High Voltage and Electrical Insulation Engineering

Dr. Ravindra Arora retired from Indian Institute of Technology Kanpur in May 2008, where he worked for thirty-four years. At IITK, he established a unique high voltage laboratory, where he conducted research activity for more than forty master's theses, two PhDs, and a large number of undergraduate projects, besides having completed several industry-sponsored projects. He has been a Senior Member of IEEE since 1988 and is a Life Member of the Institution of Engineers (India). Dr. Wolfgang Mosch retired as head and chair professor of the Institute of High Voltage Technology in the Electrical Engineering (Power) Division of Technical University Dresden, Germany, in 1993. He has been actively involved with teaching, research, and industry in high voltage and insulation engineering since 1960.

PREFACE xi ACKNOWLEDGMENTS xv CHAPTER 1 INTRODUCTION 1 1.1 Electric Charge and Discharge 2 1.2 Electric and Magnetic Fields and Electromagnetics 3 1.3 Dielectric and Electrical Insulation 5 1.4 Electrical Breakdown 5 1.4.1 Global Breakdown 6 1.4.2 Local Breakdown 6 1.5 Corona, Streamer and Aurora 6 1.6 Capacitance and Capacitor 8 1.6.1 Stray Capacitance 9 References 10 CHAPTER 2 ELECTRIC FIELDS, THEIR CONTROL AND ESTIMATION 11 2.1 Electric Field Intensity, "E" 11 2.2 Breakdown and Electric Strength of Dielectrics, "Eb" 13 2.2.1 Partial Breakdown in Dielectrics 14 2.3 Classifi cation of Electric Fields 15 2.3.1 Degree of Uniformity of Electric Fields 17 2.3.1.1 Effect of Grounding on Field Confi guration 19 2.4 Control of Electric Field Intensity (Stress Control) 20 2.5 Estimation of Electric Field Intensity 25 2.5.1 Basic Equations for Potential and Field Intensity in Electrostatic Fields 26 2.5.2 Analytical Methods for the Estimation of Electric Field Intensity in Homogeneous Isotropic Single Dielectric 29 2.5.2.1 Direct Solution of Laplace Equation 29 2.5.2.1.1 Parallel Plate Condenser 29 2.5.2.1.2 Concentric Sphere Condenser 30 2.5.2.1.3 Coaxial Cylindrical Condenser 32 2.5.2.2 "Gaussian Surface" Enclosed Charge Techniques for the Estimation and Optimization of Field 34 2.5.2.2.1 Concentric Sphere Condenser 34 2.5.2.2.2 Coaxial Cylindrical Condenser 36 2.5.3 Analysis of Electric Field Intensity in Isotropic Multidielectric System 38 2.5.3.1 Field with Longitudinal Interface 41 2.5.3.2 Field with Perpendicular Interface 42 2.5.3.2.1 Effective Permittivity of Composite Dielectrics 45 2.5.3.3 Field with Diagonal Interface 46 2.5.4 Numerical Methods for the Estimation of Electric Field Intensity 48 2.5.4.1 Finite Element Method (FEM) 49 2.5.4.2 Charge Simulation Method (CSM) 54 2.5.5 Numerical Optimization of Electric Fields 61 2.5.5.1 Optimization by Displacement of Contour Points 62 2.5.5.2 Optimization by Changing the Positions of Optimization Charges and Contour Points 63 2.5.5.3 Optimization by Modifi cation of "Contour Elements" 64 2.6 Conclusion 66 References 67 CHAPTER 3 FIELD DEPENDENT BEHAVIOR OF AIR AND OTHER GASEOUS DIELECTRICS 69 3.1. Fundamentals of Field Assisted Generation of Charge Carriers 71 3.1.1 Impact Ionization 74 3.1.2 Thermal Ionization 75 3.1.3 Photoionization and Interaction of Metastables with Molecules 76 3.2 Breakdown of