Arc Flash Hazard Analysis and Mitigation
CONTENTS
Foreword xix
Preface xxi
About the Author xxiii
1 ARC FLASH HAZARDS AND THEIR ANALYSES 1
1.1 Electrical Arcs 2
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
1.7 Fire Hazard 14
1.8 Arc Flash Hazard Analysis 15
1.9 Personal Protective Equipment 23
1.10 Hazard Boundaries 24
1.11 Maximum Duration of an Arc Flash Event and Arc Flash Boundary 26
1.12 Reasons for Internal Arcing Faults 29
1.13 Arc Flash Hazard Calculation Steps 30
1.14 Examples of Calculations 32
1.15 Reducing Arc Flash Hazard 36
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
2.7 Reliability Analysis 50
2.8 Maintenance and Operation 53
2.9 Safety Integrity Level and Safety Instrumented System 55
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
3.9 Arc Flash Test Models 76
3.10 Alternate Equations 77
3.11 Further Testing and Research 78
3.12 Effectiveness of PPE Calculated Based on IEEE 1584 Guide 79
4 ARC FLASH HAZARD AND SYSTEM GROUNDING 82
4.1 System and Equipment Grounding 82
4.2 Low Resistance Grounding 87
4.3 High Resistance Grounded Systems 87
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
4.11 Arc Flash Hazard in Solidly Grounded Systems 100
4.12 Protection and Coordination in Solidly Grounded Systems 105
4.13 Ground Fault Coordination in Low Resistance Grounded Medium Voltage Systems 114
4.14 Monitoring of Grounding Resistors 123
4.15 Selection of Grounding Systems 124
5 SHORT-CIRCUIT CALCULATIONS ACCORDING TO ANSI/IEEE STANDARDS FOR ARC FLASH
ANALYSIS 128
5.1 Types of Calculations 129
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
5.6 Network Reduction 138
5.7 Calculation Procedure 138
5.8 Capacitor and Static Converter Contributions to Short-Circuit Currents 141
5.9 Typical Computer-Based Calculation Results 141
5.10 Examples of Calculations 144
5.11 Thirty-Cycle Short-Circuit Currents 159
5.12 Unsymmetrical Short-Circuit Currents 160
5.13 Computer Methods 169
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
6.3 Reactances of a Synchronous Machine 180
6.4 Saturation of Reactances 182
6.5 Time Constants of Synchronous Machines 182
6.6 Synchronous Machine Behavior on Terminal Short Circuit 183
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
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
7.4 Overcurrent Protection 209
7.5 Low Voltage Circuit Breakers 216
7.6 Short-Circuit Ratings of Low Voltage Circuit Breakers 228
7.7 Series-Connected Ratings 233
7.8 Fuses 234
7.9 Application of Fuses for Arc Flash Reduction 239
7.10 Conductor Protection 244
7.11 Motor Protection 250
7.12 Generator 51-V Protection 259
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
8.4 High Impedance Differential Relays 276
8.5 Low Impedance Current Differential Relays 280
8.6 Electromechanical Transformer Differential Relays 285
8.7 Microprocessor-Based Transformer Differential Relays 288
8.8 Pilot Wire Protection 295
8.9 Modern Line Current Differential Protection 296
8.10 Examples of Arc Flash Reduction with Differential Relays 301
9 ARC FAULT DETECTION RELAYS 306
9.1 Principle of Operation 307
9.2 Light Intensity 307
9.3 Light Sensor Types 308
9.4 Other Hardware 313
9.5 Selective Tripping 314
9.6 Supervision with Current Elements 316
9.7 Applications 316
9.8 Examples of Calculation 318
9.9 Arc Vault Protection for Low Voltage Systems 318
10 OVERCURRENT COORDINATION 326
10.1 Standards and Requirements 327
10.2 Data for the Coordination Study 327
10.3 Computer-Based Coordination 329
10.4 Initial Analysis 329
