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HVDCTRANSMISSIONSYSTEMFORRURALALASKAAPPLICATIONSPhaseII‐PrototypingandTesting
May2012FINALREPORT,Version1.1
preparedby
polarconsultalaska,inc.1503West33rdAvenue,Suite310Anchorage,Alaska99503Phone:(907)258‐2420
fundingagency
TheDenaliCommission510LSt.,Suite410Anchorage,Alaska99501Phone:(907)271‐1414
projectadministrator
AlaskaCenterforEnergyandPowerUniversityofAlaska,Fairbanks814AlumniDr.P.O.Box755910Fairbanks,Alaska99775Phone:(907)474‐5402
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012
AbouttheCoverImage:
ThecoverimageisofademonstrationinstallationinFairbanksofaguyedfiberglasspolesimilarinsize,height,andconstructiontothepolesconsideredinthisstudyforoverheadtransmissioninruralAlaskaapplications.Thepoleisa12‐inch‐diameter,60‐foot‐tallfiberglassstructuresupportedbythreemicro‐thermopiles.Thepole’sfourguysareanchoredbytwomicro‐thermopilesandtwoscrewanchorssetinsilt‐richpermafrost.
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE I
EXECUTIVESUMMARY
ProgramObjectives
ThisreportpresentstheachievementsandfindingsofPhaseIIofthe“High‐VoltageDirectCurrent(HVDC)TransmissionSystemsforRuralAlaska”researchanddevelopment(R&D)program.ThegoalofthisprogramistoimprovetheeconomicviabilityofAlaska’sruralcommunitiesbyprovidingmoreaffordableelectricitytransmissionalternatives.PhaseIIworkwasfundedbytheDenaliCommissionandcompletedbyPolarconsultAlaska,Inc.(Polarconsult)undercontracttotheAlaskaCenterforEnergyandPower(ACEP).
TheeffectofexcessiveenergycostscontinuestodegradethequalityoflifeinAlaska’sruralcommunitiesandplacestheseindigenouspopulationsatsevererisk.Nearly80%ofruralcommunitiesaredependentondieselfuelfortheirprimaryenergyneeds.Someofthepooresthouseholdsspent47%oftheirincomeonenergyin2008,morethanfivetimestheamountinAnchorage(CWN,2012).
HVDCintertieswillsupportmorecost‐effectivedevelopmentoflocalenergyresources,suchaswind,hydro,biomass,geothermal,hydrokinetic,gas,andcoal.Reducingthecostoflow‐power(1megawatt[MW]andless)intertiesbyusingHVDCsystemscanenableincreasedinterconnectionofruralcommunitiestoAlaska’sabundantenergyresources.
HVDCintertieswillalsobenefitruralcommunitieswithreducedenergycostsbybuildingeconomicsofscaleinruralpowergridsandallowingutilitiestoconsolidatebulkfuelfacilitiesanddieselelectricpowerplantsintomoreefficientandlower‐costconfigurations.
Asaresultofongoingadvancesinpowerelectronics,small‐scaleHVDCintertiesarenowfeasible.Thisreporthasidentifiedlow‐poweroverheadandsubmarineHVDCtransmissionsystemsasaneconomicallysuperioralternativetoconventionalalternatingcurrent(AC)interties.AdditionalcostreductionscanberealizedbyintegratingHVDCsystemswithfutureexpansionofbroadbandfiber‐optictelecommunicationnetworks.ThissynergisticopportunitybetweenthetelecommunicationsandelectricindustriesisoneofseveralreasonsHVDCintertiescanhelpsurmounttheeconomicbarriersfacingAlaska’sruralcommunities.
ComparativeanalysisofHVDCtransmissionsystemswithconventionalACsystemsindicatessignificanttechnicalandeconomicadvantagesofHVDCsystems.InmanyruralAlaskaapplications,theuseofHVDCsystemswillsignificantlylowerintertiecosts.
PhaseIIObjectivesandFindings
PhaseIIofthisR&DprogramfollowsthePhaseI–PreliminaryDesignandFeasibilityAnalysisFinalReport(Polarconsult,2009).PhaseItasksincludedassessingconvertertechnicalfeasibilityandevaluatingtheeconomicsofalow‐powerHVDCsystemsizedforruralAlaskaapplications.BasedonthefavorableresultsofthePhaseIproject,thefollowingPhaseIIobjectiveswereestablished:
● ConfirmationofthetechnicalfeasibilityoftheHVDC/ACpowerconvertertechnologybydesigning,building,andtestingafull‐scaleprototypeofa1‐MWbidirectionalpowerconverterandkeytransmissionsystemelements.
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE II
● Confirmationoftheeconomicfeasibilityofthelow‐powerHVDCsysteminruralAlaskaapplicationsbydeterminingthecommercialcostoftheconverter,theconverter’sefficiency,andtheestimatedoverallcostsofanHVDCsystem.
● DevelopmentofcostestimatesforHVDCtransmissionsystemsandcomparisonwithconventionalACsystemstoquantifythebenefitsandsavingsofHVDCsystems.
PhaseIIhasdemonstratedthattheconvertertechnologyistechnicallyviableandthetransmissionsystemiseconomicallyfeasible.KeyPhaseIIfindingsare:
● Low‐powerHVDCconvertertechnologyisexpectedtobecommerciallyavailableat$250perkilowattperconverter.
● Estimatesofconstructioncostsforaconceptual25‐mileoverheadHVDCintertieindicatecapitalcostsavingsofapproximately30%comparedwithaconventionaloverheadACintertie.Estimatedlife‐cyclecostsrangefrom79%to107%ofthelife‐cyclecostofanACintertie.
● LongeroverheadHVDCintertiescanexpectcapitalcostsavingsofupto40%.
● PhaseIIanalysisalsoindicatesthatsignificantsavingsarepossibleforsubmarinecableandundergroundcableapplicationsusingHVDCsystems.Estimatedcapitalcostsavingsona25‐milelow‐powerHVDCsubmarinecableintertieareover50%comparedtoACalternatives.
BasedonPhaseIIfindings,thebenefitsoflow‐powerHVDCsystemsforAlaskaaresubstantial,andcontinueddevelopmentofthissystemisrecommended.
OpportunitiesandBarriers
BasedonanalysisandstudyconductedduringthisPhaseIIproject,PolarconsulthasconcludedthatthisHVDCtechnologypresentsthefollowingopportunitiesforAlaska’sutilityindustryandruralcommunities:
● Lessexpensiveruralelectricinterties,leadingtolower‐costenergyandincreasedenergyindependenceforruralcommunities.
● Interconnectiontocurrentlystrandedlocalenergyresources.
● Interconnectioncostsavingsbycombiningruralelectricandtelecommunicationsinterties.
Thesuccessfulcommercializationandadoptionoflow‐powerHVDCtechnologyinAlaskarequiresovercomingthefollowingbarriers:
● Completionofthecommercialdevelopmentanddemonstrationoftheconvertertechnology.Continueddevelopmentoftheprototypeconverters,culminatinginindependenttestingoftheconvertersanddeploymentonanAlaskautilitysystem,isneededtoprovethattheconvertersareacommerciallyviabletechnology.
● Acceptanceanduseoflow‐powerHVDCtechnologybyAlaska’sutilityindustry.Continuedinvolvementofin‐stateandinternationalstakeholderswiththeongoingdevelopmentofthistechnologyisconsiderednecessarytosurmountingthisbarrier.
● Developmentanddemonstrationofstandardsandcontrolprotocolsforlow‐powermultiterminaldirect‐current(MTDC)transmissionnetworks,whichareneededtobuildcost‐effectiveregionalHVDCpowernetworksinruralAlaska.
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE III
Recommendations
Basedontheconclusionsandfindingsofthisproject,thefollowingactionsarerecommended:
PhaseIIIprogramactivities:
● Continueddevelopmentofthepowerconvertertechnologytocommercializetheexistingprototypeconverterdesign.SolicitationofadditionalHVDCconvertermanufacturersiswarrantedtoencouragediversityofsuppliersandcompetition;
● Independenttestingoftheconverterstovalidateefficiencyandperformance,followedbydeploymentonanAlaskanutilitysystemtovalidatefunctionalityandreliabilityinacommercialsetting;
● FurtherdevelopmentofMTDCtransmissionsystemsinterconnectionandcontroltechnologies;and
● Continuedinvolvementofin‐statestakeholdersinthedevelopmentofthistechnology.
Stakeholderactions:
● Incorporatelow‐powerHVDCtechnologyintoAlaska’sregionalandstatewideenergyplansandpolicies;
● ContinuecoordinationwiththeStateofAlaskatoallowaproject‐specificwaiveroftheNationalElectricalSafetyCode(NESC)toallowtheuseofsingle‐wireearthreturn(SWER)circuits;
● EncourageplannedruralpowerandtelecommunicationsintertiestoincorporateHVDCtechnologyintheireconomicandtechnicalanalysis,aswellastheirenvironmentalandpermittingreviewprocesses;
● Engagethetelecommunicationsindustrytoraiseawarenessofthesynergiespossiblebetweenlow‐powerHVDCtransmissionandfibernetworksinruralAlaska;and
● Collaboratewithinternationalstakeholderstoidentifysynergiesandlessonslearnedfromparalleltechnologydevelopmentefforts.Coordinateondevelopmentofapplicablepolicies/standardsandidentificationofmarketstohelpexpeditethecommercializationandreducethecostsoflow‐powerHVDCsystems.
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE IV
TABLEOFCONTENTS
EXECUTIVESUMMARY...........................................................................................................................................................I
1.0 INTRODUCTION........................................................................................................................................................1 1.1 REPORTORGANIZATION...................................................................................................................................................2
1.2 ACKNOWLEDGEMENTS......................................................................................................................................................3
1.3 DISCLAIMER.........................................................................................................................................................................4
1.4 COPYRIGHTNOTICE...........................................................................................................................................................4
2.0 BACKGROUND............................................................................................................................................................5 2.1 PROGRAMOVERVIEW........................................................................................................................................................6
2.2 STAKEHOLDERADVICE......................................................................................................................................................7
3.0 HVDCTRANSMISSIONSYSTEMDESCRIPTION............................................................................................8 3.1 HVDCBACKGROUND........................................................................................................................................................8
3.2 HVDCSYSTEMCONFIGURATIONS................................................................................................................................10
3.3 COMPARISONOFACTOHVDCTRANSMISSION.........................................................................................................16
3.4 OVERHEADINTERTIEALTERNATIVES.........................................................................................................................17
3.5 SUBMARINECABLEINTERTIEALTERNATIVES...........................................................................................................19
4.0 HVDCCONVERTERSTATIONS.........................................................................................................................20 4.1 OVERVIEW........................................................................................................................................................................20
4.2 CONVERTERDEVELOPMENTOVERVIEW.....................................................................................................................20
4.3 ADDITIONALEQUIPMENT..............................................................................................................................................28
5.0 DESIGNCONCEPTSFOROVERHEADINTERTIES....................................................................................29 5.1 OVERHEADDESIGNAPPROACH....................................................................................................................................29
5.2 GEOTECHNICALCONDITIONS........................................................................................................................................30
5.3 ENVIRONMENTALLOADS...............................................................................................................................................30
5.4 CONSTRUCTION,RUSSTANDARDPRACTICE..............................................................................................................30
5.5 CONSTRUCTION,ALASKA‐SPECIFICCONCEPT............................................................................................................31
5.6 TESTINGOFOVERHEADDESIGNCONCEPTS...............................................................................................................32
6.0 SYSTEMECONOMICS...........................................................................................................................................37 6.1 COSTCOMPARISONOFACANDHVDCOVERHEADINTERTIES..............................................................................37
6.2 CASESTUDIES..................................................................................................................................................................41
7.0 CONCLUSIONSANDRECOMMENDATIONS................................................................................................49 7.1 CONCLUSIONS...................................................................................................................................................................49
7.2 OPPORTUNITIESANDBARRIERS...................................................................................................................................49
7.3 RECOMMENDATIONS.......................................................................................................................................................50
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE V
LISTOFTABLES
Table6‐1 EstimatedLife‐CycleCostsfor25‐mileOverheadACandHVDCInterties......................39
Table6‐2 SummaryofCaseStudies......................................................................................................................42
Table6‐3 EstimatedCostforaGreensCreek–HoonahHVDCIntertie.................................................44
Table6‐4 EstimatedBenefit‐CostRatioofGreensCreek–HoonahHVDCIntertie..........................45
Table6‐5 EstimatedInstalledCostfora5‐MWPilgrimHotSprings–NomeIntertie....................48
LISTOFFIGURES
Figure3‐1 TypicalLargeHVDCStation....................................................................................................................9
Figure3‐2 ThreeTypesofIntertiesUsedinHVDCSystems........................................................................11
Figure3‐3 MonopolarHVDCIntertieUsingSWER...........................................................................................12
Figure3‐4 MonopolarHVDCIntertiewithReturnConductor(SWER‐capableforBackup)..........13
Figure3‐5 BipolarHVDCIntertie(SWER‐capableforBackup)..................................................................14
Figure4‐1 LowVoltageAlternatingCurrent(LVAC)Enclosure:MechanicalLayout........................22
Figure4‐2 HVDCTransformerTank:MechanicalLayout.............................................................................23
Figure4‐3 CentralResonantLinkTestSetup.....................................................................................................25
Figure4‐4 Hi–PotTestSetupforHVDCTransformer.....................................................................................25
Figure4‐5 DrySystemInverterModeTestSchematicandSetup..............................................................26
Figure4‐6 System#1HVTankandLVEnclosure............................................................................................27
Figure4‐7 System#1ShowingHVMeasurementProbes.............................................................................27
Figure5‐1 InstallingMicro‐ThermopileforGuyAnchor...............................................................................33
Figure5‐2 AssemblingthePrototypeGFRPPoleSplice................................................................................34
Figure5‐3 PrototypeGFRPPoleFoundationDuringInstallation..............................................................35
Figure5‐4 PrototypePoleattheFairbanksTestSite......................................................................................36
Figure6‐1 ComparativeInstalledCost:Overhead1‐MWHVDCandACInterties..............................38
Figure6‐2 ComparativeLife‐CycleCost:Overhead1‐MWHVDCandACInterties............................40
Figure6‐3 LocationMapforPotentialHVDCProjectSites...........................................................................41
Figure6‐4 GreensCreek–HoonahIntertieRoute...........................................................................................43
Figure6‐5 ProspectiveTransmissionRoutefromPilgrimHotSpringstoNome................................47
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE VI
APPENDICES
APPENDIXA HVDCOVERVIEW............................................................................................................................A‐1
APPENDIXB ECONOMICANALYSIS...................................................................................................................B‐1
APPENDIXC CONCEPTUALDESIGNOFOVERHEADHVDCINTERTIELINES.................................C‐1
APPENDIXD CONCEPTUALDESIGNFORSUBMARINECABLES............................................................D‐1
APPENDIXE SWERCIRCUITSANDHVDCSYSTEMGROUNDING.........................................................E‐1
APPENDIXF HVDCPOWERCONVERTERDEVELOPMENT.....................................................................F‐1
APPENDIXG HVDCSYSTEMPROTECTION,CONTROLS,ANDCOMMUNICATIONS......................G‐1
APPENDIXH CANDIDATEHVDCSYSTEMDEMONSTRATIONPROJECTS..........................................H‐1
APPENDIXI STAKEHOLDERADVISORYGROUPINVOLVEMENTANDMEETINGS........................I‐1
APPENDIXJ BIBLIOGRAPHY..................................................................................................................................J‐1
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE VII
ACRONYMSANDTERMINOLOGY
°F degreesFahrenheit
A,a,i amperesoramps
AC alternatingcurrent
ACEP AlaskaCenterforEnergyandPower
ACSR aluminumconductorsteelreinforced
ADNR AlaskaDepartmentofNaturalResources
AEA AlaskaEnergyAuthority
AEL&P AlaskaElectricLightandPowerCompany
AFI ArcticFoundations,Inc.
AKDOL AlaskaDepartmentofLabor
albedo Theextenttowhichanobjectdiffuselyreflectslight.
alternatingcurrent
Theformofelectricitycommonlyusedinhomesandbusinessesinwhichthecurrentandvoltageoscillateatafrequencyof60cyclespersecond.(Thefrequencyinsomenationsis50cycles.)
Alumoweld Atypeofcableusedinelectricalsystems.Eachstrandofthecableconsistsofasteelcorewithalayerofaluminumextrudedoveritduringthepullinganddrawingprocess.Thesteelcoreprovidesincreasedstrength,andthealuminumexteriorprovidesbettercorrosionprotectionandincreasedelectricalconductivity.
amperes/amps
Ameasureoftheamountofelectricalcurrentflowingthroughacircuit(atypicalhouseholdcircuitisratedfor20amperes).
AP&T AlaskaPowerandTelephoneCompany
APA AlaskaPowerAssociation
ASCE AmericanSocietyofCivilEngineers
AVEC AlaskaVillageElectricCooperative,Inc.
AVR automaticvoltagereference
bandwidth Ameasureofthedatatransfercapabilityofagivencommunicationsmethod.Unitsofbandwidthcanvarybutaregenerallybitspersecond.
BEC BethelElectricUtility
bipolar Atypeofdirectcurrentcircuitthatusestwowirestotransmitenergy.Bipolarcircuitsoperateonewire(“pole”)atapositivepotentialandthesecondpoleatanegativepotentialrelativetoground(e.g.,+/‐600,000volts).Thesecircuitsnormallyalsohaveanearthreturnpathwayoradedicatedgroundconductorthatisusedtocompensateforanyimbalanceonthetwopolesandservesasatemporaryreturnpathwayifthenegativeorpositivepoleisoutofserviceforanyreason.
BSNC BeringStraitsNativeCorporation
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
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Btu Britishthermalunit
CEA ChugachElectricAssociation,Inc.
CIGRE InternationaledesGrandsReseauxElectriques
circuit Acircuitprovidesanelectricalpathwayfromapointofenergysupply(e.g.,ageneratororbattery)toapointofenergyuse(e.g.,motor,lighting,etc.),andthenbacktothepointofsupply.Withoutacompletepathwayfromsupplytouseandback,thecircuitwillnotfunction.Thepathwaycantakemanyforms.Mostcommonly,itismadeofmetallic(copperoraluminum)wires,butitcanalsousewater,theearth,orothermaterials.Theseothermaterialsaremostoftenusedonthereturnpathwaybacktothepointofsupply,wherethevoltagedifferentialrelativetothesurroundingenvironmentislow.
conductor Atypicallymetallicwireorcablethatisdesignedandfabricatedtoconductelectricitybetweentwolocations.
converter AnelectricaldevicethatconvertselectricityfromACtoDCand/orfromDCtoAC.“Converter”isamoregeneraltermforarectifierorinverter.
CVEA CopperValleyElectricAssociation,Inc.
DC directcurrent
directcurrent Directcurrentistheformofelectricitycommonlyusedinbattery‐powereddevicessuchascars,flashlights,etc.Thecurrentdoesnotappreciablyvarywithtime.
distributionclass
Referstolower‐voltageelectricalsystems.Definitionsvary,butsystemsoperatingatorbelownominal35kilovolts(kV)aregenerallyclassifiedasdistribution‐class.MostruralAlaskaintertiesfunctionastransmissionsystems,butoperateatdistribution‐classvoltages,typically14.4kV.
earthreturn Ameansofcompletinganelectricalcircuitbyusingtheearthasareturnpathinsteadofasecondwire.Inmanynations,thisapproachisfrequentlyusedinruralareaswhere(1)thecosttoinstallasecondwireforthereturnpathisprohibitivelyhighand(2)thelackofburiedutilitiesensuresthattechnicalissueswithgroundreturnareminimized.
EHS extra‐high‐strength
EPR ethylenepropylenerubber
fiberoptics Acommunicationsmethodthatconsistsofsendingpulsesoflightdownglassfibers.
FO fiberoptics
ft‐lb foot‐pound
gal gallon(s)
GEC GustavusElectricCompany
GFRP glass‐fiber‐reinforcedpolymer
GPS GlobalPositioningSystem
GVEA GoldenValleyElectricAssociation,Inc.
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MAY 2012 PAGE IX
HEA HomerElectricAssociation,Inc.
hertz Aunitofhowrapidlysomethingoscillates,rotates,orrepeats.Onehertzisequaltoonecompletecyclepersecond.AlternatingcurrentelectricalsystemsintheU.S.operateat60hertz,or60cyclespersecond.
high‐impedancegroundfault
Afaultorshortcircuitbetweenahigh‐voltagewireandground.Anexampleofahigh‐impedancegroundfaultwouldbeaconductorthatfallstothegroundwithoutbreaking,landingoniceorice‐richsoils.Thesesoilsareverypoorconductors,thuslittleornocurrentmayshortcircuitintotheground.Becausethewiredidnotbreak,itcancontinuetotransmitenergybetweentheconverters.Thisenergizedwireposesahazardtoanypeopleoranimalswhohappenuponit.
high‐voltagedirectcurrent
Directcurrentelectricityatahighvoltagerelativetothesurroundingenvironment.
HMI human‐machineinterface
hotwork Workingonelectricalequipmentwhileitisenergized.
HVDC high‐voltagedirectcurrent
IEC InternationalElectro‐technicalCommission
IEEE InstituteofElectricalandElectronicsEngineers
IGBT insulatedgatebipolartransistor
inverter AnelectricaldevicethatcanconvertDCelectricityintoACelectricity.
IPEC InsidePassageElectricCooperative
KEA KodiakElectricAssociation,Inc.
kHz kilohertz(1,000hertz)
kilowatt 1,000watts.OnekWisthepowerconsumedbyten100‐wattincandescentlightbulbs.
kilowatt‐hour Thequantityofenergyequaltoonekilowatt(kW)expendedforonehour.
KoEA KotzebueElectricAssociation,Inc.
kV kilovolt(1,000volts)
kVA kilovolt‐ampere
kW kilowatt(1,000watts)
kWh kilowatt‐hour
LDE LineDesignEngineering,Inc.
LFL linefaultlocator
LIDAR lightdetectionandranging
litzwire Anelectricalwireorcablemadeofmultipleindividuallyinsulatedstrandsofwire.LitzwireisusedinhighfrequencyACapplicationsandisdesignedtoreducepowerlossescausedbyskineffectsandproximityeffectsthatoccurathighfrequencies.
LVAC low‐voltagealternatingcurrent
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MAY 2012 PAGE X
MEA MatanuskaElectricAssociation
MHRC ManitobaHVDCResearchCentre
mm2 squaremillimeters
MOD motor‐operateddisconnector
monopolar Adirectcurrentcircuitthatoperatesonelegofthecircuitatanelevatedvoltageandthereturnlegatorneargroundvoltage.Thereturnlegcanuseametallicconductoror,inthecaseofearthorseareturnsystems,canusetheearthorseatocompletethecircuit.AnHVDCSWERcircuitisonetypeofmonopolarcircuit.
ms millisecond(s)
MSB Matanuska‐SusitnaBorough
MTDC multi‐terminaldirectcurrent
MVA megavoltamperes(onemillionvoltamperes)
MW megawatt(s)(1,000kilowatts)
MWh megawatt‐hours
NCC NomeChamberofCommerce
NEA NaknekElectricAssociation,Inc.
NEC NushagakElectricCooperative,Inc.
NESC NationalElectricalSafetyCode
NJUS NomeJointUtilityService
NLP NuvistaLightandPower,Inc.
NRECA NationalRuralElectricCooperativeAssociation
NSB NorthSlopeBorough
NWAB NorthwestArcticBorough
O&M operationsandmaintenance
OED CityofOuzinkieElectricDepartment
OMR&R OperationandMaintenance,Repair,Replacement,andRehabilitation
OPGW opticalgroundwire
PCB printedcircuitboard
PCE PowerCostEqualization
PLC powerlinecarrier
PPS PrincetonPowerSystems,Inc.
