Electric safety : practice and standards

Electric power engineering education traditionally covers safety of the power equipment and systems. Little attention, if any, is given to the safety of people. When they reach professional status, most power engineers are not familiar with electric safety issues such as practices governing site works or grounding techniques of dwellings, hospitals, and factories. Designed for both electrical engineering student and practicing power engineers, Electric Safety: Practice and Standards provides the knowledge and analysis they need to be well versed in electric safety.

Features:

Includes techniques to assess safety practices at worksites and provides remedies to correct safety problems Addresses the elusive stray voltage problem and provides techniques to mitigate its impact in dwellings as well as in sensitive installations such as hospitals and dairy farms Provides approximate, yet accurate, analyses and techniques that can be used to assess electric safety without the need for extensive computation or elaborate programs Includes several case studies from real events and examples demonstrating how variations in electric safety procedure implementation influence safety levels

Based on the authors' years of experience as an expert witness and electric safety training instructor, the book covers the analysis of electric safety practices as well as the interpretations of various safety codes. Including homework problems and a solutions manual, this book is a comprehensive guide to recognize and eliminate hazards of electric shocks for professionals working on electric power equipment, as well as people such as the general public in commonly used places, farms workers and animals, and hospital patients.

Preface	p. xiii
Author	p. xv
List of Acronyms	p. xvii
Disclaimer	p. xix
1 Fundamentals of Electricity	p. 1
1.1 Electric Fields	p. 2
1.2 Magnetic Fields	p. 6
1.3 Alternating Current	p. 10
1.3.1 Root Mean Square	p. 11
1.3.2 Phase Shift	p. 12
1.3.3 Concept of Phasors	p. 12
1.3.4 Complex Numbers	p. 13
1.4 Three-Phase Systems	p. 13
1.4.1 Wye-Connected Balanced Circuit	p. 15
1.4.2 Delta-Connected Balanced Circuit	p. 18
Exercises	p. 19
2 Basic Components of an Electric Grid	p. 21
2.1 Power Lines	p. 21
2.1.1 Conductors	p. 22
2.1.1.1 Cables	p. 23
2.1.1.2 Bundled Conductors	p. 27
2.1.1.3 Static Wires	p. 29
2.1.2 Insulators	p. 30
2.2 Substations	p. 32
2.2.1 Transformers	p. 33
2.2.2 Circuit Breakers	p. 33
2.2.3 Circuit Reclosers	p. 35
2.2.4 Circuit Sectionalizers	p. 35
2.2.5 Isolators and Bypasses	p. 36
2.2.6 Load Switches	p. 37
2.2.7 Fuses	p. 37
2.2.8 Surge Protectors	p. 38
2.2.9 Measuring Equipment	p. 41
2.2.9.1 Voltage Sensors	p. 41
2.2.9.2 Current Transformers	p. 44
2.2.10 Reactive Power Control Equipment	p. 45
2.2.10.1 Fixed or Switched Capacitors	p. 45
2.2.10.2 Static Reactive Power Compensators	p. 45
Exercises	p. 46
3 Physiological Effects of Electricity	p. 49
3.1 Classifications of Electric Shocks	p. 49
3.2 Factors Determining the Severity of Electric Shocks	p. 52
3.2.1 Effect of Voltage	p. 52
3.2.2 Effect of Current	p. 53
3.2.3 Effect of Body Resistance	p. 54
3.2.4 Effect of Current Pathway	p. 56
3.2.5 Effect of Shock Duration	p. 57
3.2.6 Effect of Frequency	p. 60
3.2.7 Effect of Impulse versus Continuous Current	p. 61
3.3 Symptoms and Treatments of Electric Shock	p. 63
3.4 Microshocks	p. 64
Exercises	p. 64
4 Ground Resistance	p. 65
4.1 Ground Resistance of Objects	p. 66
4.1.1 Ground Resistance of Hemisphere	p. 67
4.1.2 Ground Resistance of Circular Plate	p. 71
4.1.3 Ground Resistance of People	p. 72