Atmospheric Air in Uniform and Weakly Nonuniform Fields 77 3.2.1 Uniform Field with Space Charge 78 3.2.2 Development of Electron Avalanche 80 3.2.3 Development of Streamer or "Kanal Discharge" 86 3.2.4 Breakdown Mechanisms 87 3.2.4.1 Breakdown in Uniform Fields with Small Gap Distances (Townsend Mechanism) 88 3.2.4.2 Breakdown with Streamer (Streamer or Kanal Mechanism) 93 3.2.5 Breakdown Voltage Characteristics in Uniform Fields (Paschen's Law) 99 3.2.6 Breakdown Voltage Characteristics in Weakly Nonuniform Fields 108 3.3 Breakdown in Extremely Nonuniform Fields and Corona 109 3.3.1 Development of Avalanche Discharge 110 3.3.1.1 Positive Needle-Plane Electrode Confi guration (Positive or Anode Star Corona) 110 3.3.1.2 Negative Needle-Plane Electrode Confi guration (Negative or Cathode Star Corona) 112 3.3.2 Development of Streamer or Kanal Discharge 114 3.3.2.1 Positive Rod-Plane Electrode (Positive Streamer Corona) 115 3.3.2.2 Negative Rod-Plane Electrode (Negative Streamer Corona) 119 3.3.2.3 Symmetrical Positive and Negative Electrode Confi gurations in Extremely Nonuniform Fields 121 3.3.3 Development of Stem and Leader Corona 122 3.3.3.1 Development and Propagation of Positive Leader Corona 125 3.3.3.2 Development and Propagation of Negative Leader Corona and the Phenomenon of Space Leader 128 3.3.3.3 Electromagnetic Interference (EMI) Produced by Corona 131 3.3.4 Summary of the Development of Breakdown in Extremely Nonuniform Fields 132 3.3.5 Breakdown Voltage Characteristics of Air in Extremely Nonuniform Fields 134 3.3.5.1 Breakdown Preceded with Stable Star Corona 136 3.3.5.2 Breakdown Preceded with Stable Streamer Corona 140 3.3.5.3 Breakdown Preceded with Stable Streamer and Leader Coronas (Long Air Gaps) 146 3.3.5.4 The Requirement of Time for the Formation of Spark Breakdown with Impulse Voltages 150 3.3.5.5 Effect of Wave Shape on Breakdown with Impulse Voltages 152 3.3.5.6 Conclusions from Measured Breakdown Characteristics in Extremely Nonuniform Fields 156 3.3.5.7 Estimation of Breakdown Voltage in Extremely Nonuniform Fields in Long Air Gaps 157 3.3.6 Effects of Partial Breakdown or Corona in Atmospheric Air 159 3.3.6.1 Chemical Decomposition of Air by Corona 160 3.3.6.2 Corona Power Loss in Transmission Lines 162 3.3.6.3 Electromagnetic Interference (EMI) and Audible Noise (AN) Produced by Power System Network 164 3.3.6.4 Other Effects of High Voltage Transmission Lines and Corona on Environment 167 3.4 Electric Arcs and Their Characteristics 168 3.4.1 Static Voltage-Current, U-I, Characteristics of Arcs in Air 169 3.4.2 Dynamic U-I Characteristics of Arcs 171 3.4.3 Extinction of Arcs 173 3.5 Properties of Sulphurhexafl uoride, SF6 Gas and Its Application in Electrical Installations 174 3.5.1 Properties of Sulphurhexafl uoride, SF6 Gas 176 3.5.1.1 Physical Properties 178 3.5.1.2 Property of Electron Attachment 179 3.5.2 Breakdown in Uniform and Weakly Nonuniform Fields with SF6 Insulation 180 3.5.3 External Factors Affecting Breakdown Characteristics in Compressed Gases 187 3.5.3.1 Effect of Electrode Materials and Their Surface Roughness on Breakdown 188 3.5.3.2 Effect of Particle Contaminants in Gas Insulated Systems (GIS) 190 3.5.3.2.1 Movement of Particles 190 3.5.3.2.2 