PSCAD PowerSystemsComputerAidedDesign
psf poundspersquarefoot
R&D researchanddevelopment
RCA RegulatoryCommissionofAlaska
rectifier AnelectricaldevicethatcanconvertACelectricityintoDCelectricity.
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RMS root‐mean‐square
rootmeansquare
Therootmeansquarevoltageisthemeanabsolutevoltageoveranywholenumberofwaveformoscillations.Forasinusoidalwaveform(suchasnormalACelectricity),theroot‐mean‐square(RMS)voltageisthepeakvoltagedividedbythesquarerootof2.Nominal120voltsalternatingcurrent(VAC)electricitythushasapeakvoltageofabout+/‐170voltsrelativetoground.
RUS RuralUtilitiesService(USDA)
SAG StakeholdersAdvisoryGroup
SCADA supervisorycontrolanddataacquisition
seareturn Ameansofcompletinganelectricalcircuitbyusingthesea(ormoregenerallyrivers,lakes,andotherwaterbodies)asareturnpathinsteadofasecondwire.Thisapproachisfrequentlyusedonsubmarinecableswherethecostsavingsfromnotinstallingasecondcablejustifythisapproach.Seareturncanbeusedforsingle‐phaseACcircuitsorforDCcircuits.
SEAPA SoutheastAlaskaPowerAgency
SEC SoutheastConference
single‐wireearthreturn
Anothertermforanearthreturnorseareturncircuit.Thenameemphasizesthefactthatthesetypesofcircuitsonlyrequireonewire,ascomparedwithtwoormorewiresforothertypesofcircuits.
spurandbelt Acommonmethodofclimbingutilitypoles,trees,andsimilarobjects.Specialclimbingspursarestrappedontothefeetandalargebeltisfixedaroundtheclimber'swaist.Theclimberloopsthebeltaroundthepoleanddrivesthespursintothepole.Theclimberthen“walks”upthepolewiththespurs,andhitchesthebeltalongthepoleforsupport.
steppotential Avoltagegradientthatoccursatthegroundsurfaceduetoearthreturncurrents.Ifthevoltagegradientishighenough,itcanposeahazardtopeopleorwildlifesteppinginthevicinity.
strandedenergyresources
Energyresourceslocatedinremote,distant,orotherwiseisolatedareas“stranded”fromeither(1)integrationintomodernenergyinfrastructureandsupplychainsor(2)utilizationbylocalpopulationandindustrycenters.
SWAMC SouthwestAlaskaMunicipalConference
SWER single‐wireearthreturn
transmission‐class
Referstohigher‐voltageelectricalsystems.Definitionsvary,butinAlaskaACsystemsoperatingabovenominal35kVline‐to‐groundaregenerallyclassifiedastransmission‐class.MostruralAlaskaintertiesfunctionastransmissionsystems,butareoperatedatdistribution‐classvoltages.
twistedpair Agenerictermforcommunicationscablethatusesmultipleindividuallyinsulatedwires.Eachpairofwiresistwistedtogether,hencethename.
TWMR transmissionwithmetallicconductor‐returnpath
UAF UniversityofAlaskaFairbanks
USDA U.S.DepartmentofAgriculture
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE XII
V volt
VAC voltsalternatingcurrent
VAR volt‐amperesreactive
VDC voltsdirectcurrent
VFT variablefrequencytransformer
volt Aunitofelectricalpotential.Sometypicalvoltagesarecarbattery:12volts(DC);alkalinebattery(AAA,C,D,etc.):1.5volts(DC);householdelectricity:120volts(ACRMS).
VSC voltagesourceconverter(s)
ZAE ZarlingAeroConsulting
FINALREPORT,VERSION1.1 POLARCONSULTALASKA,INC.HVDCTRANSMISSIONSYSTEMFORRURALALASKANAPPLICATIONS PHASEII–PROTOTYPINGANDTESTING
MAY 2012 PAGE 1
1.0 INTRODUCTION
ThisreportpresentstheachievementsandfindingsofPhaseIIofthe“High‐VoltageDirectCurrent(HVDC)TransmissionSystemsforRuralAlaska”researchanddevelopment(R&D)program.
ThegoalofthisprogramistoimprovetheeconomicviabilityofAlaska’sruralcommunitiesbyprovidingmoreaffordableelectricitytransmissionalternatives.TheeffectofexcessiveenergycostscontinuestodegradethequalityoflifeinAlaska’sruralcommunitiesandplacestheseindigenouspopulationsatsevererisk.Nearly80%ofruralcommunitiesaredependentondieselfuelfortheirprimaryenergyneeds.Someofthepooresthouseholdsspent47%oftheirincomeonenergyin2008,morethanfivetimestheamountinAnchorage(CWN,2012).
Reducingthecostoflow‐power(1megawatt[MW]andless)intertiesbyusingHVDCsystemscanenableincreasedinterconnectionofruralcommunitiestoAlaska’sabundantenergyresources.HVDCintertieswillsupportmorecost‐effectivedevelopmentoflocalenergyresources,suchaswind,hydro,biomass,geothermal,hydrokinetic,gas,andcoal.
PhaseIIofthisprogramwasfundedbytheDenaliCommissionandcompletedbyPolarconsultAlaska,Inc.(Polarconsult)undercontracttotheAlaskaCenterforEnergyandPower(ACEP).ThisPhaseIIeffortandfinalreportfollowstheresultsofthePhaseIR&Dproject,completedin2009andsummarizedinPhaseI–PreliminaryDesignandFeasibilityAnalysisFinalReport(Polarconsult,2009).PhaseIofthisR&DprogramincludedevaluationofthetechnicalandeconomicfeasibilityoftheproposedHVDCsystem,includinglimitedprototypingandtestingoftheconvertertechnology.
PhaseIIoftheHVDCTransmissionSystemprogramincludeddesign,fabrication,andtestingoffull‐scaleprototypesoftheconverterandtransmissionsystemelements.ThePhaseIIeffortsinvolvedtheevaluationofdesign,efficiency,andfunctionalityoftheHVDCsystems.RuralAlaskaintertiealternativeswerealsoinvestigated,whichinvolvedcomparingHVDCtransmissionsystemstotheconventionalalternatingcurrent(AC)alternatives.ThePhaseIIfindingswereusedtofurtherdevelopconstructioncostestimatesandrefinetheeconomicanalysisofthetechnologydevelopedinPhaseI.PolarconsultistheprimecontractorandauthorofbothPhaseIandIIprojectreports.
Asaresultofongoingadvancesinpowerelectronics,small‐scaleHVDCintertiesarenowfeasible.ThisreporthasidentifiedoverheadandsubmarineHVDCtransmissionsystemsaseconomicallysuperioralternativestoconventionalACinterties.
AdditionalcostreductionscanberealizedbyintegratingHVDCsystemswithfutureexpansionofbroadbandfiber‐optictelecommunicationnetworks.ThissynergisticopportunitybetweenthetelecommunicationsandelectricindustriesisoneofseveralreasonsHVDCintertiescanhelpsurmounttheeconomicbarriersfacingAlaska’sruralcommunities.
ComparativeanalysisofHVDCtransmissionsystemswithconventionalACsystemsindicatessignificanttechnicalandeconomicadvantagesofHVDCsystems.InmanyruralAlaskaapplications,theuseofHVDCsystemswillsignificantlylowerintertiecosts.
Basedonthefavorablefindings,PolarconsultrecommendscontinuedworkonthisprojectthroughPhaseIIIworkactivities,includingdemonstrationoftheHVDCsystemonanAlaskautilitysystem.
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1.1 REPORTORGANIZATION
PhaseIIofthisprojectaddressesawiderangeoftechnicaldisciplinesandsubjectmaterial.Forbrevity,thebodyofthisreportfocusesonthekeyfindingsandconclusionsthathaveresultedfromthiswork.In‐depthinformationpertainingtospecifictopicsisincludedinthereport’sappendices.
Thisreportisorganizedasfollows:
● TheExecutiveSummaryandtheAcronymsandDefinitionssectionsareincludedatthebeginning.
● Section1.0introducesthereport.
● Section2.0providesbackgroundinformationonAlaska’sruralenergyissuesandabriefexplanationofthestakeholders’rolesinthisphaseoftheproject.
● Section3.0isadescriptionoftheHVDCtransmissionsystem,whichincludesacomparisonofACandHVDCtransmission,overheadintertiealternatives,andsubmarinecableintertiealternatives.
● Section4.0discussesHVDCconverterstations.
● Section5.0evaluatesthedesignconceptsforoverheadinterties.
● Section6.0containstheeconomicevaluationofPhaseII.
● Section7.0providestheconclusionsandrecommendationsforthePhaseIIprototypingandtestingstudy.
Inaddition,thisreportcontainsthefollowingappendices,whichincludereportsgeneratedbyPolarconsult’ssubcontractorsforthisprojectasattachments:
● AppendixA HVDCOverview
● AppendixB EconomicAnalysis
● AppendixC ConceptualDesignofOverheadHVDCIntertieLines
● AppendixD ConceptualDesignforSubmarineCables
● AppendixE SWERCircuitsandHVDCSystemGrounding
● AppendixF HVDCPowerConverterDevelopment
● AppendixG HVDCSystemProtection,Controls,andCommunications
● AppendixH CandidateHVDCSystemDemonstrationProjects
● AppendixI StakeholderAdvisoryGroupInvolvementandMeetings
● AppendixJ Bibliography
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1.2 ACKNOWLEDGEMENTS
Polarconsultacknowledgesandappreciatesthesupportandcontributionsofthemanyindividualsandentitiesthathaveparticipatedinthisproject.Theirsupport,insights,experience,andtechnicalanalysis remain invaluable to the continuing effort to bring lower‐costHVDC intertie systems toAlaskans.
MembersoftheteaminvolvedinthesecondphaseofHVDCintertiedevelopmentinclude:
● DenaliCommission(FundingAgency)
● ACEP(GrantManagement,EconomicAnalysis,Strategy)
● Polarconsult(ProjectManagement,StrategicVision,Design)
● PrincetonPowerSystems,Inc.(PPS)(ConverterDevelopment)
● UniversityofAlaskaFairbanks(UAF)/Dr.RichardWies(UAFQualityControlandTechnicalReview)
● AlaskaVillageElectricCooperative,Inc.(AVEC)(AlaskaIntegration/Practicality)
● StakeholdersAdvisoryGroup(Practicality/IndustryAcceptance)
● ManitobaHVDCResearchCentre(HVDCExpert)
● LineDesignEngineering(StructuralandCodeExpert)
● GolderAssociates(GeotechnicalExpert)
● Almita,Inc.(FoundationSupplier)
● ArcticFoundations,Inc.(AFI)(FoundationSupplier)
● ZarlingAeroConsulting(ZAE)(ThermalSoilsAnalysis)
● STG,Inc.(RuralIntertieContractor)
● Cabletricity,Inc.(SubmarineCable/HVDCExpert)
Inaddition,theStakeholdersAdvisoryGroup(SAG)membershaveplayedaninstrumentalroleinthisprogrambycontributingtheirtimeandyearsofexperience.TheSAGwaschairedbytheDenaliCommissionandfacilitatedbyACEP.SAGmembersinclude:
● AlaskaDepartmentofLabor(AKDOL)
● AlaskaEnergyAuthority(AEA)
● AlaskaPower&TelephoneCompany(AP&T)
● AlaskaPowerAssociation(APA)
● AVEC
● BeringStraitsNativeCorporation(BSNC)
● BethelElectricUtility(BEC)
● CopperValleyElectricAssociation,Inc.(CVEA)
● GoldenValleyElectricAssociation,Inc.(GVEA)
● HomerElectricAssociation,Inc.(HEA)
● InsidePassageElectricCooperative(IPEC)
● InstituteofNorthernEngineering(INE),UAF
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● KodiakElectricAssociation,Inc.(KEA)
● KotzebueElectricAssociation,Inc.(KoEA)
● MatanuskaElectricAssociation(MEA)
● NaknekElectricAssociation,Inc.(NEA)
● NationalRuralElectricCooperativeAssociation(NRECA)
● NomeChamberofCommerce(NCC)
● NomeJointUtilityService(NJUS)
● NorthSlopeBorough(NSB)
● NorthwestArcticBorough(NWAB)
● NushagakElectricAssociation
● NuvistaLightandPower,Inc.(NLP)
● SoutheastConference(SEC)
● SouthwestAlaskaMunicipalConference(SWAMC)
● U.S.DepartmentofAgriculture(USDA)RuralUtilitiesService(RUS)
● UAF
1.3 DISCLAIMER
ThisreportwaspreparedbyPolarconsultsolelyfortheUAF.TheUAFhastherighttoreproduce,use,andrelyuponthisreportforpurposesrelatedtoinvestigatingthe“HVDCTransmissionSystemforRuralAlaskanApplications,”including,withoutlimitation,therighttodeliverthisreporttoregulatoryauthoritiesinsupportof,orinresponseto,regulatoryinquiriesandproceedings.ForthepurposesofthisDisclaimer,allpartiesotherthanPolarconsultandtheUAFare“thirdparties.”NeitherPolarconsultnortheUAFrepresent,guarantee,orwarranttoanythirdparty,expresslyorbyimplication,theaccuracy,suitability,reliability,completeness,relevance,usefulness,timeliness,fitness,oravailabilityofthisreportforanypurposeortheintellectualorotherpropertyrightsofanypersonorpartyinthisreport.
Thirdpartiesshallnotuseanyinformation,product,orprocessdisclosed,described,orrecommendedinthisreportandshallnotrelyuponanyinformation,statement,orrecommendationcontainedinthisreport.Shouldanythirdpartyuseorrelyuponanyinformation,statement,recommendation,product,orprocessdisclosed,contained,described,orrecommendedinthisreport,theydosoentirelyattheirownrisk.Tothemaximumextentpermittedbyapplicablelaw,innoeventshallPolarconsultortheUAFacceptanyliabilityofanykindarisinginanywayoutoftheuseorreliancebyanythirdpartyuponanyinformation,statement,recommendation,product,orprocessdisclosed,contained,described,orrecommendedinthisreport.
1.4 COPYRIGHTNOTICE
ThisreportiscopyrightprotectedbyPolarconsultandmaynotbereproducedinwholeorpartwithoutthepriorwrittenconsentofPolarconsult.
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2.0 BACKGROUND
Energycoststhroughoutmostofrural1Alaskaaresignificantlyhigherthaninthestate’surbanareas.Overthepastdecade,ruralenergycostshaveescalateddramatically,tothepointwherelifeinmanyruralAlaskancommunitiesisinastateofeconomicperil.TheprimaryreasonsforthesehighenergycostsisruralAlaska’sdependenceondieselfuelforpowergenerationandheating,thelackofeconomiesofscaleinruralcommunities,andthetransportationchallengescommoninruralAlaska.
FormostruralAlaskancommunities,adiesel‐electricplantisthepowergenerationresourceofchoicesincetheseplantsandtheirsupportinginfrastructuresuchasbulkfuelfacilitiesarereadilyadaptedtotheneedsofrurallocalities.However,generatingelectricitywithdieselfuelisexpensiveduetothesecommunities’smallscaleandgeographicisolation.Consequently,ruralAlaskahassignificantlyhigherenergycostscomparedtocommunitiesinorconnectedwithAlaska’surbancenters.ThehighcostofruralenergynegativelyaffectboththequalityandsustainabilityoflifeinruralAlaska.
Manypowergenerationcostsarebeyondacommunity’scontrol.Thefuelpricefortheseplantsisdeterminedbyanincreasinglyvolatileglobalenergymarket.Inaddition,asubstantialcomponentofthefuelcostistransportation.Inrecentyears,thelimitedshippinganddeliverywindowscausedbyseasonaliceandlowwaterconditionsinmanypartsofthestatehaveresultedinvillagespayingrecordpricesforfuel.Interiorcommunities,locatedneartheupperlimitsofnavigablewaterwaysandthussusceptibletolowwaterconditions,paidasmuchas$11pergallonin2010(DCRA,2010).Severalruralcommunitiesfrequentlyflyinfuelduetoalackofreliablebargeaccessorservice.
Alternativestodieselgenerationoftenexistintheformoflocalenergyresourcessuchashydro,wind,geothermal,tidal,solar,gas,coal,andbiomass.However,manyofthese“strandedenergyresources”arenoteconomicallyviableduetothecostoftheconventionalACelectrictransmissionsystemsrequiredtointerconnectthemandtheprohibitivelyhighcosttodeveloptheselocalenergyresourcestoservesmallloads.HVDCintertiescanhelpsurmountbothofthesebarriersbyloweringthecosttoreachstrandedenergyresourcesandbyreducingthecosttointerconnectcommunities(ACEP,2012).
AlthoughcommercialHVDCtransmissiontechnologyhasbeenavailableforover50years,ithasbeenlimitedtolarge‐scaletransmissionoftenstothousandsofMWsofpower.ThesesystemsarefartoolargeandexpensivetousefortheinterconnectionofAlaska’sruralcommunities,whichtypicallyhaveloadsmeasuredinthehundredstothousandsofkilowatts(kWs).Currently,nocommerciallyavailableHVDCconvertersystemexiststhatissuitableforinterconnectingtheseruralcommunities.However,innovativetechnologiesinthepowerelectronicsindustryhavemadethedevelopmentoflow‐power,cost‐effectiveconvertersfeasible.
PolarconsulthasinvestigatedalternativestoACintertiesandfoundthatinmanyapplications,HVDCtransmissionsystemsusinginnovativepowerconversiontechnologiesofferthemosteconomicalsolutiontointerconnectwithstrandedenergyresources.Further,thereplacementofaconventionaloverheadACthree‐orfour‐wiretransmissionlinewithaone‐ortwo‐wireHVDC
1 RuralAlaskaforthepurposesofthisreportreferstoisolatedcommunitiesoffthemainroadsystemthathavehigh
energycostsduetotheirlocation,size,orotherfactors.
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transmissionlinehassignificantcostadvantages.Thechangeinoverheadinfrastructureresultsinreducedstructuralloads,allowingfewersupportstructurespermileoftransmissionline.ThedecreaseinmaterialsandconstructiontimeisoneofseveralreasonsthatoverheadHVDCintertiesarelesscostlythanACinterties.SubmarineandburiedHVDCintertiescanalsobelesscostlythantheirACalternatives.
2.1 PROGRAMOVERVIEW
TheHVDCdevelopmenteffortconsistsofthefollowingphases:
PhaseI–PreliminaryDesignandFeasibilityAnalysis(2008‐2009)
DuringPhaseI,PolarconsultevaluatedthetechnicalandeconomicfeasibilityoftheproposedHVDCsystem.TasksincludeddefiningtheHVDCsystem’spreliminarydesignparameters,definingdesignconsiderationsforthetransmissionandconvertercomponents,andestimatingcostsforthesesystems.PhaseIalsoincludedlimitedprototypingandsuccessfultestingoftheconvertertechnology.
PhaseII–PrototypingandTesting(2010‐2012)
PhaseIIincludedconstructionandtestingoffull‐scaleprototypesofthetransmissionandconvertersystems.ThiseffortvalidatedthedesignofthesesystemsandvalidatedthefeasibilityoftheconstructionmethodsnecessarytomakethesystemasuccessinruralAlaskaapplications.TheinformationfromPhaseIItestingwasusedtorefinetheconstructionmethodsanddevelopcostestimatesusedintheeconomicanalysisofthetechnologydescribedinthisreport.ThisreportisthefinaldeliverableforPhaseII.
PhaseIII–DemonstrationProject(Proposed)
PhaseIIIwillincludefulltestingoftheconvertersystem,includingthemanufacturerandthird‐partyfunctional,compliance,andperformancetestingneededtomovetheconvertertechnologyfromadvancedprototypestoacommercialproduct.PhaseIIIwillalsoincludeafull‐scalefielddemonstrationoftheHVDCtechnologyonautilitysysteminAlaska.Thespecificprojectdetailsaredependantonthecandidatelocationselectedfortheintertie.PhaseIIIisintendedtobethefinalproof‐of‐conceptproject,tobefollowedbycommercialdeploymentofthesystem.
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2.2 STAKEHOLDERADVICE
ThisprojectseekstodevelopahighlyinnovativepowertransmissiontechnologyfordeploymentinruralAlaskaapplications.Becausemanyaspectsofthissystemmarkadeparturefromacceptedpracticeinruralpowersystems,widespreadindustryunderstanding,aswellasacceptance,ofthistechnologyisconsideredcriticaltothesuccessofthiseffort.Additionally,theoverviewandfeedbackofindustryisconsideredcriticaltothesuccessfuldevelopmentoftheinnovativesystemsneededforthisHVDCtechnology.
TheDenaliCommissionandACEPrecognizedthatthebestmeanstoachievethisunderstanding,acceptance,andfeedbackwouldbetodirectlyengagethestakeholdersandend‐usersoftheproposedsysteminthedevelopmentstagesofthetechnology.Tothisend,aSAGwasformedaspartofthePhaseIIefforttofamiliarizeandfacilitatefeedbackfromindustryleadersonthedevelopmentofthissystem.
TheSAGisanadvisorybodycomprisedofrepresentativesofAlaska’sruralelectricutilityindustryandrelatedprofessionals.ThepurposeoftheSAGistoprovidecomments,feedback,review,andrecommendationstotheHVDCproject.TheSAGheldthefollowingthreemeetingsoverthecourseoftheproject:
● SAGMeeting#1–Fairbanks,Alaska‐‐April27,2010;
● SAGMeeting#2–Anchorage,Alaska–January14,2011;and
● SAGMeeting#3–Anchorage,Alaska–October25,2011.
Severaladditionaloutreachactivitiesoccurredoverthecourseoftheproject.Theseincluded:
● SoutheastConferenceMid‐SessionSummit–Juneau,Alaska(March2,2010);
● EmergingEnergyTechnologyForum–Juneau,Alaska(February14,2011);
● Brown‐BagWorkSession–Anchorage,Alaska(August29,2011);and
● HVDCConverterDemonstration–Lawrenceville,NewJersey(November14,2011).
AppendixIprovidesthefollowingdetailedinformationregardingSAGmeetingsanddiscussions:
● ListofSAGmembers;
● SummaryofSAGroleandpolicies;
● SummaryofkeyinformalcorrespondencebetweenSAGmembersandPolarconsultoverthecourseoftheproject;
● HandoutsfromthethreeSAGmeetings;and
● Handoutsfromothermeetingsandoutreachactivitiesconductedoverthecourseoftheproject.
AdditionaldetailsassociatedwiththeSAGmeetingsandproceedingsarepresentedinAppendixI.TranscriptsoftheSAGmeetingsareavailableuponrequest.
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3.0 HVDCTRANSMISSIONSYSTEMDESCRIPTION
HVDCtransmissionsystemscantakeonawidevarietyofconfigurations.Thissectiondescribesthoseconfigurationsrelevanttolow‐powerHVDCapplicationsinruralAlaskaapplications.
● Section3.1providesageneraloverviewofthehistoryofHVDCpowertransmissionandthemajorcomponentsofanHVDCtransmissionsystem.
● Section3.2providesageneraloverviewofthedifferentconfigurationsofHVDCsystemsforpowertransmissionapplications.
● Section3.3providesacomparisonofHVDCandACpowertransmissionalternatives.
● Section3.4providesadescriptionofoverheadlinealternativesforACandHVDCapplications.
● Section3.5providesadescriptionofsubmarinecablelinealternativesforACandHVDCapplications.
