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Arc Flash Hazard Analysis and Mitigation

Das, J. C.

IEEE Press Series on Power Engineering

Cover

2. Edition February 2021
640 Pages, Hardcover
Wiley & Sons Ltd

ISBN: 978-1-119-70974-9
John Wiley & Sons

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This new edition of the definitive arc flash reference guide, fully updated to align with the IEEE's updated hazard calculations

An arc flash, an electrical breakdown of the resistance of air resulting in an electric arc, can cause substantial damage, fire, injury, or loss of life. Professionals involved in the design, operation, or maintenance of electric power systems require thorough and up-to-date knowledge of arc flash safety and prevention methods. Arc Flash Hazard Analysis and Mitigation is the most comprehensive reference guide available on all aspects of arc flash hazard calculations, protective current technologies, and worker safety in electrical environments. Detailed chapters cover protective relaying, unit protection systems, arc-resistant equipment, arc flash analyses in DC systems, and many more critical topics.

Now in its second edition, this industry-standard resource contains fully revised material throughout, including a new chapter on calculation procedures conforming to the latest IEEE Guide 1584. Updated methodology and equations are complemented by new practical examples and case studies. Expanded topics include risk assessment, electrode configuration, the impact of system grounding, electrical safety in workplaces, and short-circuit currents. Written by a leading authority with more than three decades' experience conducting power system analyses, this invaluable guide:
* Provides the latest methodologies for flash arc hazard analysis as well practical mitigation techniques, fully aligned with the updated IEEE Guide for Performing Arc-Flash Hazard Calculations
* Explores an inclusive range of current technologies and strategies for arc flash mitigation
* Covers calculations of short-circuits, protective relaying, and varied electrical system configurations in industrial power systems
* Addresses differential relays, arc flash sensing relays, protective relaying coordination, current transformer operation and saturation, and more
* Includes review questions and references at the end of each chapter

Part of the market-leading IEEE Series on Power Engineering, the second edition of Arc Flash Hazard Analysis and Mitigation remains essential reading for all electrical engineers and consulting engineers.

