Essen%alsof

EarthingDesignIEEE80-2000

PTDCCommi:ee2017AnnualNa%onalConven%on19Nov2017 AdelGarcia,Jr.–PEE

Mobile:+639175222225Email-adelgarcia@gmail.com

Essen%alsofIEEE80-2000EarthingDesign

AbstractØ  Emphasizetheimportanceofcorrectlydesignedearthing

systemØ UnderstandthevariousfactorsthatdriveearthingdesignØ  ProvideageneralguidetoElectricalEngineershowtodesign

anearthingsystemtocomplywithIEEE80-2000Ø Understandthemetricsofacorrectlydesignedearthing

systemthatcompliestoIEEE80-2000

Note:Thispresenta/ondoesnotintendtopresentthecalcula/ondetailsofearthingdesigndueto/melimita/on.IIEE-PTDCoffersa16hourdetailedcoursedesignedtobeCPD-accredited,completewithactualdesignworkshop.Forthosewhoareinterested,pleasecontact:

IIEE-PTDCemail:trainingiiee@yahoo.com

The Importance of Correct Earthing Design

•  Establish,asdesignbasis,safelimitsofpotenLaldifferencesinasubstaLonunderfaultcondiLonsbetweenpointsthatcanbecontactedbythehumanbody.

•  ReviewearthingpracLceswithspecialreferencetosafetyanddevelopcriteriaforasafedesign.

•  ProvideadesignprocedureofpracLcalearthingsystems,basedonthesecriteria.

•  DevelopanalyLcalmethodstounderstandandsoluLonoftypicalgradientproblems

Condition of Danger Factors that Drive Earthing Design

DuringtypicalearthfaultcondiLons,theflowofcurrenttoearthwillproducepotenLalgradientswithinandaroundasubstaLon.Earthingdesignmustaddressthecircumstancesthatmakeelectricshockaccidentspossible,asfollows:

–  Rela/velyhighfaultcurrenttogroundinrelaLontotheareaofgroundsystemanditsresistancetoremoteearth

–  Soilresis/vityanddistribu/onofgroundcurrentssuchthathighpotenLalgradientsmayoccuratpointsattheearth’ssurface

–  Presenceofanindividualatsuchapoint,/me,andposi/onthatthebodyisbridgingtwopointsofhighpotenLaldifference.

–  Absenceofsufficientcontactresistanceorotherseriesresistancetolimitcurrentthroughthebodytoasafevalueunderabovecircumstances

–  Dura/onofthefaultandbodycontact,andhence,oftheflowofcurrentthroughahumanbodyforasufficientLmetocauseharmatthegivencurrentintensity

Tolerable Body Current Limit Factors that Drive Earthing Design

Themostcommonphysiologicaleffectsofelectriccurrentonthebody,inorderofincreasingcurrentmagnitudeare:a)thresholdpercep/on;b)muscularcontrac/on;c)unconsciousness;d)fibrilla/onoftheheart;e)respiratorynerveblockage;f)burning.•  1mA-thresholdofpercep/on;currentmagnitudeatwhichapersonisjustable

todetectaslight/nglingsensa/oncausedbythepassingcurrent•  1–6mA-“let-go”currents,unpleasanttosustain,butgenerallydonotimpair

theabilityofapersonholdinganenergizedobjecttocontrolhismusclesandreleaseit

•  9–25mA-painfulanddifficultorimpossibletoreleaseenergizedobjectsgraspedbythehand.Highercurrentsmuscularcontrac/onscouldmakebreathingdifficult

•  60–100mA-ventricularfibrilla/on,stoppageoftheheart,orinhibi/onofrespira/onmightoccurandcauseinjuryordeath

Range of Tolerable Current Factors that Drive Earthing Design

Thecurrentmagnitude(IB)andduraLon(ts)that99.5%ofallpersonscansafelywithstand,withoutventricularfibrillaLonisgivenbythefollowingformula:

IB=0.116÷√ts;for50kgbodyweight

IB=0.157÷√ts;for70kgbodyweight

Where:IB=Tolerablebodycurrentts=Timeofexposuretofaultcurrent

Accidental Earthed Circuit Factors that Drive Earthing Design

HumanResistance(IEEE-80)=1000ohmsHandandFootContact=0ohmGloveandShoeResistance=0ohmCurrentPathsthruthebodyarebetween:-Handtooneorbothfeet(touchpotenLal)-Bothfeet(steppotenLal)

Tolerable Voltage Factors that Drive Earthing Design

•  Ib=bodycurrent,inA•  RA=effecLvebodyresistanceinΩ•  VA=effecLvevoltageoftheaccidentalcircuit(touchorstepvoltage)inV

50kg:IB=0.116÷√ts

70kg:

IB=0.157÷√ts

Tolerable Voltage Factors that Drive Earthing Design

Thepermissibletotalequivalentvoltageis:

•  Etouch=IBx(RB+1.5ρ)

•  Estep=IBx(RB+6.0ρ)Where:

Ib-bodycurrentthroughtheaccidentalcircuit,inARB-totaleffecLveresistanceoftheaccidentalcircuitinΩρ-homogeneousearthresisLvity,inΩ-meter

Surface Material Resistivity Factors that Drive Earthing Design

•  AlayerofhighresisLvitymaterial(gravel)isojenspreadabovetheearthgridtoincreasecontactresistancebetweenthesoilandthefeetofpersonsinthesubstaLon

•  ThecurrentthroughthebodywillbeloweredconsiderablywiththeaddiLonofthesurfacematerialbecauseofthegreatercontactresistancebetweentheearthandthefeet

•  ThereducLondependsontherelaLvevaluesofthesoilandthesurfacematerialresisLviLes,andonthethicknessofthesurfacematerial.

Magnitude of Fault Current Factors that Drive Earthing Design

SymmetricalEarthFaultCurrent-  ThemaximumRMSvalueofsymmetricalfaultcurrentajertheinstantofaearthfaultiniLaLon

-  RepresentstheRMSvalueofthesymmetricalcomponentinthefirsthalf-cycleofacurrentwavethatdevelopsajertheinstantoffaultatLmezero.

Forphase-to-groundfaults:

If(0+)=3Iʹʹ0Where:

If(0+)- IniLalRMSsymmetricalgroundfaultcurrentI”0 - RMSvalueofzero-sequencesymmetricalcurrentthatdevelops

immediatelyajertheinstantoffaultiniLaLon,reflecLngthesubtransientreactancesofrotaLngmachinescontribuLngtothefault

SymmetricalEarthFaultCurrent=If=3I0

Duration of Fault Current Factors that Drive Earthing Design

TolerableEarthFaultCurrentisinverselyrelatedtothesquarerootofexposure/me:

IBαk÷√ts*Shortexposure/memeanshightolerablevalues*Longexposure/memeanslowtolerablevalues

TheallowedcurrentvaluemustbebasedonCLEARINGTIMEof:

Ø  PrimaryprotecLvedevicesØ  BackupprotecLvedevices

Primaryprotec7onclearing7meispossibleduetolowcombinedprobabilitythatrelaymalfunc7onswillcoincidewithallotheradversefactorsnecessaryforanaccident

Backupprotec7onclearing7meismoreconserva7vebecauseofgreatersafetymargin

Researchprovidesevidencethatahumanheartbecomesincreasinglysuscep/bletoventricular

fibrilla/onwhenthe/meofexposuretocurrentisapproachingtheheartbeatperiod,butthedangerismuchsmallerifthe/meofexposuretocurrentisintheregionof0.06sto0.3s(3.6cyclesto18cycles)

System X/R Ratio Factors that Drive Earthing Design

Therateofdecay(“DecrementFactor”)ofasymetricalfaultcurrenttosymmetricalvalueis

dictatedbythesystemX/Rra/oatthepointoffault.

