Arc Flash Hazard Analysis and Mitigation

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.

• Foreword xixPreface to Second Edition xxiPreface to First Edition xxiiiAcknowledgement xxvAbout the Author xxvii1 Arc Flash Hazards and Their Analyses 11.1 Electrical Arcs 21.1.1 Arc as a Heat Source 31.1.2 Arcing Phenomena in a Cubicle 31.2 Arc Flash Hazard and Personal Safety 41.3 Time Motion Studies 51.4 Arc Flash Hazards 51.5 Arc Blast 61.6 Electrical Shock Hazard 91.6.1 Resistance of Human Body 111.7 Fire Hazard 131.8 Arc Flash Hazard Analysis 151.8.1 Ralph Lee’s and NFPA Equations 171.8.2 IEEE 1584 Guide Equations 171.9 Personal Protective Equipment 211.10 Hazard Boundaries 231.10.1 Working Distance 241.10.2 Arc Flash Labels 241.11 Maximum Duration of an Arc Flash Event and Arc Flash Boundary 251.11.1 Arc Flash Hazard with Equipment Doors Closed 251.12 Reasons for Internal Arcing Faults 271.13 Arc Flash Hazard Calculation Steps 281.13.1 NFPA Table 130.7(C)(15)(a) 291.14 Examples of Calculations 301.15 Reducing Arc Flash Hazard 331.15.1 Reduction 341.15.2 Arc Flash Labels 37Review Questions 38References 382 Safety and Prevention Through Design: A New Frontier 412.1 Electrical Standards and Codes 422.2 Prevention through Design 442.3 Limitations of Existing Codes, Regulations, and Standards 452.4 Electrical Hazards 462.5 Changing the Safety Culture 492.6 Risk Analysis for Critical Operation Power Systems 492.6.1 Existing Systems 502.6.2 New Facilities 502.7 Reliability Analysis 512.7.1 Data for Reliability Evaluations 522.7.2 Methods of Evaluation 532.7.3 Reliability and Safety 532.8 Maintenance and Operation 542.8.1 Maintenance Strategies 552.8.2 Reliability-Centered Maintenance (RCM) 562.9 Safety Integrity Level and Safety Instrumented System 562.10 Electrical Safety in the Workplaces 582.10.1 Risk Assessment 582.10.2 Responsibility 582.10.3 Risk Parameters 582.11 Risk Reduction 612.12 Risk Evaluation 622.13 Risk Reduction Verification 632.14 Risk Control 63Review Questions 64References 643 Calculations According To IEEE Guide 1584, 2018 683.1 Model for Incident Energy Calculations 683.2 Electrode Configuration 693.3 Impact of System Grounding 693.4 Intermediate Average Arcing Current 703.5 Arcing Current Variation Factor 713.6 Calculation of Intermediate Incident Energy 733.7 Intermediate Arc Flash Boundary (AFB) 753.8 Enclosure Size Correction Factor 773.8.1 Shallow and Typical Enclosures 773.9 Determine Equivalent Height and Width 773.10 Determine Enclosure Size Correction Factor 773.11 Determination of Iarc, E, and AFB (600 V < Voc ≤ 15,000 V) 783.11.1 Arcing Current 783.11.2 Incident Energy (E) 783.11.3 Arc Flash Boundary (AFB) 793.12 Determination of Iarc, E, and AFB (Voc ≤ 600 V) 803.12.1 Arcing Current 803.12.2 Incident Energy 803.12.3 Arc Flash Boundary (AFB) 803.13 A Flow Chart for the Calculations 803.14 Examples of Calculations 81References 824 Arc Flash Hazard and System Grounding 844.1 System and Equipment Grounding 844.1.1 Solidly Grounded Systems 854.2 Low Resistance Grounding 894.3 High Resistance Grounded Systems 894.3.1 Fault Detection, Alarms, and Isolation 924.4 Ungrounded Systems 964.5 Reactance Grounding 974.6 Resonant Grounding 974.7 Corner of Delta-Grounded Systems 974.8 Surge Arresters 984.9 Artificially Derived Neutrals 