Methodology and Technology for Power System Grounding

Methodology and Technology for Power System Grounding

By: Rong Zeng (author), Jinliang He (author), Bo Zhang (author)Hardback

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Description

Grounding is the fundamental measures to ensure the safe operation of power systems, including power apparatus and control/monitoring systems, and guarantee the personal safety. Grounding technology is an interdiscipline involving electrical engineering, high voltage technology, electric safety, electromagnetics, numerical analysis, and geological exploration Methodology and Technology for Power System Grounding : Covers all topics related to power system grounding Presents fundaments and theories of grounding systems Well balances technology and methodology related to grounding system design Helps to understand the grounding analysis softwares Highlights the advanced research works in the field of grounding systems Comprehensively introduces numerical analysis methods Discovers impulse ionization phenomenon of soil around the grounding conductors Touches on lightning impulse characteristics of grounding devices for towers and buildings As a comprehensive treatment of the topic, Methodology and Technology for Power System Grounding is ideal for engineers and researchers in power system, lightning protection, and grounding. The book will also better equip postgraduates, senior undergraduate students in electrical engineering.

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Contents

Preface xiii

Acknowledgements xv

1 Fundamental Concepts of Grounding 1

1.1 Conduction Mechanism of Soil 1

1.1.1 Soil Structure 1

1.1.2 Conduction Mechanism of Soil 1

1.2 Functions of Grounding Devices 2

1.2.1 Concept of Grounding 2

1.2.2 Classification of Grounding 3

1.2.3 Purpose of Grounding 5

1.3 Definition and Characteristics of Grounding Resistance 7

1.3.1 Definition of Grounding Resistance 7

1.3.2 Relationship between Grounding Resistance and Capacitance8

1.3.3 Shielding Effect among Grounding Conductors 9

1.4 Grounding Resistance of Grounding Devices 11

1.4.1 Grounding Resistance of General Grounding Devices 11

1.4.2 Grounding Resistance of Grounding Device inNon-Homogeneous Soil 14

1.5 Body Safety and Permitted Potential Difference 19

1.5.1 Allowable Body Current Limit 19

1.5.2 Allowable Body Voltage 20

1.5.3 Allowable Potential Difference 21

1.5.4 Influence of Resistivity of Surface Soil Layer on BodySafety 23

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

2.1.1 Soil Resistivity 27

2.1.2 Influence of Different Factors on Soil Resistivity 29

2.1.3 Permittivity of Soil 30

2.1.4 Frequency Characteristics of Soil Parameters 31

2.2 Basic Properties of a Constant Current Field in the Earth36

2.2.1 Current Density in the Earth 36

2.2.2 Continuity of Earth Current Field 36

2.2.3 Potential of Stable Current Field 37

2.2.4 Current Field at the Interface of Layered Soil 37

2.3 Current Field Created by a Point Source in Uniform Soil38

2.3.1 Laplace s Equation 38

2.3.2 Current Field Created by a Point Source in Soil 39

2.3.3 Earth Current Field Produced by Two Opposite Point CurrentSources on the Ground Surface 41

2.3.4 Earth Current Field in Non-Uniform Soil 41

2.4 Potential Produced by a Point Source on the Ground Surfacein Non-Uniform Soil 43

2.4.1 Horizontally Layered Soil 44

2.4.2 Horizontal Double-Layer Soil 45

2.4.3 Horizontal Triple-Layer Soil 46

2.4.4 Vertically Layered Soil 46

2.5 Potential Produced by a Point Source in Multi-Layered Soil48

2.5.1 Analysis of Potential Produced by a Point Current Source48

2.5.2 Numerical Integral Method to Calculate Green sFunction of a Point Current Source 52

2.6 Computer Program Derivation Method of Green s Function55

2.6.1 Method of Obtaining Analytic Expression 55

2.6.2 Expression of Green s Function Derived from SoftwareProgram 59

2.6.3 Calculation of Current Field in Multi-Layered Soil 62

2.7 Fast Calculation Method of Green s Function inMulti-Layered Soil 62

2.7.1 Development of a Two-Stage Fitting Method 63