Estimation of Induced Charge and Lifting Field Intensity of Particles 191 3.5.3.3 Particle Initiated PB and Breakdown Measurements in GIS 196 3.5.3.4 Preventive Measures for the Effect of Particles in GIS 198 3.5.4 Breakdown in Extremely Nonuniform and Distorted Weakly Nonuniform Fields with Stable PB in SF6 Gas Insulation 199 3.5.5 Electrical Strength of Mixtures of SF6 with Other Gases 202 3.5.6 Decomposition of SF6 and Its Mixtures in Gas Insulated Equipment 206 3.5.7 SF6 Gas and Environment 209 References 211 CHAPTER 4 LIGHTNING AND BALL LIGHTNING, DEVELOPMENT MECHANISMS, DELETERIOUS EFFECTS, PROTECTION 217 4.1 The Globe, A Capacitor 218 4.1.1 The Earth's Atmosphere and the Clouds 219 4.1.1.1 The Troposphere 220 4.1.1.2 The Stratosphere 220 4.1.1.3 The Ionosphere 220 4.1.2 Clouds and Their Important Role 221 4.1.2.1 Classifi cation of Clouds 221 4.1.2.1.1 Low Altitude Clouds 221 4.1.2.1.2 Middle Altitude Clouds 221 4.1.2.1.3 High Altitude Clouds 223 4.1.3 Static Electric Charge in the Atmosphere 223 4.1.3.1 External Source of Electric Charge 223 4.1.3.2 Charges Due to Ionization within the Atmospheric Air 224 4.1.3.2.1 Radiation from the Sun 225 4.1.3.2.2 Friction and Air Currents 225 4.1.3.3 Charging Mechanisms and Thunderstorms 226 4.2 Mechanisms of Lightning Strike 227 4.2.1 Mechanisms of Breakdown in Long Air Gap 228 4.2.2 Mechanisms of Lightning Strike on the Ground 229 4.2.3 Preference of Locations for the Lightning to Strike 231 4.3 Deleterious Effects of Lightning 232 4.3.1 Loss of Life of the Living Beings 233 4.3.2 Fire Hazards Due to Lightning 233 4.3.3 Blast Created by Lightning 233 4.3.4 Development of Transient Over-Voltage Due to Lightning Strike on the Electric Power System Network and Its Protection 234 4.4 Protection from Lightning 236 4.4.1 Protection of Lives 237 4.4.2 Protection of Buildings and Structures 238 4.4.2.1 Air Termination Network 239 4.4.2.2 Down Conductor 239 4.4.2.3 Earth Termination System 240 4.4.3 The Protected Area 240 4.4.3.1 Protected Volume Determined by a Cone 240 4.4.3.2 Protected Volume Evolved by Rolling a Sphere 241 4.5 Ball Lightning 242 4.5.1 The Phenomenon of Ball Lightning 243 4.5.2 Injurious Effects of Ball Lightning 243 4.5.3 Models and Physics of Ball Lightning 244 4.5.4 Ball Lightning without Lightning Strike 245 4.5.4.1 The Weather and Climatic Conditions 245 4.5.4.2 The Man Made Sources of Charge/Current 246 References 247 CHAPTER 5 ELECTRICAL PROPERTIES OF VACUUM AS HIGH VOLTAGE INSULATION 249 5.1 Pre-breakdown Electron Emission in Vacuum 250 5.1.1 Mechanism of Electron Emission from Metallic Surfaces 250 5.1.2 Non-Metallic Electron Emission Mechanisms 253 5.2 Pre-Breakdown Conduction and Spark Breakdown in Vacuum 258 5.2.1 Electrical Breakdown in Vacuum Interrupters 265 5.2.1.1 High Current Arc Quenching in Vacuum 265 5.2.1.2 Delayed Re-Ignition of Arcs 266 5.2.1.3 Effect of Insulator Surface Phenomena 266 5.2.2 Effect of Conditioning of Electrodes on Breakdown Voltage 267 5.2.3 Effect of Area of Electrodes on Breakdown in Vacuum 268 5.3 Vacuum as Insulation in Space Applications 269 5.3.1 Vacuum-Insulated Power Supplies for Space 270 5.3.2 Vacuum Related Problems in Low Earth Orbit Plasma Environment 270 5.4 Conclusion 271 References 