Methodology and Technology for Power System Grounding

566 Pages·2013·15.97 MB·English

by  Jinliang He

METHODOLOGY AND
TECHNOLOGY FOR
POWER SYSTEM
GROUNDING
METHODOLOGY AND
TECHNOLOGY FOR
POWER SYSTEM
GROUNDING
Jinliang He
Rong Zeng
Bo Zhang
DepartmentofElectricalEngineering,TsinghuaUniversity,China
Thiseditionfirstpublished2013
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LibraryofCongressCataloging-in-PublicationData
He,Jinliang.
Methodologyandtechnologyforpowersystemgrounding/JinliangHe,RongZeng,BoZhang.
pagescm
Includesbibliographicalreferencesandindex.
ISBN978-1-118-25495-0(cloth)
1. Electriccurrents–Grounding. 2. Electricpowersystems–Protection. I. Zeng,Rong,1971- II. Zhang,Bo,
1976- III. Title.
TK3227.H4252012
621.31902–dc23
2012024667
ISBN9781118254950
Setin9/11ptTimesbyThomsonDigital,Noida,India
Contents
Preface xiii
Acknowledgements xv
1 FundamentalConceptsofGrounding 1
1.1 ConductionMechanismofSoil 1
1.1.1 SoilStructure 1
1.1.2 ConductionMechanismofSoil 1
1.2 FunctionsofGroundingDevices 2
1.2.1 ConceptofGrounding 2
1.2.2 ClassificationofGrounding 3
1.2.3 PurposeofGrounding 5
1.3 DefinitionandCharacteristicsofGroundingResistance 7
1.3.1 DefinitionofGroundingResistance 7
1.3.2 RelationshipbetweenGroundingResistanceandCapacitance 8
1.3.3 ShieldingEffectamongGroundingConductors 9
1.4 GroundingResistanceofGroundingDevices 11
1.4.1 GroundingResistanceofGeneralGroundingDevices 11
1.4.2 GroundingResistanceofGroundingDeviceinNon-HomogeneousSoil 14
1.5 BodySafetyandPermittedPotentialDifference 19
1.5.1 AllowableBodyCurrentLimit 19
1.5.2 AllowableBodyVoltage 20
1.5.3 AllowablePotentialDifference 21
1.5.4 InfluenceofResistivityofSurfaceSoilLayeronBodySafety 23
1.6 StandardsRelatedtoPowerSystemGrounding 25
References 26
2 CurrentFieldintheEarth 27
2.1 ElectricalPropertyofSoil 27
2.1.1 SoilResistivity 27
2.1.2 InfluenceofDifferentFactorsonSoilResistivity 29
2.1.3 PermittivityofSoil 30
2.1.4 FrequencyCharacteristicsofSoilParameters 31
2.2 BasicPropertiesofaConstantCurrentFieldintheEarth 36
2.2.1 CurrentDensityintheEarth 36
2.2.2 ContinuityofEarthCurrentField 36
2.2.3 PotentialofStableCurrentField 37
2.2.4 CurrentFieldattheInterfaceofLayeredSoil 37
vi Contents
2.3 CurrentFieldCreatedbyaPointSourceinUniformSoil 38
2.3.1 Laplace’sEquation 38
2.3.2 CurrentFieldCreatedbyaPointSourceinSoil 39
2.3.3 EarthCurrentFieldProducedbyTwoOppositePointCurrentSources
ontheGroundSurface 41
2.3.4 EarthCurrentFieldinNon-UniformSoil 41
2.4 PotentialProducedbyaPointSourceontheGroundSurfacein Non-UniformSoil 43
2.4.1 HorizontallyLayeredSoil 44
2.4.2 HorizontalDouble-LayerSoil 45
2.4.3 HorizontalTriple-LayerSoil 46
2.4.4 VerticallyLayeredSoil 46
2.5 PotentialProducedbyaPointSourceinMulti-LayeredSoil 48
2.5.1 AnalysisofPotentialProducedbyaPointCurrentSource 48
2.5.2 NumericalIntegralMethodtoCalculateGreen’sFunctionofaPoint
CurrentSource 52
2.6 ComputerProgramDerivationMethodofGreen’sFunction 55
2.6.1 MethodofObtainingAnalyticExpression 55
2.6.2 ExpressionofGreen’sFunctionDerivedfromSoftwareProgram 59
2.6.3 CalculationofCurrentFieldinMulti-LayeredSoil 62
2.7 FastCalculationMethodofGreen’sFunctioninMulti-LayeredSoil 62
2.7.1 DevelopmentofaTwo-StageFittingMethod 63