2.7.2 Application of the Fast Calculation of Green sFunction in Multi-Layered Soils 66

2.8 Current and Potential Distributions Produced by a DC GroundElectrode 69

2.8.1 Current and Potential Distributions of DC in Uniform Soil69

2.8.2 Current and Potential Distributions of DC Current inNon-Uniform Soil 72

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

3.2.1 Sampling Analysis Method of Soil Resistivity 83

3.2.2 Electrical Sounding Methods 83

3.2.3 Test Probe Configuration for Four-Probe Method 88

3.2.4 Field Test Technique of Soil Resistivity 90

3.2.5 Electromagnetic Sounding Method 93

3.3 Simple Analysis Method for Soil Resistivity Test Data 94

3.3.1 Electrical Sounding Curve Method for Two-LayeredHorizontal Soil Model 94

3.3.2 Analysis of a Three-Layered Horizontal GeologicalStructure 99

3.3.3 Resistivity of Vertically Layered Soil Structure 101

3.3.4 Estimation of Soil Model Parameter using the Three-ProbeMethod 102

3.4 Numerical Analysis for a Multi-Layered Soil Model 102

3.4.1 Typical Curves of Multi-Layered Soil Apparent Resistivity102

3.4.2 Expression of Apparent Soil Resistivity 105

3.4.3 Inverting Soil Parameters 107

3.4.4 Numerical Analysis Method for Two-Layered Soil Model108

3.5 Multi-Layered Soil Model by Solving Fredholm sEquation 109

3.5.1 Solving the Forward Integral Equation 109

3.5.2 Inversing Parameters of Soil Models 113

3.5.3 Application in Estimation of Soil Parameters 116

3.6 Estimation of Multi-Layered Soil Model by Using the ComplexImage Method 118

3.6.1 Estimation of Multi-Layered Soil Structure 119

3.6.2 Fast Calculation of the Soil Apparent Resistivity 119

3.6.3 Partial Derivatives of Calculated Apparent Resistivity121

3.6.4 The Partial Derivative Expressions of f(l) 123

3.6.5 Determination of the Initial Soil Parameters 123

3.7 Engineering Applications 123

References 128

4 Numerical Analysis Method of Grounding 131

4.1 Calculation Method for Parameters of Substation GroundingSystems 131

4.1.1 Calculation of Grounding Parameters with EmpiricalFormulas 131

4.1.2 Numerical Analysis Method for Grounding System Parameters132

4.2 Equal Potential Analysis of Grounding Grid 135

4.2.1 Approach of Green s Function for CalculatingGrounding Parameters 135

4.2.2 Superposition Method Under the Assumption of Nodal LeakageCurrent 139

4.2.3 Multi-Step Method Under the Assumption of Nodal LeakageCurrent 141

4.2.4 Integration Method Under the Assumption of Branch LeakageCurrent 143

4.3 Unequal Potential Analysis of a Large-Scale Grounding System146

4.3.1 Analysis Model of a Grounding System with UnequalPotential 147

4.3.2 Problems in the Analytical Method for Solving a MutualResistance Coefficient 148

4.3.3 Numerical Integration Method for Mutual ResistanceCoefficient Calculation 148

4.3.4 Multi-Step Method for Uniform Soil 149

4.4 Analyzing Grounding Grid with Grounded Cables 151

4.4.1 Principles of Setting up Equations 151

4.4.2 Calculating Self-Admittances of Conductors and Cables153

4.5 MoM Approach for Grounding Grid Analysis in Frequency Domain153

4.5.1 Basis Functions of MoM 153

4.5.2 Setting up the Equations 154

4.5.3 Green s Functions and Generalized SommerfeldIntegral 155

4.6 Finite Element Method for a Complex Soil Structure 159

4.7 Time Domain Method for Electromagnetic Transient Simulationof a Grounding System 161

4.7.1 Generalized MMC Method under EMQS Assumption 161

4.7.2 Numerical Approach Based on Time Domain Integral Equationin a Lossy Medium 171

4.7.3 Finite Difference Time Domain Method 181

References 186

5 Ground Fault Current of a Substation 191

5.1 Power Station and Substation Ground Faults 191

5.1.1 Types of Power Station and Substation Ground Faults191

5.1.2 Principle to Determine Maximum Ground Fault Current191

5.1.3 Location of the Maximum Ground Fault Current 193

5.2 Maximum Fault Current through a Grounding Grid to the Earth194

5.2.1 Maximum Grounding Grid Fault Current 194

5.2.2 Zero-Sequence Fault Current 194

5.2.3 Determining the Fault Current Division Factor 195

5.2.4 Determining the Decrement Factor 196

5.2.5 Determining the Correction Coefficient for Future Planning198

