.7.1 Data for Reliability Evaluations 51
2.7.2 Methods of Evaluation 52
2.7.3 Reliability and Safety 52
2.8 Maintenance and Operation 53
2.8.1 Maintenance Strategies 54
2.8.2 Reliability-Centered Maintenance (RCM) 55
2.9 Safety Integrity Level and Safety Instrumented System 55
Review Questions 57
References 57
3
CRITIQUE OF IEEE GUIDE 1584 ARC FLASH CALCULATIONS 60
3.1 Variations of Arcing Currents 60
3.2 Gap between Electrodes 62
3.3 Variations of Incident Energy 64
3.4 Some Anomalies in IEEE Equations 64
3.5 Lee’s Arc Model 66
3.6 IEEE Experimental Model Setup 68
3.7 Electrical Arc Burn Hazard 70
3.8 Effect of Insulating Barriers 72
3.8.1 Without Barrier 72
3.8.2 With Barriers 75
3.9 Arc Flash Test Models 76
3.10 Alternate Equations 77
3.11 Further Testing and Research 78
CONTENTS vii
3.12 Effectiveness of PPE Calculated Based on IEEE 1584 Guide 79
Review Question 80
References 80
4
ARC FLASH HAZARD AND SYSTEM GROUNDING 82
4.1 System and Equipment Grounding 82
4.1.1 Solidly Grounded Systems 83
4.2 Low Resistance Grounding 87
4.3 High Resistance Grounded Systems 87
4.3.1 Fault Detection, Alarms, and Isolation 90
4.4 Ungrounded Systems 94
4.5 Reactance Grounding 95
4.6 Resonant Grounding 95
4.7 Corner of Delta-Grounded Systems 95
4.8 Surge Arresters 96
4.9 Artifi cially Derived Neutrals 97
4.10 Multiple Grounded Systems 100
4.10.1 Comparison of Grounding Systems 100
4.11 Arc Flash Hazard in Solidly Grounded Systems 100
4.12 Protection and Coordination in Solidly Grounded Systems 105
4.12.1 Self-Extinguishing Ground Faults 108
4.12.2 Improving Coordination in Solidly Grounded Low
Voltage Systems 111
4.13 Ground Fault Coordination in Low Resistance Grounded
Medium Voltage Systems 114
4.13.1 Remote Tripping 117
4.13.2 Ground Fault Protection of Industrial Bus-Connected
Generators 117
4.13.3 Directional Ground Fault Relays 122
4.14 Monitoring of Grounding Resistors 123
4.15 Selection of Grounding Systems 124
Review Questions 125
References 126
5
SHORT-CIRCUIT CALCULATIONS ACCORDING TO ANSI/IEEE
STANDARDS FOR ARC FLASH ANALYSIS 128
5.1 Types of Calculations 129
5.1.1 Assumptions: Short-Circuit Calculations 129
5.1.2 Short-Circuit Currents for Arc Flash Calculations 130
viii CONTENTS
5.2 Rating Structure of HV Circuit Breakers 130
5.3 Low-Voltage Motors 133
5.4 Rotating Machine Model 134
5.5 Calculation Methods 134
5.5.1 Simplifi ed Method X/R≤ 17 134
5.5.2 Simplifi ed Method X/R> 17 135
5.5.3 E/Z Method for AC and DC Decrement Adjustments 135
5.6 Network Reduction 138
5.7 Calculation Procedure 138
5.7.1 Analytical Calculation Procedure 139
5.8 Capacitor and Static Converter Contributions to
Short-Circuit Currents 141
5.9 Typical Computer-Based Calculation Results 141
5.9.1 First-Cycle or Momentary Duty Calculations 141
5.9.2 Interrupting Duty Calculations 144
5.9.3 Low Voltage Circuit Breaker Duty Calculations 144
5.10 Examples of Calculations 144
5.10.1 Calculation of Short-Circuit Duties 150
5.10.2 K-Rated 15 kV Circuit Breakers 150
5.10.3 4.16-kV Circuit Breakers and Motor Starters 155
5.10.4 Transformer Primary Switches and Fused Switches 155
5.10.5 Low Voltage Circuit Breakers 159
5.11 Thirty-Cycle Short-Circuit Currents 159
5.12 Unsymmetrical Short-Circuit Currents 160
5.12.1 Single Line-to-Ground Fault 161