2.7.2 ApplicationoftheFastCalculationofGreen’sFunction
inMulti-LayeredSoils 66
2.8 CurrentandPotentialDistributionsProducedbyaDCGroundElectrode 69
2.8.1 CurrentandPotentialDistributionsofDCinUniformSoil 69
2.8.2 CurrentandPotentialDistributionsofDCCurrentinNon-UniformSoil 72
References 78
3 MeasurementandModelingofSoilResistivity 81
3.1 IntroductiontoSoilResistivityMeasurement 81
3.2 MeasurementMethodsofSoilResistivity 83
3.2.1 SamplingAnalysisMethodofSoilResistivity 83
3.2.2 ElectricalSoundingMethods 83
3.2.3 TestProbeConfigurationforFour-ProbeMethod 88
3.2.4 FieldTestTechniqueofSoilResistivity 90
3.2.5 ElectromagneticSoundingMethod 93
3.3 SimpleAnalysisMethodforSoilResistivityTestData 94
3.3.1 ElectricalSoundingCurveMethodforTwo-LayeredHorizontal
SoilModel 94
3.3.2 AnalysisofaThree-LayeredHorizontalGeologicalStructure 99
3.3.3 ResistivityofVerticallyLayeredSoilStructure 101
3.3.4 EstimationofSoilModelParameterusingtheThree-ProbeMethod 102
3.4 NumericalAnalysisforaMulti-LayeredSoilModel 102
3.4.1 TypicalCurvesofMulti-LayeredSoilApparentResistivity 102
3.4.2 ExpressionofApparentSoilResistivity 105
3.4.3 InvertingSoilParameters 107
3.4.4 NumericalAnalysisMethodforTwo-LayeredSoilModel 108
3.5 Multi-LayeredSoilModelbySolvingFredholm’sEquation 109
3.5.1 SolvingtheForwardIntegralEquation 109
3.5.2 InversingParametersofSoilModels 113
3.5.3 ApplicationinEstimationofSoilParameters 116
Contents vii
3.6 EstimationofMulti-LayeredSoilModelbyUsingtheComplexImageMethod 118
3.6.1 EstimationofMulti-LayeredSoilStructure 119
3.6.2 FastCalculationoftheSoilApparentResistivity 119
3.6.3 PartialDerivativesofCalculatedApparentResistivity 121
3.6.4 ThePartialDerivativeExpressionsoff(l) 123
3.6.5 DeterminationoftheInitialSoilParameters 123
3.7 EngineeringApplications 123
References 128
4 NumericalAnalysisMethodofGrounding 131
4.1 CalculationMethodforParametersofSubstationGroundingSystems 131
4.1.1 CalculationofGroundingParameterswithEmpiricalFormulas 131
4.1.2 NumericalAnalysisMethodforGroundingSystemParameters 132
4.2 EqualPotentialAnalysisofGroundingGrid 135
4.2.1 ApproachofGreen’sFunctionforCalculatingGroundingParameters 135
4.2.2 SuperpositionMethodUndertheAssumptionofNodalLeakageCurrent 139
4.2.3 Multi-StepMethodUndertheAssumptionofNodalLeakageCurrent 141
4.2.4 IntegrationMethodUndertheAssumptionofBranchLeakageCurrent 143
4.3 UnequalPotentialAnalysisofaLarge-ScaleGroundingSystem 146
4.3.1 AnalysisModelofaGroundingSystemwithUnequalPotential 147
4.3.2 ProblemsintheAnalyticalMethodforSolvingaMutualResistance
Coefficient 148
4.3.3 NumericalIntegrationMethodforMutualResistanceCoefficient
Calculation 148
4.3.4 Multi-StepMethodforUniformSoil 149
4.4 AnalyzingGroundingGridwithGroundedCables 151
4.4.1 PrinciplesofSettingupEquations 151
4.4.2 CalculatingSelf-AdmittancesofConductorsandCables 153
4.5 MoMApproachforGroundingGridAnalysisinFrequencyDomain 153
4.5.1 BasisFunctionsofMoM 153
4.5.2 SettinguptheEquations 154
4.5.3 Green’sFunctionsandGeneralizedSommerfeldIntegral 155
4.6 FiniteElementMethodforaComplexSoilStructure 159
4.7 TimeDomainMethodforElectromagneticTransientSimulation
ofaGroundingSystem 161
4.7.1 GeneralizedMMCMethodunderEMQSAssumption 161
4.7.2 NumericalApproachBasedonTimeDomainIntegralEquation