3.1 HVDCBACKGROUND
ThomasEdisonpioneeredthefirstutility‐scaleapplicationofelectricpowerinNewYorkCityinthe1880swithadirectcurrent(DC)electricutilitysystem.Concurrently,GeorgeWestinghousewasmarketinganACelectricutilitysysteminventedbyNikolaTesla.ACwasbettersuitedtosteppingupvoltages,whichisvitaltoeconomicalelectrictransmissionacrosstownandbetweencities.Bythe1890s,Westinghouse’sACsystemhadprevailedoverEdison'sDCsystem,andACbecametheindustrystandard.
Inthe1950s,technologicaladvancesenabledDCsystemstoreentertheelectricutilityindustry.Withthecommercializationofthemercuryarc‐valve,voltagetransformationofDCandconversionbetweenDCandACelectricityonalargescalebecamecost‐effective.ThisallowedutilitiestobeginusingHVDCtransmissionlinksintheirsystems.
BecauseofthehighcapitalcostoftheseearlyHVDCconverters,utilityusageofHVDCremainedlimitedtotransmissionfunctions.ACremainedtheindustrystandardforelectricitygeneration,distribution,andconsumption.
Today,HVDCconvertertechnologyhasadvancedtousehighefficiencysolid‐statehardware,andHVDClinksareusedforelectricaltransmissionthroughouttheworld.Thesmallestavailableutility‐gradeHVDCsystemsaredesignedtotransmitapproximately50MW2.Asaresult,thecurrentcommerciallyavailableHVDCconvertersareoversizedandprohibitivelyexpensiveforAlaskanintertiesthattypicallyrequirethetransferoflessthan1MW.Figure3‐1isanimageofalargeHVDCstation.
2“HVDCLite,”distributedbyABB,isoneexampleofthesmallerutility‐gradeHVDCsystems.
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HVDCtransmissionsystemsincludethefollowingmajorcomponents:
● HVDCConverterStations.EachconnectionpointbetweentheHVDCtransmissionlineandaloadcenterrequiresanHVDCconverterstation.TheconverterstationconvertstheHVDCelectricityintoACelectricitythatcanbemovedthroughalocalpowergridandused.Theconverterstationincludesthepowerconverters,groundingstations,communicationsandcontrolsystems,andprotectiveequipmentasrequiredbytheparticularsystemdesignrequirements.ThepowerconvertersarediscussedinAppendixF.ThegroundingstationsarediscussedinAppendixE.
● HVDCTransmissionLine.TheHVDCtransmissionlineistheoverheadwire,submarinecable,undergroundcable,orcombinationofthesethatconnectstheconverterstationstogetherandformsthetransmissioncircuit.Theconfigurationanddesignofthetransmissionlinewilldependonlocalconditionsandsystemrequirements.OverheadtransmissionlineconceptsarediscussedinAppendixC.SubmarinecabletransmissionlineconceptsarediscussedinAppendixD.
● ControlsandCommunications.TheHVDCtransmissionsystemrequiresameansofcommunicatingbetweentheconverterstationsandthecontrolthesystem.ThesimplestcontrolandcommunicationschemewouldusetheDClinevoltageasacontrolsignal.Thiswouldbesuitableforapoint‐to‐pointHVDCsystemthatfeedspowerinonedirection.Powerreversalovertheintertiewouldbepossiblewithmanualintervention.ControlandcommunicationoptionsforHVDCsystemsarediscussedinAppendixG.
Figure 3-1 Typical Large HVDC Station
5,000MW+/‐800kVHVDCYunnan‐GuangdongConverterStation.(TDW,2012)
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3.2 HVDCSYSTEMCONFIGURATIONS
ThevarioussystemconfigurationsforHVDCcanbeclassifiedintothreedifferentcategories,withseveraloptionswithineachcategory.Thethreecategoriesandmajoroptionsareshownbelow.Eachcategoryisdescribedinmoredetailinthefollowingsections.
TypesofHVDCUtilityPowerSystems
HVDCApplication‐HowtheHVDCtechnologyisused:
● Point‐to‐PointDCPowerTransmission
● MultiterminalDirectCurrent(MTDC)PowerTransmission
HVDCCircuit‐Howtheelectricityistransported:
● MonopolarwithSingle‐WireEarthReturn(SWER)
● MonopolarwithMetallicReturn
● Bipolar
IntertieType‐Howthewirestransportingtheelectricityareconfigured:
● Overhead
● Submarine
● Underground
3.2.1 HVDCSystemApplications
TherearethreebasicapplicationsofHVDCtechnologyintoday’selectricutilityindustry.Theseare:
● Point‐to‐pointpowertransmission.ThemajorityofHVDCsystemsinusetodayarepoint‐to‐pointtransmissionsystems.Thesetransportbulkenergy(100sor1,000sofMWs)overlongdistances(100sor1,000sofmiles)moreefficientlythanACtransmissionsystems.
Point‐to‐pointnetworkswillbeasignificantapplicationforthelow‐powerHVDCtechnologybeingdevelopedwiththisproject.
● Multiterminalpowertransmission.MTDCnetworksareamoreflexibleandcomplicatedapplicationofHVDCtransmissiontechnology.Insteadofthetwoterminalsinaconventionalpoint‐to‐pointHVDCsystem,MTDCsystemshavemorethantwoterminalsandcanroutepowertoorfromtheseterminalsasneeded.MTDCsystemsarecurrentlyreceivingsignificantindustryinterestastechnologyevolvestohandlethesemorecomplicatedsystemsandregionalgridsdemandthesuperiorperformanceandenhancedcapabilitiesthatMTDCsystemsofferoverACtransmissionnetworksforcertainapplications.Thereareahandfuloflarge‐scaleMTDCsystemsplannedorinoperation.ExamplesincludetheQuebec–NewEnglandMTDCsystemandtheSardinia–Corsica–ItalyMTDCsystem.
ManyregionalenergysolutionsinruralAlaskausingHVDCwillbeintheformofMTDCnetworks.ThepowerconvertersdevelopedforthisprojectcansupportMTDCoperation,providedsuitablecontrolsystemsandprotectiveequipmentarepresent.MTDCsystemsandcontrolconsiderationsarediscussedingreaterdetailinAppendixG.
Atthemostabstractlevel,anelectricalcircuitrequirestwocurrentpathways,normallymetalwires.Onewiregoesfromthepowersupplytotheload,andasecondwiregoesfromtheloadback
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INCREASING COST AND COMPLEXITY
1. Monopolar with earth return (SWER) 2. Monopolar with return conductor 3. Bipolar
tothepowersupply.Bothsingle‐phaseACandDCcircuitsrelyonthisbasicconfiguration.Thewirefromthepowersupplytotheloadisusuallyatanincreasedvoltagerelativetoground,andsoitisinsulatedforsafetyandtopreventshortcircuits.Thewirefromtheloadbacktothepowersupplyisusuallyatamuchlowervoltagerelativetogroundandisusually,butnotalways,insulated.
TherearethreetypesofHVDCcircuitsinusearoundtheworld.Eachofthesecircuitsmayutilizeoverheadwires,undergroundcables,submarinecables,oracombinationofthese.ThesethreecircuitsarelistedonFigure3‐2anddescribedonthefollowingpages.
Figure 3-2 Three Types of Interties Used in HVDC Systems
MorecomplexHVDCcircuitconfigurationsnormallyincorporateelementsofthesimplercircuitsforefficiency,reliability,redundancy,and/orsafety.Forexample,allbipolarHVDCsystemsincludeearthelectrodesandsometimesagroundconductorsotheycanoperateeitherpoleinmonopolarormonopolarSWERmodeduringmaintenanceoremergencies.Generally,themorecomplexbipolarcircuitconfigurationsareusedforlarge,importantintertieswheretheincreasedreliability,efficiency,andpowerthroughputcapabilityjustifythehighercostofthesesystems.
3.2.1.1 SingleWireEarthReturn(SWER)CircuitsSWERcircuitsusethesubsurfacegeologyasareturncurrentpathway.Seareturncircuitsaresimilartoearthreturncircuits.Theonlydifferenceisthatthesea,oranywaterbody,isusedasthepredominantreturncurrentpathway.Parallelpathways,suchastheseabed,arealsoavailableforcurrentflow.TheprimaryadvantagesofferedbySWERcircuitsinclude:
● Lowercosts(eliminatethesecondconductor).
● Higherefficiency(lowerelectricallosses).
TheprimaryconcernsassociatedwithSWERcircuitsinclude:
● Avoidingaccelerated“inducedcurrent”corrosionofburiedmetallicobjects.
● Aswithallelectricalsystems,safety.SWERcircuitsarewidelyusedforutilitytransmissionanddistributionofelectricityallovertheworld.NumerousHVDCintertiesareSWERcircuits,consistingofasinglehigh‐voltagecableandanearthorseareturntocompletethetransmissioncircuit.ManyoftheseareinstalledinclimatesandconditionssimilartoAlaska,notablyinScandinavia.Inmanynations,single‐phaseACSWERcircuitsareacceptedpracticeandareindustrystandardforservingruralareas.
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Twosingle‐phaseACSWERcircuitshavebeensuccessfullybuiltandoperatedinAlaska.TheseACSWERcircuitsdemonstratethatSWERisaproven,beneficial,andappropriatetechnologyforruralAlaskatransmissionapplications.
3.2.1.2 MonopolarHVDCCircuitUsingSWER
AmonopolarHVDCintertieusingSWER(seeFigure3‐3)forthereturnpathwaywillgenerallybethelowest‐costalternativeforHVDCpowertransmissioninruralAlaskaapplications.Thiscircuitconfigurationwillconsistofthefollowingmajorcomponents:
● AC/DCconvertermoduleinthegeneratingvillage.
● High‐voltageconductor.Thiscanbeanoverheadline,buriedcable,orsubmarinecable.
● DC/ACconverterinthereceivingvillage.
● Groundingelectrodesinbothvillagestocompletetheintertiecircuitusingearthreturn.
Figure 3-3 Monopolar HVDC Intertie Using SWER
TherearenumerousexamplesofmonopolarHVDCintertiesusingSWERcircuits.The500‐MWsubmarineHVDClinkcompletedbetweenVictoriaandTasmania,Australia,in2006isoneexampleofarecentlyconstructedSWERHVDCsystem.BipolarandmonopolarHVDCcircuitsarenormallydesignedtooperateinamonopolarSWERconfigurationwhenneededtomaximizesystemreliability.
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3.2.1.3 MonopolarHVDCCircuitwithReturnConductor
AmonopolarHVDCintertiewithareturnconductor(seeFigure3‐4)issimilartoamonopolarSWERHVDCintertie.Theprimarydifferenceisthattheearthreturnisreplacedwithadedicatedreturnconductortominimizeearthcurrentsinducedbytheintertie.Often,suchintertieswillstillhavetheearthelectrodesnecessarytooperateinSWERmodeandwilloperateinSWERmodeduringmaintenanceoremergencysituations.ThisHVDCcircuitconfigurationincludesthefollowingmajorcomponents:
● AC/DCconvertermoduleinthegeneratingvillage.
● High‐voltageconductor.Thiscanbeanoverheadline,buriedcable,orsubmarinecable.
● DC/ACconverterinthereceivingvillage.
● Returnconductor.Thiscanbeanunder‐builtlineonthehigh‐voltagepoles,aseparatecable,orincorporatedintothesamecableasthehigh‐voltageconductor,suchasaconcentricneutralonanACcable.
● Groundingelectrodesinbothvillages.Thesewillnotnormallybeusedtocompletetheintertiecircuit,buttheywillbeusedduringmaintenanceoremergencies.
MonopolarreturnconductorsarewarrantedinareaswhereaSWERcircuitisnotviableordesirable.Generally,thisisduetotheriskofinducingcorrosioninburiedmetallicutilities.Thelackofsuitablegroundconditionsforeconomicalearthelectrodeswouldalsowarrantuseofareturnconductor.Usinganreturnconductorwiththesameelectricalresistanceasthehigh‐voltageconductorwillnearlydoubletheconductorlossesrelativetoaSWERtransmissioncircuit.
Figure 3-4 Monopolar HVDC Intertie with Return Conductor (SWER-capable for Backup)
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3.2.1.4 BipolarHVDCCircuit
AbipolarHVDCintertie(seeFigure3‐5)isgenerallythemostcostlyandmostreliableHVDCcircuitconfiguration.Itemploystwoparallelhigh‐voltageconductors,oneoperatedatpositivevoltageandthesecondatnegativevoltage.Thesystemrequirestwoconvertersateachendoftheintertie(fourtotal),comparedtooneconverterperendformonopolarcircuits(twototal).Thus,thebipolarHVDCconfigurationincludesthesemajorcomponents:
● TwoAC/DCconvertermodulesinthegeneratingvillage.One(+)andone(–).
● Twohigh‐voltageconductors.Thesecouldbeoverheadlines,buriedcables,orsubmarinecables.
● Athirdneutralconductortocarryanycurrentduetominorimbalancebetweenthepowertransmissionlevelsonthepositiveandnegativepoles.Somebipolarsystemsdonothaveaneutralconductorandinsteadrelyonthegroundingelectrodestobalancethepoles.
● TwoDC/ACconvertersinthereceivingvillage.One(+)andone(–).
● Groundingelectrodesinbothvillages.Thesewillnotnormallybeusedtocompletetheintertiecircuit,buttheywillbeusedtobalancethesystemandforSWERoperationduringmaintenanceoremergencies.
TheadditionalcostsofabipolarHVDCintertiearelargelyduetotheadditionalconvertersandthesecondhigh‐voltageconductor.AbipolarHVDCintertiewillberoughlytwiceascostlyasamonopolarHVDCintertie,butwithtwicethecapacityandincreasedreliability.
Theprincipaladvantageofabipolarintertiecomparedtoamonopolarintertieisincreasedreliability.Ifsomethingbreaksononeofthetwopoles,theotherpolecanbeoperatedasamonopolarintertie.Thiswillreducethepowertransfercapability,buttheintertiecancontinuetofunction.
FormanyruralAlaskaapplications,theadditionalcostofbipolarcircuitsisnotjustified.Operatingbackupdieselgeneratorsinvillageswouldbemorecost‐effectivethanconstructingabipolarHVDCintertie.
Figure 3-5 Bipolar HVDC Intertie (SWER-capable for Backup)
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3.2.2 HVDCIntertieTypes
HVDCintertiescanbebuiltusingoverheadwires,submarinecables,orundergroundcables.Combinationsofthesecanbeusedforasingleintertie.OverheadwireintertieoptionsarediscussedinSection3.4andAppendixC.SubmarinecableintertieoptionsarediscussedinSection3.5andAppendixD.UndergroundcableoptionsarediscussedinAppendixG.
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3.3 COMPARISONOFACTOHVDCTRANSMISSION
ThefollowingabbreviatedcomparisonispresentedtoillustratewhenanHVDCintertieisanticipatedtobeagoodalternativetoacomparableACintertieinruralAlaskaapplications.AmoredetailedcomparisonispresentedinAppendicesAandB.
HVDCAdvantages:
● Lowerper‐mileoverheadtransmissionlinecostthanAClines;
● Abilitytouseundergroundorsubmarinecablesforlongdistances;
● Bettercompatibilitywithmigratorybirdsduetofeweroverheadconductors(1or2wiresinsteadof3or4wires);
● Asynchronousconnection;and
● Lowerper‐mileconductorenergylosses.
HVDCDisadvantages:
● AnHVDCconverterismoreexpensive,requiresmoremaintenance,andislessreliablethanacomparableACtransformer;
● Convertercostsareabarriertoservingloadsalongthetransmissionlineroute;
● UnconventionaltechnologyandlimitedequipmentsupplierscomparedtoAC;
● HVDCconvertersgenerallyhavehigherenergylossesthanacomparableACtransformer;and
● HVDCintertiesmayhavefewerfundingopportunitiesthanconventionalAClinesbecausetheyareuncommon.
Implications:
● Ifanintertiemustemploylong‐distancesubmarineorburiedcables,HVDCoffersatechnicallysuperiorsolutiontoAC.ACcableintertiesarenottechnicallyfeasibleforlong‐distancetransmissionsystems.
● Wherebothsystemsaretechnicallyfeasible,thedecisionislargelyeconomic.AnHVDCintertiewillhavehigherterminalcostsandlowerper‐milecosts.Accordingly,anACintertieismorecost‐effectiveforshortinterties,andHVDCismorecost‐effectiveforlonginterties.Thelongertheintertie,thegreaterthecostsavingsofanHVDCversusACsystem.Theeconomiccrossoverpointisprojectspecificbutforthescaleofintertiesunderconsiderationinthisreport,itwillgenerallyoccuratadistanceof6and31miles.
● SincetheHVDCconvertersdevelopedunderthisprogramusenewtechnology,andbecauseitrepresentsadeparturefromconventionalACtransmissionsystems,substantialsavingswillbeafactorinencouragingutilitiestoadoptthistechnologyinlieuofprovenbutmorecostlyintertiesolutions.
● MostACintertiesareoverheadandmaynotbeenvironmentallyacceptableinmanypartsofAlaska.HVDCintertiesareeitherburiedorhavefewerwiresandstructuresandmaybemoreacceptablewithinrefugesandothersensitiveareas.
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3.4 OVERHEADINTERTIEALTERNATIVES
3.4.1 ConventionalACInterties
Thetypicalcostforconstructingaconventionaloverheaddistribution‐classACintertieinruralAlaskacanrangefromaslittleas$100,000permileinareaswithgoodlogisticsupportandtransportationinfrastructure(roadsystem,southeast)toover$600,000permile3inruralpartsofthestatewithchallenginglogisticsandlittleornotransportationinfrastructure(remoteinterior,northwest,orYukon‐Kuskokwimdeltaregions).Becauseofthisprohibitiveexpense,relativelyfewruralintertieshavebeenbuilt.
ThehighcostofruraloverheadACintertiesistheresultofseveralfactors.TwosignificantcostcontributorscommontomanyAlaskanintertieprojectsarelogisticsandfoundations.ACsystemsrelyonmulti‐wiretransmissionlines;thisleadstohighmaterialscostsandhighloadsplacedonstructuresandfoundations.ThestructuresneededtosupportthemultipleaerialwiresofanACsystemarecostly.TheresultingACintertieusuallyhasshortspans,250to400feetbeingtypical,thusresultinginmanytransmissioncomponentssuchaspoles,hardware,wire,andfoundationsthatmustbepurchased,shipped,installed,andmaintained.
Whenthecostsofshipping,geotechnicalconditions,constructionfactors,logisticsandenvironmentalrequirementsareallfactoredin,conventionalACconstructionoftenresultsinaprohibitivelyexpensiveintertie.Asaresult,manyruralcommunitiesaredeniedtheopportunitytobenefitfrominterconnectiontoeachotherorlocalenergyresources.
3.4.2 HVDCTransmissionInterties
PolarconsulthasinvestigatedalternativestoACintertiesandfoundthatinmanyapplications,HVDCtransmissionsystemsofferthemosteconomicalsolution.
ReplacingaconventionaloverheadACthree‐orfour‐wiretransmissionlinewithaone‐ortwo‐wireHVDCtransmissionlinehassignificantcostadvantages.Thechangeinoverheadinfrastructureresultsinreducedstructuralloadsthusallowingfewersupportstructurespermileoftransmissionline.ThedecreaseinmaterialsandconstructiontimeistheprimaryreasonoverheadHVDCintertiesaremoreeconomicallyviablethanACinterties.
AmonopolarHVDCintertiedesignedasaSWERcircuitneedsonlyasinglewirealoft,whichsignificantlyreducestheloadscomparedwithathree‐orfour‐wireACintertie.Usingasinglewireprofoundlysimplifiesthetransmissionlinedesign,whichtranslatestosignificantcostsavingscomparedwithanACline.
BecauseSWERcircuitsinduceareturncurrentintheearth,theyrequirespecialattentioninthedesignandplanningphasetoavoidadverseeffectsfromthisearthcurrent.Theprimaryconcernsare(1)thesteppotential4intheimmediatevicinityofthegroundingstationsand(2)acceleratedcorrosionofburiedmetallicobjectsinthevicinityofthereturncurrentpathwaysthroughtheearth.
3SeeSectionB.6.1inAppendixBforcostbasisinformation.4Avoltagegradientthatoccursatthegroundsurfaceduetoearthreturncurrents.Ifthevoltagegradientishighenough,itcanposeahazardtopeopleorwildlifesteppinginthevicinity.
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InmostruralAlaskalocalities,theseconcernscanbereadilyaddressedthroughproperplanningandsystemdesign.
Becauseofthesespecialfactors,SWERcircuitsarenotallowedbytheNationalElectricalSafetyCode(NESC),whichistheapplicablecodeforelectricutilitytransmissionanddistributionsystems.PolarconsulthasdiscussedthisHVDCsystemandconceptindetailwiththestatecodeauthorityandfindsthatSWERcircuitscanbeapprovedonaproject‐specificbasisbyissuanceofacodewaiver.ThereisprecedentforcodewaiversbeingissuedforSWERsystemsinAlaska.TheuseofSWERcircuitsisdiscussedfurtherinAppendixEofthisreport.
Asanalternativetousinganearthreturncircuit,two‐wiremonopolarHVDClines(usinganoverheadwireasthereturncircuit)alsoachieveacostsavingsrelativetoACintertiesalthoughthesavingswilltypicallybelessthanforanHVDCSWERtransmissionline.
BipolarHVDCintertiesrequiretheuseoftwoadditionalconvertersbutcantransfertwicetheenergyofacomparablemonopolarsystem.Intheeventofaconverterfailureorlossofaconductor,abipolarsystemcanbeconfiguredtooperateasamonopolarSWERormonopolartwo‐wiresystem.Thisofferssignificantreliabilityadvantages;however,italsoincursthecostoftheadditionalconvertersandsecondhigh‐voltageconductor.Theadvantagesoftheincreaseincapacityandreliabilityaretheprimaryreasonsforuseofbipolarsystems.
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3.5 SUBMARINECABLEINTERTIEALTERNATIVES
AnotheradvantageofHVDCtransmissionoverACisitsintrinsicabilitytocarryenergybyburiedorsubmarinecableoverlongdistanceswithoutthetechnicallimitationsandadditionalequipmentrequiredforsimilartransmissionbyAC.MonopolarHVDCusingasinglecablecanconnectvillagesseparatedbylakes,bays,fjords,orlandswhereoverheadtransmissionisnotpractical,cost‐effective,ordesirable.Forthisreason,low‐powerHVDCtechnologyhassignificantimplicationsforinterconnectingcommunitiesinAlaskaseparatedbywaterbodies,particularlyinthesoutheast.
CabletricitywasretainedbyPolarconsultasasubconsultanttoinvestigatesubmarinecablesoptimizedforusewiththisHVDCsystem.AppendixDincludestheCabletricityreportdetailingresultsoftheirinvestigations.
Thereportbeginswithadescriptionoftheelectricalsystemtowhichthecableswillbeconnected,andthenadvancestotheregionalenvironmenttheymustwithstandandontodescriptionsofsubmarinecablestandards,cabledesigns,typicalinstallationmethods,andcostestimatesforacasestudy.
Cabletricityevaluatedsubmarinecablessuitablefor1‐MWmonopolarHVDCintertiesat50kilovolts(kV),withpotentialupgradeoftheconverterstationsto5‐MWserviceinamonopolarcircuit.Cabletricityalsoevaluatedthefeasibilityandcostofintegratingopticalfibersintothepowertransmissionsystemtoservethecommunicationsneedsofruralcommunities.Tomakethissystempractical,simplicityandreliabilityarecriticaldesignconsiderations.
Cabletricity’sinvestigationsfocusedonsinglecoreinsulatedconductorsubmarinecableswithearthorseareturnthatwouldbegenerallysuitablefortheruggedanddeepinter‐islandandfjordcrossingstypicalofsoutheastAlaska.Theobjectiveistoidentifysuitableconventionalorinnovativesubmarinecabledesignstomeettheoverallprojectobjectiveswherewatercrossingsarerequired.