5.2.6 Impact of Substation Grounding Resistance 199

5.2.7 Impact of Fault Resistance 200

5.2.8 Impact of Overhead Ground Wires and Neutral Lines 200

5.2.9 Impact of Buried Conduits and Cables 200

5.2.10 Steps to Determine a Proper Design Value of the MaximumGrounding Grid Current 200

5.3 Simplified Calculation of a Fault Current Division Factor201

5.3.1 Fault Current Division Factor Within a Local Substation201

5.3.2 Fault Current Division Factor Outside a Local Substation202

5.4 Numerical Calculation of the Fault Current Division Factor203

5.4.1 Numerical Calculation Method of the Fault Current DivisionFactor 203

5.4.2 Matrix Method to Calculate the Fault Current DivisionFactor 207

5.4.3 Phase Coordinate Transformer Model for Calculating theFault Current Division Factor 207

5.5 Typical Values of the Fault Current Division Factor 213

5.5.1 Influence of Substation Grounding Resistance 213

5.5.2 Influence of Transmission Towers 214

5.5.3 Influence of Fault Location 216

5.5.4 Influence of Incoming Cables 216

5.5.5 Influence of Transmission Line Number 216

5.5.6 Influence of Transmission Line Length 217

5.5.7 Influence of Transformer 217

5.6 Influence of Seasonal Freezing on the Fault Current DivisionFactor 219

5.6.1 Influence of Seasonally Frozen Soil on the Fault CurrentDivision Factor 219

5.6.2 Influence of Transmission Line Numbers Affected by FrozenSoil 221

References 221

6 Grounding System for Substations 223

6.1 Purpose of Substation Grounding 223

6.1.1 Function of Substation Grounding 223

6.1.2 Design Objective of a Substation Grounding System 224

6.1.3 Requirement on the Grounding System of a Substation225

6.1.4 Specificity of Power Plant Grounding 225

6.1.5 Requirements for Grounding System Design 226

6.1.6 Design and Construction Procedures for a Grounding System226

6.2 Safety of Grounding Systems for Substations and Power Plants227

6.2.1 Design Criteria of Grounding Systems 227

6.2.2 Calculation of the Grounding Resistance of a GroundingSystem 228

6.2.3 Analysis of Grounding in Inhomogeneous Soil 230

6.2.4 Simplified Formula for Calculating Step, Touch and MeshVoltages 234

6.2.5 Formulas in IEEE Standard 80-2000 for Calculating Mesh andStep Voltages 235

6.2.6 Formulas to Calculate Touch and Step Voltages in ChineseStandards 237

6.2.7 Transfer Potential 238

6.2.8 Methods for Improving the Safety of a Grounding System238

6.3 Methods for Decreasing the Grounding Resistance of aSubstation 240

6.3.1 Basic Methods for Decreasing Grounding Resistance 240

6.3.2 Using Long Vertical Ground Rods to Decrease GroundingResistance 241

6.3.3 Explosion Grounding Technique 248

6.3.4 Deep Ground Well 250

6.3.5 Slanting Grounding Electrode 253

6.4 Equipotential Optimal Arrangement of a Grounding Grid254

6.4.1 Principle of the Unequal-Spacing Arrangement 254

6.4.2 Regularity of the Unequal-Spacing Arrangement 256

6.4.3 Unequal-Spacing Arrangement with Exponential Distribution263

6.4.4 Influence of Vertical Grounding Electrodes on OCR 267

6.5 Numerical Design of a Grounding System 268

6.5.1 Grounding System Design of a 220-kV Substation 268

6.5.2 Grounding System Design of a 1000-kV UHV Substation270

References 272

7 Grounding of Transmission and Distribution Lines275

7.1 Requirement for a Tower Grounding Device 275

7.1.1 Requirement of Transmission Tower Grounding Resistance276

7.1.2 Seasonal Factor for the Grounding Resistance of a TowerGrounding Device 276

7.2 Structures of Tower Grounding Devices 277

7.2.1 Basic Structures of Tower Grounding Devices 277

7.2.2 Using Natural Footings as Tower Grounding Devices 280

7.3 Properties of a Concrete-Encased Grounding 280

7.3.1 Function of a Concrete-Encased Grounding Device 280

7.3.2 Hygroscopic Properties of Concrete 281

7.3.3 Permissible Current through a Concrete-Encased GroundingDevice 283

7.4 Computational Methods for Tower Grounding Resistance 284

7.4.1 Equivalent Cylindrical Conductor Method 284

7.4.2 Grounding Resistance of a Vertical Ground Rod Covered withConcrete 285

7.4.3 Grounding Resistance of a Fabricated Concrete-EncasedFooting 286