Foreword xix

Preface to Second Edition xxi

Preface to First Edition xxiii

Acknowledgement xxv

About the Author xxvii

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 5

1.5 Arc Blast 6

1.6 Electrical Shock Hazard 9

1.6.1 Resistance of Human Body 11

1.7 Fire Hazard 13

1.8 Arc Flash Hazard Analysis 15

1.8.1 Ralph Lee's and NFPA Equations 17

1.8.2 IEEE 1584 Guide Equations 17

1.9 Personal Protective Equipment 21

1.10 Hazard Boundaries 23

1.10.1 Working Distance 24

1.10.2 Arc Flash Labels 24

1.11 Maximum Duration of an Arc Flash Event and Arc Flash Boundary 25

1.11.1 Arc Flash Hazard with Equipment Doors Closed 25

1.12 Reasons for Internal Arcing Faults 27

1.13 Arc Flash Hazard Calculation Steps 28

1.13.1 NFPA Table 130.7(C)(15)(a) 29

1.14 Examples of Calculations 30

1.15 Reducing Arc Flash Hazard 33

1.15.1 Reduction 34

1.15.2 Arc Flash Labels 37

Review Questions 38

References 38

2 Safety and Prevention Through Design: A New Frontier 41

2.1 Electrical Standards and Codes 42

2.2 Prevention through Design 44

2.3 Limitations of Existing Codes, Regulations, and Standards 45

2.4 Electrical Hazards 46

2.5 Changing the Safety Culture 49

2.6 Risk Analysis for Critical Operation Power Systems 49

2.6.1 Existing Systems 50

2.6.2 New Facilities 50

2.7 Reliability Analysis 51

2.7.1 Data for Reliability Evaluations 52

2.7.2 Methods of Evaluation 53

2.7.3 Reliability and Safety 53

2.8 Maintenance and Operation 54

2.8.1 Maintenance Strategies 55

2.8.2 Reliability-Centered Maintenance (RCM) 56

2.9 Safety Integrity Level and Safety Instrumented System 56

2.10 Electrical Safety in the Workplaces 58

2.10.1 Risk Assessment 58

2.10.2 Responsibility 58

2.10.3 Risk Parameters 58

2.11 Risk Reduction 61

2.12 Risk Evaluation 62

2.13 Risk Reduction Verification 63

2.14 Risk Control 63

Review Questions 64

References 64

3 Calculations According To IEEE Guide 1584, 2018 68

3.1 Model for Incident Energy Calculations 68

3.2 Electrode Configuration 69

3.3 Impact of System Grounding 69

3.4 Intermediate Average Arcing Current 70

3.5 Arcing Current Variation Factor 71

3.6 Calculation of Intermediate Incident Energy 73

3.7 Intermediate Arc Flash Boundary (AFB) 75

3.8 Enclosure Size Correction Factor 77

3.8.1 Shallow and Typical Enclosures 77

3.9 Determine Equivalent Height and Width 77

3.10 Determine Enclosure Size Correction Factor 77

3.11 Determination of Iarc, E, and AFB (600 V Voc <= 15,000 V) 78

3.11.1 Arcing Current 78

3.11.2 Incident Energy (E) 78

3.11.3 Arc Flash Boundary (AFB) 79

3.12 Determination of Iarc, E, and AFB (Voc <= 600 V) 80

3.12.1 Arcing Current 80

3.12.2 Incident Energy 80

3.12.3 Arc Flash Boundary (AFB) 80

3.13 A Flow Chart for the Calculations 80

3.14 Examples of Calculations 81

References 82

4 Arc Flash Hazard and System Grounding 84

4.1 System and Equipment Grounding 84

4.1.1 Solidly Grounded Systems 85

4.2 Low Resistance Grounding 89

4.3 High Resistance Grounded Systems 89

4.3.1 Fault Detection, Alarms, and Isolation 92

4.4 Ungrounded Systems 96

4.5 Reactance Grounding 97

4.6 Resonant Grounding 97

4.7 Corner of Delta-Grounded Systems 97

4.8 Surge Arresters 98

4.9 Artificially Derived Neutrals 99

4.10 Multiple Grounded Systems 102

4.10.1 Comparison of Grounding Systems 102

4.11 Arc Flash Hazard in Solidly Grounded Systems 102

4.12 Protection and Coordination in Solidly Grounded Systems 107

4.12.1 Self-Extinguishing Ground Faults 110

4.12.2 Improving Coordination in Solidly Grounded Low Voltage Systems 113