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4.0 HVDCCONVERTERSTATIONS
4.1 OVERVIEW
TheHVDCconverterstationswillincludethemajorcomponentslistedbelow:
● HVDCpowerconverterssuchasthosebeingdevelopedbyPPS;
● Converterenclosures,whichmayconsistofdedicatedenclosuresoruseofanexistingbuilding,suchasanexistingpowerplant;
● Protection,control,andswitchingequipmentontheACandHVDCsidesoftheconverters;
● ACtransformers,dependingontheACinterfacevoltageandwiring;and
● Groundingstations,includingthegroundconductorfromtheconverterstationtothegroundingstation.
4.2 CONVERTERDEVELOPMENTOVERVIEW
PolarconsultsubcontractedwithPPSforthedevelopmentoftheHVDCpowerconverters.PPSwastaskedwiththedevelopmentofonefull‐scaleandfull‐functionality1‐MWpowerconverter,consistingoftwo500‐kilowatt(kW)modules.Developmentworkincludedpreparationofspecifications,design,construction,andtestingoftheprototypeconverter.
TheHVDCconverterisa1‐MWpowerconvertercapableofbidirectionalpowerconversionbetweenthree‐phase480voltsalternatingcurrent(VAC)and50kVHVDC.TheconvertercapacityisappropriatetosupplytheelectricalneedsofmostAlaskavillageseconomically.Incontrast,existingHVDCpowerconvertersystemsareonlyavailableatmuchlargertransmissioncapacities,startingatapproximately50MWandextendingupto1,000sofMWsofcapacity.
Each500‐kWPPSconverterconsistsoftwomodules:anair‐cooledlow‐voltagecabinet(Figure4‐1),andanoilcooledhigh‐voltagetank(Figure4‐2).ACpowercablesconnecttothelow‐voltagecabinet,whichconditionsthepowerandtransformsittoaspecialhigh‐frequencyAC,whichistransmittedtothehigh‐voltagetankviapowercable.Thehigh‐voltagetanktransformsthehigh‐frequencyACto50kVDC.Thehigh‐voltagetankhastwobushingsthatoutputupto500kWat50kVDC.Eitherbushingcanbegroundedtoproduceapositive50‐kVHVDCoutputoranegative50‐kVHVDCoutput.
MultiplePPSHVDCconverterscanbe“paralleled”toachievehigherpowertransmissioncapacitieswhereneeded.BasedonPhaseIIdevelopmentwork,thepriceofacommerciallyproduced1‐MWHVDCpowerconverterisestimatedtobe$250,000.Atleasttwo1‐MWconvertersareneededforacomplete1‐MWHVDCtransmissionsystem.
PPShassuccessfullydemonstratedoperationandpowerflowatthefull50kVDCinbothinverter(HVDCtoAC)modeandrectifier(ACtoHVDC)modeinacontrolledtestfacilitysetting.Thesetestingeffortsvalidatethedesignandbasicfunctionalityoftheconverter.
Inthecourseoftesting,PPSidentifiedtwohardwareproblemsthatpreventedfull‐powertestingoftheprototypeconverters.PPShasinvestigatedtheseproblemsandidentifiedtheactionsnecessarytocorrectbothproblems.TheproblemsandsolutionsarediscussedinAppendixF.
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Thefollowingfiguresillustratetheconverterfeatures:
o Figures4‐1and4‐2showthetwobasicmodulesthatmakeupacomplete500‐kWconvertersystem.ThesearefurtherdiscussedinAppendixF.
o Figure4‐3showsthetestsetupfortestingofthecentralresonantlinkcircuitinthehigh‐voltageDCtransformer.
o Figure4‐4showsthein‐airhighpotential(hi‐pot)testsetupofthehigh‐voltageDCtransformerassembly.Thistestidentifiedsomeinsulationdefectsthatwerecorrected.ThetestdemonstratedthattheDCtransformerassemblywillwithstandthevoltagesexperiencedatfulloperatingvoltageof50kVDC.
o Figure4‐5showsthedrysystemtestsetupandschematic.BeforetheDCtransformerwasimmersedinoil,itwastestedatlowvoltageinairtovalidatefunctionandfacilitatetroubleshooting.Thiswasprimarilydoneforconvenience,toavoidthedelaysandmessassociatedwithrepeatedlyimmersingtheDCtransformerinoilandremovingit.
o Figure4‐6showsacomplete500‐kWconvertermodule,consistingoftheHVDCtankandthelow‐voltagealternatingcurrent(LVAC)cabinet.
o Figure4‐7showsfourhigh‐voltagemeasurementprobesusedtomonitorthevoltagesatdifferentpointsintheDCtransformer.ThetestshowedexcellentvoltagesharingbetweentheDCtransformerstages,indicatingthatthesystemisperforminginaccordancewithdesign.Uniformvoltagesharingisakeysuccess,asitmeansthepowerelectronicscomponentswillnotbesubjectedtounevenvoltagesstresses.Excessivevoltagestressescouldseverelyshortenthelifeofthecomponents,reducingthereliabilityoftheconverter.
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Figure 4-1 Low Voltage Alternating Current (LVAC) Enclosure: Mechanical Layout
Notes:Cabinetsize:66”Wx42”Dx66”H;Cabinetweight:Approximately2,200pounds.
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Figure 4-2 HVDC Transformer Tank: Mechanical Layout
Notes:Tanksize:88”Wx39”Dx59.25”H;Tankweightwithoil:4,200pounds.
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Figure 4-3 Central Resonant Link Test Setup
Figure 4-4 Hi–Pot Test Setup for HVDC Transformer
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Figure 4-5 Dry System Inverter Mode Test Schematic and Setup
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Figure 4-6 System #1 HV Tank and LV Enclosure
Figure 4-7 System #1 Showing HV Measurement Probes
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4.3 ADDITIONALEQUIPMENT
4.3.1 ConverterEnclosure
WhiletheconverterspecificationspermittheconverterstobeinstalledoutdoorsinmostAlaskaenvironments,itisassumedthattheconverterswillbeinstalledinsideanenclosure.Thiswillprovideforacontrolledoperatingenvironmentandgreatersecurityfortheconverters,extendingtheirusefulservicelife.
Theconceptualdesignassumesthatamodular,prefabricatedenclosurewillbesenttothecommunitywiththetwo500‐kWpowerconverterunitsalreadyinstalled.Thisconvertermodulewillthenbesetinplaceonasuitablefoundation.
IncommunitiesthatwillbeprimarilyservedbyanHVDCintertie,itmaybeappropriatetolocatetheconvertersinsidetheexistingpowerhouseorothersuitableexistingstructure.Thiswouldhavethefollowingadvantages:
● Theexistingpowerhousemayalreadyhaveasuitablestep‐downtransformersizedforthefullcommunityload;
● Wasteheatfromtheconverterswouldprovideallorpartoftheheatforthepowerplantbuilding;and
● Achievesprojectcostreductionbyeliminatingtheneedforadedicatedconverterenclosureandpurchasingorleasinglandtositetheconverter.
4.3.2 ProtectionandSwitchyardEquipment
SwitchgearwillbeneededontheACsideoftheconverterstoisolateandprotecttheconverterfromtheACgridandtomonitorpowerflowbetweentheconverterandthegrid.
Similarisolation,protection,andmonitoringequipmentisneededontheHVDCsideoftheconverter.Ataminimum,manualdisconnectswitches(nonloadbreak),surgearrestors,andprotectivefusesareneededontheHVDCside.Moreautomatedcontrolapparatuscanalsobeused,butatincreasedcost.
4.3.3 ACTransformers
Thegridinterfaceonthepowerconvertersisthree‐phase480‐voltAC.Incommunitieswheretheconverterisconnecteddirectlytothe480‐voltpowerplantbus,notransformerisrequired.Incommunitieswheretheconverterconnectstothelocaldistributiongrid,astep‐uptransformerisrequired.Thetransformerwilltypicallybeathree‐phase480/12.47‐kVtransformer.
4.3.4 GroundingStations
AgroundingstationwillneedtobeprovidedateachHVDCconverterstation,regardlessoftheHVDCcircuitconfiguration.Theconceptualdesignofa1‐MW,50‐kVDCgroundingstationispresentedinAppendixE(FigureE‐1).
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5.0 DESIGNCONCEPTSFOROVERHEADINTERTIES
ThefollowingsummarizesdesigncriteriadevelopedfortheconceptualdesignoftheHVDCoverheadintertielines.DesigncriteriaandconceptualdesignsarepresentedindetailinAppendixC.
5.1 OVERHEADDESIGNAPPROACH
Theoverheadintertiedesignconceptspresentedrequiredconsiderationoftypicalsiteconditions,codes,utilityandlenderrequirements,constructionmethodologies,standarddesignpractices,andprojecteconomics.ThefollowingtwodesignapproachesforoverheadHVDCintertieshavebeenevaluated,eachwithacapacitytosupply1MWthroughamonopolar50‐kVDCsystem:
5.1.1 RUSDesignApproach,ModifiedforHVDCInterties
ThefirstconceptualdesignapproachisbasedontheuseofstructuresthatareconstructedinaccordancewithUSDARUS‐typeconstruction(RUSstandardpractice)forconventional12.4/24.9‐kVACdistributionlines.5TheseRUSstandardpracticesarecurrentlyusedtodevelopACintertiesthroughoutAlaskaandarewidelyacceptedbytheutilityindustry.HVDCtransmissionrequiresfewerconductorsthanAC,resultinginreducedloadsonthesupportingstructures.Asaresult,theconceptualdesignsdevelopedusingtheRUSapproachhavelongerrulingspansthantypicalAClines.ThisresultsinfewertransmissionstructuresfortheHVDCintertieandanassociatedcomparativereductioninconstructioncost.
5.1.2 Alaska‐SpecificDesignApproachforHVDCInterties
ThesecondconceptualdesignapproachtakesthelogisticandtechnicalchallengesofconstructioninruralAlaskaintoconsiderationandfocusesonmethodstoreduceconstructioncostswithoutcompromisingperformanceorlong‐termmaintainability.Thisdesignapproachincorporatescost‐savingfeaturesmadepossiblethroughHVDC‐specificdesignalternatives,materials,andconstructionmethods.DesignfeaturesofthisconceptincludetheuseofguyedcompositestructurestoallowsignificantlylongerrulingspansthanispossiblewithRUSstandardpractice.Thereducednumberofstructures,lesscostlyfoundations,andreducednumberofconductorsallresultinadditionalsavingscomparedwithintertiesbuiltinaccordancewithRUSstandardpractices.
ThefollowingthreeHVDCtransmissioncircuitconfigurationsareconsideredforeachoftheHVDCconceptualdesignapproaches:
● Monopolarsingle‐wiretransmissionwithearth‐returnpath(SWER);
● Monopolartwo‐wiretransmissionwithmetallicconductor‐returnpath(TWMR);
● Bipolartwo‐wiretransmission(2‐MWcapacity).
5 Inthisreport,theterm“RUSstandardpractice”referstooverheadintertielinedesignsbasedonthemethodsand
materialspresentedinRUSdesignmanualsfortransmissionanddistributionlineconstruction,includingbutnotlimitedto:REA,1982,RUS,1998,2002,2003a,2003b,2003c,and2009.
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SchematicfiguresareprovidedforeachoftheseconceptualdesignsinAppendixC.DetailedreportsthataddressvarioustechnicalaspectsoftheassumedconditionsandloadingsusedtodeveloptheseconceptualdesignsareprovidedasattachmentstoAppendixC.
5.2 GEOTECHNICALCONDITIONS
Basedontheanalysisdescribedbelow,conceptualfoundationdesignalternativesforaguyedpoleutilizethreethermoprobemicropilesforthepolebaseandhelicalanchorsfortheguys.TheoverheadsystemtestsiteinFairbanks,Alaska,featuresinstallationsofbothoftheseprototypefoundations.
5.3 ENVIRONMENTALLOADS
FivestandardNESCloadingcaseswereanalyzedforeachconceptualdesign.TheseloadcasesareconsideredsufficientformostruralAlaskaoverheadintertieapplications.Specificlocationsmaybesubjecttohigherand/orlowerwindand/oriceloadings.6Exceptwherespecificallystatedotherwise,eachoftheconceptualdesignspresentedinthissectioncomplywiththemoststringentoftheseloadconditions.
5.4 CONSTRUCTION,RUSSTANDARDPRACTICETheconceptualdesignsofoverheadintertielinespresentedinthissectionhavebeendevelopedtotakeadvantageofthefollowingfactors:
● Alaskacontractors,linecrews,andutilitylinepersonnelarefamiliarwithRUSstandardpracticematerials,designs,andconstructionpractices,thustheywillbemorefamiliarwiththetechniquesandproceduresforbuilding,maintaining,andrepairingtheselines.
● AlaskaalreadyhasmanymilesofRUSstandard‐practicedistributionandtransmissionlinesbuiltandinservicethroughoutthestate.Utilitiesunderstandtheperformancerecordandissueswiththistypeoflineconstruction.
● Utilitylenders,whichincludesRUS,understandandacceptRUSstandardconstructionpractice,whichcansimplifyobtainingfundsforconstructingnewinterties.
Totakeadvantageofthesefactors,conceptualdesignforHVDCpreservedRUSstandardpracticeconstructiontotheextentpossible,modifyingthepoletopassemblytoaccommodatetheconductor(s),insulator(s),andclearancesforHVDCoperation.TherulingspanisalsoincreasedtotakeadvantageofthefewerwiresandreducedstructureloadsassociatedwiththeHVDCcircuitconfigurations.
StructuralanalysisofconventionaloverheadHVDCtransmissionstructures(adaptedfromRUSstandardpractice)wasperformedbyPolarconsult.AconceptualdesignsummaryispresentedinAppendixCforeachofthelineconfigurationsproposed.
6 Section4.6ofthePhaseIFinalReportprovidesasummaryofenvironmentalloadingsaroundAlaska(Polarconsult,
2009)
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5.5 CONSTRUCTION,ALASKA‐SPECIFICCONCEPT
TheconceptualdesignsofoverheadintertielinespresentedinthissectionhavebeendevelopedtoreduceconstructioncostsonruralAlaskainterties.Costreductionisachievedthroughspecialattentiontothefactorslistedbelow.
● Minimizingtherelianceonheavyequipmentthatmustbemobilizedtoaconstructionsite.Iflighterequipmentorlocalequipmentcanbeusedforconstruction,mobilizationcostswillbeless,reducingprojectcosts.
● Maximizingtheflexibilityinconstructionmethodsandseasons.Bydesigningfortheuseofsmallerequipment,greateruseofhelicoptersforconstructionsupport,andsimilartechniques,all‐seasonconstructionbecomespossible,providingincreasedflexibilityforconstructiontechniquesandmethods.Thisincreasedflexibilitycreatesnewopportunitiestoincreaseutilizationofequipment,increasecompetitionforlineconstructionprojects,andreduceprojectcosts.
Thesefactorshavebeenincorporatedintotheconceptualdesignelementslistedbelow.
● Useoftallerstructuresandlongerspans.BecauseHVDCcircuitsrequireonlyoneortwowires,theycanutilizelongerspansthanacomparablethree‐orfour‐wireACcircuit.Increasingspansreducesthenumberofstructuresandfoundationsforagivenlengthofoverheadline,whichreducescosts.Withthisapproach,tallerstructuresareneededtomaintainrequiredclearancesbetweentheconductorandtheground.
● Useofglass‐fiber‐reinforcedpolymer(GFRP)polesinsteadofwoodorsteelpoles.GFRPpoleshavebeenusedforover50yearsinelectricutilityapplications7buthavelittletonohistoryinAlaska’selectricutilityindustry.GFRPpolesarelighterthanwoodorsteelpolessotheycanbetransportedbyasmallhelicoptersuchasaHughes500orBellUH‐1“Huey.”Theyarealsorot‐resistantanddonotleachtoxicpreservativesintothesoilsaroundthepole.ThePhaseIIprojectincludeddemonstrationofafield‐friendlyspliceforGFRPpoles,whichpermitstallpolestobeshippedinpartsandassembledinthefield.ThissplicecanalsobeusedforfieldrepairofdamagedGFRPpoles.
● Useofguyedstructuresinareaswheregeotechnicalconditionspreventcantileveredpolesfrombeingdirectlyburiedinthesoil.Acceptedpracticeforsuchconditionsistodriveasteelpileupto40feetdeepandthenfastenawoodpoletothesteelpile.Installingthesteelpilerequiresmobilizingacraneorotherheavyequipmenttotheprojectsite.Aguyedstructurecanbeinstalledinsuchconditionswithamuchsmallerbasefoundation,astheguyscarrymostofthemoment,andthestructurebasemostlycarriescompressiveloads.
7Ibrahim,2000.
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5.6 TESTINGOFOVERHEADDESIGNCONCEPTS
TheconceptualoverheaddesignsdescribedinAppendixCusecommerciallyavailableandacceptedmaterials,designs,andconstructionmethods.CertainaspectsoftheconceptualdesignspresentedrepresentinnovationsinoverheadlinedesignthatdonothaveaprovenrecordwithintheutilityindustryinAlaskaconditions.Inordertoevaluatetheperformanceofthesecomponents,theywereinstalledatatestsiteinFairbanks,Alaska.ThissectionsummarizestheobjectivesandinstallationoftheFairbanksTestSite.DetailsofthetestprogramarepresentedinAppendixC.
5.6.1 TestObjectives
TheprimarytestobjectivesoftheFairbanksTestSitearelistedbelow.
● Demonstrateperformanceandassemblytimeofaspliceforaconstant‐sectionGFRPutilitypole.
● Demonstrateinstallationandperformanceofmicro‐thermopilepolefoundations.
● Demonstrateinstallationandperformanceofmicro‐thermopileguyanchors.
● Demonstrateinstallationandperformanceofscrewguyanchors.
● DemonstratetheinstallationandperformanceoftheoverallguyedGFRPpolestructure.
● Demonstratemaintenanceandoperationalcharacteristics.
5.6.2 TestSite
ThetestsiteislocatedonprivatepropertysouthofFarmer’sLoopRoadandnorthofCreamers’FieldinFairbanks.Thesiteconsistsofwarmice‐richsiltypermafrostsoils.Thesitehasanorganiclayerconsistingofdeciduousshrubsandblackspruce.Peatwaspresentatdepthsof1to5feetbelowgroundsurface.TheactivelayerinSeptember2011extendedtoadepthof3feet,withstandingwaterencounteredwithinthevegetativematnearthesurface.Geotechnicalconditionsatthesitearecharacteristicofmarginalwarmpermafrostconditions,asfurtherdescribedinAppendixC.
Figures5‐1through5‐4showtheinstallationofinnovativematerialsandsystemsatthetestsiteinFairbanks.
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Figure 5-1 Installing Micro-Thermopile for Guy Anchor
ContractorGeoTekAlaska,Inc.drillingaholeforinstallationofamicro‐thermopileata45‐degreebatterangleusingaGeoProbe8040seriesdrillrig.Themicro‐thermopilewillserveasaguyanchorfortheprototypeguyed
GFRPpoleinstallationattheFairbanksTestSite.(Polarconsult,2011).
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Figure 5-2 Assembling the Prototype GFRP Pole Splice
ContractorCityElectric,Inc.installingthefieldsplicefortheprototypeGFRPpole.40‐footand20‐footGFRPpolesegmentsweresplicedtocreatethe60‐footpoleerectedatthesite.Thespliceslidesoverthepolesegmentsandcarriesmomentthroughcontactbetweenthepoleandsplicewalls.Verticalloadsarecarriedthroughthebuttendsofthepolesegments.Noglueoradhesiveisnecessaryforthesplicetodevelopthefullmechanicalstrengthofthepole.Thescrewsservetopreventdifferentialmovementbetweenthepoleandsplice.(Polarconsult,2011)
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Figure 5-3 Prototype GFRP Pole Foundation During Installation
DetailofprototypeGFRPpolebaseattheFairbanksTestSite.Theadapterplatewasadjustedduringinstallationsothehingeisorientedinlinewiththeguyanchorinthedistance(orangeflagging).Thiswillallowuseofthe
guyanchortolowerthepolewithawinchifneeded.(Polarconsult,2011)
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Figure 5-4 Prototype Pole at the Fairbanks Test Site
ViewoftheprototypeguyedGFRPpoleinstalledattheFairbanksTestSite.Thisphotographistakenatadistanceofapproximately25yardsfromthe60‐foot‐tallpole.Thefourguysandthepolesplicearevisibleinthis
photograph.(Polarconsult,2011)
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6.0 SYSTEMECONOMICS
TheextremevarietyofenvironmentalandtechnicalconditionsfoundacrossruralAlaskaresultsinasignificantvariationinintertiecosts.Thetypicalcostforconstructingaconventionaloverheaddistribution‐classACintertieinruralAlaskacanvaryfromaslittleas$100,000permiletoover$600,000permile8inpartsofthestatewithchallenginglogisticsandlittleornotransportation.Intertiecostvariationsalsoaffectsubmarinecables,undergroundcables,andotheroverheadintertieconfigurations.ThedetailsofsystemeconomicsarepresentedinAppendixB.
6.1 COSTCOMPARISONOFACANDHVDCOVERHEADINTERTIES
TwodistinctoverheadHVDCintertieconfigurationshavebeencomparedtoaconventionalACintertietoillustratearangeofHVDCintertieeconomicswithdifferentoverheaddesigns.ThetwoHVDCintertieconfigurationsare:
● Atwo‐wiremonopolarHVDCintertieusingRUSstandardpracticeconstructionmethods.ThisintertieconfigurationrepresentstheupperrangeofestimatedcostforanHVDCoverheadintertieinruralAlaskaapplications.
● AmonopolarSWERHVDCintertieusingAlaska‐specificconstructionmethods.ThisintertieconfigurationrepresentsthelowerrangeofestimatedcostforanHVDCoverheadintertieinruralAlaskaapplications.
TheestimatedcostforHVDCintertiesinmostruralAlaskaapplicationsisexpectedtofallbetweenthecostscitedforthesetwoconfigurations.
6.1.1 InstallationCostComparison
Figure6‐1presentstheestimatedinstalledcostrelativetotheintertielengthforthreedifferentkindsofintertiesbuiltinruralAlaskaconditions:
● AconventionalruralAlaskaintertie,
● Atwo‐wiremonopolarHVDCintertieusingRUS‐typeconstructionmethods,and
● AmonopolarSWERHVDCintertieusingAlaska‐specificconstructionmethods.
Additionally,Figure6‐1illustratestheeconomicbreak‐evenlengthandrelativeincreaseinsavingsforlongerHVDCinterties.ThepointsatwhichtheAC“costline”crosseseitheroftheHVDC“costlines”representstheeconomicbreak‐evenlength.TheestimatedHVDCcostsshowahypotheticalrangeofinstalledcostsanticipatedforlow‐power(under1MW)ruralAlaskaHVDCsystems.
8SeeSectionB.6.1inAppendixBforcostbasisinformation.
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Figure 6-1 Comparative Installed Cost: Overhead 1-MW HVDC and AC Interties
$0
$5,000,000
$10,000,000
$15,000,000
$20,000,000
$25,000,000
$30,000,000
$35,000,000
$40,000,000
$45,000,000
0 10 20 30 40 50 60 70 80 90 100
Intertie Length (miles)
Probab
le In
stalled Cost of Overhead HVDC vs. AC In
terties
AC Intertie (Standard RUS Construction)
HVDC Intertie (Monopolar, TWMR, Standard RUS Construction)
HVDC Intertie (Monopolar, SWER, Alaska‐Specific Construction)
BREAK‐EVEN COST FOR HVDC INTERTIES: 6 to 22 MILES
(INSTALLED‐COST BASIS)
Note: This chart is based on the assumptions and comparative system costs
presented in Appendix B. The break‐even point will vary for every intertie project.