272 CHAPTER 6 LIQUID DIELECTRICS, THEIR CLASSIFICATION, PROPERTIES, AND BREAKDOWN STRENGTH 275 6.1 Classifi cation of Liquid Dielectrics 276 6.1.1 Mineral Insulating Oils 277 6.1.1.1 Mineral Insulating Oil in Transformers 278 6.1.2 Vegetable Oils 278 6.1.3 Synthetic Liquid Dielectrics, the Chlorinated Diphenyles 280 6.1.3.1 Halogen Free Synthetic Oils 281 6.1.4 Inorganic Liquids as Insulation 282 6.1.5 Polar and Nonpolar Dielectrics 282 6.2 Dielectric Properties of Insulating Materials 283 6.2.1 Insulation Resistance Offered by Dielectrics 283 6.2.2 Permittivity of Insulating Materials 285 6.2.3 Polarization in Insulating Materials 286 6.2.3.1 Effect of Time on Polarization 288 6.2.3.1.1 Polarization under Direct Voltage 288 6.2.3.1.2 Polarization under Alternating Voltage 290 6.2.4 Dielectric Power Losses in Insulating Materials 293 6.3 Breakdown in Liquid Dielectrics 296 6.3.1 Electric Conduction in Insulating Liquids 297 6.3.1.1 Liquid Dielectrics in Motion and Electrohydrodynamics (EHD) 298 6.3.2 Intrinsic Breakdown Strength 301 6.3.3 Practical Breakdown Strength Measurement at Near Uniform Fields 302 6.3.3.1 Effect of Moisture and Temperature on Breakdown Strength 305 6.3.4 Breakdown in Extremely Nonuniform Fields and the Development of Streamer 307 6.4 Aging in Mineral Insulating Oils 313 References 316 CHAPTER 7 SOLID DIELECTRICS, THEIR SOURCES, PROPERTIES, AND BEHAVIOR IN ELECTRIC FIELDS 319 7.1 Classifi cation of Solid Insulating Materials 320 7.1.1 Inorganic Insulating Materials 320 7.1.1.1 Ceramic Insulating Materials 320 7.1.1.2 Glass as an Insulating Material 323 7.1.2 Polymeric Organic Materials 323 7.1.2.1 Thermoplastic Polymers 324 7.1.2.2 Thermoset Polymers 324 7.1.2.3 Polymer Compounds 325 7.1.2.4 Polyvinylchloride (PVC) 325 7.1.2.5 Polyethylene (PE) 326 7.1.2.5.1 Chemical Process for XLPE 327 7.1.2.5.2 Radiation Process for XLPE 328 7.1.2.5.3 Silane Cross-Linked Polyethylene (SXLPE) 328 7.1.2.5.4 Electrical Properties of PE and XLPE 328 7.1.2.6 Epoxyresins (EP-resins) 330 7.1.2.7 Natural and Synthetic Rubber 332 7.1.3 Composite Insulating System 333 7.1.3.1 Impregnated Paper as a Composite Insulation System 333 7.1.3.2 Insulating Board Materials 336 7.1.3.3 Fiber Reinforced Plastics (FRP) 336 7.2 Partial Breakdown in Solid Dielectrics 337 7.2.1 Internal Partial Breakdown 337 7.2.2 Surface Discharge (Tracking) 345 7.2.3 Degradation of Solid Dielectrics Caused by PB 347 7.2.3.1 Inhibition of Partial Breakdown/Treeing in Solid Dielectrics 347 7.2.4 Partial Breakdown Detection and Measurement 349 7.2.4.1 Indirect Methods of PB Detection 349 7.2.4.2 Direct Methods of PB Detection and Measurement 351 7.3 Breakdown and Pre-Breakdown Phenomena in Solid Dielectrics 351 7.3.1 Intrinsic Breakdown Strength of Solid Dielectrics 352 7.3.2 Thermal Breakdown 355 7.3.3 Mechanism of Breakdown in Extremely Nonuniform Fields 359 7.3.4 "Treeing" a Pre-Breakdown Phenomenon in Polymeric Dielectrics 360 7.3.4.1 Forms of Treeing Patterns 360 7.3.4.2 Classifi cation of Treeing Process 360 7.3.5 Requirement of Time for Breakdown 363 7.3.6 Estimation of Life Expectancy Characteristics 366 7.3.7 Practical Breakdown Strength and Electric Stress in Service of Solid Dielectrics 368 References 369 INDEX 371