4.13 Ground Fault Coordination in Low Resistance Grounded Medium Voltage Systems 116

4.13.1 Remote Tripping 119

4.13.2 Ground Fault Protection of Industrial Bus-Connected Generators 119

4.13.3 Directional Ground Fault Relays 124

4.14 Monitoring of Grounding Resistors 125

4.15 Selection of Grounding Systems 126

Review Questions 127

References 128

5 Short-Circuit Calculations According To ANSI/IEEE Standards For Arc Flash Analysis 130

5.1 Types of Calculations 131

5.1.1 Assumptions: Short-Circuit Calculations 131

5.1.2 Short-Circuit Currents for Arc Flash Calculations 132

5.2 Rating Structure of HV Circuit Breakers 132

5.3 Low-Voltage Motors 135

5.4 Rotating Machine Model 136

5.5 Calculation Methods 136

5.5.1 Simplified Method X/R <= 17 136

5.5.2 Simplified Method X/R > 17 137

5.5.3 E/Z Method for AC and DC Decrement Adjustments 137

5.6 Network Reduction 140

5.7 Calculation Procedure 140

5.7.1 Analytical Calculation Procedure 141

5.8 Capacitor and Static Converter Contributions to Short-Circuit Currents 143

5.9 Typical Computer-Based Calculation Results 143

5.9.1 First-Cycle or Momentary Duty Calculations 143

5.9.2 Interrupting Duty Calculations 146

5.9.3 Low Voltage Circuit Breaker Duty Calculations 146

5.10 Examples of Calculations 146

5.10.1 Calculation of Short-Circuit Duties 152

5.10.2 K-Rated 15 kV Circuit Breakers 152

5.10.3 4.16-kV Circuit Breakers and Motor Starters 157

5.10.4 Transformer Primary Switches and Fused Switches 157

5.10.5 Low Voltage Circuit Breakers 161

5.11 Thirty-Cycle Short-Circuit Currents 161

5.12 Unsymmetrical Short-Circuit Currents 162

5.12.1 Single Line-to-Ground Fault 163

5.12.2 Double Line-to-Ground Fault 165

5.12.3 Line-to-Line Fault 168

5.13 Computer Methods 171

5.13.1 Line-to-Ground Fault 172

5.13.2 Line-to-Line Fault 173

5.13.3 Double Line-to-Ground Fault 173

5.14 Short-Circuit Currents for Arc Flash Calculations 175

Review Questions 176

References 176

6 Accounting For Decaying Short-Circuit Currents In Arc Flash Calculations 178

6.1 Short Circuit of a Passive Element 178

6.2 Systems with No AC Decay 181

6.3 Reactances of a Synchronous Machine 182

6.3.1 Leakage Reactance 182

6.3.2 Subtransient Reactance 183

6.3.3 Transient Reactance 183

6.3.4 Synchronous Reactance 183

6.3.5 Quadrature-Axis Reactances 183

6.3.6 Negative Sequence Reactance 184

6.3.7 Zero Sequence Reactance 184

6.4 Saturation of Reactances 184

6.5 Time Constants of Synchronous Machines 184

6.5.1 Open-Circuit Time Constant 184

6.5.2 Subtransient Short-Circuit Time Constant 184

6.5.3 Transient Short-Circuit Time Constant 185

6.5.4 Armature Time Constant 185

6.6 Synchronous Machine Behavior on Terminal Short Circuit 185

6.6.1 Equivalent Circuits during Fault 186

6.6.2 Fault Decrement Curve 190

6.7 Short Circuit of Synchronous Motors and Condensers 194

6.8 Short Circuit of Induction Motors 194

6.9 A New Algorithm for Arc Flash Calculations with Decaying Short-Circuit Currents 197

6.9.1 Available Computer-Based Calculations 198

6.9.2 Accumulation of Energy from Multiple Sources 198

6.9.3 Comparative Calculations 200

6.10 Crowbar Methods 203

Review Questions 204

References 205

7 Protective Relaying 206

7.1 Protection and Coordination from Arc Flash Considerations 206

7.2 Classification of Relay Types 210

7.3 Design Criteria of Protective Systems 210

7.3.1 Selectivity 211

7.3.2 Speed 211

7.3.3 Reliability 211

7.3.4 Backup Protection 212

7.4 Overcurrent Protection 212

7.4.1 Overcurrent Relays 213

7.4.2 Multifunction Overcurrent Relays 215

7.4.3 IEC Curves 217

7.5 Low Voltage Circuit Breakers 219