COST SAVINGS
RANGE
AC
HVDC
HVDC
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6.1.2 Life‐CycleCostComparison
Operatingcosts,maintenancecosts,andelectricalefficiencyaffectthelong‐termeconomicvalueofanintertie.Table6‐1presentscomparativelife‐cyclecostsforhypothetical25‐mile‐longoverheadACandHVDCintertiesinruralAlaska.Alengthof25mileswasselectedasitconservativelyrepresentsthesavingsanticipatedforshortHVDCinterties.Theestimatedlife‐cyclecostfora25‐mile‐longHVDCintertierangesfrom79%to107%ofthelife‐cyclecostofanACintertie.
Table 6-1 Estimated Life-Cycle Costs for 25-mile Overhead AC and HVDC Interties
ParameterStandardRUSACIntertie
MonopolarTwo‐WireHVDCIntertie(RUSConstruction2)
MonopolarSWERHVDCIntertie
(Alaska‐SpecificDesign1)
CostofDiesel($/gallon[gal]) $7.00pergallon
GenerationEfficiency(kWh/gal) 13kWhpergallon
IntertieEfficiency4 97.7% 93.4% 94.5%
NetAnnualEnergyTransmission(kWh) 1,664,400
AnnualTransmissionLosses4(kWh) 38,300 133,000 114,000
AnnualizedValueofTransmissionLosses($) $21,000 $71,000 $61,000
IntertieDesignLife(years) 20years
IntertieAnnualOperationsandMaintenance(O&M)Costs
$40,000 $58,000 $54,000
EffectiveDiscountRate 3%
PresentWorthofTransmissionLosses $307,000 $1,063,000 $912,000
PresentWorthofO&MCosts $595,000 $867,000 $796,000
ConverterStationsInstalledCost $20,000 $2,080,000 $1,160,000
IntertieInstalledCost $9,480,000 $7,120,000 $5,340,000
EstimatedLife‐CycleCost $10,402,000 $11,130,000 $8,208,000
HVDCLife‐CycleCostasPercentofACLife‐CycleCost 107% 79%
PresentWorthSavings(Cost)ofHVDCvs.AC ($728,000) $2,194,000
Notes:1. “Alaska‐SpecificDesign”referstothedesignconceptspresentedinAppendixCofthisreport.2. “RUSConstruction”referstostandardRUSdesignandconstructionmethodsforACinterties,adaptedtoHVDC
applicationsasdescribedinAppendixCofthisreport.3. Allmonetaryvaluesarein2012dollars.4. Efficiencyandlossinformationincludesalltransmissionsystemcomponents.
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Figure6‐2illustratestheeconomicbreak‐evenlengthandrelativeincreaseinsavingsforlongerHVDCinterties.ThepointsatwhichtheAC“costline”crosseseitheroftheHVDC“costlines”representstheeconomicbreak‐evenlength.TheestimatedHVDCcostsrepresentahypotheticalrangeoflife‐cyclecostsanticipatedforlow‐power(under1MW)ruralAlaskaHVDCsystems.
Figure 6-2 Comparative Life-Cycle Cost: Overhead 1-MW HVDC and AC Interties
$0
$5,000,000
$10,000,000
$15,000,000
$20,000,000
$25,000,000
$30,000,000
$35,000,000
$40,000,000
$45,000,000
0 10 20 30 40 50 60 70 80 90 100
Intertie Length (miles)
Probab
le Life‐Cycle Cost of Overhead HVDC vs. AC In
terties
AC Intertie (Standard RUS Construction)
HVDC Intertie (Monopolar, TWMR, Standard RUS Construction)
HVDC Intertie (Monopolar, SWER, Alaska‐Specific Construction)
BREAK‐EVEN COST FOR HVDC INTERTIES: 12 to 31 MILES
(LIFE CYCLE COST BASIS)
Note: This chart is based on the assumptions and comparative system costs
presented in Appendix B. The break‐even point will vary for every intertie project.
AC
HVDC
HVDC
COST SAVINGS
RANGE
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6.2 CASESTUDIES
Thecasestudiesinthissectionprovideproject‐specificexamplesoftheexpectedcostsandresultingbenefitsofusingHVDCsystemstointerconnectcommunitiesandresources.Thesecasestudiesrelyonexistinginformationregardingtheproposedintertieroutes,loads,andrelatedprojectinformation.Figure6‐3presentsafewofthemanypotentiallow‐powerHVDCprojectsitesthroughoutAlaska.
Figure 6-3 Location Map for Potential HVDC Project Sites
Forthepurposesofthisreport,twospecificHVDCprojectsiteswereselectedforevaluation.The“GreensCreek–Hoonah”andthe“Nome–PilgrimHotSprings”intertieprojectsaretypicalofthedesignapproachandeconomicscommontootherHVDCAlaskaninterties.Table6‐2summarizesthecasestudiesconsideredinthissection.
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Table 6-2 Summary of Case Studies
HVDCIntertieCaseStudy
TransmissionCircuit
IntertieType
HVDCIntertieCost
Estimate1
ACIntertieCost
Estimate1
EstimatedHVDCSavings1
PercentCapitalCost
Savings
GreensCreek–Hoonah
5‐MWmonopolarHVDCcircuitwithseareturn2
SubmarineCable
$22.2million
$49million
$26.8million 55%
Nome–PilgrimHotSprings
5MWbipolarHVDCcircuit
OverheadLine
$25.7million
$36.3million
$10.6million 29%
Notes:
1. Allcostestimatesarepresentedin2012dollars.
2. Thecasestudyprovidesasubmarineandoverheadintertiecapacityof5MWandconverterstationcapacityof2MW.ThisprovidesanamplemarginforloadgrowthinHoonah.Theconverterstationcapacitycanbeupgradedasneededin500‐kWincrementsupto5MW.
6.2.1 Green’sCreek–HoonahCaseStudy
AnintertiebetweenGreensCreek,ontheAlaskaElectricLightandPowerCompany(AEL&P)gridthatservesJuneau,andthevillageofHoonah,anisolatedmicro‐gridoperatedbytheIPEC,hasbeenunderconsiderationforoveradecade.AEL&PandtheIPEChavecompletedextensivestudiesanddesignworkonthisintertie.Studiesidentifieda25‐mile‐longACsubmarinecableandapproximately4milesofoverheadlinenearHoonahasthemosteconomicalmeanstocompletethisinterconnection.9TheproposedintertierouteisshownonFigure6‐4.
Asthedevelopmentofthisprojectcontinued,thecostsoftheACsubmarinecablehaveescalated,untiltheprojectwasfinallyputonholdduetoitsexcessivecost.Hoonahiscurrentlyexploringlocalhydropowerresourcestoreduceitsenergycostsbutcontinuestoviewanintertieasthebestlong‐termsolutionforitsenergyneeds.
ThisHVDCsystemrepresentsatechnologicaladvancethatcanreducethecostoftheGreensCreek–HoonahintertieandincreaseitseconomicfeasibilityascomparedwithHoonah’sotherenergyoptions.Thefollowingsubsectionsofthiscasestudyprovideahigh‐levelanalysisofthemeritsofanHVDCintertieforHoonah.
Forthepurposesofthiscasestudy,a5‐MWmonopolarHVDCtransmissioncircuitwithseareturnwasselectedtoconnectHoonahwithGreen’sCreek.Thiscircuitconsistsof25milesofsubmarinecableand4milesofoverheadline.Amonopolarcircuitwasselectedbecauseitisexpectedtobetheleast‐costintertiesolutionbetweenHoonahandGreen’sCreek.Otherpotentialconfigurations,suchasabipolarHVDCcircuitutilizingtwosingle‐conductorcables,wouldbemoreexpensivethanthemonopolardesignselected.
9(PowerEngineers,2004)
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Theestimatedcapitalcostsincludea5‐MWtransmissioncircuit(submarinecableandoverheadline),and2‐MWconverterstationsatHoonahandGreen’sCreek.Theconverterstationscanbeupgradedto5MWbyadding500‐kWconvertermodulesasHoonah’sloadincreases.IfHoonah’sloadgrowsbeyond5MW,asecondsubmarinecablecanbeinstalledtoprovidea10‐MWbipolartransmissionsystem.
Figure 6-4 Greens Creek – Hoonah Intertie Route
6.2.1.1 EconomicAnalysis
Table6‐3presentstheeconomicanalysisfortheGreensCreek–Hoonahintertiealternatives.TheestimatedinstalledcostfortheHVDCintertieis$22.2million,ascomparedtothecostof$49millionforaconventionalACintertie.TheACintertiecostestimateisbasedonthe2009estimatedcostof$37.5million10adjustedto2012dollars.
10IPEC,2009.
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Table 6-3 Estimated Cost for a Greens Creek – Hoonah HVDC Intertie
CostItem EstimatedCost
PreconstructionRight‐of‐wayacquisition,engineering,survey,permitting $1,600,000
Administration/Management $900,000
HVDCConverterStations(powerconverters,seaelectrodes,enclosures,ACandDCsidestationequipment) $2,700,000
SubmarineCableSupplyandInstallation $12,400,000
OverheadHVDCLine:SpaaskiBaytoHoonah $900,000
Contingency(onentireproject,25%)1 $3,700,000
TotalEstimatedCost $22,200,000
Notes:1.Acontingencyof25%isappliedtothecostsdevelopedforthisprojectbasedontheuncertaintiesassociatedwiththeproject.Asignificantamountofworkhasalreadybeendonetocharacterizethebathymetryandseafloorconditionsalongtheproposedcableroute.
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Table6‐4presentsestimatedbenefit‐costratiosfortheGreensCreek–Hoonahintertieunderseveralloadgrowthscenarios.ThisanalysisindicatesacleareconomicadvantagetoanHVDCintertiebasedonreasonableloadgrowthforecastsforHoonah.
Table 6-4 Estimated Benefit-Cost Ratio of Greens Creek – Hoonah HVDC Intertie
ItemLoadGrowthScenario
ExistingLoad 165%Growth 200%Growth6
AnnualHoonahEnergyGeneration(kWh/yr)1 5,150,000 8,500,000 9,780,000
AEL&PAvoidedCostofEnergy(Juneau)2 $0.06perkWh
IPECAvoidedCostofEnergy(Hoonah)1 $0.20perkWh
IntertieOutageRate3 2%
AnnualHoonahSavings4 $707,000 $1,170,000 $1,340,000
IPECOperation,Maintenance,Repair,ReplacementandRehabilitation(OMR&R)AnnualCosts5 $90,000 $90,000 $100,000
NetAnnualSavings(Cost) $617,000 $1,150,000 $1,340,000
IntertieLifeandDiscountRate 30years,3%
PresentWorthofAnnualSavings(Costs) $12,070,000 $21,090,000 $24,500,000
EstimatedInstalledCost $22,200,000 $22,200,000 $22.200,000
EstimatedBenefit‐CostRatio 0.54 0.95 1.10
Notes:
1. BasedonPowerCostEqualization(PCE)reportsfor2007through2009(AEA,2010a).
2. ApproximateAEL&Penergycost.IPEChascapacity,sonodemandorcapacitychargesareincluded.
3. Assumedvalue.
4. AnnualsavingsarebasedonthedifferentialcostofenergyanddonotconsidereconomicbenefitsinHoonahfromlowercostenergy,oreffectstoAEL&Pofincreasedenergysales.
5. IPEC’sestimatedoperations,maintenance,repair,androutinereplacementcostsincludecostsfortheconverterstations,savingsfromdecreasedoperationandoverhaulofthedieselpowerplantinHoonah,andaone‐timecablerepaireventoverthe30‐yearanalysisperiod.
6. Hoonah’speakloadsundera200%loadgrowthscenariowouldexceedthe2‐MWcapacityoftheintertieconverterstations.Intertiethroughputisreducedby5%toreflectdieselgenerationinHoonah.
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6.2.2 PilgrimHotSprings–Nome
PilgrimHotSpringsisageothermalresourcelocatedapproximately60milesnorthofNome.IthasbeenproposedasapowersourcetoreduceNome’srelianceondieselfuelforelectricalgeneration.ACEPiscurrentlystudyingthePilgrimHotSpringsgeothermalresourcetobettercharacterizetheresource’spotentialforpowergenerationandotherapplications.ForpurposesofsizingthetransmissionlinefromPilgrimHotSprings,anelectricalgeneratingcapacityandtransmissioncapacityof5MWisassumed,basedonconversationswithACEP’smanagerforthePilgrimHotSpringsassessmentproject.11TheproposedtransmissionrouteisshownonFigure6‐5.
AbipolarHVDCcircuitusingoverheadlineswasselectedfortheHVDCintertie.Thebipolarconfigurationwasselectedbecauseitprovidesincreasedreliabilitycomparedtoamonopolarlineatareasonableadditionalcost.
ConceptualpowerlinecostsforoverheadACandHVDCintertieswereestimatedtoevaluatethebenefitsofconnectingPilgrimHotSpringstoNomeusinganHVDCintertie.ThecostestimatesindicatethatanHVDCtransmissionlinewouldcost29%lessthananACtransmissionline.
Aroutingstudywasnotperformedaspartofthiscasestudy.Powerlineswereroutedalongtheexistingroadcorridor.Thisisassumedtobetheleast‐costrouteforthepowerlines,astheroadcanbeusedtosupporttheconstructionandlong‐termmaintenanceoftheline.Aroutingstudymayidentifyotherroutesthataremorefavorableduetogeotechnical,landstatus,environmental,orotherfactors.
11PersonalcommunicationwithMarcusMager,2012.
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Figure 6-5 Prospective Transmission Route from Pilgrim Hot Springs to Nome
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6.2.2.1 EconomicAnalysis
Table6‐5presentstheeconomicanalysisforthePilgrimHotSprings–Nomeintertiealternatives.TheestimatedinstalledcostfortheHVDCintertiealternativeis$25.7million,ascomparedtothecostof$36.3millionforaconventionalACintertie.
NoinformationisavailablefortheinstalledcostofageothermalpowerplantatPilgrimHotSpringsorthecostoftheenergyitwouldgenerate,soabenefit‐costratiooftheintertiealternativeswasnotevaluated.
Table 6-5 Estimated Installed Cost for a 5-MW Pilgrim Hot Springs – Nome Intertie
CostItem
EstimatedInstalledCostforBipolarHVDC
Intertie
EstimatedInstalledCostforACIntertie
EstimatedHVDCSavings
PercentCostSavings
PreconstructionActivities(right‐of‐wayacquisition,design,survey,permitting)
$3,400,000 $3,400,000 ‐ ‐
Administration/Management $1,000,000 $1,300,000 ‐ ‐
ConverterStationConstruction $4,600,000 $3,000,000 ‐ ‐
OverheadIntertieConstruction $10,800,000 $20,200,000 ‐ ‐
Contingency(30%)1 $5,900,000 $8,400,000 ‐ ‐
TotalEstimatedCost $25,700,000 $36,300,000 $10,600,000 29%
Note:1. A30%contingencywasappliedtothecostsforthisprojectbecausenoinformationwasavailableforthe
transmissionroute.Thislackofdatacreatesrisksduetofactorssuchaslandavailability,geotechnicalconditions,structural(windandice)loadings,andenvironmental(bird,wildlife,andaesthetics)factors.Someoftheserisksaremitigatedbytheuseofcostdatafortherobustconceptualdesigns(i.e.,Alaska‐specificconstruction)usedfortheHVDCsystem.TheAlaska‐specificconceptualdesignisassumedtobeadequatefortheexpectedgeotechnicalandstructuralconditionsalongtheroute.Environmentalandlandavailabilityissues,whichcouldrequirealongerrouteordeparturefromtheroadcorridor,poserelativelygreaterrisksthanlinedesignconsiderations.Thenetresultofthesefactorsresultsinthe30%contingencyusedforthecasestudyeconomics.
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7.0 CONCLUSIONSANDRECOMMENDATIONS
7.1 CONCLUSIONS
PhaseIIhasdemonstratedthattheconvertertechnologyistechnicallyviableandthetransmissionsystemiseconomicallyfeasible.KeyPhaseIIfindingsare:
● Low‐powerHVDCconvertertechnologyisexpectedtobecommerciallyavailableat$250perkilowattperconverter.
● Estimatesofconstructioncostsforaconceptual25‐mileoverheadHVDCintertieindicatecapitalcostsavingsofapproximately30%comparedwithaconventionaloverheadACintertie.Estimatedlife‐cyclecostsrangefrom79%to107%ofthelife‐cyclecostofanACintertie.
● LongeroverheadHVDCintertiescanexpectcapitalcostsavingsofupto40%.
● SignificantsavingsarepossibleforsubmarinecableandundergroundcableapplicationsusingHVDCsystems.Estimatedcapitalcostsavingsona25‐milelow‐powerHVDCsubmarinecableintertieareover50%comparedtoACalternatives.
BasedonPhaseIIfindings,thebenefitsoflow‐powerHVDCsystemsforAlaskaaresubstantial,andcontinueddevelopmentofthissystemisrecommended.
7.2 OPPORTUNITIESANDBARRIERS
BasedonanalysisandstudyconductedduringthisPhaseIIproject,PolarconsulthasconcludedthatthisHVDCtechnologypresentsthefollowingopportunitiesforAlaska’sutilityindustryandruralcommunities:
● Lessexpensiveruralelectricinterties,leadingtolower‐costenergyandincreasedenergyindependenceforruralcommunities.
● Interconnectiontocurrentlystrandedenergyresources.
● Interconnectioncostsavingsbycombiningruralelectricandtelecommunicationsinterties.
Thesuccessfulcommercializationandadoptionoflow‐powerHVDCtechnologyinAlaskarequiresovercomingthefollowingbarriers:
● Completionofthecommercialdevelopmentanddemonstrationoftheconvertertechnology.Continueddevelopmentoftheprototypeconverters,culminatinginindependenttestingoftheconvertersanddeploymentonanAlaskautilitysystem,isneededtoprovethattheconvertersareacommerciallyviabletechnology.
● Acceptanceanduseoflow‐powerHVDCtechnologybyAlaska’sutilityindustry.Continuedinvolvementofin‐stateandinternationalstakeholderswiththeon‐goingdevelopmentofthistechnologyisconsiderednecessarytosurmountingthisbarrier.
● DevelopmentanddemonstrationofstandardsandcontrolprotocolsforMTDCtransmissionnetworks,whichareneededtobuildcost‐effectiveregionalHVDCpowernetworksinruralAlaska.
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7.3 RECOMMENDATIONS
Basedontheconclusionsandfindingsofthisproject,thefollowingactionsarerecommended.
PhaseIIIprogramactivities:
● Continueddevelopmentofthepowerconvertertechnologytocommercializetheexistingprototypeconverterdesign.SolicitationofadditionalHVDCconvertermanufacturersiswarrantedtoencouragediversityofsuppliersandcompetition;
● Independenttestingoftheconverterstovalidateefficiencyandperformance,followedbydeploymentonanAlaskanutilitysystemtovalidatefunctionalityandreliabilityinacommercialsetting;
● FurtherdevelopmentofMTDCtransmissionsystemsinterconnectionandcontroltechnologies;and
● Continuedinvolvementofin‐statestakeholdersinthedevelopmentofthistechnology.
Stakeholderactions:
● Incorporatelow‐powerHVDCtechnologyintoAlaska’sregionalandstatewideenergyplansandpolicies;
● ContinuecoordinationwiththeStateofAlaskatoallowaproject‐specificwaiveroftheNESCtoallowtheuseofSWERcircuits;
● EncourageplannedruralpowerandtelecommunicationsintertiestoincorporateHVDCtechnologyintheireconomicandtechnicalanalysis,aswellastheirenvironmentalandpermittingreviewprocesses;
● Engagethetelecommunicationsindustrytoraiseawarenessofthesynergiespossiblebetweenlow‐powerHVDCtransmissionandfibernetworksinruralAlaska;and
● Collaboratewithinternationalstakeholderstoidentifysynergiesandlessonslearnedfromparalleltechnologydevelopmentefforts.Coordinateondevelopmentofapplicablepolicies/standardsandidentificationofmarketstohelpexpeditethecommercializationandreducethecostsoflow‐powerHVDCsystems.
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APPENDIXA
HVDCOVERVIEW
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TABLEOFCONTENTS
A.1 HIGH‐VOLTAGEDIRECTCURRENT(HVDC)TECHNOLOGY..................................................................5
A.2 SINGLE‐WIREEARTHRETURN(SWER)CIRCUITS...................................................................................7 A.2.1 WHYUSESWER?.............................................................................................................................................................7
A.3 SWERINALASKA.....................................................................................................................................................8 A.3.1 BETHEL–NAPAKIAKACSWERLINE..........................................................................................................................8 A.3.2 KOBUK–SHUNGNAKACSWERLINE..........................................................................................................................8 A.3.3 FUTUREOFSWERINALASKA........................................................................................................................................8
A.4 HVDCFORALASKA.................................................................................................................................................9
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A.1 HIGH‐VOLTAGEDIRECTCURRENT(HVDC)TECHNOLOGY
High‐voltagedirectcurrent(HVDC)convertertechnologyhasadvancedtousehigh‐efficiencysolid‐statehardware,andHVDClinksareutilizedforelectricaltransmissionthroughouttheworld.Whilethetechnologyhasadvancedconsiderablysincethe1950s,utilityapplicationofHVDCremainslimitedtotransmissionfunctions.Thesmallestutility‐gradeHVDCsystemsaredesignedtotransmitapproximately50megawatts(MW)12.SomenotableHVDCinstallationsinclude:
● SwedishMainlandtoGotlandIsland:20MW,100kilovolt(kV),monopolarsubmarinecablewithseareturn.Commissionedin1956,thiswasoneofthefirstHVDCintertiesinstalledintheworld.Thisoriginalsystemwasdecommissionedin198713.
● PacificIntertie–Celilo,Oregon,toSylmar,California:846‐mile,3,100MW,500kV,bipolaroverheadline.Commissionedin1970.
● BritishColumbiaMainlandtoVancouverIsland,Canada:45‐mile,682MW,260‐280kV,bipolarsubmarineandoverheadsystem.Thefirstpolewascommissionedin1968,andasecondpolewascommissionedin197714.
● NelsonRiverBipolarSystem,NelsonRiverHydroComplextoSouthernManitoba,Canada:TwobipolartransmissionsystemsoperatebetweenthehydropowerprojectsalongtheNelsonRiverinnorthernManitobaandWinnipeginthesouthernpartoftheprovince.Thefirstsystemisa540‐mile,1,620MW,450kVoverheadbipolarcircuitcommissionedin1977.Thesecondisa560‐mile,1,800MW,500kVoverheadbipolarcircuitcommissionedinstagesbetween1978and1985.Notably,bothsystemstraversepermafrostterrainsimilartothatfoundinAlaskaandcanoperateinSWERmode,moving1,000sofamperesofcurrentthroughearth‐return15.
● Cross‐SoundCable,NewHaven,Connecticut,toLongIsland,NewYork:24‐mile,330MW,150kVbipolarsubmarinecable.Commissionedin2002,thiscableusesABB'sHVDCLitetechnology.BothHVDCconductorsandafiber‐optictelecommunicationscablearebundledintoasinglecabletosimplifyinstallation16.
● England–FranceCrossChannelIntertie:38‐mile,160MW,100kVbipolarsubmarinecable.Theoriginalsystemwascommissionedin1961andreplacedin1986byalargersystemoperatingat270kVand2,000MW.Abipolarsystemwasoriginallyinstalledtoreducemagneticanomaliesthatcouldinterferewithshipping.