Earthing Design Guide IEEE 80-2000

Earthing Design Guide IEEE 80-2000

LevelsofDesignEngineeringCalculaLons:Ø  TechnicalSpecificaLon(LimiLngValues)

•  SystemPerformanceCriteria•  EquipmentSelecLonfor:

o  RegulatoryandStandardsComplianceo  Procurement

Ø  ProtecLon,ControlandInstrumentaLon(PCI)Semng•  PrimaryPCIsemngs•  BackupPCIsemngs•  ProtecLonZonesCoordinaLonsemngs

Earthing Design Guide IEEE 80-2000

LevelsofFaultCalculaLons:Ø  LimiLngValue@PCC

•  LimitedbytechnicalraLngsofcommerciallyavailableequipment

Ø  PCIValue

•  ActualFaultLevelatPCC

ShortCircuit(SC)valuesatPCCareprovidedbyGridOwners;however,intheabsenceofsuchdata,theEngineermustbeabletodeterminethemostappropriateSCvaluetobeusedinthe

Limi/ngValuecalcula/ontobeabletowritethespecifica/onofthedesignwork.

Earthing Design Guide IEEE 80-2000

1.  DetermineandselectEarthConductorSize,usingEquaLon37ofIEEE80-2000:

Where:

I - ThreePhaseShortCircuitRMSCurrent,kAAmm2 - MinimumConductorCrossSecLon,mm2

TCAP - ThermalCapacityperUnitVolume,J/cm3.°Ctc - DuraLonofShortCircuitCurrent,secondαr - ThermalCoefficientofResisLvityatReferenceTemp,1/°Cρr - ResisLvityofEarthConductoratReferenceTemp,υΩ-cm1/αº - Ko,°CTm - MaxAllowable(Fusing)Temp,°CTa - AmbientTemp,°CTr - ReferenceTempforMaterialConstant,°C

Earthing Design Guide IEEE 80-2000

2.  CalculateEarthGridResistance2.1 DetermineandSetEarthGridArrangement;parameterstobeset

are:nrorr - NoofRowsLg - LengthofRowncorc - No.ofColumnWg - LengthofColumn,meterLc - TotalLengthofEarthConductor,meterLp - LengthofPerimeter,meterConductorSize asdeterminedfromstep1D - CrossSecLonalDiameterofearthconductor,meterNumberofElectrodesEarthingElectrodeLength-normally3metersLR - TotalLengthofEarthingElectrode,meterLT - TotalLengthofBuriedConductors,meter

Earthing Design Guide IEEE 80-2000

2.2 CalculateSurfaceLayerDeraLngFactor,asperEquaLon27ofIEEE80-2000:

Where:

ρ - SoilResisLvity,Ω-mρs - ResisLvityofSurfaceMaterial,Ω-mhs - ThicknessofSurfaceLayer,meterCs - SurfaceLayerDeraLngFactor

2.3 CalculateEarthingGridResistance,asperEquaLon52ofIEEE80-2000:

Where:

h - DepthofConductor,meterA - AreaOccupiedbyConductor,m2

Rg - EarthGridResistance,

𝐶𝑠 = 1−(0.09(1−𝜌/𝜌𝑠)/(2ℎ𝑠+0.09))

𝑅𝑔=𝜌[1/𝐿𝑡+(1/√20𝐴)∗(1+(1/((1+ℎ∗√20/𝐴))]

Earthing Design Guide IEEE 80-2000

3.  CalculateMaximumGridCurrent3.1 CalculateMaximumSymmetricalEarthFaultCurrent

Ig=(Iomax)xSfWhere:

Iomax - MaxSymmetricalEarthfaultCurrentSf - CurrentDivisionFactorIg - SymmetricalGridCurrent

3.2 CalculateDCTimeOffset,asperEquaLon74ofIEEE80-2000:Where:

X/R - X/RRaLoatFaultf - FrequencyTA - DCTimeOffset,Ta

Earthing Design Guide IEEE 80-2000

3.3 CalculateDecrementFactor,asperEquaLon79ofIEEE80-2000:Where:

Ta - DCTimeOffsettcortf- TimeduraLonofFaultDf - DecrementFactor

3.4 CalculateMaxEarthGridCurrent:IG=IgxDf

Where:Ig - SymmetricalGridCurrentDf - DecrementFactorIG - MaximumEarthGridCurrent

Earthing Design Guide IEEE 80-2000

4.  CalculateVoltageGradientLimits4.1 CalculateMaximumTolerableTouchPotenLal:

For50kg:For70kg:

Where:Cs - SurfaceLayerDeraLngFactorρs - ResisLvityofSurfaceMaterial,Ω-mts - TimeduraLonofFault

4.2 CalculateMaximumStepPotenLal:For50kg:

For70kg:Where:

Cs - SurfaceLayerDeraLngFactorρs - ResisLvityofSurfaceMaterial,Ω-mts - TimeduraLonofFault

Earthing Design Guide IEEE 80-2000

4.3 CalculateEarthPotenLalRise:

GPR=IGxRgWhere:

IG - MaximumEarthGridCurrentRG - EarthGridResistance,usingthevalueasatStep2.3GPR - GroundPotenLalRise–ascalculated

4.4 CalculateEarthPotenLalLimit:

GPR=IGxRgWhere:

IG - MaximumEarthGridCurrentRG - EarthGridResistance;usingthemaxvalueasallowedbytechnical

specifica/onsGPR - GroundPotenLalRiseLimit

Earthing Design Guide IEEE 80-2000

4.5 EarthDesignValidaLonandVerificaLonTouchVoltageCriteria:CalculatedGPR<Etouchlimit;EarthGridDesignisSAFE

StepVoltageCriteria:CalculatedGPR<Esteplimit;EarthGridDesignisSAFE

IftheabovevoltagelimitsofEtouchandEsteparenotmet,the

earthingdesignmustcon7nuetoStep5andbeyond.

Earthing Design Guide IEEE 80-2000

Earthing Design Guide IEEE 80-2000

5  EarthGridDesignVerificaLon5.1 CalculateGeometricFactor“n”,asperEquaLon84ofIEEE

80-2000: 5.1.1 CalculateGeometricFactor“na”,asperEquaLon85ofIEEE80-2000:5.1.2 CalculateGeometricFactor“nb”,asperEquaLon86ofIEEE80-2000:Where:

Lc - TotalLengthofConductorLp - LengthofGridConductorontheperimeterna - GeometricFactornc - 1.0nd - 1.0A - areaofearthgrid

Earthing Design Guide IEEE 80-2000

5.2 Calculate AverageSpacingBetweenParallelGridConductors:

Where:

nr - NoofRowsLg - LengthofRownc - No.ofColumnWg - LengthofColumn,meter

5.3 Calculate WeighingFactorforDepthofBurial: Where:

h - depthofconductorkh - WeighingFactorforDepthBurial

5.4 Weighing Factor for Earth Electrode = 1; for electrodes along the earth grid perimeter

𝑘h=√(1+h)

Earthing Design Guide IEEE 80-2000

5.5 Calculate GeometricMeanSpacing,asperEquaLon81ofIEEE80-2000:

Where:

D - SpacingBetweenParallelgridConductors,metersh - DepthofBuriedGridConductors,meterd - CrossSecLonalDiameterofearthgridconductorkh - WeighLngFactorfordepthofConductorkii - WeighLngFactorforElectrodesoncornermeshn - GeometricfactorKm - GeometricMeanSpacing

5.6 Calculate IrregularityFactor,asperEquaLon89ofIEEE80-2000: Where:

n - GeometricfactorKi - IrregularityFactor

Earthing Design Guide IEEE 80-2000

5.7 Calculate EffecLveBuriedLengthofEarthGrid–forMeshVoltage:

Where:

LM - EffecLveBuriedLengthofgridconductors,meterLC - TotalLengthofConductor,meterLr - LengthEarthElectrodeLx - LengthofEarthGridRowLy - LengthofEarthGridColumnLR - TotalLengthofEarthElectrode

Earthing Design Guide IEEE 80-2000

5.8 Calculate MaximumMeshVoltage: Where:

ρs - SoilResisLvityKm - GeometricMeanSpacingKi - IrregularityFactorIG - MaximumEarthGridCurrentLM - EffecLveBuriedLength,formeshvoltageEm - MaximumMeshVoltage

5.9 Calculate Geometric Mean Spacing Factor, as per Equation

94 IEEE 80-2000: Where:

h - DepthofConductorhD - AverageSpacingbetweenParallelGridConductorDn - GeometricFactor,nnKs - GeometricSpacingFactor