7.5.1 Molded Case Circuit Breakers (MCCBs) 219

7.5.2 Current-Limiting MCCBs 225

7.5.3 Insulated Case Circuit Breakers (ICCBs) 227

7.5.4 Low Voltage Power Circuit Breakers (LVPCBs) 228

7.5.5 Short-Time Bands of LVPCBs Trip Programmers 230

7.6 Short-Circuit Ratings of Low Voltage Circuit Breakers 231

7.6.1 Single-Pole Interrupting Capability 235

7.6.2 Short-Time Ratings 235

7.7 Series-Connected Ratings 236

7.8 Fuses 237

7.8.1 Current-Limiting Fuses 238

7.8.2 Low Voltage Fuses 240

7.8.3 High Voltage Fuses 240

7.8.4 Electronic Fuses 241

7.8.5 Interrupting Ratings 242

7.9 Application of Fuses for Arc Flash Reduction 243

7.9.1 Low Voltage Motor Starters 243

7.9.2 Medium Voltage Motor Starters 243

7.9.3 Low Voltage Switchgear 244

7.10 Conductor Protection 247

7.10.1 Load Current Carrying Capabilities of Conductors 248

7.10.2 Conductor Terminations 249

7.10.3 Considerations of Voltage Drops 249

7.10.4 Short-Circuit Considerations 249

7.10.5 Overcurrent Protection of Conductors 251

7.11 Motor Protection 252

7.11.1 Coordination with Motor Thermal Damage Curve 253

7.12 Generator 51-V Protection 261

7.12.1 Arc Flash Considerations 262

Review Questions 265

References 265

8 Unit Protection Systems 267

8.1 Overlapping the Zones of Protection 269

8.2 Importance of Differential Systems for Arc Flash Reduction 271

8.3 Bus Differential Schemes 272

8.3.1 Overcurrent Differential Protection 272

8.3.2 Partial Differential Schemes 273

8.3.3 Percent Differential Relays 273

8.4 High Impedance Differential Relays 274

8.4.1 Sensitivity for Internal Faults 277

8.4.2 High Impedance Microprocessor-Based Multifunction Relays 278

8.5 Low Impedance Current Differential Relays 278

8.5.1 CT Saturation 282

8.5.2 Comparison with High Impedance Relays 282

8.6 Electromechanical Transformer Differential Relays 283

8.6.1 Harmonic Restraint 285

8.7 Microprocessor-Based Transformer Differential Relays 286

8.7.1 CT Connections and Phase Angle Compensation 287

8.7.2 Dynamic CT Ratio Corrections 290

8.7.3 Security under Transformer Magnetizing Currents 293

8.8 Pilot Wire Protection 294

8.9 Modern Line Current Differential Protection 296

8.9.1 The Alpha Plane 297

8.9.2 Enhanced Current Differential Characteristics 299

8.10 Examples of Arc Flash Reduction with Differential Relays 300

Review Questions 303

References 303

9 Arc Fault Detection Relays 305

9.1 Principle of Operation 306

9.2 Light Intensity 306

9.3 Light Sensor Types 307

9.4 Other Hardware 312

9.5 Selective Tripping 313

9.6 Supervision with Current Elements 315

9.7 Applications 315

9.7.1 Medium Voltage Systems 315

9.7.2 Low Voltage Circuit Breakers 317

9.7.3 Self-Testing of Sensors 317

9.8 Examples of Calculation 317

9.9 Arc Vault(TM) Protection for Low Voltage Systems 317

9.9.1 Detection System 321

Review Questions 323

References 323

10 Overcurrent Coordination 325

10.1 Standards and Requirements 326

10.2 Data for the Coordination Study 326

10.3 Computer-Based Coordination 328

10.4 Initial Analysis 328

10.5 Coordinating Time Interval 329

10.5.1 Relay Overtravel 329

10.6 Fundamental Considerations for Coordination 329

10.6.1 Settings on Bends of Time-Current Coordination Curves 331

10.7 Coordination on Instantaneous Basis 331

10.7.1 Selectivity between Two Series-Connected Current-Limiting Fuses 333

10.7.2 Selectivity of a Current-Limiting Fuse Downstream of Noncurrent-Limiting Circuit Breaker 333

10.7.3 Selectivity of Current-Limiting Devices in Series 337

10.8 NEC Requirements of Selectivity 340

10.8.1 Fully Selective Systems 342