inaLossyMedium 171
4.7.3 FiniteDifferenceTimeDomainMethod 181
References 186
5 GroundFaultCurrentofaSubstation 191
5.1 PowerStationandSubstationGroundFaults 191
5.1.1 TypesofPowerStationandSubstationGroundFaults 191
5.1.2 PrincipletoDetermineMaximumGroundFaultCurrent 191
5.1.3 LocationoftheMaximumGroundFaultCurrent 193
5.2 MaximumFaultCurrentthroughaGroundingGridtotheEarth 194
5.2.1 MaximumGroundingGridFaultCurrent 194
5.2.2 Zero-SequenceFaultCurrent 194
5.2.3 DeterminingtheFaultCurrentDivisionFactor 195
5.2.4 DeterminingtheDecrementFactor 196
viii Contents
5.2.5 DeterminingtheCorrectionCoefficientforFuturePlanning 198
5.2.6 ImpactofSubstationGroundingResistance 199
5.2.7 ImpactofFaultResistance 200
5.2.8 ImpactofOverheadGroundWiresandNeutralLines 200
5.2.9 ImpactofBuriedConduitsandCables 200
5.2.10 StepstoDetermineaProperDesignValueoftheMaximumGrounding
GridCurrent 200
5.3 SimplifiedCalculationofaFaultCurrentDivisionFactor 201
5.3.1 FaultCurrentDivisionFactorWithinaLocalSubstation 201
5.3.2 FaultCurrentDivisionFactorOutsideaLocalSubstation 202
5.4 NumericalCalculationoftheFaultCurrentDivisionFactor 203
5.4.1 NumericalCalculationMethodoftheFaultCurrentDivisionFactor 203
5.4.2 MatrixMethodtoCalculatetheFaultCurrentDivisionFactor 207
5.4.3 PhaseCoordinateTransformerModelforCalculatingtheFault
CurrentDivisionFactor 207
5.5 TypicalValuesoftheFaultCurrentDivisionFactor 213
5.5.1 InfluenceofSubstationGroundingResistance 213
5.5.2 InfluenceofTransmissionTowers 214
5.5.3 InfluenceofFaultLocation 216
5.5.4 InfluenceofIncomingCables 216
5.5.5 InfluenceofTransmissionLineNumber 216
5.5.6 InfluenceofTransmissionLineLength 217
5.5.7 InfluenceofTransformer 217
5.6 InfluenceofSeasonalFreezingontheFaultCurrentDivisionFactor 219
5.6.1 InfluenceofSeasonallyFrozenSoilontheFaultCurrentDivisionFactor 219
5.6.2 InfluenceofTransmissionLineNumbersAffectedbyFrozenSoil 221
References 221
6 GroundingSystemforSubstations 223
6.1 PurposeofSubstationGrounding 223
6.1.1 FunctionofSubstationGrounding 223
6.1.2 DesignObjectiveofaSubstationGroundingSystem 224
6.1.3 RequirementontheGroundingSystemofaSubstation 225
6.1.4 SpecificityofPowerPlantGrounding 225
6.1.5 RequirementsforGroundingSystemDesign 226
6.1.6 DesignandConstructionProceduresforaGroundingSystem 226
6.2 SafetyofGroundingSystemsforSubstationsandPowerPlants 227
6.2.1 DesignCriteriaofGroundingSystems 227
6.2.2 CalculationoftheGroundingResistanceofaGroundingSystem 228
6.2.3 AnalysisofGroundinginInhomogeneousSoil 230
6.2.4 SimplifiedFormulaforCalculatingStep,TouchandMeshVoltages 234
6.2.5 FormulasinIEEEStandard80-2000forCalculatingMeshandStep
Voltages 235
6.2.6 FormulastoCalculateTouchandStepVoltagesinChineseStandards 237
6.2.7 TransferPotential 238
6.2.8 MethodsforImprovingtheSafetyofaGroundingSystem 238
6.3 MethodsforDecreasingtheGroundingResistanceofaSubstation 240
6.3.1 BasicMethodsforDecreasingGroundingResistance 240
6.3.2 UsingLongVerticalGroundRodstoDecreaseGroundingResistance 241
6.3.3 ExplosionGroundingTechnique 248
Contents ix
6.3.4 DeepGroundWell 250
6.3.5 SlantingGroundingElectrode 253
6.4 EquipotentialOptimalArrangementofaGroundingGrid 254
6.4.1 PrincipleoftheUnequal-SpacingArrangement 254
6.4.2 RegularityoftheUnequal-SpacingArrangement 256