5.12.2 Double Line-to-Ground Fault 163
5.12.3 Line-to-Line Fault 166
5.13 Computer Methods 169
5.13.1 Line-to-Ground Fault 170
5.13.2 Line-to-Line Fault 171
5.13.3 Double Line-to-Ground Fault 171
Review Questions 173
References 174
6
ACCOUNTING FOR DECAYING SHORT-CIRCUIT CURRENTS
IN ARC FLASH CALCULATIONS 176
6.1 Short Circuit of a Passive Element 176
6.2 Systems with No AC Decay 179
CONTENTS ix
6.3 Reactances of a Synchronous Machine 180
6.3.1 Leakage Reactance 180
6.3.2 Subtransient Reactance 181
6.3.3 Transient Reactance 181
6.3.4 Synchronous Reactance 181
6.3.5 Quadrature-Axis Reactances 181
6.3.6 Negative Sequence Reactance 182
6.3.7 Zero Sequence Reactance 182
6.4 Saturation of Reactances 182
6.5 Time Constants of Synchronous Machines 182
6.5.1 Open-Circuit Time Constant 182
6.5.2 Subtransient Short-Circuit Time Constant 182
6.5.3 Transient Short-Circuit Time Constant 183
6.5.4 Armature Time Constant 183
6.6 Synchronous Machine Behavior on Terminal Short Circuit 183
6.6.1 Equivalent Circuits during Fault 184
6.6.2 Fault Decrement Curve 188
6.7 Short Circuit of Synchronous Motors and Condensers 192
6.8 Short Circuit of Induction Motors 192
6.9 A New Algorithm for Arc Flash Calculations with
Decaying Short-Circuit Currents 195
6.9.1 Available Computer-Based Calculations 196
6.9.2 Accumulation of Energy from Multiple Sources 196
6.9.3 Comparative Calculations 198
Review Questions 201
References 202
7
PROTECTIVE RELAYING 203
7.1 Protection and Coordination from Arc Flash Considerations 203
7.2 Classifi cation of Relay Types 207
7.3 Design Criteria of Protective Systems 207
7.3.1 Selectivity 208
7.3.2 Speed 208
7.3.3 Reliability 208
7.3.4 Backup Protection 209
7.4 Overcurrent Protection 209
7.4.1 Overcurrent Relays 210
7.4.2 Multifunction Overcurrent Relays 212
7.4.3 IEC Curves 214
x CONTENTS
7.5 Low Voltage Circuit Breakers 216
7.5.1 Molded Case Circuit Breakers (MCCBs) 216
7.5.2 Current-Limiting MCCBs 222
7.5.3 Insulated Case Circuit Breakers (ICCBs) 223
7.5.4 Low Voltage Power Circuit Breakers (LVPCBs) 225
7.5.5 Short-Time Bands of LVPCBs Trip Programmers 227
7.6 Short-Circuit Ratings of Low Voltage Circuit Breakers 228
7.6.1 Single-Pole Interrupting Capability 232
7.6.2 Short-Time Ratings 232
7.7 Series-Connected Ratings 233
7.8 Fuses 234
7.8.1 Current-Limiting Fuses 235
7.8.2 Low Voltage Fuses 237
7.8.3 High Voltage Fuses 238
7.8.4 Electronic Fuses 238
7.8.5 Interrupting Ratings 239
7.9 Application of Fuses for Arc Flash Reduction 239
7.9.1 Low Voltage Motor Starters 239
7.9.2 Medium Voltage Motor Starters 241
7.9.3 Low Voltage Switchgear 241
7.10 Conductor Protection 244
7.10.1 Load Current Carrying Capabilities of Conductors 246
7.10.2 Conductor Terminations 247
7.10.3 Considerations of Voltage Drops 247
7.10.4 Short-Circuit Considerations 247
7.10.5 Overcurrent Protection of Conductors 249
7.11 Motor Protection 250
7.11.1 Coordination with Motor Thermal Damage Curve 252
7.12 Generator 51-V Protection 259
7.12.1 Arc Flash Considerations 261
Review Questions 263
References 264
8
UNIT PROTECTION SYSTEMS 266
8.1 Overlapping the Zones of Protection 268
8.2 Importance of Differential Systems for Arc Flash Reduction 270
8.3 Bus Differential Schemes 272
8.3.1 Overcurrent Differential Protection 272