10.8.2 Selection of Equipment Ratings and Trip Devices 343

10.9 The Art of Compromise 346

Review Questions 356

References 357

11 Transformer Protection 358

11.1 NEC Requirements 358

11.2 Arc Flash Considerations 360

11.3 System Configurations of Transformer Connections 361

11.3.1 Auto-Transfer of Bus Loads 366

11.4 Through Fault Current Withstand Capability 366

11.4.1 Category I 367

11.4.2 Category II 367

11.4.3 Category III and IV 367

11.4.4 Observation on Faults during Life Expectancy of a Transformer 369

11.4.5 Dry-Type Transformers 370

11.5 Constructing the through Fault Curve Analytically 374

11.5.1 Protection with Respect to Through Fault Curves 374

11.6 Transformer Primary Fuse Protection 375

11.6.1 Variations in the Fuse Characteristics 375

11.6.2 Single Phasing and Ferroresonance 377

11.6.3 Other Considerations of Fuse Protection 377

11.7 Overcurrent Relays for Transformer Primary Protection 377

11.8 Listing Requirements 379

11.9 Effect of Transformer Winding Connections 383

11.10 Requirements of Ground Fault Protection 385

11.11 Through Fault Protection 385

11.11.1 Primary Fuse Protection 385

11.11.2 Primary Relay Protection 387

11.12 Overall Transformer Protection 387

11.13 A Practical Study for Arc Flash Reduction 388

11.13.1 System Configuration 388

11.13.2 Coordination Study and Observations 388

11.13.3 Arc Flash Calculations: High Hazard Risk Category (HRC) Levels 393

11.13.4 Reducing HRC Levels with Main Secondary Circuit Breakers 395

11.13.5 Maintenance Mode Switches on Low Voltage Trip Programmers 395

11.13.6 Addition of Secondary Relay 401

Review Questions 404

References 405

12 Current Transformers 406

12.1 Accuracy Classification of CTs 407

12.1.1 Metering Accuracies 407

12.1.2 Relaying Accuracies 407

12.1.3 Relaying Accuracy Classification X 408

12.1.4 Accuracy Classification T 409

12.2 Constructional Features of CTs 409

12.3 Secondary Terminal Voltage Rating 411

12.3.1 Saturation Voltage 412

12.3.2 Saturation Factor 412

12.4 CT Ratio and Phase Angle Errors 412

12.5 Interrelation of CT Ratio and C Class Accuracy 415

12.6 Polarity of Instrument Transformers 417

12.7 Application Considerations 418

12.7.1 Select CT Ratio 418

12.7.2 Make a Single-Line Diagram of the CT Connections 420

12.7.3 CT Burden 420

12.7.4 Short-Circuit Currents and Asymmetry 420

12.7.5 Calculate Steady-State Performance 420

12.7.6 Calculate Steady-State Errors 421

12.8 Series and Parallel Connections of CTs 425

12.9 Transient Performance of the CTs 425

12.9.1 CT Saturation Calculations 426

12.9.2 Effect of Remanence 427

12.10 Practicality of Application 428

12.11 CTs for Low Resistance-Grounded Medium Voltage Systems 430

12.12 Future Directions 430

Review Questions 433

References 433

13 Arc-Resistant Equipment 435

13.1 Calculations of Arc Flash Hazard in Arc-Resistant Equipment 436

13.1.1 Probability of Arcing Fault 436

13.2 Qualifications in IEEE Guide 437

13.3 Accessibility Types 438

13.3.1 Type 1 438

13.3.2 Type 2 438

13.3.3 Suffix B 438

13.3.4 Suffix C 438

13.3.5 Suffix D 439

13.4 IEC Accessibility Types 439

13.5 Arc-Resistant Ratings 440

13.5.1 Duration Ratings 440

13.5.2 Device-Limited Ratings 441

13.5.3 Effect of Cable Connections 444

13.6 Testing According to IEEE Guide 444

13.6.1 Criterion 1 444

13.6.2 Criterion 2 445

13.6.3 Criterion 3 445

13.6.4 Criterion 4 445

13.6.5 Criterion 5 445

13.6.6 Maintenance 446

13.7 Pressure Relief 446

13.8 Venting and Plenums 448

13.8.1 Venting into Surrounding Area 448

13.8.2 Plenums 450

