arc flash hazard analysis and mitigation - gbv electrical standards andcodes 41 2.2 prevention...

ARC FLASH HAZARD

ANALYSIS AND

MITIGATION

J.C. Das

IEEEPRESSSERIES0N

POWERENGINEERING

Mohamed E. El-Hawary, Series Editor

IEEEIEEE PRESS

©WILEYA JOHN WILEY & SONS, INC., PUBLICATION

CONTENTS

Foreword xix

Preface xxi

About the Author xxiri

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 Artificially 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 Simplified Method X/R<\7 134

5.5.2 Simplified 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 tf-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 S ingle 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


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 Sub-transient 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


References 202

7 PROTECTIVE RELAYING 203

7.1 Protection and Coordination from Arc Flash Considerations 203

7.2 Classification 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


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

STENTS Xi

8.3.2 Partial Differential Schemes 273

8.3.3 Percent Differential Relays 273

8.4 High Impedance Differential Relays 276

8.4.1 Sensitivity for Internal Faults 278

8.4.2 High impedance Microprocessor-BasedMultifunction Relays 280

8.5 Low Impedance Current Differential Relays 280

8.5.1 CT Saturation 282

8.5.2 Comparison with High Impedance Relays 283

8.6 Electromechanical Transformer Differential Relays 285

8.6.1 Harmonic Restraint 288

8.7 Microprocessor-Based Transformer Differential Relays 288

8.7.1 CT Connections and Phase Angle Compensation 288

8.7.2 Dynamic CT Ratio Corrections 293

8.7.3 Security under Transformer Magnetizing Currents 293

8.8 Piiot Wire Protection 295

8.9 Modern Line Current Differential Protection 296

8.9.1 The Alpha Plane 298

8.9.2 Enhanced Current Differential Characteristics 299

8.10 Examples of Arc Flash Reduction with Differential Relays 301


References 304

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

9.7.1 Medium Voltage Systems 316

9.7.2 Low Voltage Circuit Breakers 318

9.7.3 Self-Testing of Sensors 318

9.8 Examples of Calculation 318

9.9 Arc Vault Protection for Low Voltage Systems 31?

9.9.1 Detection System 32

Review Questions 3'

