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ARC Flash Hazard Analysis and Mitigation

ISBN: 978-1-118-16381-8
644 pages
October 2012, Wiley-IEEE Press
ARC Flash Hazard Analysis and Mitigation (1118163818) cover image
Up-to-date analysis methodologies and practical mitigation for a major electrical safety concern

Arc Flash Hazard Analysis and Mitigation is the first book to focus specifically on arc flash hazards and provide the latest methodologies for its analysis as well as practical mitigation techniques.

Consisting of sixteen chapters, this fully up-to-date handbook covers all aspects of arc flash hazard calculations and mitigation. It addresses the calculations of short circuits, protective relaying, and varied electrical systems configurations in electrical power systems. It also examines protection systems, including differential relays, arc flash sensing relays, protective relaying coordination, current transformer operation and saturation, and applications to major electrical equipment from the arc flash point of view. Current technologies and strategies for arc flash mitigation are explored. Using the methodology, analysis, and preventive measures discussed in the book, the arc flash hazard incident energy can be reduced to 8 cal/cm2 or less for the new and existing electrical distribution systems.

This powerful resource:

  • Features the most up-to-date arc flash analysis methodologies
  • Presents arc flash hazard calculations in dc systems
  • Supplies practical examples and case studies
  • Provides end-of-chapter reviews and questions
  • Includes a Foreword written by Lanny Floyd, a world-renowned leader in electrical safety who is DuPont's Principal Consultant on Electrical Safety and Technology

Arc Flash Hazard Analysis and Mitigation is a must-have guide for electrical engineers engaged in design, operation, and maintenance, consulting engineers, facility managers, and safety professionals.

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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 Confi gurations 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 Qualifi cations 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

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J. C. Das is a Staff Consultant on Electrical Power Systems with AMEC Inc., in Tucker, Georgia. He is Life Fellow of IEEE (UK), Fellow of IET (India), and has authored approximately sixty technical papers and published 190 study reports of real-world power systems. He is the author of two other books, Power System Analysis: Short-Circuit Load Flow and Harmonics, Second Edition, and Transients in Electrical Systems: Analysis, Recognition, and Mitigation. He is a registered P.E. in the states of Georgia and Oklahoma, C.Eng. in UK, and Eur Ing in Europe. J. C. Das is also a member of CIGRE, Federation of European Engineers, and other technical associations and organizations.

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“If you need to perform arc flash hazard calculations, then this book will not only give you the equations and background necessary to obtain the correct classification, but it will also provide an understanding of how these equations were derived and their limitations.”  (IEEE Electrical Insulation Magazine, 1 March 2013)

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