4.1.4 Ground Resistance of Rod	p. 76
4.1.4.1 Ground Resistance of Rods Inserted in Concrete	p. 78
4.1.4.2 Ground Resistance of a Cluster of Rods	p. 79
4.1.5 Ground Resistance of Buried Wires	p. 82
4.1.5.1 Ground Resistance of Buried Wires in Grid Arrangement	p. 83
4.1.5.2 Ground Resistance of Combined Grids and Rods 86
4.2 Soil Resistivity	p. 89
4.2.1 Measuring Ground Resistance	p. 89
4.2.2 Measuring Soil Resistivity	p. 91
4.2.2.1 Wenner Four-Pin Method	p. 91
4.2.2.2 SchLumberger Four-Pin Method	p. 93
4.2.2.3 Driven-Rod Method	p. 94
4.2.2.4 Nonuniform Soils	p. 95
4.2.2.5 Comments on the Three Methods	p. 100
4.3 Soil Treatment	p. 100
4.4 Factors Affecting Ground Resistance	p. 101
4.4.1 Effect of Voltage Gradient	p. 101
4.4.2 Effect of Current	p. 102
4.4.3 Effect of Moisture, Temperature, and Chemical Content 102'
4.4.4 Surface Material	p. 103
Exercises	p. 103
5 General Hazards of Electricity	p. 105
5.1 Touch Potential	p. 105
5.1.1 Touch Potential of Energized Objects	p. 106
5.1.2 Touch Potential of Unintentionally Energized Objects	p. 108
5.1.3 Touch Potential of De-Energized Objects	p. 115
5.2 Step Potential	p. 118
Exercises	p. 123
6 Induced Voltage due to Electric Field	p. 125
6.1 Equipotential Surface	p. 126
6.2 Induced Voltage on a Conductor without Field Distortion	p. 128
6.2.1 Effect of Line Length on Induced Voltage	p. 132
6.2.2 Generalized Method for Short Lines	p. 134
6.2.3 Approximate Method for Long Lines	p. 136
6.3 Electric Field Distortion due to Earth	p. 140
6.3.1 Image Charge	p. 141
6.3.2 Error When Earth Effect Is Ignored	p. 146
6.3.3 Bundled Conductors	p. 147
6.4 Induced Voltage due to Multiple Energized Phases	p. 148
6.4.1 Computation of Conductor Charge	p. 151
6.4.2 Computational Steps for Induced Voltage on De-Energized Conductors	p. 155
6.5 Effect of Line Configuration on Induced Voltage	p. 158
6.6 Induced Voltage due to Energized Cables	p. 161
Exercises	p. 162
7 Induced Voltage due to Magnetic Field	p. 165
7.1 Flux and Flux Linkage	p. 165
7.2 Induced Voltage due to Single Energized Conductor	p. 168
7.3 Induced Voltage due to Multiple Energized Conductors	p. 172
7.3.1 Induced Voltage due to Steady-State Current	p. 173
7.3.2 Induced Voltage due to Transient Current	p. 177
7.4 Induced Voltage due to Electric and Magnetic Fields	p. 179
Exercises	p. 181
8 De-Energized Line Work	p. 183
8.1 Definition of a De-Energized Conductor	p. 183
8.2 Methods of Detecting Induced Voltage	p. 185
8.3 Main Protection Techniques	p. 186
8.3.1 Isolation	p. 186
8.3.2 Insulation	p. 187
8.3.3 Grounding	p. 188
8.4 Grounding System	p. 191
8.4.1 Protective Grounds	p. 191
8.4.2 Sizing of Temporary Ground Conductors	p. 195
8.5 Grounding Methods	p. 197
8.5.1 Equipotential Zone	p. 197
8.5.1.1 Single-Point Grounding	p. 199
8.5.1.2 Bonding to Best Ground at the Site	p. 203
8.5.1.3 Single versus Three-Phase Grounding	p. 205
8.5.2 Examples of Equipotential Zone Design	p. 206
8.5.2.1 Worksite 1: Aerial Work Away from Towers with Isolated Ground Equipment	p. 207
8.5.2.2 Worksite 2: Aerial Work near Towers with Isolated Ground Equipment	p. 211
8.5.2.3 Worksite 3: Aerial and Ground Work	p. 215
8.5.3 Bracketed Grounds	p. 219
8.5.4 Circulating Current	p. 223
8.6 Case Studies	p. 225
8.6.1 Case Study 1	p. 225
8.6.2 Case Study 2	p. 232
8.6.3 Case Study 3	p. 234
8.6.4 Case Study 4	p. 238
8.6.5 Case Study 5	p. 239
8.6.6 Case Study 6	p. 240
Exercises	p. 240
9 Live-Line Work	p. 243
9.1 Hot Stick Method	p. 243
9.2 Insulate and Isolate Method	p. 247
9.3 Bare-Hand Method	p. 248
9.4 Case Study	p. 253
Exercises	p. 255
10 Arc Flash	p. 257
10.1 Arc Fl ash Phases	p. 257
10.1.1 Arc Fault	p. 258