7.4.4 Grounding Resistance of a Tower Grounding Device withDifferent Structures 287

7.4.5 Utilization Coefficient 289

7.5 Step and Touch Voltages Near a Transmission Tower 290

7.5.1 Step Voltage and Touch Voltage 290

7.5.2 Shock Accident Possibilities Caused by Step and TouchVoltages 292

7.6 Short-Circuit Fault on Transmission Tower 294

7.6.1 Fault Current of Transmission Line 294

7.6.2 Distribution of Ground Potential around TransmissionTowers 295

7.6.3 Methods to Improve Potential Distribution 296

7.7 Grounding Device of Distribution Lines 299

7.7.1 Vertically Driven Rods 300

7.7.2 Grounding of Wood Poles 301

7.7.3 Requirement for Grounding the Distribution Line 301

References 301

8 Impulse Characteristics of Grounding Devices 303

8.1 Fundamentals of Soil Impulse Breakdown 303

8.1.1 Electric Field Strength of Soil Breakdown 303

8.1.2 Phenomenon of Electrical Breakdown in Soil 312

8.1.3 Impulse Breakdown Delay Characteristics of Soil 319

8.1.4 Mechanism of Electrical Breakdown in Soil 321

8.1.5 Residual Resistivity of Ionized Soil 323

8.2 Numerical Analysis of the Impulse Characteristics ofGrounding Devices 325

8.2.1 Equivalent Circuit Model 325

8.2.2 MoM Coupled with Circuit Theory 331

8.2.3 An Interpolation Model to Accelerate the Frequency DomainResponse Calculation 335

8.3 Impulse Characteristics of Tower Groundings 346

8.3.1 Field Test of Grounding Devices Impacted by a LargeImpulse Current 346

8.3.2 Lightning Current Decay Along a Grounding Electrode348

8.3.3 Definition of Impulse Grounding Resistance 350

8.3.4 Influence of Different Factors on the Impulse GroundingResistance of Grounding Devices 352

8.3.5 Influence of Different Factors on Impulse Coefficient355

8.3.6 Regressive Formulas to Calculate Impulse Coefficients357

8.3.7 Impulse Coefficient and Utilization Efficient Suggested inthe Literature 359

8.3.8 Low Resistivity Material Effects to Decrease ImpulseGrounding Resistance 360

8.4 Impulse Effective Length of Grounding Electrodes 362

8.4.1 Phenomenon of Impulse Effective Length 362

8.4.2 Regressive Formulas to Calculate the Effective Length ofCounterpoise Wires 364

8.4.3 Influence of LRM on the Impulse Effective Length ofCounterpoise Wires 368

8.5 Impulse Characteristics of a Grounding Grid 370

8.5.1 Influence of the Structure of the Grounding Grid 370

8.5.2 Influence of Soil Parameters 374

8.5.3 Influence of Impulse Current Waveform on the TransientPerformance of Grounding Grids 375

8.5.4 Impulse Effective Regions of Grounding Grids 378

8.6 Lightning Electromagnetic Field Generated by a GroundingElectrode 381

8.6.1 Computation Methodologies 381

8.6.2 Disposal of a Lightning Current 383

8.6.3 Influence of Soil Ionization 383

References 385

9 DC Ground Electrode 391

9.1 Technical Requirements of a DC Ground Electrode 391

9.1.1 Technical Characteristics of a DC Ground Electrode 391

9.1.2 Basic Principles of DC Ground Electrode Design 392

9.2 Structure Types of DC Ground Electrodes 394

9.2.1 Land Electrode 394

9.2.2 Shore Ground Electrode 400

9.2.3 Sea Electrode 401

9.3 Main Design Aspects of a DC Ground Electrode 401

9.3.1 Main Design Items 401

9.3.2 Determination of DC Ground Electrode Size 403

9.3.3 Determination of Coke Section 405

9.3.4 Diameter of Feeding Rod 406

9.3.5 Burial Depth of Electrode 407

9.3.6 Selection of Ground Electrode Material 407

9.4 Numerical Analysis Methods for a Ground Electrode 413

9.4.1 Numerical Analysis of a Ground Electrode by MoM and BEM414

9.4.2 Simplified Numerical Analysis Method 417

9.5 Heat Generation Analysis of a DC Ground Electrode 418

9.5.1 Numerical Analysis of the Heat Dissipation of a GroundElectrode 419

9.5.2 Maximum Temperature Rise Limit 422

9.6 Common Ground Electrode of a Multiple Converter System423

9.6.1 Demands on a Common Ground Electrode 424

9.6.2 Parameters of the Common Ground Electrode 427

9.6.3 Common Ground Electrode Design 429

9.7 Influence of DC Grounding on AC System 433

9.7.1 Influence of DC Electrode s Current Field on ACSystem 433

9.7.2 Numerical Analysis of DC Current Entering a NeutralGrounded Transformer 436

