Methodology and Technology for Power System Grounding

Preface xiii Acknowledgements xv 1 Fundamental Concepts of Grounding 1 1.1 Conduction Mechanism of Soil 1 1.2 Functions of Grounding Devices 2 1.3 Definition and Characteristics of Grounding Resistance 7 1.4 Grounding Resistance of Grounding Devices 11 1.5 Body Safety and Permitted Potential Difference 19 1.6 Standards Related to Power System Grounding 25 References 26 2 Current Field in the Earth 27 2.1 Electrical Property of Soil 27 2.2 Basic Properties of a Constant Current Field in the Earth 36 2.3 Current Field Created by a Point Source in Uniform Soil 38 2.4 Potential Produced by a Point Source on the Ground Surface in Non-Uniform Soil 43 2.5 Potential Produced by a Point Source in Multi-Layered Soil 48 2.6 Computer Program Derivation Method of Green's Function 55 2.7 Fast Calculation Method of Green's Function in Multi-Layered Soil 62 2.8 Current and Potential Distributions Produced by a DC Ground Electrode 69 References 78 3 Measurement and Modeling of Soil Resistivity 81 3.1 Introduction to Soil Resistivity Measurement 81 3.2 Measurement Methods of Soil Resistivity 83 3.3 Simple Analysis Method for Soil Resistivity Test Data 94 3.4 Numerical Analysis for a Multi-Layered Soil Model 102 3.5 Multi-Layered Soil Model by Solving Fredholm's Equation 109 3.6 Estimation of Multi-Layered Soil Model by Using the Complex Image Method 118 3.7 Engineering Applications 123 References 128 4 Numerical Analysis Method of Grounding 131 4.1 Calculation Method for Parameters of Substation Grounding Systems 131 4.2 Equal Potential Analysis of Grounding Grid 135 4.3 Unequal Potential Analysis of a Large-Scale Grounding System 146 4.4 Analyzing Grounding Grid with Grounded Cables 151 4.5 MoM Approach for Grounding Grid Analysis in Frequency Domain 153 4.6 Finite Element Method for a Complex Soil Structure 159 4.7 Time Domain Method for Electromagnetic Transient Simulation of a Grounding System 161 References 186 5 Ground Fault Current of a Substation 191 5.1 Power Station and Substation Ground Faults 191 5.2 Maximum Fault Current through a Grounding Grid to the Earth 194 5.3 Simplified Calculation of a Fault Current Division Factor 201 5.4 Numerical Calculation of the Fault Current Division Factor 203 5.5 Typical Values of the Fault Current Division Factor 213 5.6 Influence of Seasonal Freezing on the Fault Current Division Factor 219 References 221 6 Grounding System for Substations 223 6.1 Purpose of Substation Grounding 223 6.2 Safety of Grounding Systems for Substations and Power Plants 227 6.3 Methods for Decreasing the Grounding Resistance of a Substation 240 6.4 Equipotential Optimal Arrangement of a Grounding Grid 254 6.5 Numerical Design of a Grounding System 268 References 272 7 Grounding of Transmission and Distribution Lines 275 7.1 Requirement for a Tower Grounding Device 275 7.2 Structures of Tower Grounding Devices 277 7.3 Properties of a Concrete-Encased Grounding 280 7.4 Computational Methods for Tower Grounding Resistance 284 7.5 Step and Touch Voltages Near a Transmission Tower 290 7.6 Short-Circuit Fault on Transmission Tower 294 7.7 Grounding Device of Distribution Lines 299 References 301 8 Impulse Characteristics of Grounding Devices 303 8.1 Fundamentals of Soil Impulse Breakdown 303 8.2 Numerical Analysis of the Impulse Characteristics of Grounding Devices 325 8.3 Impulse Characteristics of Tower Groundings 346 8.4 Impulse Effective Length of Grounding Electrodes 362 8.5 Impulse Characteristics of a Grounding Grid 370 8.6 Lightning Electromagnetic Field Generated by a Grounding Electrode 381 References 385 9 DC Ground Electrode 391 9.1 Technical Requirements of a DC Ground Electrode 391 9.2 Structure Types of DC Ground Electrodes 394 9.3 Main Design Aspects of a DC Ground Electrode 401 9.4 Numerical Analysis Methods for a Ground Electrode 413 9.5 Heat Generation Analysis of a DC Ground Electrode 418 9.6 Common Ground Electrode of a Multiple Converter System 423 9.7 Influence of DC Grounding on AC System 433 9.8 Methods to Decrease Winding DC Current of a Neutral Grounding Transformer 445 9.9 Corrosion of Underground Metal Pipes Caused by a DC Ground Electrode 455 References 458 10 Materials for Grounding 461 10.1 Choice of Material and Size for Conductors 461 10.2 Soil Corrosion of Grounding Conductor 470 10.3 Corrosion of Concrete-Encased Electrodes 476 10.4 Low-Resistivity Material 478 10.5 Performance of LRM 488 10.6 Construction Method of LRM 495 References 497 11 Measurement of Grounding 499 11.1 Methods for Grounding Resistance Measurement 499 11.2 Instruments for Measuring Grounding Resistance 510 11.3 Factors Influencing the Results from the Fall of Potential Method 519 11.4 Grounding Resistance Test in Vertically Layered Soil 532 11.5 Influence of Overhead Ground Wires on Substation Grounding Resistance Measurement 535 11.6 Measurement of Potential Distribution 539 11.7 Corrosion Diagnosis of Grounding Grids 542 References 550 Index 553