994.10 Multiple Grounded Systems 1024.10.1 Comparison of Grounding Systems 1024.11 Arc Flash Hazard in Solidly Grounded Systems 1024.12 Protection and Coordination in Solidly Grounded Systems 1074.12.1 Self-Extinguishing Ground Faults 1104.12.2 Improving Coordination in Solidly Grounded Low Voltage Systems 1134.13 Ground Fault Coordination in Low Resistance Grounded Medium Voltage Systems 1164.13.1 Remote Tripping 1194.13.2 Ground Fault Protection of Industrial Bus-Connected Generators 1194.13.3 Directional Ground Fault Relays 1244.14 Monitoring of Grounding Resistors 1254.15 Selection of Grounding Systems 126Review Questions 127References 1285 Short-Circuit Calculations According To ANSI/IEEE Standards For Arc Flash Analysis 1305.1 Types of Calculations 1315.1.1 Assumptions: Short-Circuit Calculations 1315.1.2 Short-Circuit Currents for Arc Flash Calculations 1325.2 Rating Structure of HV Circuit Breakers 1325.3 Low-Voltage Motors 1355.4 Rotating Machine Model 1365.5 Calculation Methods 1365.5.1 Simplified Method X/R ≤ 17 1365.5.2 Simplified Method X/R > 17 1375.5.3 E/Z Method for AC and DC Decrement Adjustments 1375.6 Network Reduction 1405.7 Calculation Procedure 1405.7.1 Analytical Calculation Procedure 1415.8 Capacitor and Static Converter Contributions to Short-Circuit Currents 1435.9 Typical Computer-Based Calculation Results 1435.9.1 First-Cycle or Momentary Duty Calculations 1435.9.2 Interrupting Duty Calculations 1465.9.3 Low Voltage Circuit Breaker Duty Calculations 1465.10 Examples of Calculations 1465.10.1 Calculation of Short-Circuit Duties 1525.10.2 K-Rated 15 kV Circuit Breakers 1525.10.3 4.16-kV Circuit Breakers and Motor Starters 1575.10.4 Transformer Primary Switches and Fused Switches 1575.10.5 Low Voltage Circuit Breakers 1615.11 Thirty-Cycle Short-Circuit Currents 1615.12 Unsymmetrical Short-Circuit Currents 1625.12.1 Single Line-to-Ground Fault 1635.12.2 Double Line-to-Ground Fault 1655.12.3 Line-to-Line Fault 1685.13 Computer Methods 1715.13.1 Line-to-Ground Fault 1725.13.2 Line-to-Line Fault 1735.13.3 Double Line-to-Ground Fault 1735.14 Short-Circuit Currents for Arc Flash Calculations 175Review Questions 176References 1766 Accounting For Decaying Short-Circuit Currents In Arc Flash Calculations 1786.1 Short Circuit of a Passive Element 1786.2 Systems with No AC Decay 1816.3 Reactances of a Synchronous Machine 1826.3.1 Leakage Reactance 1826.3.2 Subtransient Reactance 1836.3.3 Transient Reactance 1836.3.4 Synchronous Reactance 1836.3.5 Quadrature-Axis Reactances 1836.3.6 Negative Sequence Reactance 1846.3.7 Zero Sequence Reactance 1846.4 Saturation of Reactances 1846.5 Time Constants of Synchronous Machines 1846.5.1 Open-Circuit Time Constant 1846.5.2 Subtransient Short-Circuit Time Constant 1846.5.3 Transient Short-Circuit Time Constant 1856.5.4 Armature Time Constant 1856.6 Synchronous Machine Behavior on Terminal Short Circuit 1856.6.1 Equivalent Circuits during Fault 1866.6.2 Fault Decrement Curve 1906.7 Short Circuit of Synchronous Motors and Condensers 1946.8 Short Circuit of Induction Motors 1946.9 A New Algorithm for Arc Flash Calculations with Decaying Short-Circuit Currents 1976.9.1 Available Computer-Based Calculations 1986.9.2 Accumulation of Energy from Multiple Sources 1986.9.3 Comparative Calculations 2006.10 