13.9 Cable Entries 450

Review Questions 452

References 452

14 Recent Trends and Innovations 454

14.1 Statistical Data of Arc Flash Hazards 454

14.2 Zone-Selective Interlocking 456

14.2.1 Low Voltage ZSI Systems 456

14.2.2 Zone Interlocking in Medium Voltage Systems 463

14.3 Microprocessor-Based Low Voltage Switchgear 466

14.3.1 Microprocessor-Based Switchgear Concept 466

14.3.2 Accounting for Motor Contributions 467

14.3.3 Faults on the Source Side 469

14.3.4 Arc Flash Hazard Reduction 470

14.4 Low Voltage Motor Control Centers 470

14.4.1 Desirable MCC Design Features 471

14.4.2 Recent Design Improvements 471

14.4.3 Higher Short-Circuit Withstand MCCs 478

14.5 Maintenance Mode Switch 478

14.6 Infrared Windows and Sight Glasses 480

14.7 Fault Current Limiters 483

14.8 Partial Discharge Measurements 487

14.8.1 Online versus Offline Measurements 488

14.8.2 Test Methods 489

14.8.3 Current Signature Analysis: Rotating Machines 491

14.8.4 Dissipation Factor Tip-Up 491

Review Questions 493

References 494

15 Arc Flash Hazard Calculations In Dc Systems 496

15.1 Calculations of the Short-Circuit Currents in DC Systems 497

15.2 Sources of DC Short-Circuit Currents 497

15.3 IEC Calculation Procedures 498

15.4 Short Circuit of a Lead Acid Battery 501

15.5 Short Circuit of DC Motors and Generators 505

15.6 Short-Circuit Current of a Rectifier 510

15.7 Short Circuit of a Charged Capacitor 515

15.8 Total Short-Circuit Current 516

15.9 DC Circuit Breakers and Fuses 517

15.9.1 DC Circuit Breakers 517

15.9.2 DC Rated Fuses 520

15.10 Arcing in DC Systems 520

15.11 Equations for Calculation of Incident Energy in DC Systems 525

15.12 Protection of the Semiconductor Devices 527

15.12.1 Controlled Converters 529

Review Questions 530

References 531

16 Application of Ethernet and IEC 61850 Communications 533

16.1 IEC 61850 Protocol 534

16.2 Modern IEDs 535

16.3 Substation Architecture 536

16.4 IEC 61850 Communication Structure 537

16.5 Logical Nodes 539

16.6 Ethernet Connection 539

16.7 Networking Media 543

16.7.1 Copper Twisted Shielded and Unshielded 543

16.7.2 Fiber Optic Cable 544

16.8 Network Topologies 545

16.8.1 Prioritizing GOOSE Messages 547

16.8.2 Technoeconomical Justifications 547

16.9 Application to Arc Flash Relaying and Communications 549

Review Questions 549

References 549

Appendix A Statistics and Probability Applied to Electrical Engineering 551

A.1 Mean Mode and Median 551

A.2 Mean and Standard Deviation 552

A.3 Skewness and Kurtosis 553

A.4 Normal or Gaussian Distribution 554

A.5 Curve Fitting: Least Square Line 556

References 559

Appendix B Tables for Quick Estimation of Incident Energy and PPE in Electrical Systems 560

Index 588
J.C. DAS, PHD, is President and Principal of Power System Studies, Inc. He is the former Head of Power System Analysis at Amec Foster Wheeler, where he served for thirty years. He is specialist in conducting power system studies, including short-circuit, load flow, harmonics, stability, arc-flash hazard, grounding, switching transients, and protective relaying. He is the author 70 technical publications, hundreds of study reports for real-world power systems, and several books, including Power System Harmonics and Passive Filter Designs and Understanding Symmetrical Components for Power System Modeling. Mr. Das is a member of the IEEE Industry Applications and IEEE Power Engineering societies, a Fellow of Institution of Engineering Technology, and recipient of the IEEE Meritorious Award in Engineering.

J. C. Das, Indian Institute of Technology