● Sardinia–Corsica–ItalianMainland,Italy:500MW,200kVbothearthandseareturns.Thefirst200MWpoleofthissystemwascommissionedin1965.Asecond300MWpolewasinstalledin1992.Thissystemisunusualbecauseitisamultipointsystem(servingthreeloadcenters),unlikemostHVDCinterties,whichtransmitpowerbetweenonlytwopoints.
12“HVDCLite,”distributedbyABB,isoneexampleofthesmallerutility‐gradeHVDCsystems.13 Theoriginalsystemusedon‐shoregroundinggridstocompletethetransmissioncircuitviaseaand/orseabedpathways.This
firstHVDClinkwasaugmentedbyasecond150MWmonopolarHVDClinktotheislandin1983,andathird150MWmonopolarlinkin1987.Today,thesetwonewercircuitsareoperatedtogetherasabipolartransmissionlink.
14 Thefirstmonopolarlineisratedfor312MWat260kV,andthesecondmonopolarlineisratedat370MWat280kV.15 http://www.hydro.mb.ca/corporate/facilities/ts_nelson.shtml16 CrossSoundCableConnectorProjectLiterature,www.abb.com
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● Fiveback‐to‐backHVDCconverterstations17interconnecttheTexasgridandU.S.electricgridinneighboringstates.Mostofthesestationswerecommissionedinthe1980s.Becauseofthesestations,TexashasanasynchronousgridconnectiontotheremainderoftheLower48.
● ThreeGorgesDamtoShanghai,China:530‐mile,3,000MW,500kV,bipolaroverheadline.FourHVDClinesareplannedbetweenThreeGorgesandChina'seasterncoastalregions.Thefirstbipolarcircuitwascommissionedin2003andthesecondin2006.
● VictoriatoTasmania,Australia:500MW,400kV,monopolarsubmarinecablewithseareturn.Commissionedin2005.
● SwedentoGermany,BalticCable:600MW,450kV,withearthreturnviadeepholeelectrodes.Commissionedin1993.
HVDClinkscanbesuperiortohigh‐voltagealternatingcurrent(AC)linksforseveralkeyreasons:
● HVDClinksarelesscostlyand/ormoreefficientthanAClinksundercertaincircumstances.
● Longintertiesutilizinginsulatedcables(asforsubmarineapplications)arepossiblewithHVDCelectricity,butprohibitivelydifficultwithACelectricityduetocablecapacitanceandreactivepowerlosses.
● HVDClinksprovideanasynchronousconnectionbetweenACelectricalgrids.Analogoustoaclutchonamechanicalsystem,anHVDCintertieallowseachACsystemtooperateatitsownphaseandfrequencyandstillallowpowertransferbetweenthesystems.ThiscanincreasethestabilityofbothACgrids.
● Foragivenpowertransferrequirement,HVDCintertiescanrequirelessright‐of‐waythancomparableACinterties.Theycanalsohaveavarietyofotherregulatory,permitting,orenvironmentaladvantagescomparedtoACinterties.
BecauseofthehighcostoftheconvertersystemsnecessarytoconvertHVDCtoamorereadilyusedACwaveform,HVDCisgenerallylimitedtotransmissionapplications.Accordingly,mostorallutilityHVDCsystemsinusetodayarepoint‐to‐pointtransmissionlines,withnointermediatetake‐offpointsorsubstationsforcommunitiesenroute.
Forthesmall‐scaleruralAlaskaHVDCapplicationsconsideredinthisstudy,thereisstillaneconomicbarrierduetothecostoftheHVDCconverters(estimatedat$250,000perMWin2012dollars).Forexample,aremotelodgeorfishcamplikelycannotjustifythecosttotaptheHVDCline,butmostvillagescan.
AsHVDCintertiesareconsideredforruralAlaskaapplications,utilitiesmaydesiretoextendACdistributionasanunderbuildoroverbuildonanoverheadHVDCline.Similarly,otherutilitiesmaydesiretoutilizetheoverheadstructurestoco‐locatetheircables.Thispracticeispossiblesolongasapplicablecoderequirementsandsafetyprovisionsarefollowed.Itmaybedesirabletouseconventionalconstructionintheimmediatevicinityofvillagestofacilitatecolocationofmultipleutilitycables,transitioningtoadifferent,optimizedoverheadstructureforHVDConceawayfromthevillage.
17 ThefiveHVDCsystemsarethe220‐MWback‐to‐backNorthDCTie,600‐MWback‐to‐backEastDCTie,36MVAback‐to‐back
EGPSDCTie,150MVAback‐to‐backRAILDCTie,and80MVALaredovariablefrequencytransformer(VFT)Tie.(www.ercot.com).
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A.2 SINGLE‐WIREEARTHRETURN(SWER)CIRCUITS
Initssimplestform,anelectricalcircuitrequirestwocurrentpathways,typicallywires.Onewiregoesfromthepowersupplytotheload,andasecondwiregoesfromtheloadbacktothepowersupply.Bothsingle‐phaseACandDCcircuitsrelyonthisbasicconfiguration.Thewirefromthepowersupplytotheloadisusuallyatanincreasedvoltagerelativetoground,andsoitisinsulatedforsafetyandtopreventshortcircuits.Thewirefromtheloadbacktothepowersupplyisusuallyatamuchlowervoltagerelativetogroundandthusisusuallybutnotalwaysinsulated.
Insingle‐wireearthreturn(SWER)circuits,thewirethatservesasthesecondcurrentpathwayfromtheloadbacktothepowersupplyisreplacedwithasuitable,convenient,andsafecurrentpathway.Inthemostgeneralcase,this“non‐wire”pathwaycanbeacarortruckchassis,themetalhandleofaflashlight,theearth,naturalwaterbodies,orotherobjectsthatcansafelycompletetheelectricalcircuit.
Seareturncircuitsaresimilartoearthreturncircuits.Theonlydifferenceisthatthesea,oranywaterbody,isusedasthepredominantreturncircuitpathway.Parallelpathways,suchastheseabed,arealsoavailableforcurrentflow.
A.2.1 WhyUseSWER?
TheprimaryadvantagesofferedbySWERcircuitsinclude:
● Lowercosts(eliminatethesecondconductor).
● Higherefficiency(lowerelectricallosses).
TheprimaryconcernsassociatedwithSWERcircuitsinclude:
● AvoidingcorrosionofburiedorsubmarinemetallicobjectsinthevicinityoftheSWERcircuit.
● Aswithallelectricalsystems,safety.
SWERcircuitsarewidelyusedforutilitytransmissionanddistributionofelectricityallovertheworld.NumerousHVDCintertiesareSWERcircuits,consistingofasinglehigh‐voltagecableandanearthorseareturntocompletethetransmissioncircuit.ManyoftheseareinstalledinclimatesandconditionssimilartoAlaska,notablyinScandinavia.Inmanynations,single‐phaseACSWERcircuitsareacceptedpracticeandareindustrystandardforservingruralareas.
NationsandjurisdictionsthatuseSWERACcircuitstoservetheirruralareaseconomicallyincludethefollowing18,19.
● Australia(over100,000milesinservice)
● Cambodia(Electricite’duCambodge)
● NewZealand
● Vietnam
● Laos(Electricite’duLaos)
● SouthAfrica(EskonDistribution)
18 “SingleWireEarthReturnforRemoteRuralDistribution,ReducingCostandImprovingReliability.”ConradW.Holland.
MaunsellLtd.,AnAECOMCompany.19 “SingleWirePowerinAlaska.”StateofAlaska,DivisionofEnergyandPowerDevelopment.R.W.RutherfordAssociates.1982.
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● Saskatchewan
● India
● Brazil
A.3 SWERINALASKA
Atleasttwosingle‐phaseACSWERcircuitshavebeensuccessfullybuiltandoperatedinAlaska.TheseACSWERcircuitsdemonstratethatSWERisaproven,beneficial,andappropriatetechnologyforruralAlaskatransmissionapplications.
A.3.1 Bethel–NapakiakACSWERLine
In1981,a10.5‐mile14.4kVsingle‐phaseACSWERlinewasconstructedtoconnectthesmallvillageofNapakiaktotheCityofBethel.Thislineusedbipodstructurestosuspenda7#8Alumoweldconductor.
Thislinewasconstructedatacostof$23,000permile(1980$)andoperatedsuccessfullyformanyyears.Arguably,thelinehadtwoshortcomings,neitherrelatedtoitsSWERoperation:(1)thestructuraldesignofthelinereliedupontheconductortoprovidelongitudinalsupporttothebipodpolesbetweendeadends,andonatleastoneoccasionaconductorbreakcausedaseriesofstructurestofalldown;and(2)overtime,theloadinNapakiakexceededtheline'scapacity.However,thelinewasanunqualifiedsuccessatdemonstratingthatSWERcanreducethecostsofpowertransmissioninruralAlaska.
Commonmisperceptionsaboutthislinehavegivenitanegativereputation,whichisoftenincorrectlyattributedtoits“innovative”SWERdesign.Thelinedidsufferhighlosses,butthesecanbeattributedtounmeteredloadsinNapakiakandthepoorconditionofthedistributionsysteminNapakiak.
TheAlaskaEnergyAuthorityreplacedtheBethel‐Napakiaklinewithaconventionalthree‐phaselinein2010.Theinstalledcostofthisreplacementwasapproximately$344,000permilein2012dollars,approximatelythreetimesgreaterthantheinflation‐adjustedcostoftheoriginalline20.
A.3.2 Kobuk–ShungnakACSWERLine
A10‐milesingle‐phaseACSWERlinewasconstructedtoconnectthevillageofShungnaktoKobukinnorthwesternAlaska.ThelineandtheSWERsystemworkedsuccessfully;however,thesupportstructureswereconstructedoflocalsprucetrees,andeventuallythebasesrotted.LiketheBethel–NapakiakSWERline,thislinealsosuccessfullydemonstratedSWERviabilityinpermafrostregions.In1991,this10‐milelinewasreplacedwithaconventionalthree‐phase7.2/12.4kVAClinewithpolesattachedtodrivensteelH‐pilesatacostof$1.1million,orabout$110,000permilein1991dollars21.
A.3.3 FutureofSWERinAlaska
ThetransitionofmostAlaskavillagestothree‐phasedistributionsystemshasdiminishedthevalueofsingle‐phaseACSWERinterties.ACphaseconverterswouldbenecessarytointerfacetheintertiewithoneorbothvillagegrids.Inaddition,thenationalelectricalcodesadoptedbytheStateofAlaskadonotallowtheuseofSWERcircuitsforroutinepowertransmissionordistribution.Perhapsbecauseofthesefactors,thereiscurrentlyagenerallackofinterestinSWERtechnologyinAlaska.
20 (AEA,2007);(DC,2010).21 Petrie,Brent.AlaskaVillageElectricCooperative,Inc.PersonalCommunication.February2008.
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Despitesuchfactors,SWERcircuitsremainaprovenandcost‐effectiveoptionforruralAlaskaapplications,andtheywarrantseriousconsideration.CoupledwithHVDC,SWERofferscostandtechnicaladvantagesthathavethepotentialtorevolutionizeruralpowertransmissioninAlaska.
AffordableenergyisavitalunderpinningofcreatingasustainableeconomicbaseforAlaska'sruralareas.Affordabletransmissioniskeytoachievingaffordableenergy,andthecouplingofSWERandHVDCpresentsthebrightestopportunityforachievingaffordabletransmissioninAlaska.Accordingly,thefutureofSWERinAlaskaisverypromising.
A.4 HVDCFORALASKA
ThelistofexistingHVDCprojectsinSectionA.2illustratesthefactthattoday'scommercialHVDCtechnologyremainslimitedtolarge‐scaletransferofelectricity,normallymeasuredinthe100sor1,000sofmegawatts.SuchtechnologyhasverylimitedapplicationinAlaska,asourlargestutilitygrid,alongtherailbelt,hasapeakloadofwellunder1,000MW.Mostruralloadsaremeasuredinthe100sofkW.
ThelackofcommercialHVDCtechnologyinthekilowattclassnecessaryforruralAlaskaapplicationsmeansthatthenumerousbenefitsofferedbyHVDCtransmissionarenotpresentlyavailabletoAlaska'sruralcommunities.ThekeyobjectiveandimpetusforthisprojectistolowerthecostofruralAlaskaintertiesbyextendingthereachofcommerciallyavailableHVDCtechnologydowntothekilowattclassneededtoserveAlaska'sruralenergytransmissionneeds.
TheapplicationsforthistechnologyinAlaskaarenumerousandinclude:
● ConnectingBethelandnearbyvillageswithawindfarmalongtheBeringSeacoast.
● ConnectingvillagesalongtheYukonRiversuchasKoyukuk,Nulato,Ruby,andKaltagwiththeproposedToshibanuclearbatteryinGalena.
● Connecting25southwesterncommunitiestoaproposed25‐MWgeothermalplantnearKingSalmon.
● ConnectingNorthSlopecommunitiessuchasAtqusukwithBarrowtoshareinthelow‐costelectricityderivedfromBarrow’sgasfields.
● DevelopingthegeothermalresourceatPilgrimHotSpringsandtransmitthepowertoNomeviaHVDCintertie.
● CompletingconnectionsintheSoutheastIntertieviaanaffordableHVDCsubmarinecable.
A.3.9 DesignConsiderationsforSmallAlaskaHVDCInterties
ManyofthetechnicalaspectsofdesigningandbuildingsmallHVDCintertiesinAlaskaaremuchthesameasforbuildingintertiesanywhere.ThesingledominatingfactorthatsetsconstructioninruralAlaskaapartislogistics.Mostprojectshavelittleornosupportinfrastructure,rangingfromthebasicssuchasmodernlodgingforworkerstoavailabilityoftransportationinfrastructure,heavyequipment,skilledlabor,andsoon.
ManymajorconstructionprojectsaddressthelogisticalchallengesofruralAlaskabyimportingeverythingnecessarytogetthejobdonebyconventionalmeans.Thisworks,butisverycostly.
Adifferentsolutiontothelogisticschallengeistotailorthedesigntouseavailablelocalresourcestotheextentpossible.Thisisaverychallengingproposition,buttherewards–lowerconstructioncosts–aresubstantial.Ingeneralterms,designingforAlaskalogisticsmeans:
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● Usematerialsandequipmentthatarereadilyshippedbycommontransportationmethods,suchassmallcargoaircraft22.Usematerialsandconstructionmethodsthatcanutilizesmall,lowgroundpressureequipmenttoenableconstructionduringsummerorautumnthawedconditions.
● Usematerialsandconstructionmethodsthatemploylocallyavailableequipmentfortransportandconstructionasmuchaspossible.
● Reducetheamountofconstructionandfabricationrequiredinthefieldandontheline.Pre‐manufactureandpreassemblebeforeshippingtothevillagesorinthevillagesbeforeshippingtothefieldtoreducecostsandincreasequality.
● Optimizetheconstructionandassemblymethodstoemploylocallyavailablelabor.
22 ThelargestcargoaircraftsuitableforAlaskalogisticplanningisaHerculesC‐130,butmanyvillageairstripscannot
accommodateaHercules.AmoreuniversalcargoaircraftforremoteAlaskaprojectsisaSherpaSD‐330orsimilarsmallcargoaircraft.
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APPENDIXB
ECONOMICANALYSIS
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TABLEOFCONTENTS
B.1 INTRODUCTION........................................................................................................................................................7
B.2 ECONOMICANALYSIS............................................................................................................................................8 B.2.1 COMPARATIVECOST:ACVERSUSHVDCOVERHEADINTERTIES.............................................................................8 B.2.2 INSTALLATIONCOSTCOMPARISON................................................................................................................................8 B.2.3 LIFE‐CYCLECOSTCOMPARISON...................................................................................................................................10
B.3 COSTANALYSISBASIS.........................................................................................................................................12 B.3.1 GENERATIONANDLOADASSUMPTIONS......................................................................................................................12 B.3.2 SYSTEMEFFICIENCYASSUMPTIONS.............................................................................................................................12 B.3.3 OPERATION,MAINTENANCE,ANDREPAIRASSUMPTIONS.......................................................................................12 B.3.4 ECONOMICASSUMPTIONS..............................................................................................................................................13 B.3.5 INSTALLEDCOSTASSUMPTIONS...................................................................................................................................13
B.4 CASESTUDIES.........................................................................................................................................................14 B.4.1 GREEN’SCREEK–HOONAHCASESTUDY....................................................................................................................14 B.4.2 PILGRIMHOTSPRINGS–NOME....................................................................................................................................19
B.5 DETAILEDHVDCINTERTIECOSTINFORMATION..................................................................................23 B.5.1 OVERHEADINTERTIECOSTDETAIL.............................................................................................................................23 B.5.2 SUBMARINECABLEINTERTIECOSTDETAIL...............................................................................................................25 B.5.3 UNDERGROUNDCABLEINTERTIECOSTDETAIL........................................................................................................25 B.5.4 CONVERTERSTATIONCOSTDETAIL............................................................................................................................26
B.6 DETAILEDACINTERTIECOSTINFORMATION........................................................................................30 B.6.1 COSTBASELINESFOROVERHEADACINTERTIES......................................................................................................31 B.6.2 COSTBASELINEFORSUBMARINECABLEACINTERTIES..........................................................................................33
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LISTOFTABLES
TableB‐1 EstimatedLife‐CycleCostsfor25‐mileOverheadACandHVDCInterties.......................10
TableB‐2 SummaryofCaseStudies......................................................................................................................14
TableB‐3 EstimatedCostforanGreensCreek–HoonahHVDCIntertie...............................................17
TableB‐4 EstimatedBenefit‐CostRatioofGreensCreek–HoonahHVDCIntertie..........................18
TableB‐5 EstimatedInstalledCostfora5‐MWPilgrimHotSprings–NomeIntertie.....................22
TableB‐6 EstimatedCostfora25‐mileOverheadHVDCIntertie............................................................24
TableB‐7 EstimatedCostsfora25‐mileUndergroundHVDCIntertie..................................................26
TableB‐8 1‐MWHVDCConverterStationCostEstimate.............................................................................27
TableB‐9 HVDCConverterEnclosureCostDetail...........................................................................................27
TableB‐10 SwitchgearandSwitchyardCostDetail..........................................................................................28
TableB‐11 HVDCGroundingStationCostDetail................................................................................................29
TableB‐12 CostBaselinesforRemoteAlaskaACIntertieConstruction..................................................30
TableB‐13 EstimatedCostsforOverheadACInterties...................................................................................31
TableB‐14 InstalledCostsofRecentRemoteAlaskaOverheadACInterties.........................................32
TableB‐15 InstalledCostsofRecentRemoteAlaskaSubmarineCableInterties.................................33
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LISTOFFIGURES
FigureB‐1 ComparativeInstalledCost:Overhead1‐MWHVDCandACInterties.................................9
FigureB‐2 ComparativeLife‐CycleCost:Overhead1‐MWHVDCandACInterties............................11
FigureB‐3 GreensCreek–HoonahIntertieRoute............................................................................................15
FigureB‐4 ProspectiveTransmissionRoutefromPilgrimHotSpringstoNome................................20
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B.1 INTRODUCTION
TheextremevarietyofenvironmentalandtechnicalconditionsfoundacrossruralAlaskaresultsinasignificantvariationinintertiecosts.Thetypicalcostforconstructingaconventionaloverheaddistribution‐classalternatingcurrent(AC)intertieinruralAlaskacanvaryfromaslittleas$100,000permileinareaswithgoodlogisticsupportgeotechnicalconditionsandtransportationinfrastructure(roadsystem,southeast)toover$600,000permile23inpartsofthestatewithchallenginglogisticsandlittleornotransportationinfrastructure(remoteinterior,northwest,orYukon‐Kuskokwimdeltaregions).
Intertiecostvariationsalsoaffectsubmarinecables,undergroundcables,andotheroverheadintertieconfigurations.
Thisappendixprovidesthefollowingeconomicanalyses:
● ComparativepresentworthanalysisofconceptualACandhigh‐voltagedirectcurrent(HVDC)interties;
● CasestudiesofAlaskaHVDCinterties;
● EstimatedcostsforconceptualHVDCinterties;and
● BaselinecostsforruralAlaskaACinterties.
23SeeSectionB.6.1forinformationonthecostbasisofruralAlaskaACinterties.
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B.2 ECONOMICANALYSIS
ThissectionevaluatescomparativecostsforconceptualACandHVDCinterties.BecauseHVDCintertiesincurtheaddedexpenseofconverterstations,shortHVDCinterties(underapproximately6to31miles)willgenerallynotbecost‐effectivecomparedwithACinterties,dependingonproject‐specificconditions.
Astheintertielengthincreases,thelowerper‐milecostofthetransmissionlineoffsetstheadditionalcostofthepowerconverters.HVDCintertiesshorterthanacertaineconomic“break‐even”lengthwillbemorecostlythanacomparableACintertie.TherelativesavingspossiblewithanHVDCtransmissionsystemincreasesforintertielengthsabovethisbreak‐evenlength.
Basedonspecificprojectconditions,andontheassumptionsandanalysisdescribedherein,theconceptualbreak‐evenlengthforoverheadintertiesisapproximately6to22milesonaninstalled‐costbasis,and12to31milesonalife‐cyclecostbasis.Theconditionsandassumptionsusedtodeveloptheseeconomicbreak‐evenlengthestimatesareprovidedinthisappendix.
B.2.1 ComparativeCost:ACversusHVDCOverheadInterties
TwodistinctHVDCintertieconfigurationshavebeencomparedtoaconventionalACintertietoillustratethedifferenceinprojecteconomics.ThetwoHVDCintertieconfigurationsare:
● Atwo‐wiremonopolarHVDCintertieusingU.S.DepartmentofAgriculture(USDA)RuralUtilitiesService(RUS)‐typeconstructionmethods.ThisintertieconfigurationrepresentstheupperrangeofestimatedcostforanHVDCoverheadintertieinruralAlaskaapplications.
● Amonopolarsingle‐wireearthreturn(SWER)HVDCintertieusingAlaska‐specificconstructionmethods.ThisintertieconfigurationrepresentsthelowerrangeofestimatedcostforanHVDCoverheadintertieinruralAlaskaapplications.
ThecostforHVDCintertiesinmostruralAlaskaapplicationsareexpectedtofallbetweenthecostestimatescitedforthesetwoconfigurations.
B.2.2 InstallationCostComparison
FigureB‐1presentstheestimatedinstalledcostrelativetotheintertielengthforthreedifferentkindsofoverheadintertiesbuiltinruralAlaskaconditions:
● AconventionalruralAlaskaintertie,
● Atwo‐wiremonopolarHVDCintertieusingRUS‐typeconstructionmethods,and
● AmonopolarSWERHVDCintertieusingAlaska‐specificconstructionmethods.
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Inaddition,FigureB‐1illustratestheeconomicbreak‐evenlength,andrelativeincreaseinsavingsforlongerHVDCinterties.ThepointsatwhichtheAC“costline”crosseseitheroftheHVDC“costlines”representstheeconomicbreak‐evenlength.TheestimatedHVDCcostsrepresentahypotheticalrangeofinstalledcostsanticipatedforlow‐power(under1megawatt[MW])ruralAlaskaHVDCsystems.
Figure B-1 Comparative Installed Cost: Overhead 1-MW HVDC and AC Interties
$0
$5,000,000
$10,000,000
$15,000,000
$20,000,000
$25,000,000
$30,000,000
$35,000,000
$40,000,000
$45,000,000
0 10 20 30 40 50 60 70 80 90 100
Intertie Length (miles)
Probab
le In
stalled Cost of Overhead HVDC vs. AC In
terties
AC Intertie (Standard RUS Construction)
HVDC Intertie (Monopolar, TWMR, Standard RUS Construction)
HVDC Intertie (Monopolar, SWER, Alaska‐Specific Construction)
BREAK‐EVEN COST FOR HVDC INTERTIES: 6 to 22 MILES
(INSTALLED‐COST BASIS)
Note: This chart is based on the assumptions and comparative system costs
presented in Appendix B. The break‐even point will vary for every intertie project.