Crowbar Methods 203Review Questions 204References 2057 Protective Relaying 2067.1 Protection and Coordination from Arc Flash Considerations 2067.2 Classification of Relay Types 2107.3 Design Criteria of Protective Systems 2107.3.1 Selectivity 2117.3.2 Speed 2117.3.3 Reliability 2117.3.4 Backup Protection 2127.4 Overcurrent Protection 2127.4.1 Overcurrent Relays 2137.4.2 Multifunction Overcurrent Relays 2157.4.3 IEC Curves 2177.5 Low Voltage Circuit Breakers 2197.5.1 Molded Case Circuit Breakers (MCCBs) 2197.5.2 Current-Limiting MCCBs 2257.5.3 Insulated Case Circuit Breakers (ICCBs) 2277.5.4 Low Voltage Power Circuit Breakers (LVPCBs) 2287.5.5 Short-Time Bands of LVPCBs Trip Programmers 2307.6 Short-Circuit Ratings of Low Voltage Circuit Breakers 2317.6.1 Single-Pole Interrupting Capability 2357.6.2 Short-Time Ratings 2357.7 Series-Connected Ratings 2367.8 Fuses 2377.8.1 Current-Limiting Fuses 2387.8.2 Low Voltage Fuses 2407.8.3 High Voltage Fuses 2407.8.4 Electronic Fuses 2417.8.5 Interrupting Ratings 2427.9 Application of Fuses for Arc Flash Reduction 2437.9.1 Low Voltage Motor Starters 2437.9.2 Medium Voltage Motor Starters 2437.9.3 Low Voltage Switchgear 2447.10 Conductor Protection 2477.10.1 Load Current Carrying Capabilities of Conductors 2487.10.2 Conductor Terminations 2497.10.3 Considerations of Voltage Drops 2497.10.4 Short-Circuit Considerations 2497.10.5 Overcurrent Protection of Conductors 2517.11 Motor Protection 2527.11.1 Coordination with Motor Thermal Damage Curve 2537.12 Generator 51-V Protection 2617.12.1 Arc Flash Considerations 262Review Questions 265References 2658 Unit Protection Systems 2678.1 Overlapping the Zones of Protection 2698.2 Importance of Differential Systems for Arc Flash Reduction 2718.3 Bus Differential Schemes 2728.3.1 Overcurrent Differential Protection 2728.3.2 Partial Differential Schemes 2738.3.3 Percent Differential Relays 2738.4 High Impedance Differential Relays 2748.4.1 Sensitivity for Internal Faults 2778.4.2 High Impedance Microprocessor-Based Multifunction Relays 2788.5 Low Impedance Current Differential Relays 2788.5.1 CT Saturation 2828.5.2 Comparison with High Impedance Relays 2828.6 Electromechanical Transformer Differential Relays 2838.6.1 Harmonic Restraint 2858.7 Microprocessor-Based Transformer Differential Relays 2868.7.1 CT Connections and Phase Angle Compensation 2878.7.2 Dynamic CT Ratio Corrections 2908.7.3 Security under Transformer Magnetizing Currents 2938.8 Pilot Wire Protection 2948.9 Modern Line Current Differential Protection 2968.9.1 The Alpha Plane 2978.9.2 Enhanced Current Differential Characteristics 2998.10 Examples of Arc Flash Reduction with Differential Relays 300Review Questions 303References 3039 Arc Fault Detection Relays 3059.1 Principle of Operation 3069.2 Light Intensity 3069.3 Light Sensor Types 3079.4 Other Hardware 3129.5 Selective Tripping 3139.6 Supervision with Current Elements 3159.7 Applications 3159.7.1 Medium Voltage Systems 3159.7.2 Low Voltage Circuit Breakers 3179.7.3 Self-Testing of Sensors 3179.8 Examples of Calculation 3179.9 Arc Vault™ Protection for Low Voltage Systems 3179.9.1 Detection System 321Review Questions 323References 32310 Overcurrent Coordination 32510.1 Standards and Requirements 32610.2 Data for the Coordination Study 32610.3 Computer-Based