9.7.3 Allowable DC Current of a Transformer 443

9.8 Methods to Decrease Winding DC Current of a NeutralGrounding Transformer 445

9.8.1 Injecting Reverse DC Current Method 445

9.8.2 Inserting Capacitor Method 446

9.8.3 Inserting Resistor Method 447

9.9 Corrosion of Underground Metal Pipes Caused by a DC GroundElectrode 455

9.9.1 Mechanism of Electrochemical Corrosion of UndergroundMetal Pipes 455

9.9.2 Leakage Current through a Metal Pipe Caused by GroundElectrodes 455

9.9.3 Protection Measures 456

References 458

10 Materials for Grounding 461

10.1 Choice of Material and Size for Conductors 461

10.1.1 Requirement on Material and Size of Grounding Conductors461

10.1.2 Materials for a Grounding Conductor 463

10.1.3 Determination of Conductor Size 464

10.1.4 Grounding Conductor Size Determined by Ground FaultProtection 470

10.2 Soil Corrosion of Grounding Conductor 470

10.2.1 Features of Soil Corrosion 471

10.2.2 Natural Corrosion 471

10.2.3 Electrical Corrosion in Soil 474

10.3 Corrosion of Concrete-Encased Electrodes 476

10.4 Low-Resistivity Material 478

10.4.1 Principle of Reducing Grounding Resistance by LRM 478

10.4.2 Ingredients of LRM 482

10.4.3 Basic Requirements for LRM 485

10.4.4 Evaluation of LRM 487

10.5 Performance of LRM 488

10.5.1 Power Frequency Performance of LRM 488

10.5.2 Lightning Impulse Performance of LRM 493

10.6 Construction Method of LRM 495

10.6.1 Influence of LRM Bulk Shape on Reducing the GroundingResistance Effect 495

10.6.2 Amount of LRM and Construction Method 495

10.6.3 Construction of a Complex Ground Device 497

References 497

11 Measurement of Grounding 499

11.1 Methods for Grounding Resistance Measurement 499

11.1.1 Simple Methods for Measuring the Grounding Resistance ofSmall Grounding Devices 500

11.1.2 Principle of the Fall of Potential Method 501

11.1.3 Method of Far Placed Current Probe for Fall of PotentialMethod 502

11.1.4 Compensation Location of a Potential Probe for the Fallof Potential Method 504

11.1.5 Compensation Method for the Fall of Potential Method506

11.2 Instruments for Measuring Grounding Resistance 510

11.2.1 Ammeter Voltmeter Method 510

11.2.2 Ammeter Wattmeter Method 510

11.2.3 Ratio Meter Method 511

11.2.4 Bridge Method 513

11.2.5 Potentiometer Method 514

11.2.6 Single Equilibrium Transformer 514

11.2.7 ZC-8 Grounding Resistance Tester 515

11.2.8 Digital Measurement System of Grounding Resistance516

11.3 Factors Influencing the Results from the Fall of PotentialMethod 519

11.3.1 Electromagnetic Interferences During Measurements 519

11.3.2 Impact and Elimination of Power Frequency Interference520

11.3.3 Components of the Measured Voltage Signal for theGrounding Resistance Test 521

11.3.4 Mutual Inductance Between Potential and Current LeadWires 521

11.3.5 Short Measuring Leads Method 527

11.3.6 Accurate Location of Test Probe Positioning by GPS529

11.3.7 Influence of a Metal Structure Buried Nearby 529

11.3.8 Method to Eliminate Measuring Interference 531

11.4 Grounding Resistance Test in Vertically Layered Soil532

11.4.1 Grounding System Built in a Middle Low Resistivity Region532

11.4.2 Grounding System Built in a Middle High ResistivityRegion 534

11.4.3 Discussion of Analysis Results 535

11.5 Influence of Overhead Ground Wires on Substation GroundingResistance Measurement 535

11.5.1 General Analysis Model 536

11.5.2 General Discussion 536

11.5.3 Analysis of a 500 kV Substation 538

11.6 Measurement of Potential Distribution 539

11.6.1 Equipotential Line 539

11.6.2 Measurement of Equipotential Lines 540

11.6.3 Measurement of Step Voltage and Touch Voltage 541

11.7 Corrosion Diagnosis of Grounding Grids 542

11.7.1 Corrosion Diagnosis Model of a Grounding Grid 543

11.7.2 Implementation of the Diagnosis System 546

11.7.3 Field Test Results 547

References 550

Index 553

Product Details

  • publication date: 18/01/2013
  • ISBN13: 9781118254950
  • Format: Hardback
  • Number Of Pages: 550
  • ID: 9781118254950
  • weight: 1004
  • ISBN10: 1118254953

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