6.4.3 Unequal-SpacingArrangementwithExponentialDistribution 263
6.4.4 InfluenceofVerticalGroundingElectrodesonOCR 267
6.5 NumericalDesignofaGroundingSystem 268
6.5.1 GroundingSystemDesignofa220-kVSubstation 268
6.5.2 GroundingSystemDesignofa1000-kVUHVSubstation 270
References 272
7 GroundingofTransmissionandDistributionLines 275
7.1 RequirementforaTowerGroundingDevice 275
7.1.1 RequirementofTransmissionTowerGroundingResistance 276
7.1.2 SeasonalFactorfortheGroundingResistanceofaTowerGroundingDevice 276
7.2 StructuresofTowerGroundingDevices 277
7.2.1 BasicStructuresofTowerGroundingDevices 277
7.2.2 UsingNaturalFootingsasTowerGroundingDevices 280
7.3 PropertiesofaConcrete-EncasedGrounding 280
7.3.1 FunctionofaConcrete-EncasedGroundingDevice 280
7.3.2 HygroscopicPropertiesofConcrete 281
7.3.3 PermissibleCurrentthroughaConcrete-EncasedGroundingDevice 283
7.4 ComputationalMethodsforTowerGroundingResistance 284
7.4.1 EquivalentCylindricalConductorMethod 284
7.4.2 GroundingResistanceofaVerticalGroundRodCoveredwithConcrete 285
7.4.3 GroundingResistanceofaFabricatedConcrete-EncasedFooting 286
7.4.4 GroundingResistanceofaTowerGroundingDevicewithDifferent
Structures 287
7.4.5 UtilizationCoefficient 289
7.5 StepandTouchVoltagesNearaTransmissionTower 290
7.5.1 StepVoltageandTouchVoltage 290
7.5.2 ShockAccidentPossibilitiesCausedbyStepandTouchVoltages 292
7.6 Short-CircuitFaultonTransmissionTower 294
7.6.1 FaultCurrentofTransmissionLine 294
7.6.2 DistributionofGroundPotentialaroundTransmissionTowers 295
7.6.3 MethodstoImprovePotentialDistribution 296
7.7 GroundingDeviceofDistributionLines 299
7.7.1 VerticallyDrivenRods 300
7.7.2 GroundingofWoodPoles 301
7.7.3 RequirementforGroundingtheDistributionLine 301
References 301
8 ImpulseCharacteristicsofGroundingDevices 303
8.1 FundamentalsofSoilImpulseBreakdown 303
8.1.1 ElectricFieldStrengthofSoilBreakdown 303
8.1.2 PhenomenonofElectricalBreakdowninSoil 312
8.1.3 ImpulseBreakdownDelayCharacteristicsofSoil 319
8.1.4 MechanismofElectricalBreakdowninSoil 321
8.1.5 ResidualResistivityofIonizedSoil 323
x Contents
8.2 NumericalAnalysisoftheImpulseCharacteristicsofGroundingDevices 325
8.2.1 EquivalentCircuitModel 325
8.2.2 MoMCoupledwithCircuitTheory 331
8.2.3 AnInterpolationModeltoAcceleratetheFrequencyDomainResponse
Calculation 335
8.3 ImpulseCharacteristicsofTowerGroundings 346
8.3.1 FieldTestofGroundingDevicesImpactedbyaLargeImpulseCurrent 346
8.3.2 LightningCurrentDecayAlongaGroundingElectrode 348
8.3.3 DefinitionofImpulseGroundingResistance 350
8.3.4 InfluenceofDifferentFactorsontheImpulseGroundingResistance
ofGroundingDevices 352
8.3.5 InfluenceofDifferentFactorsonImpulseCoefficient 355
8.3.6 RegressiveFormulastoCalculateImpulseCoefficients 357
8.3.7 ImpulseCoefficientandUtilizationEfficientSuggestedintheLiterature 359
8.3.8 LowResistivityMaterialEffectstoDecreaseImpulseGroundingResistance 360
8.4 ImpulseEffectiveLengthofGroundingElectrodes 362
8.4.1 PhenomenonofImpulseEffectiveLength 362
8.4.2 RegressiveFormulastoCalculatetheEffectiveLengthofCounterpoise
Wires 364
8.4.3 InfluenceofLRMontheImpulseEffectiveLengthofCounterpoiseWires 368
8.5 ImpulseCharacteristicsofaGroundingGrid 370
8.5.1 InfluenceoftheStructureoftheGroundingGrid 370