Coordination 32810.4 Initial Analysis 32810.5 Coordinating Time Interval 32910.5.1 Relay Overtravel 32910.6 Fundamental Considerations for Coordination 32910.6.1 Settings on Bends of Time–Current Coordination Curves 33110.7 Coordination on Instantaneous Basis 33110.7.1 Selectivity between Two Series-Connected Current-Limiting Fuses 33310.7.2 Selectivity of a Current-Limiting Fuse Downstream of Noncurrent-Limiting Circuit Breaker 33310.7.3 Selectivity of Current-Limiting Devices in Series 33710.8 NEC Requirements of Selectivity 34010.8.1 Fully Selective Systems 34210.8.2 Selection of Equipment Ratings and Trip Devices 34310.9 The Art of Compromise 346Review Questions 356References 35711 Transformer Protection 35811.1 NEC Requirements 35811.2 Arc Flash Considerations 36011.3 System Configurations of Transformer Connections 36111.3.1 Auto-Transfer of Bus Loads 36611.4 Through Fault Current Withstand Capability 36611.4.1 Category I 36711.4.2 Category II 36711.4.3 Category III and IV 36711.4.4 Observation on Faults during Life Expectancy of a Transformer 36911.4.5 Dry-Type Transformers 37011.5 Constructing the through Fault Curve Analytically 37411.5.1 Protection with Respect to Through Fault Curves 37411.6 Transformer Primary Fuse Protection 37511.6.1 Variations in the Fuse Characteristics 37511.6.2 Single Phasing and Ferroresonance 37711.6.3 Other Considerations of Fuse Protection 37711.7 Overcurrent Relays for Transformer Primary Protection 37711.8 Listing Requirements 37911.9 Effect of Transformer Winding Connections 38311.10 Requirements of Ground Fault Protection 38511.11 Through Fault Protection 38511.11.1 Primary Fuse Protection 38511.11.2 Primary Relay Protection 38711.12 Overall Transformer Protection 38711.13 A Practical Study for Arc Flash Reduction 38811.13.1 System Configuration 38811.13.2 Coordination Study and Observations 38811.13.3 Arc Flash Calculations: High Hazard Risk Category (HRC) Levels 39311.13.4 Reducing HRC Levels with Main Secondary Circuit Breakers 39511.13.5 Maintenance Mode Switches on Low Voltage Trip Programmers 39511.13.6 Addition of Secondary Relay 401Review Questions 404References 40512 Current Transformers 40612.1 Accuracy Classification of CTs 40712.1.1 Metering Accuracies 40712.1.2 Relaying Accuracies 40712.1.3 Relaying Accuracy Classification X 40812.1.4 Accuracy Classification T 40912.2 Constructional Features of CTs 40912.3 Secondary Terminal Voltage Rating 41112.3.1 Saturation Voltage 41212.3.2 Saturation Factor 41212.4 CT Ratio and Phase Angle Errors 41212.5 Interrelation of CT Ratio and C Class Accuracy 41512.6 Polarity of Instrument Transformers 41712.7 Application Considerations 41812.7.1 Select CT Ratio 41812.7.2 Make a Single-Line Diagram of the CT Connections 42012.7.3 CT Burden 42012.7.4 Short-Circuit Currents and Asymmetry 42012.7.5 Calculate Steady-State Performance 42012.7.6 Calculate Steady-State Errors 42112.8 Series and Parallel Connections of CTs 42512.9 Transient Performance of the CTs 42512.9.1 CT Saturation Calculations 42612.9.2 Effect of Remanence 42712.10 Practicality of Application 42812.11 CTs for Low Resistance-Grounded Medium Voltage Systems 43012.12 Future Directions 430Review Questions 433References 43313 Arc-Resistant Equipment 43513.1 Calculations of Arc Flash Hazard in Arc-Resistant