Earthing Design Guide IEEE 80-2000

5.10 Calculate EffecLveBuriedLengthofEarthGrid–forStepVoltage:

Where:

Lc - TotalLengthofConductorLR - TotalLengthofEarthingElectrodeLs - EffecLveBuriedLength-ForStepVoltage

5.11 Calculate Step Voltage, as per Equation 92 IEEE 80-2000:

Where:

ρs - SoilResisLvityKS - GeometricSpacingFactorKi - IrregularityFactorIG - MaximumEarthGridCurrentLs - EffecLveBuriedLength,forStepVoltageEs - StepVoltage

Earthing Design Guide IEEE 80-2000

Earthing Design Guide IEEE 80-2000

5.12 Earth Grid Design Validation and Verification: TouchVoltageCriteria:

MeshVoltage(Em)<MaximumTolerableTouchVoltage(Etouch)EarthGridDesignisSAFE

StepVoltageCriteria:

StepVoltage(Es)<MaximumTolerableStepVoltage(Estep)EarthGridDesignisSAFE

IftheabovevoltagelimitsofEtouchandEsteparenotmet,theearthingdesignmustberevisedtoreviewvaluesandassump7onson:

Ø  Timedura7onoffaultØ  MaximumsymmetricalfaultvalueØ  SoilResis7vity;depthofearthconductorØ  SurfaceLayerResis7vityandthickness;wetordryassump7onsØ  X/RRa7oofsystematPCCØ  RequiredearthresistanceØ  Areacoveredbyearthgrid

Short Resume

Adelino V. Garcia, Jr. Professional Electrical Engineer – 1584

Chairman and President

AVGarcia Power Systems, Corp. Quezon City, Philippines

www.avgarciapowersystems.com

President

Biyao Hydro Power Corporation

Technical Director Caraga Renewable Energy Corp.

Chairman

Alto Verde Corp.

Chairman Ballesteros Memorial Park

40 Years of Energy Systems Engineering and Integration

Project Management, Execution and Implementation Business Development and Management

Short Resume Adelino V. Garcia Jr. PEE

Expertise and Qualifications: Ø Energy Engineering and Systems Integration of

various technologies such as: Coal Thermal; Combustion Gas Turbine; Heavy/Light Fuel Oil; Biomass and Biogas; Hydroelectric, Solar PV, Wind and Fuel Cell Energy Generation Facilities

Ø Business and Project Development of Conventional and Renewable Energy Generation Technologies

Short Resume Adelino V. Garcia Jr. PEE

Expertise and Qualifications: Ø Project Development, Design and Engineering, Project

Execution and Management, Operation and Maintenance of various Power Generation Facilities (PGFs) Technologies:

Ø More than 3,000MW of Coal: Thermal and Gasification Ø More than 1,500MW of HFO/LFO Diesel: Low; Medium; High Speed Ø More than1200MW Combustion Turbine: Simple and Combined

Cycle Ø More than 100MW of Biomass/Biogas: Thermal; Pyrolysis;

Anaerobic Ø More than 100MW of Hydroelectric: Run-of-River; Pump Storage Ø More than 100MW of Solar: PV and Concentrating Ø More than 50MW of Fuel Cell (Hydrogen Technology): Molten

Carbonate Ø More than 100MW of Kinetic Power: CAES + Buoyancy

Short Resume Adelino V. Garcia Jr. PEE

Expertise and Qualifications: Ø Engineering and Execution of Grid Connection

Facilities for PGFs: Ø 2000MW of 500kV Switchyards Ø 1,500MW of 230kV Switchyards Ø 1,000MW of 115/138kV Switchyards Ø 1,000MW of 72kV Switchyards & Substations Ø 100MW of 36kV Switchyards & Substations

Ø 100MW of 15kV Switchyards & Substations

Q&A

PTDC Committee 2017 Mid Year Convention, Bacolod City 20May2017

Adel Garcia, Jr. – PEE Mobile: +63 917 522 2225 Email - adelgarcia@gmail.com