10.5 Coordinating Time Interval 330
10.6 Fundamental Considerations for Coordination 330
10.7 Coordination on Instantaneous Basis 332
10.8 NEC Requirements of Selectivity 343
10.9 Energy Boundary Curves 346
10.10 The Art of Compromise 353
11 TRANSFORMER PROTECTION 365
11.1 NEC Requirements 365
11.2 Arc Flash Considerations 367
11.3 System Configurations of Transformer Connections 368
11.4 Through Fault Current Withstand Capability 373
11.5 Constructing the Through Fault Curve Analytically 381
11.6 Transformer Primary Fuse Protection 382
11.7 Overcurrent Relays for Transformer Primary Protection 384
11.8 Listing Requirements 386
11.9 Effect of Transformer Winding Connections 390
11.10 Requirements of Ground Fault Protection 392
11.11 Through Fault Protection 392
11.12 Overall Transformer Protection 394
11.13 A Practical Study for Arc Flash Reduction 395
12 CURRENT TRANSFORMERS 413
12.1 Accuracy Classification of CTs 414
12.2 Constructional Features of CTs 416
12.3 Secondary Terminal Voltage Rating 418
12.4 CT Ratio and Phase Angle Errors 419
12.5 Interrelation of CT Ratio and C Class Accuracy 422
12.6 Polarity of Instrument Transformers 424
12.7 Application Considerations 425
12.8 Series and Parallel Connections of CTs 432
12.9 Transient Performance of the CTs 432
12.10 Practicality of Application 435
12.11 CTs for Low Resistance-Grounded Medium Voltage Systems 437
12.12 Future Directions 437
13 ARC-RESISTANT EQUIPMENT 442
13.1 Calculations of Arc Flash Hazard in Arc-Resistant Equipment 443
13.2 Qualifications in IEEE Guide 444
13.3 Accessibility Types 445
13.4 IEC Accessibility Types 446
13.5 Arc-Resistant Ratings 447
13.6 Testing According to IEEE Guide 451
13.7 Pressure Relief 453
13.8 Venting and Plenums 455
13.9 Cable Entries 457
14 RECENT TRENDS AND INNOVATIONS 461
14.1 Statistical Data of Arc Flash Hazards 461
14.2 Zone-Selective Interlocking 463
14.3 Microprocessor-Based Low Voltage Switchgear 473
14.4 Low Voltage Motor Control Centers 477
14.5 Maintenance Mode Switch 485
14.6 Infrared Windows and Sight Glasses 487
14.7 Fault Current Limiters 490
14.8 Partial Discharge Measurements 494
15 ARC FLASH HAZARD CALCULATIONS IN DC SYSTEMS 503
15.1 Calculations of the Short-Circuit Currents in DC Systems 504
15.2 Sources of DC Short-Circuit Currents 504
15.3 IEC Calculation Procedures 505
15.4 Short Circuit of a Lead Acid Battery 508
15.5 Short Circuit of DC Motors and Generators 512
15.6 Short-Circuit Current of a Rectifier 517
15.7 Short Circuit of a Charged Capacitor 522
15.8 Total Short-Circuit Current 523
15.9 DC Circuit Breakers and Fuses 524
15.10 Arcing in DC Systems 527
15.11 Equations for Calculation of Incident Energy in DC Systems 532
15.12 Protection of the Semiconductor Devices 534
16 APPLICATION OF ETHERNET AND IEC 61850 COMMUNICATIONS 540
16.1 IEC 61850 Protocol 541
16.2 Modern IEDs 542
16.3 Substation Architecture 543
16.4 IEC 61850 Communication Structure 544
16.5 Logical Nodes 546
16.6 Ethernet Connection 546
16.7 Networking Media 550
16.8 Network Topologies 552
16.9 Application to Arc Flash Relaying and Communications 556
Review Questions 556
References 556
Appendix A Statistics and Probability Applied to Electrical Engineering 558
A.1 Mean Mode and Median 558
A.2 Mean and Standard Deviation 559
A.3 Skewness and Kurtosis 560
A.4 Normal or Gaussian Distribution 561
A.5 Curve Fitting: Least Square Line 563
References 566
Appendix B Tables for Quick Estimation of Incident Energy and PPE in Electrical Systems 567
Index 605