Equipment 43613.1.1 Probability of Arcing Fault 43613.2 Qualifications in IEEE Guide 43713.3 Accessibility Types 43813.3.1 Type 1 43813.3.2 Type 2 43813.3.3 Suffix B 43813.3.4 Suffix C 43813.3.5 Suffix D 43913.4 IEC Accessibility Types 43913.5 Arc-Resistant Ratings 44013.5.1 Duration Ratings 44013.5.2 Device-Limited Ratings 44113.5.3 Effect of Cable Connections 44413.6 Testing According to IEEE Guide 44413.6.1 Criterion 1 44413.6.2 Criterion 2 44513.6.3 Criterion 3 44513.6.4 Criterion 4 44513.6.5 Criterion 5 44513.6.6 Maintenance 44613.7 Pressure Relief 44613.8 Venting and Plenums 44813.8.1 Venting into Surrounding Area 44813.8.2 Plenums 45013.9 Cable Entries 450Review Questions 452References 45214 Recent Trends and Innovations 45414.1 Statistical Data of Arc Flash Hazards 45414.2 Zone-Selective Interlocking 45614.2.1 Low Voltage ZSI Systems 45614.2.2 Zone Interlocking in Medium Voltage Systems 46314.3 Microprocessor-Based Low Voltage Switchgear 46614.3.1 Microprocessor-Based Switchgear Concept 46614.3.2 Accounting for Motor Contributions 46714.3.3 Faults on the Source Side 46914.3.4 Arc Flash Hazard Reduction 47014.4 Low Voltage Motor Control Centers 47014.4.1 Desirable MCC Design Features 47114.4.2 Recent Design Improvements 47114.4.3 Higher Short-Circuit Withstand MCCs 47814.5 Maintenance Mode Switch 47814.6 Infrared Windows and Sight Glasses 48014.7 Fault Current Limiters 48314.8 Partial Discharge Measurements 48714.8.1 Online versus Offline Measurements 48814.8.2 Test Methods 48914.8.3 Current Signature Analysis: Rotating Machines 49114.8.4 Dissipation Factor Tip-Up 491Review Questions 493References 49415 Arc Flash Hazard Calculations In Dc Systems 49615.1 Calculations of the Short-Circuit Currents in DC Systems 49715.2 Sources of DC Short-Circuit Currents 49715.3 IEC Calculation Procedures 49815.4 Short Circuit of a Lead Acid Battery 50115.5 Short Circuit of DC Motors and Generators 50515.6 Short-Circuit Current of a Rectifier 51015.7 Short Circuit of a Charged Capacitor 51515.8 Total Short-Circuit Current 51615.9 DC Circuit Breakers and Fuses 51715.9.1 DC Circuit Breakers 51715.9.2 DC Rated Fuses 52015.10 Arcing in DC Systems 52015.11 Equations for Calculation of Incident Energy in DC Systems 52515.12 Protection of the Semiconductor Devices 52715.12.1 Controlled Converters 529Review Questions 530References 53116 Application of Ethernet and IEC 61850 Communications 53316.1 IEC 61850 Protocol 53416.2 Modern IEDs 53516.3 Substation Architecture 53616.4 IEC 61850 Communication Structure 53716.5 Logical Nodes 53916.6 Ethernet Connection 53916.7 Networking Media 54316.7.1 Copper Twisted Shielded and Unshielded 54316.7.2 Fiber Optic Cable 54416.8 Network Topologies 54516.8.1 Prioritizing GOOSE Messages 54716.8.2 Technoeconomical Justifications 54716.9 Application to Arc Flash Relaying and Communications 549Review Questions 549References 549Appendix A Statistics and Probability Applied to Electrical Engineering 551A.1 Mean Mode and Median 551A.2 Mean and Standard Deviation 552A.3 Skewness and Kurtosis 553A.4 Normal or Gaussian Distribution 554A.5 Curve Fitting: Least Square Line 556References 559Appendix B Tables for Quick Estimation of Incident Energy and PPE in Electrical Systems 560Index 588

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