COST SAVINGS
RANGE
AC
HVDC
HVDC
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B.2.3 Life‐CycleCostComparison
Operatingcosts,maintenancecosts,andefficiencyaffectthelong‐termeconomicvalueofanintertie.TableB‐1presentscomparativelife‐cyclecostsforhypothetical25‐mile‐longoverheadACandHVDCintertiesinruralAlaska.Alengthof25mileswasselectedasitrepresentsthesavingspossibleusingarelativelyshortHVDCintertie.Theestimatedlife‐cyclecostfora25‐mile‐longHVDCintertierangesfrom79%to107%ofthelife‐cyclecostofanACintertie.
Table B-1 Estimated Life-Cycle Costs for 25-mile Overhead AC and HVDC Interties
ParameterStandardRUSAC
Intertie
MonopolarTwo‐WireHVDCIntertie(RUSConstruction2)
MonopolarSWERHVDCIntertie
(AlaskaSpecificDesign1)
CostofDiesel($/gal) $7.00pergallon
GenerationEfficiency(kWh/gal) 13kWhpergallon
IntertieEfficiency4 97.7% 93.4% 94.5%
NetAnnualEnergyTransmission(kWh) 1,664,400
AnnualTransmissionLosses4(kWh) 38,300 133,000 114,000
AnnualizedValueofTransmissionLosses($) $21,000 $71,000 $61,000
IntertieDesignLife(years) 20years
IntertieAnnualO&MCosts $40,000 $58,000 $54,000
EffectiveDiscountRate 3%
PresentWorthofTransmissionLosses $307,000 $1,063,000 $912,000
PresentWorthofO&MCosts $595,000 $867,000 $796,000
ConverterStationsInstalledCost $20,000 $2,080,000 $1,160,000
IntertieInstalledCost $9,480,000 $7,120,000 $5,340,000
ESTIMATEDLIFE‐CYCLECOST $10,402,000 $11,130,000 $8,208,000
HVDCLIFE‐CYCLECOSTASPERCENTOFACLIFE‐CYCLECOST 107% 79%
PRESENTWORTHSAVINGS(COST)OFHVDCVS.AC ($728,000) $2,194,000
Notes:1. “Alaska‐SpecificDesign”referstothedesignconceptspresentedinAppendixCofthisreport.2. “RUSConstruction”referstostandardRUSdesignandconstructionmethodsforACinterties,adaptedtoHVDCapplications
asdescribedinAppendixCofthisreport.3. Allmonetaryvaluesarein2012dollars.4. Efficiencyandlossinformationincludesalltransmissionsystemcomponents.
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FigureB‐2illustratestheeconomicbreak‐evenlength,andrelativeincreaseinsavingsforlongerHVDCinterties.ThepointsatwhichtheAC“costline”crosseseitheroftheHVDC“costlines”representstheeconomicbreak‐evenlength.TheestimatedHVDCcostsrepresentahypotheticalrangeoflife‐cyclecostsanticipatedforlow‐power(under1MW)ruralAlaskaHVDCsystems.
Figure B-2 Comparative Life-Cycle Cost: Overhead 1-MW HVDC and AC Interties
$0
$5,000,000
$10,000,000
$15,000,000
$20,000,000
$25,000,000
$30,000,000
$35,000,000
$40,000,000
$45,000,000
0 10 20 30 40 50 60 70 80 90 100
Intertie Length (miles)
Probab
le Life‐Cycle Cost of Overhead HVDC vs. AC In
terties
AC Intertie (Standard RUS Construction)
HVDC Intertie (Monopolar, TWMR, Standard RUS Construction)
HVDC Intertie (Monopolar, SWER, Alaska‐Specific Construction)
BREAK‐EVEN COST FOR HVDC INTERTIES: 12 to 31 MILES
(LIFE CYCLE COST BASIS)
Note: This chart is based on the assumptions and comparative system costs
presented in Appendix B. The break‐even point will vary for every intertie project.
AC
HVDC
HVDC
COST SAVINGS
RANGE
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B.3 COSTANALYSISBASIS
B.3.1 GenerationandLoadAssumptions
Thefollowinggenerationandloadassumptionsareusedasthebasisofthecostanalysis:
● Energytransmittedoverallintertieconfigurationsisassumedtobegeneratedbyadiesel‐electricplantoperatingataconstantefficiencyof13kilowatt‐hours(kWh)pergallon;
● Thepriceofdieselisassumedtobe$7.00pergallon;and
● Noescalatorisappliedtothepriceoffuelovertime.
B.3.2 SystemEfficiencyAssumptions
ThefollowingcircuitpathisassumedfortheACintertiecase:
● Generationat480voltsalternatingcurrent(VAC)incommunity“A”;
● Stepupto7.2/12.47kilovolts(kV)ACatthepowerplantincommunity“A”;and
● Transmissionat7.2/12.47kVACtothereceivingcommunity“B.”
ThefollowingcircuitpathisassumedfortheHVDCintertiecases:
● Generationat480VACincommunity“A,”
● Conversionfrom480VACto50kVdirectcurrent(DC)atthecommunity“A”powerplant,
● Transmissionat50kVDCtothereceivingcommunity“B,”
● Conversionfrom50kVDCto480VACatthepowerplantincommunity“B,”and
● Step‐upfrom480VACto7.2/12.47kVACincommunity“B.”
Thefollowingadditionalassumptionshavebeenmade:
● Bothloadpathsincludeasingle480Vto7.2/12.47kVACtransformer;thecomparativeanalysisdoesnotneedtoconsiderlossesinthistransformer.
● IntertielinelossesarebasedontheoperatingvoltagesandconductorsdescribedinAppendixCforeachintertieconfiguration.
● TwodifferentHVDCconverterefficiencieswereusedtocharacterizetherangeofcomparativeeconomicsforHVDCinterties:
● TheRUS‐basedHVDCintertiecaseusesaconverterefficiencyof96.2%,whichistheefficiencypublishedbyPrincetonPowerSystems,Inc.(PPS)fortheprototypeconverterat50%load(seeAppendixF).
● TheAlaska‐specificHVDCintertiecaseusesahigherconverterefficiencyof97.2%.Thishypotheticalefficiencyresultsinimprovedcomparativeeconomicperformance.
● Transmissionsystemlossesarevaluedbasedontheavoidedcostoffuel.Allotherutilitycostsareassumedtobefixedandnotaffectedbytransmissionsystemlosses.
B.3.3 Operation,Maintenance,andRepairAssumptions
Anannualbudgetof$7,500to$12,300perconverterisprovidedformaintenance,repair,andscheduledcomponentsreplacement.ForHVDCinterties,the$12,300figureisusedfortheRUS‐basedHVDCintertiecase,and$7,500isusedfortheAlaska‐specificHVDCintertiecase.The$7,500perconverter
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maintenance,repair,andreplacementbudgetisbasedontheexpectedlifeandreplacementcostofmajorcomponents.Thesecomponentsincludethepowerelectronicsboards,controller,andothermajoritemsthatareexpectedtorequirereplacementduringthe20‐yearlifeofthesystem.SeeAppendixFfordetailsonconvertercomponentlifeandreplacementcosts.
Anannualmaintenanceandrepairbudgetof$1,500permileisassumedforallthreeoverheadintertieconfigurations.
B.3.4 EconomicAssumptions
Adiscountrateof3%hasbeenappliedtobringfuturecashflows(linelosses;OperationandMaintenance,Repair,Replacement,andRehabilitation[OMR&R]costs)topresentvalues.Forpurposesofthiscomparativeanalysis,aprojectlifeof20yearsisusedforallinterties,andnosalvagevalue,disposal,orreplacementcostareconsideredattheendofthe20‐yearlife.
B.3.5 InstalledCostAssumptions
TherangeofinstalledcostsdevelopedfortheconverterstationsinSectionB.5wasusedforthecomparativeeconomicanalysis.ForHVDCinterties,aninstalledcostof$1,040,000perstationisusedfortheRUS‐basedHVDCintertiecase,and$580,000isusedfortheAlaska‐specificHVDCintertiecase
Therangeofinstalledcostsforthethreeintertieconfigurationsarebasedontheestimatedintertiecostspresentedinthefollowingsectionsofthisappendix.
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B.4 CASESTUDIES
Thecasestudiesinthissectionprovideproject‐specificexamplesoftheexpectedcostsandresultingbenefitsofusingHVDCsystemstointerconnectcommunitiesandresources.Thesecasestudiesrelyonexistinginformationregardingtheproposedintertieroutes,loads,andrelatedprojectinformation.
TableB‐2summarizesthecasestudiesconsideredinthissection.
Table B-2 Summary of Case Studies
HVDCIntertieCaseStudy
TransmissionCircuit
IntertieType
HVDCIntertieCost
Estimate1
ACIntertieCost
Estimate1
EstimatedHVDCSavings1
PercentCapitalCost
Savings
GreensCreek–Hoonah
5‐MWmonopolarHVDCcircuitwithseareturn2
SubmarineCable
$22.2million $49million
$26.8million 55%
Nome–PilgrimHotSprings
5MWbipolarHVDCcircuit
OverheadLine
$25.7million
$36.3million
$10.6million 29%
Notes:
1. Allcostestimatesarepresentedin2012dollars.
2. Thecasestudyprovidesasubmarineandoverheadintertiecapacityof5MW,andconverterstationcapacityof2MW.ThisprovidesamplemarginforloadgrowthinHoonah.Theconverterstationcapacitycanbeupgradedas‐neededin500kWincrementsupto5MW.
B.4.1 Green’sCreek–HoonahCaseStudy
AnintertiebetweenGreensCreek,ontheAlaskaElectricLightandPower,Inc.(AEL&P)gridthatservesJuneau,andthevillageofHoonah,anisolatedmicro‐gridoperatedbytheInsidePassageElectricCooperative,Inc.(IPEC)hasbeenunderconsiderationforoveradecade.AEL&PandIPEChavecompletedextensivestudyanddesignworkonthisintertie.Studiesidentifieda25‐mile‐longACsubmarinecableandapproximately4milesofoverheadlinenearHoonahasthemosteconomicalmeanstocompletethisinterconnection.24TheproposedintertierouteisshownonFigureB‐3.
Asthedevelopmentofthisprojectcontinued,thecostsoftheACsubmarinecablehaveescalated,untiltheprojectwasfinallyputonholdduetoitsexcessivecost.Hoonahiscurrentlyexploringlocalhydropowerresourcestoreduceitsenergycostsbutcontinuestoviewanintertieasthebestlong‐termsolutionforitsenergyneeds.
ThisHVDCsystemrepresentsatechnologicaladvancethatcanreducethecostoftheGreensCreek–HoonahintertieandincreaseitseconomicfeasibilityascomparedwithHoonah’sotherenergyoptions.Thefollowingsubsectionsofthiscasestudyprovideahigh‐levelanalysisofthemeritsofanHVDCintertieforHoonah.
24(PowerEngineers,2004)
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Forpurposesofthiscasestudy,a5‐MWmonopolarHVDCtransmissioncircuitwithseareturnwasselectedtoconnectHoonahwithGreen’sCreek.Thiscircuitconsistsof25milesofsubmarinecableand4milesofoverheadline.Amonopolarcircuitwasselectedbecauseitisexpectedtobetheleast‐costintertiesolutionbetweenHoonahandGreen’sCreek.Otherpotentialconfigurations,suchasabipolarHVDCcircuitutilizingtwosingle‐conductorcables,wouldbemoreexpensivethanthemonopolardesignselected.
Theestimatedcapitalcostsincludea5MWtransmissioncircuit(submarinecableandoverheadline),and2MWconverterstationsatHoonahandGreen’sCreek.Theconverterstationscanbeupgradedto5MWbyadding500kWconvertermodulesasHoonah’sloadincreases.IfHoonah’sloadgrowsbeyond5MW,asecondsubmarinecablecanbeinstalledtoprovidea10MWbipolartransmissionsystem.
Figure B-3 Greens Creek – Hoonah Intertie Route
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B.4.1.1 ConceptualDesignBasis
B.4.1.1.1 Load
Hoonah’sannualkWhgenerationisapproximately5,000to5,500megawatt‐hours(MWh).ThepeakloadinHoonahisestimatedat1,200kW.25Aninitialintertiepowercapacityof2,000kWwouldserve100%ofthecommunity’sexistingneedsandprovidea67%marginforfutureloadgrowth(forhandlingpeakload).
B.4.1.1.2 ConceptualIntertieDesign
AmonopolarHVDCintertiecircuitwithsea‐returnisconsideredfortheconceptualdesignoftheGreensCreek–Hoonahintertie.Theintertiehasaninitialcapacityof2,000kW,buttheproposedsubmarinecablecanbeoperatedat5,000kWbyinstallingadditionalmodularpowerconvertersandrelatedupgradesateitherendoftheHVDCsystem.Ahigher‐capacityupgradeto10MWispossiblethroughfurtherconverterstationexpansionandinstallationofasecondcabletoformabipolarHVDCsystem.TheinitialHVDCsystemwouldconsistofthefollowingmajorcomponents:
● AnHVDCconverterstationatHawkInletontheGreensCreekendoftheintertiewitharatedcapacityof2,000kW.Thisstationwouldrequirea69‐kVto480‐volt(V)step‐downtransformer,four500‐kWHVDCconvertermodules,aseareturnelectroderatedfor40amperesofcurrent,andassociatedcontrolsandprotectiveequipment.
● 25milesofmonopolarHVDCsubmarinecable.Thiscablewouldhavearatedcapacityof5MWat50kVDC(100amperes).Thiscablewouldincludea35squaremillimeter(mm2)copperconductor,across‐linkedpolyethylenedielectric,anextrudedleadalloysheath,andtwolayersofcounter‐laidgalvanizedsteelarmorwire.26Afiber‐opticbundleisassumedtobeincludedeitherinthecableconstructionorwithinoneofthearmorwirepositionstofacilitatebroadbandcommunications.
● AsubmarinecablelandingstationatSpasskiBaynearHoonah.ThisstationwouldhousetheshoreendofthesubmarinecableandtransitiontoanoverheadHVDCconductor.Thestationwouldalsoincludeasecondsea‐returnelectrodetocompletethesea‐returncircuit.
● A3.5‐mileoverheadmonopolarHVDCtransmissionlinewithmetallicreturnfromSpasskiBaytotheexistingHoonahpowerhouse.Thistwo‐wireoverheadlinewouldhaveonewireat+50kVDCandthesecondwireclosetoearthpotential.
● Asecond2,000‐kWHVDCconverterstationadjacenttotheexistingHoonahpowerhouse.Thisstationwouldhousethefour500‐kWHVDCpowerconvertersandanACtransformertoconverterthe480VACoutputto4,160VACtointerfacewiththepowerplantbusvoltage.
25AEA,2010a;AEA,2010b26SeeFigure2inAttachmentD‐1toAppendixDofthisreport.
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B.4.1.2 EconomicAnalysis
TableB‐3presentstheeconomicanalysisfortheGreensCreek–Hoonahintertiealternatives.TheestimatedinstalledcostfortheHVDCintertieis$22.2million,ascomparedtothecostof$49millionforaconventionalACintertie.TheACintertiecostestimateisbasedonthe2009estimatedcostof$37.5million27adjustedto2012dollars.
Table B-3 Estimated Cost for an Greens Creek – Hoonah HVDC Intertie
CostItem EstimatedCost
PreconstructionRight‐of‐wayacquisition,engineering,survey,permitting $1,600,000
Administration/Management $900,000
HVDCConverterStations(powerconverters,seaelectrodes,enclosures,ACandDCsidestationequipment) $2,700,000
SubmarineCableSupplyandInstallation $12,400,000
OverheadHVDCLine:SpaaskiBaytoHoonah $900,000
Contingency(onentireproject,25%)1 $3,700,000
TotalEstimatedCost $22,200,000
Notes:1.Acontingencyof25%isappliedtothecostsdevelopedforthisprojectbasedontheuncertaintiesassociatedwiththeproject.Asignificantamountofworkhasalreadybeendonetocharacterizethebathymetryandseafloorconditionsalongtheproposedcableroute.
27IPEC,2009.
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TableB‐4presentsestimatedbenefit‐costratiosfortheGreensCreek–Hoonahintertieunderseveralloadgrowthscenarios.ThisanalysisindicatesacleareconomicadvantagetoanHVDCintertiebasedonreasonableloadgrowthforecastsforHoonah.
Table B-4 Estimated Benefit-Cost Ratio of Greens Creek – Hoonah HVDC Intertie
ItemLoadGrowthScenario
ExistingLoad 165%Growth 200%Growth6
AnnualHoonahEnergyGeneration(kWh/yr)1 5,150,000 8,500,000 9,780,000
AEL&PAvoidedCostofEnergy(Juneau)2 $0.06perkWh
IPECAvoidedCostofEnergy(Hoonah)1 $0.20perkWh
IntertieOutageRate3 2%
AnnualHoonahSavings4 $707,000 $1,170,000 $1,340,000
IPECOperation,Maintenance,Repair,ReplacementandRehabilitation(OMR&R)AnnualCosts5 $90,000 $90,000 $100,000
NetAnnualSavings(Cost) $617,000 $1,150,000 $1,340,000
IntertieLifeandDiscountRate 30years,3%
PresentWorthofAnnualSavings(Costs) $12,070,000 $21,090,000 $24,500,000
EstimatedInstalledCost $22,200,000 $22,200,000 $22.200,000
EstimatedBenefit‐CostRatio 0.54 0.95 1.10
Notes:
1. BasedonPowerCostEqualization(PCE)reportsfor2007through2009(AEA,2010a).
2. ApproximateAEL&Penergycost.IPEChascapacity,sonodemandorcapacitychargesareincluded.
3. Assumedvalue.
4. AnnualsavingsarebasedonthedifferentialcostofenergyanddonotconsidereconomicbenefitsinHoonahfromlowercostenergy,oreffectstoAEL&Pofincreasedenergysales.
5. IPEC’sestimatedoperations,maintenance,repair,androutinereplacementcostsincludecostsfortheconverterstations,savingsfromdecreasedoperationandoverhaulofthedieselpowerplantinHoonah,andaone‐timecablerepaireventoverthe30‐yearanalysisperiod.
6. Hoonah’speakloadsundera200%loadgrowthscenariowouldexceedthe2‐MWcapacityoftheintertieconverterstations.Intertiethroughputisreducedby5%toreflectdieselgenerationinHoonah.
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B.4.2 PilgrimHotSprings–Nome
PilgrimHotSpringsisageothermalresourcelocatedapproximately60milesnorthofNome.IthasbeenproposedasapowersourcetoreduceNome’srelianceondieselfuelforelectricalgeneration.ACEPiscurrentlystudyingthePilgrimHotSpringsgeothermalresourcetobettercharacterizetheresource’spotentialforpowergenerationandotherapplications.ForpurposesofsizingthetransmissionlinefromPilgrimHotSprings,anelectricalgeneratingcapacityandtransmissioncapacityof5MWisassumed,basedonconversationswithACEP’smanagerforthePilgrimHotSpringsassessmentproject.28TheproposedtransmissionrouteisshownonFigureB‐4.
AbipolarHVDCcircuitusingoverheadlineswasselectedfortheHVDCintertie.Thebipolarconfigurationwasselectedbecauseitprovidesincreasedreliabilitycomparedtoamonopolarlineatareasonableadditionalcost.
ConceptualpowerlinecostsforoverheadACandHVDCintertieswereestimatedtoevaluatethebenefitsofconnectingPilgrimHotSpringstoNomeusinganHVDCintertie.ThecostestimatesindicatethatanHVDCtransmissionlinewouldcost29%lessthananACtransmissionline.
28PersonalcommunicationwithMarcusMager,2012.
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Figure B-4 Prospective Transmission Route from Pilgrim Hot Springs to Nome
B.4.2.1 ConceptualDesignBasis
Aroutingstudywasnotperformedaspartofthiscasestudy.Theintertierouteisassumedtofollowtheapproximately70‐mileroadcorridorfromNometoPilgrimHotSprings.Thisisassumedtobetheleast‐costrouteforthepowerlines,astheroadcanbeusedtosupporttheconstructionandlong‐termmaintenanceoftheline.Aroutingstudymayidentifyotherroutesthataremorefavorableduetogeotechnical,landstatus,environmental,orotherfactors.
Forthisanalysis,thetransmissionroutedistanceisassumedtobe60miles.
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B.4.2.1.1 Load
Nome’saverageannualelectricityusageisapproximately3,500kW,andmonthlypeakdemandisbetween4and10MW.TheassumedsizeofthePilgrimHotSpringsgeothermalpowerplantisassumedtobe5MW.Theintertieisthereforeassumedtohaveacapacityof5MWandoperateatbetween2and5MW,dependingoninstantaneousdemandinNome.
B.4.2.1.2 ConceptualACIntertieDesign
TheconceptualdesignfortheACintertieisathree‐wire69‐kVACoverheadlineseton45‐footwoodpoleswitharulingspanof400feet.Allpolesareassumedtobefastenedtosteelpilefoundationsformomentsupportandtoresistfrostjackingforces.
TheACtransmissionsystemwouldconsistofthefollowingmajorcomponents:
● A5‐MWgeothermalpowerplantatPilgrimHotSpringsgeneratingat4,160V.
● Asubstationandswitchyardtoincreasevoltagefrom4,160Vto69kV.
● Anapproximately60‐mile‐longoverheadintertiefromPilgrimHotSpringstoNome.
● AsubstationandswitchyardinNometoisolateNomefromthetransmissionlineandstepdownthevoltagefrom69kVto12.47kVfordistributioninNome.
B.4.2.1.3 ConceptualHVDCIntertieDesign
TheconceptualdesignfortheHVDCintertieisabipolarcircuitoperatingat+50and–50kVDC.Thetwocircuitswouldbesupportedonaguyedglass‐fiber‐reinforcedpolymer(GFRP)polefittedwithacrossarmandsuspensioninsulators.Arulingspanof1,000feetisassumed.ThedesignissimilartothatshownonFigureC‐9.
TheHVDCtransmissionsystemwouldconsistofthefollowingmajorcomponents:
● A5‐MWgeothermalpowerplantatPilgrimHotSpringsgeneratingat480V.Itmaybepreferabletoinsteadgenerateat4,160Vandhaveastep‐downtransformertothe480Vinterfacevoltagetothepowerconverters.
● AbipolarHVDCconverterstationconsistingoftwobanksoffive500‐kWpowerconverters.Eachbankwouldforma2.5‐MWpoleonthebipolartransmissionsystem.
● Anapproximately60‐mile‐longbipolarHVDCtransmissionlinefromPilgrimHotSpringstoNome.
● AsecondbipolarHVDCconverterstationinNome.
● AnACtransformertostepuptheACoutputfromtheconvertersfrom480Vupto7.2/12.47kVfordistributioninNome.
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B.4.2.2 EconomicAnalysis
TableB‐5presentstheeconomicanalysisforthePilgrimHotSprings–Nomeintertiealternatives.TheestimatedinstalledcostfortheHVDCintertiealternativeis$25.7million,ascomparedtothecostof$36.3millionforaconventionalACintertie.
NoinformationisavailablefortheinstalledcostofageothermalpowerplantatPilgrimHotSpringsorthecostoftheenergyitwouldgenerate,soabenefit‐costratiooftheintertiealternativeswasnotevaluated.