10.1.2 Arc Flash	p. 258
10.1.3 Arc Blast	p. 258
10.2 Assessment of Arc Flash	p. 259
10.2.1 Calculation of Arc Flash Current	p. 259
10.2.2 Calculation of Incident Energy	p. 261
10.3 Calculation of Arc Flash Protection Boundary	p. 263
10.4 Personal Protection Equipment	p. 264
10.5 Approach Boundaries	p. 266
Exercises	p. 268
11 Atmospheric Discharge	p. 269
11.1 Characteristics of Lightning Discharge	p. 269
11.2 Protection from Lightning Strikes	p. 274
11.2.1 Lightning Pole and Lightning Discharge Tower	p. 274
11.2.2 Overhead Ground Wire	p. 279
11.2.3 Surge Arresters	p. 282
11.2.4 Spark Gap	p. 284
11.3 Safe Distance from Lightning Protection Devices	p. 285
Exercises	p. 287
12 Stray and Contact Voltages	p. 289
12.1 Neutral versus Ground	p. 290
12.1.1 Grounding Chassis	p. 294
12.1.2 Bonding Chassis to Neutral	p. 296
12.1.3 Grounding Chassis and Bonding Ground to Neutral	p. 299
12.1.4 Receptacles and Plugs	p. 303
12.1.5 Ground Fault Circuit Interrupter	p. 306
12.2 Service Transformer	p. 308
12.3 Voltage on Neutral Conductor	p. 314
12.4 Stray Voltage	p. 315
12.4.1 Power Distribution of a Dwelling	p. 316
12.4.2 Stray Voltage in Farms	p. 320
12.4.3 Stray Voltage in Swimming Pools	p. 322
12.4.4 Stray Voltage in Outdoor Showers	p. 328
12.4.5 Stray Voltage in Hospitals	p. 331
12.4.5.1 Microshock due to Grounded System	p. 331
12.4.5.2 Microshock in Isolated System	p. 334
12.5 Detection of Stray Voltage	p. 339
12.6 Mitigation of Stray Voltage	p. 342
12.6.1 Double-Bushing Transformers	p. 342
12.6.2 Isolation Transformer	p. 344
12.6.3 Neutral Isolator	p. 346
12.6.4 Four-Wire System	p. 347
12.6.5 Cable Television, Phone Lines, and Metal Pipes	p. 348
12.6.6 Equipotential Area	p. 351
12.6.7 Reducing Grounding Resistance	p. 355
12.7 Mitigation of Stray Voltage in Hospitals	p. 357
12.7.1 Equipotential Grounding	p. 358
12.7.2 Neutral Isolation	p. 359
12.7.3 Protection against Microshock	p. 363
12.8 Contact and Structure Voltages	p. 364
12.8.1 Light Rail Systems	p. 365
12.8.2 Fences and Gates	p. 370
12.8.2.1 Effect of Ground Currents	p. 370
12.8.2.2 Effect of Electric Coupling	p. 374
12.8.3 Street Structures	p. 379
12.9 Neutral Deterioration	p. 382
12.10 World's Residential Grounding Practices	p. 386
12.10.1 Two-Wire System	p. 386
12.10.2 Two-Wire Bonded System	p. 387
12.10.3 Two-Wire EGC System	p. 387
12.10.4 Three-Wire EGC System	p. 388
Exercises	p. 389
13 Electric Safety under Power Lines	p. 393
13.1 Electric Field Calculation	p. 393
13.2 Electric Field near Objects	p. 397
13.3 Electric Field Profile under Power Lines	p. 403
13.4 Allowable Limits for Electric Fields	p. 405
13.4.1 Electric Safety Limits	p. 406
13.4.2 Health Limits	p. 407
13.5 Minimum Vertical Clearance Methods	p. 407
13.5.1 Method 1: MVC for Systems with Unknown Switching Surges	p. 408
13.5.2 Method 2: MVC for Systems with Voltage Exceeding 98 kV and with Known Switching Surges	p. 409
13.6 Measurement of Electric Field Strength	p. 411
13.6.1 Free-Body Meter	p. 413
13.6.1.1 Dipole Free-Body Meter	p. 413
13.6.1.2 Isotropic Free-Body Meter	p. 414
13.6.2 Ground-Reference Meter	p. 414
13.6.3 Electro-Optic Meter	p. 415
13.7 Mitigation of Electric Field	p. 416
Exercises	p. 416
14 Coupling between Power Lines and Pipelines, Railroads, and Telecommunication Cables	p. 419
14.1 Electric Field Coupling	p. 420
14.2 Magnetic Field Coupling	p. 423
14.2.1 Electrically Continuous Underground Pipeline	p. 426
14.2.2 Electrically Discontinuous Underground Pipeline	p. 428
14.3 Mitigation of Electromagnetic Coupling	p. 429
14.4 Ground Current	p. 430
Exercises	p. 434
Index	p. 437

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