References -

xii CONTENTS

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

10.5.1 Relay Overtravel 330

10.6 Fundamental Considerations for Coordination 330

10.6.1 Settings on Bends of Time-Current

Coordination Curves 332

10.7 Coordination on Instantaneous Basis 332

10.7.1 Selectivity between Two Series-Connected

Current-Limiting Fuses 334

10.7.2 Selectivity of a Current-Limiting Fuse Downstream

of Noncurrent-Limiting Circuit Breaker 334

10.7.3 Selectivity of Current-Limiting Devices in Series 339

10.8 NEC Requirements of Selectivity 343

10.8.1 Fully Selective Systems 343

10.8.2 Selection of Equipment Ratings and Trip Devices 346

10.9 Energy Boundary Curves 346

10.10 The Art of Compromise 353


References 363

11 TRANSFORMER PROTECTION 365

11.1 NEC Requirements 365

11.2 Arc Flash Considerations 367

11.3 System Configurations of Transformer Connections 368

11.3.1 Auto-Transfer of Bus Loads 373

11.4 Through Fault Current Withstand Capability 373

11.4.1 Category I 374

11.4.2 Category II 374

11.4.3 Category III and IV 374

11.4.4 Observation on Faults during Life Expectancy

of a Transformer 376

11.4.5 Dry-Type Transformers 377

11.5 Constructing the Through Fault Curve Analytically 381

11.5.1 Protection with Respect to Through Fault Curves 381

CONTENTS Xiii

11.6 Transformer Primary Fuse Protection 382

11.6.1 Valuations in the Fuse Characteristics 382

11.6.2 Single Phasing and Ferroresonance 384

11.6.3 Other Considerations of Fuse Protection 384

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

11.11.1 Primary Fuse Protection 392

11.11.2 Primary Relay Protection 394

11.12 Overall Transformer Protection 394

11.13 A Practical Study for Arc Flash Reduction 395

11.13.1 System Configuration 395

11.13.2 Coordination Study and Observations 395

11.13.3 Arc Flash Calculations: High Hazard Risk

Category (HRC) Levels 400

11.13.4 Reducing HRC Levels with Main SecondaryCircuit Breakers 402

11.13.5 Maintenance Mode Switches on Low Voltage TripProgrammers 402

11.13.6 Addition of Secondary Relay 408


References 412

12 CURRENT TRANSFORMERS 413

12.1 Accuracy Classification of CTs 414

12.1.1 Metering Accuracies 414

12.1.2 Relaying Accuracies 414

12.1.3 Relaying Accuracy Classification X 415

12.1.4 Accuracy Classification T 416

12.2 Constructional Features of CTs 416

12.3 Secondary Terminal Voltage Rating 418

12.3.1 Saturation Voltage 419

12.3.2 Saturation Factor 419

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

xiv CONTENTS

12.7 Application Considerations 425

12.7.1 Select CT Ratio 425

12.7.2 Make a Single-Line Diagram of the CT Connections 427

12.7.3 CT Burden 427

12.7.4 Short-Circuit Currents and Asymmetry 427

12.7.5 Calculate Steady-State Performance 427

12.7.6 Calculate Steady-State Errors 428

12.8 Series and Parallel Connections of CTs 432

12.9 Transient Performance of the CTs 432

12.9.1 CT Saturation Calculations 433

12.9.2 Effect of Remanence 434

12.10 Practicality of Application 435

12.11 CTs for Low Resistance-Grounded Medium Voltage Systems 437

12.12 Future Directions 437


References 440

13 ARC-RESISTANT EQUIPMENT 442

13.1 Calculations of Arc Flash Hazard in Arc-Resistant

Equipment 443

13.1.1 Probability of Arcing Fault 443

13.2 Qualifications in IEEE Guide 444

13.3 Accessibility Types 445

13.3.1 Type 1 445

13.3.2 Type 2 445

13.3.3 Suffix B 445

13.3.4 Suffix C 445

13.3.5 Suffix D 446

13.4 IEC Accessibility Types 446

13.5 Arc-Resistant Ratings 447

13.5.1 Duration Ratings 447

13.5.2 Device-Limited Ratings 448

J 3.5.3 Effect of Cable Connections 451

13.6 Testing According to IEEE Guide 451

13.6.1 Criterion 1 451




CONTENTS XV

13.6J Criterion 5 452

13.6.6 Maintenance 453

13.7 Pressure Relief 453

13.8 Venting and Plenums 455

13.8.1 Venting into Surrounding Area 455

13.8.2 Plenums 457

13.9 Cable Entries 457


References 459

14 RECENT TRENDS AND INNOVATIONS 461

14.1 Statistical Data of Arc Flash Hazards 461

14.2 Zone-Selective Interlocking 463

14.2.1 Low Voltage ZSI Systems 463

14.2.2 Zone Interlocking in Medium Voltage Systems 470

14.3 Microprocessor-Based Low Voltage Switchgear 473

14.3.1 Microprocessor-Based Switchgear Concept 473

14.3.2 Accounting for Motor Contributions 474

14.3.3 Faults on the Source Side 476

14.3.4 Arc Flash Hazard Reduction 477

14.4 Low Voltage Motor Control Centers 477

14.4.1 Desirable MCC Design Features 478

14.4.2 Recent Design Improvements 478

14.4.3 Higher Short-Circuit Withstand MCCs 485

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

14.8.1 Online versus Offline Measurements 495

14.8.2 Test Methods 496

14.8.3 Current Signature Analysis: Rotating Machines 498

14.8.4 Dissipation Factor Tip-Up 498


References 501

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

xvi CONTENTS

15.3 IEC Calculation Procedures 505

] 5.4 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

15.9.1 DC Circuit Breakers 524

15.9.2 DC Rated Fuses 527

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

15.12.1 Controlled Converters 536


References 538

16 APPLICATION OF ETHERNET AND IEC 61850

COMMUNICATIONS 540

16.1 IEC 61850 Protocol 541

16.2 Modern lEDs 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

16.7.1 Copper Twisted Shielded and Unshielded 550

16.7.2 Fiber Optic Cable 551

16.8 Network Topologies 552

16.8.1 Prioritizing GOOSE Messages 554

16.8.2 Technoeconomical Justifications 554

16.9 Application to Arc Flash Relaying and Communications 556


References 556

Appendix A Statistics and Probability Appliedto Electrical Engineering 558

A. 1 Mean Mode and Median 558

A.2 Mean and Standard Deviation 559

CONTENTS xvii

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

arc flash hazard analysis and mitigation - gbv electrical standards andcodes 41 2.2 prevention...

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