8.5.2 InfluenceofSoilParameters 374
8.5.3 InfluenceofImpulseCurrentWaveformontheTransientPerformance
ofGroundingGrids 375
8.5.4 ImpulseEffectiveRegionsofGroundingGrids 378
8.6 LightningElectromagneticFieldGeneratedbyaGroundingElectrode 381
8.6.1 ComputationMethodologies 381
8.6.2 DisposalofaLightningCurrent 383
8.6.3 InfluenceofSoilIonization 383
References 385
9 DCGroundElectrode 391
9.1 TechnicalRequirementsofaDCGroundElectrode 391
9.1.1 TechnicalCharacteristicsofaDCGroundElectrode 391
9.1.2 BasicPrinciplesofDCGroundElectrodeDesign 392
9.2 StructureTypesofDCGroundElectrodes 394
9.2.1 LandElectrode 394
9.2.2 ShoreGroundElectrode 400
9.2.3 SeaElectrode 401
9.3 MainDesignAspectsofaDCGroundElectrode 401
9.3.1 MainDesignItems 401
9.3.2 DeterminationofDCGroundElectrodeSize 403
9.3.3 DeterminationofCokeSection 405
9.3.4 DiameterofFeedingRod 406
9.3.5 BurialDepthofElectrode 407
9.3.6 SelectionofGroundElectrodeMaterial 407
9.4 NumericalAnalysisMethodsforaGroundElectrode 413
9.4.1 NumericalAnalysisofaGroundElectrodebyMoMandBEM 414
9.4.2 SimplifiedNumericalAnalysisMethod 417
Contents xi
9.5 HeatGenerationAnalysisofaDCGroundElectrode 418
9.5.1 NumericalAnalysisoftheHeatDissipationofaGroundElectrode 419
9.5.2 MaximumTemperatureRiseLimit 422
9.6 CommonGroundElectrodeofaMultipleConverterSystem 423
9.6.1 DemandsonaCommonGroundElectrode 424
9.6.2 ParametersoftheCommonGroundElectrode 427
9.6.3 CommonGroundElectrodeDesign 429
9.7 InfluenceofDCGroundingonACSystem 433
9.7.1 InfluenceofDCElectrode’sCurrentFieldonACSystem 433
9.7.2 NumericalAnalysisofDCCurrentEnteringaNeutralGroundedTransformer 436
9.7.3 AllowableDCCurrentofaTransformer 443
9.8 MethodstoDecreaseWindingDCCurrentofaNeutralGroundingTransformer 445
9.8.1 InjectingReverseDCCurrentMethod 445
9.8.2 InsertingCapacitorMethod 446
9.8.3 InsertingResistorMethod 447
9.9 CorrosionofUndergroundMetalPipesCausedbyaDCGroundElectrode 455
9.9.1 MechanismofElectrochemicalCorrosionofUndergroundMetalPipes 455
9.9.2 LeakageCurrentthroughaMetalPipeCausedbyGroundElectrodes 455
9.9.3 ProtectionMeasures 456
References 458
10 MaterialsforGrounding 461
10.1 ChoiceofMaterialandSizeforConductors 461
10.1.1 RequirementonMaterialandSizeofGroundingConductors 461
10.1.2 MaterialsforaGroundingConductor 463
10.1.3 DeterminationofConductorSize 464
10.1.4 GroundingConductorSizeDeterminedbyGroundFaultProtection 470
10.2 SoilCorrosionofGroundingConductor 470
10.2.1 FeaturesofSoilCorrosion 471
10.2.2 NaturalCorrosion 471
10.2.3 ElectricalCorrosioninSoil 474
10.3 CorrosionofConcrete-EncasedElectrodes 476
10.4 Low-ResistivityMaterial 478
10.4.1 PrincipleofReducingGroundingResistancebyLRM 478
10.4.2 IngredientsofLRM 482
10.4.3 BasicRequirementsforLRM 485
10.4.4 EvaluationofLRM 487
10.5 PerformanceofLRM 488
10.5.1 PowerFrequencyPerformanceofLRM 488
10.5.2 LightningImpulsePerformanceofLRM 493
10.6 ConstructionMethodofLRM 495
10.6.1 InfluenceofLRMBulkShapeonReducingtheGroundingResistanceEffect 495
10.6.2 AmountofLRMandConstructionMethod 495
10.6.3 ConstructionofaComplexGroundDevice 497
References 497
11 MeasurementofGrounding 499
11.1 MethodsforGroundingResistanceMeasurement 499
11.1.1 SimpleMethodsforMeasuringtheGroundingResistanceofSmall
GroundingDevices 500