Table B-5 Estimated Installed Cost for a 5-MW Pilgrim Hot Springs – Nome Intertie
CostItemEstimatedInstalledCostforBipolarHVDCIntertie
EstimatedInstalledCostforACIntertie
EstimatedHVDCSavings
PercentCostSavings
PreconstructionActivities(right‐ofwayacquisition,design,survey,permitting)
$3,400,000 $3,400,000 ‐ ‐
Administration/Management $1,000,000 $1,300,000 ‐ ‐
ConverterStationConstruction $4,600,000 $3,000,000 ‐ ‐
OverheadIntertieConstruction $10,800,000 $20,200,000 ‐ ‐
Contingency(30%)1 $5,900,000 $8,400,000 ‐ ‐
TotalEstimatedCost $25,700,000 $36,300,000 $10,600,000 29%
Note:
1. A30%contingencywasappliedtothecostsforthisprojectbecausenoinformationwasavailableforthetransmissionroute.Thislackofdatacreatesrisksduetofactorssuchaslandavailability,geotechnicalconditions,structural(windandice)loadings,andenvironmental(bird,wildlife,andaesthetics)factors.Someoftheserisksaremitigatedbytheuseofcostdatafortherobustconceptualdesigns(i.e.,Alaska‐specificconstruction)usedfortheHVDCsystem.TheAlaska‐specificconceptualdesignisassumedtobeadequatefortheexpectedgeotechnicalandstructuralconditionsalongtheroute.Environmentalandlandavailabilityissues,whichcouldrequirealongerrouteordeparturefromtheroadcorridor,poserelativelygreaterrisksthanlinedesignconsiderations.Thenetresultofthesefactorsresultsinthe30%contingencyusedforthecasestudyeconomics.
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B.5 DETAILEDHVDCINTERTIECOSTINFORMATION
B.5.1 OverheadIntertieCostDetail
ThisreportconsidersdifferentoverheaddesignconceptsforHVDCinterties.Thissectionpresentsarangeofestimatedcostsfortheseconcepts.
Thetwo‐wiremonopolarintertieadaptedfromstandardRUSpracticeisestimatedtohavethehighestinstalledcost.Incontrast,themonopolarSWERintertiebasedonAlaska‐specificdesignconceptsisestimatedtohavethelowestinstalledcost.
TableB‐6presentsabreakdownoftheestimatedinstalledcostsfor25‐mileoverheadintertiesinruralAlaskausingthedesigncasesandconceptspresentedinAppendixC.
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Table B-6 Estimated Cost for a 25-mile Overhead HVDC Intertie
CostItemMonopolarSWER,AlaskaSpecificConstruction
Two‐WireMonopolarHVDC,RUS–BasedConstruction
Per‐MileCost ProjectCost Per‐MileCost ProjectCost
PreconstructionRight‐of‐wayacquisition,design,survey,permitting $58,000 $1,450,000 $56,000 $1,400,000
Administration/Management $13,000 $325,000 $17,000 $425,000
Materials(intertieonly) $48,000 $1,200,000 $47,000 $1,175,000
ConverterStations(onper‐milebasis) $62,000 $1,550,000 $62,000 $1,550,000
Shipping $15,000 $375,000 $25,000 $625,000
Mobilization/Demobilization $37,000 $925,000 $94,000 $2,350,000
Labor $67,000 $1,675,000 $71,000 $1,775,000
TotalCost $300,000 $7,500,000 $372,000 $9,300,000
Note:Lineitemcostsincludeanembedded25%contingency.
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B.5.2 SubmarineCableIntertieCostDetail
Anumberofsite‐specificfactorsinfluencethecostofsubmarinecableapplicationsforHVDCapplicationsinAlaska.Thesearethefollowing:
● CablelayingvesselsarespecializedequipmentthatmustbemobilizedtoAlaska.MobilizingthesevesselstoAlaskaiscostlyandprojectdependant.Mobilizationcostsresultinshortsubmarineintertiesbeingsignificantlymoreexpensiveonaper‐milebasisthanlongsubmarineinterties.
● Marinetrafficinfluencessubmarineintertiecosts.Shallowercableroutesmustconsidercommercialfishingactivity,anchoring,andrelatedmarinetrafficthatmayposeahazardtothecable.
● Theseafloorconditionsalongthecableroutealsoinfluencecosts.Steepslopes,ruggedexposedrock,orunstableslopeswilltendtoincreasecostsorprojectrisk.
● Thedepthofthecableroutewillinfluencecosts.Deeperroutesrequirestronger,heavier,andmorecostlycables,whichinturncanrequirelarger,moreexpensivecablelayingvessels.
Asaresult,agenericper‐milecostoflow‐powersubmarinecablesisnotmeaningfulwithoutconsiderationoftheproject‐specificfactors.
B.5.3 UndergroundCableIntertieCostDetail
Anumberofsite‐specificfactorswillstronglyinfluencethetechnicalfeasibilityandcostofundergroundcableapplicationsforlow‐powerHVDCapplicationsinAlaska.Thesearethefollowing:
● Presenceofgroundsusceptibletofrostcrackingorpolygonalcracking.Thesegroundcrackscanimposelargetensionforcesoncablesandcausemechanicalfailureofthecable,resultinginelectricalfaults.
● Geotechnicalconditionsalongthecableroutewillinfluencethecostofcableinstallation.
● Steepterrainorotherlocalconditionsmaypreventuseofundergroundcable.
EstimatedcostsforHVDCintertiesusingundergroundcablesarepresentedinTableB‐7.
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Table B-7 Estimated Costs for a 25-mile Underground HVDC Intertie
CostItem EstimatedPer‐MileCost
PreconstructionRight‐of‐wayacquisition,design,survey,permitting $45,000
Administration/Management $13,000
Materials(intertieonly) $80,000
Converterstations(onpermilebasis) $62,000
Shipping $20,000
Mobilization/Demobilization $10,000
Labor $20,000
TotalCost $250,000
Note:Lineitemcostsincludeanembedded25%contingency.
TheestimatedcostsinTableB‐7arebasedonthefollowingassumptions:
● Terrainandconditionsaresuitableforuseofatrack‐mountedtrenchersuchasaDitchWitchRT115Quad,whichcancutatrenchthroughfrozengroundduringthewintermonthsovermostterrain;
● 1/0fullconcentricneutraljacketed35‐kVACcablewithethylenepropylenerubber(EPR)dielectricina2‐inchduct;
● Awaterblockingantifreezegelcompoundisused;
● Afiber‐opticcableinductisinstalledinthesametrench;
● Limitedbrushingisnecessarytocleartheroute;
● Cablereelsarespottedalongthelinewithahelicopter;and
● Thecableinstallationdepthisaminimumof18inches.
B.5.4 ConverterStationCostDetail
TheHVDCconverterstationswillincludethemajorcomponents:
● HVDCpowerconverters;
● Converterenclosures,whichmayconsistofdedicatedenclosuresoruseofanexistingbuilding,suchasanexistingpowerplant;
● ProtectionandswitchingequipmentontheACandHVDCsidesoftheconverters;
● ACtransformers,dependingontheACinterfacevoltageandwiring;and
● Groundingstations,includingthegroundconductorfromtheconverterstationtothegroundingstation.
Theestimatedinstalledcomponentcostsfora1‐MWmonopolarHVDCconverterstationispresentedinTableB‐8.Therangeofcostsisbasedonthepresenceofexistinginfrastructureandproject‐specificconditions.
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Table B-8 1-MW HVDC Converter Station Cost Estimate
CostItem EstimatedCost
1‐MWHVDCPowerConverter $220,000to$280,000
ConverterEnclosure $40,000to$160,000
AC‐SideandHVDC‐SideProtectiveandSwitchingEquipment $100,000to$190,000
1‐megavoltamperes(MVA)ACTransformer(7.2/12.4kV–480V) $0to$30,000
GroundingStation $100,000to$170,000
Contingency(25%) $120,000to$210,000
Total,1‐MWHVDCConverterStation $580,000to$1,040,000
B.5.4.1 ConverterCostDetail
BasedonPhaseIIdevelopmentefforts,PPSestimatesthatthecommercialcostoftheHVDCpowerconverterswillbe$250,000+/‐10%per1‐MWpowerconverter.PPSstatesthatasmanufacturingvolumesincrease,theper‐convertercostshoulddecrease.PPSforecastsa5%to10%discountat10unitsanda20%to30%discountat100units.SeeAppendixFforamoredetaileddiscussionofconvertercosts.
B.5.4.2 ConverterEnclosureCostDetail
Estimatedcostsassumethatamodular,prefabricatedenclosurewillbesenttothecommunitywiththetwo500‐kWpowerconverterunitsalreadyinstalled.Thisconvertermodulewillthenbesetinplaceonasuitablefoundation.EstimatedcostsarelistedinTableB‐9.
Table B-9 HVDC Converter Enclosure Cost Detail
CostItem EstimatedCost
PowerConverterEnclosure $68,000
Foundation $30,000
Labor $27,000
Shipping $35,000
Total,1‐MWHVDCConverterEnclosure $160,000
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IncommunitiesthatwillbeprimarilyservedbyanHVDCintertie,itmaybeappropriatetolocatetheconvertersinsidetheexistingpowerhouseorothersuitableexistingstructure.Thiswouldhavethefollowingadvantages:
● Theexistingpowerhousewouldalreadyhaveastep‐downtransformersizedforthefullcommunityload,
● Wasteheatfromtheconverterswouldprovideallorpartoftheheatforthepowerplantbuilding,and
● Thiswouldachieveprojectcostreductionbyeliminatingtheneedforadedicatedconverterenclosureandtheneedtopurchaseorleaselandtositetheconverter.
B.5.4.3 SwitchgearandSwitchyardEquipmentCostDetail
SwitchgearisrequiredontheACsideoftheconvertersforisolationandprotectionpurposes.Dependingonthedesireddegreeofsystemautomation,theswitchgearmayalsointerfacebetweentheconvertercontrolsandthepowerplantcontrolstoallowremotedispatchofgeneratorsandtheHVDCpowerconverter.
Similarisolation,protection,andmonitoringequipmentisneededintheHVDCswitchyardontheHVDCsideoftheconverter.Ataminimum,manualdisconnectswitches(nonloadbreak),surgearrestors,andfusesarerequired.CurrentandvoltagesensorsareneededontheHVDClineaswell.
EstimatedswitchgearandswitchyardcostsarepresentedinTableB‐10.
Table B-10 Switchgear and Switchyard Cost Detail
CostItem EstimatedCost
ACSwitchgearSection(Fuses,DisconnectSwitches[loadbreak]) $25,000to$35,000
HVDCManualDisconnectSwitch(nonloadbreak) $2,000to$20,000
HVDCSurgeArrestor $10,000to$15,000
HVDCFuse $2,000to$8,000
ACandDCSensors $30,000to$48,000
OtherMaterials $12,000to$16,000
Shipping $5,000to$18,000
Labor $14,000to$20,000
Total,1‐MWHVDCConverterStationSwitchgearandSwitchyard $100,000to$190,000
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B.5.4.4 ACTransformerCostDetail
Thegridinterfaceonthepowerconvertersisthree‐phase480‐VAC.Incommunitieswheretheconverterisconnecteddirectlytothe480‐Vpowerplantbuss,noadditionaltransformerisrequired.Incommunitieswheretheconverterconnectstothelocaldistributiongrid,astep‐uptransformerisrequired.Thetransformerisassumedtobeathree‐phase480/12.47kVtransformer.
B.5.4.5 GroundingStationCostDetail
AgroundingstationwillneedtobeprovidedateachHVDCconverterstation,regardlessoftheHVDCcircuitconfiguration.Theconceptualdesignofa1‐MW50kVDCgroundingstationispresentedinAppendixE.EstimatedcostsforthisstationarepresentedinTableB‐11,andinclude1mileofoverheadlinebetweentheconverterstationandthegroundingstation.
Costsforgroundingstationswilldependonthelocalgeotechnicalconditions,thedistancebetweentheconverterandgroundingstations,andotherfactors.
Table B-11 HVDC Grounding Station Cost Detail
CostItem ConceptualCost
SiteInvestigations $26,000to$33,000
Materials $25,000to$45,000
Labor $34,000to$46,000
Equipment $7,000to$12,000
Shipping $8,000to$34,000
Total,1‐MWHVDCGroundingStation $100,000to$170,000
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B.6 DETAILEDACINTERTIECOSTINFORMATION
ThissectionpresentscostbaselinesforremoteAlaskaACintertiestoallowcomparisontotheHVDCalternativespresentedinthisreport.CostbaselinesforACintertieprojectsweredevelopedusingtwomethods.Thefirstmethodwastodevelopconceptualcostestimatesconsideringunitcostsforlabor,materials,mobilization,etc.Thesecondmethodwastoreview,whereavailable,theactualcostsofrecentrelevantACintertieprojectsinAlaska.Forbothmethods,twotypesofintertieswereanalyzed:
1. OverheadintertielinesinarcticandsubarcticregionsofwesternAlaska.Theseregionspresentsomeofthegreatestgeotechnicalandlogisticalchallenges;therefore,theytendtohavethehighestinstalledcostsforoverheadinterties.
2. SubmarinecableintertiesinruralAlaska.FormanypartsofAlaska,andinparticularthesoutheast,submarinecablesaretheonlyviablemeansofbuildingapowerintertie.
ThecostbaselinesaresummarizedinTableB‐12.
Table B-12 Cost Baselines for Remote Alaska AC Intertie Construction
TypeofACElectricIntertie1CostBaselineby
UnitCost/QuantityMethodCostBaselinefromRecent
ProjectExperience
OverheadInterties2 $440,000permile $450,000permile+/‐50%
SubmarineCableInterties3 N/A $1,300,000permile+/‐35%
Notes:1. Intertiepowercapacitywillaffectcost.Seesubsequentnotesforthespecifictypesofintertiesconsideredtodevelop
theseconceptualcosts.2. IntertiesarestandardRUSthree‐phase14.4/24.9kVconstruction,usingsteelpilefoundations.3. Intertiesaresingle‐bundledthree‐conductorarmoredcable.
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B.6.1 CostBaselinesforOverheadACInterties
B.6.1.1 CostBaselineforOverheadACIntertiesUsingUnitCostsandQuantities
AcostbaselinefortypicalACtransmissionsystemshasbeenestimatedfor10‐mileand25‐mileintertieconcepts.Theseconceptsarebasedonastandardfour‐wirethree‐phase14.4/24.9kVRUSpowerlineusingdrivensteelpilefoundations.TheestimatedinstalledcostsarepresentedinTableB‐13.
Table B-13 Estimated Costs for Overhead AC Interties
CostItem10‐MileIntertie 25‐Mileintertie
Per‐MileCost
ProjectCostPer‐MileCost
ProjectCost
PreconstructionRight‐of‐wayacquisition,design,survey,permitting
$61,000 $610,000 $39,000 $975,000
Administration/Management $18,000 $180,000 $18,000 $425,000
Materials $71,000 $710,000 $71,000 $1,775,000
Shipping $36,000 $360,000 $33,000 $825,000
Mobilization/Demobilization $136,000 $1,360,000 $125,000 $3,125,000
Labor $111,000 $1,110,000 $111,000 $2,675,000
TotalCost $440,000 $4,400,000 $397,000 $9,875,000
Theper‐milecostofoverheadACintertiesdecreasesastheintertiegetslonger.Thisisinfluencedbythefollowingfactors:
● Thescopeandcomplexityofenvironmental,right‐of‐way,design,andpermittingissuesfortheproject.
● Thequalityofaccesscorridorsalongtheintertieroute.Theestimatedcostsassumethatper‐milelaborcostsareindependentofintertielength.
● Theconstructionplanandschedule.Theestimatedcostsassumethatper‐milemobilization/demobilizationcostsdecreaseslightlywithincreasingintertielength.
Thisreportfindsthatper‐milecostsfortypicaloverheadACintertiesdecreaseapproximately10%astheintertielengthincreasesfrom10to25miles.Further,anadditionaldecreaseof5%occursfrom25to50miles.Costsareconstantonaper‐milebasisfrom50to100miles.
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B.6.1.2 CostBaselineforOverheadACIntertiesUsingComparableProjectCosts
ConstructioncostdatacompiledforsevenremoteoverheadintertielinesbuiltinwesternAlaskaoverthepast20yearsarepresentedinTableB‐14.ThelinesselectedareconsideredrepresentativeofthemostdifficultlogisticalandgeotechnicalconditionscommoninAlaska.BasedonTableB‐14,theconceptualper‐milecostforaremoteAlaskaoverheadACintertieis$450,000permile,+/‐50%(2012$).
ThecostdataarepresentedasageneralcostbaselineforremoteAlaskaoverheadinterties.
Table B-14 Installed Costs of Recent Remote Alaska Overhead AC Interties
IntertieProjectInstalledCost1
YearBuilt
Length
(miles)Per‐MileCost(2012$)2
Kobuk–Shungnak3 $1.1M 1991 11 $276,500
ToksookBay–Tununak4,5 $2.0M 2005 6.6 $440,200
Nunapitchuk–OldKasigluk–AkulaHts.5,6 $1.9M 2006 4.2 $594,400
ToksookBay–Nightmute7,8 $6.9M 2009 18 $495,800
Bethel–Napakiak5,9 $3.1M 2010 10.5 $344,400
BrevigMission–Teller10 $4.7M 2011 6.8 $730,200
Emmonak–Alakanuk11 $2.9M 2011 11 $267,300
AverageCostperMile,2012Dollars: $449,800
AverageCostperMile,(ExcludingHighestandLowest‐CostProjects): $430,300
Notes:1. Installedcostsareinnominaldollarsatthetimeofconstruction.Duetothelimiteddetailandvarietyofsourcesforcost
data,itisnotalwayspossibletodiscernifcostsforagivenprojectincludepreconstruction,construction,sharedmobilizationwithseparatebutconcurrentprojects,andsimilarcomplicatingfactors.Adjustingfortheseunknownfactorsmayincreaseordecreasetheprojectcostthatispresentedinthetable.
2. Projectcostsareadjustedto2012dollarsusingacustomescalatorbasedonAlaskalaborcostsandcommoditypricesrelevanttooverheadintertieconstruction.
3. Estimatedcostfortheproject.TheprojectconsistedofreplacinganACSWERintertiewithaconventionalRUSACintertie(Petrie,personalcommunication,2012).
4. TheprojectconsistedofanewoverheadACintertie(DenaliCommission,2008b).5. EntireintertiewassetonH‐pileorroundpilefoundations(DenaliCommission,2008a,2008b,and2010).6. TheprojectconsistedofreplacinganexistingoverheadACintertiewithanewoverheadACintertie.Thecostwas
reducedby$300,000forstep‐downtransformersforservicesalongtheintertieroutethatarenotpartofthe“intertie”cost(DenaliCommission,2008a)
7. TheprojectconsistedofanewoverheadACintertie(DenaliCommission,2009).8. Approximately30%ofintertieissetonsteelpilefoundations(DenaliCommission,2009).9. TheprojectconsistedofreplacinganACSWERintertiewithaconventionalRUSACintertie(DenaliCommission,2010).10. TheprojectconsistedofanewACintertieincludingoverhead,underground,andsubmarinecablesegments.Cost
includespreconstructionandbudgetedconstruction(DenaliCommission,2011).11. Thisistheestimatedcostforaproposedintertiebuiltin2011.Theintertieprojectsharedmobilizationcostswith
concurrentinstallationofwindturbinesinEmmonak(AVEC,2008).
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B.6.2 CostBaselineforSubmarineCableACInterties
ConstructioncostdatawerecompiledforthreeACsubmarinepowercablesinstalledorproposedinAlaskaoverthepast15years;thesedataarepresentedinTableB‐15.Veryfew“low‐power”ACsubmarinecableshavebeenbuiltinAlaska–thecablesinTableB‐15eachhaveacapacityof10to15MW.Theselineswerereviewedbecausetheyarethesmallestsubmarinecableswithavailablecostdata.Theindicatedconceptualper‐milecostforaACsubmarineintertieinAlaskais$1,300,000permile,+/‐35%(2012$).
Submarinecablecostsareprojectdependentandhaveasignificantcostvariability.Shortcableprojectsinparticularcanbeexpectedtohavesignificantlyhigherper‐milecostduetothefixedmobilizationcostofspecializedcable‐layingvessels.
ThecostdataprovideageneralcostbaselineforremoteAlaskasubmarinepowercables.
Table B-15 Installed Costs of Recent Remote Alaska Submarine Cable Interties
IntertieProjectInstalledCost1
YearBuilt/Proposed
Length(miles)
Per‐MileCost(2012$)2
Haines–Skagway3 $5.86M 1998 15 $880,000
Homer–SouthKatchemakBay5 $2.5M 2001 4.5 $1,200,000
Green’sCreek–Hoonah4 $37.5M 2009 29 $1,700,000
AverageCostperMile,2012Dollars: $1,300,000
Notes:1. Installedcostsareinnominaldollarsatthetimeofconstruction.Duetothelimiteddetailandvarietyofsourcesforcost
data,itisnotalwayspossibletodiscernifcostsforagivenprojectincludepreconstruction,construction,sharedmobilizationwithseparatebutconcurrentprojects,andsimilarcomplicatingfactors.Adjustingfortheseunknownfactorsmayincreaseordecreasetheprojectcostthatispresentedinthetable.
2. Projectcostsareadjustedto2012dollarsusingacustomescalatorbasedonAlaskalaborcostsandcommoditypricesrelevanttopowerlineconstruction.
3. TheHaines‐Skagwaycablehasamaximumdepthof1,500feetandaratedcapacityof15MW(INEEL,1998).4. TheGreen’sCreek–Hoonahcablehasnotbeenbuiltduetoitscost.Installedcostsarethemostrecentestimates
available.Thiscablerouteincludesdepthsto2,600feet.Costsincludeapproximately4milesofoverheadline(IPEC,2009).
5. TheHomer–SouthKatchemakBaycablehasamaximumdepthof600feetandaratedcapacityofapproximately12MW(AJOC,2001).
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APPENDIXC
CONCEPTUALDESIGNOF
OVERHEADHVDCINTERTIELINES
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TABLEOFCONTENTS
C.1 INTRODUCTION........................................................................................................................................................7 C.1.1 RURALUTILITIESSERVICE(RUS)DESIGNAPPROACH,MODIFIEDFORHVDCINTERTIES................................7 C.1.2 ALASKA‐SPECIFICDESIGNAPPROACHFORHVDCINTERTIES..................................................................................7
C.2 DESIGNCRITERIAFOROVERHEADINTERTIELINES.............................................................................8 C.2.1 GEOTECHNICALCONDITIONS...........................................................................................................................................8 C.2.2 ENVIRONMENTALLOADS.................................................................................................................................................8
C.3 CONCEPTUALDESIGNOFOVERHEADHVDCTRANSMISSION,RUSSTANDARDPRACTICE10 C.3.1 CONVENTIONALACINTERTIEDESIGN........................................................................................................................10 C.3.2 MONOPOLARSINGLE‐WIRETRANSMISSIONWITHEARTH‐RETURNPATH(SWER),CONVENTIONALLYBUILT
............................................................................................................................................................................................13 C.3.3 MONOPOLARTWO‐WIRETRANSMISSIONWITHMETALLICCONDUCTOR‐RETURNPATH(TWMR),
CONVENTIONALLYBUILT...............................................................................................................................................16 C.3.4 BIPOLARTWO‐WIRETRANSMISSION,CONVENTIONALLYBUILT...........................................................................19
C.4 CONCEPTUALDESIGNOFOVERHEADHVDCTRANSMISSION,ALASKA‐SPECIFICMETHODS22 C.4.1 MONOPOLARSINGLE‐WIRETRANSMISSIONWITHEARTH‐RETURNPATH(SWER,ALASKA‐SPECIFICDESIGN
............................................................................................................................................................................................23 C.4.2 MONOPOLARTWO‐WIRETRANSMISSIONWITHMETALLICCONDUCTOR‐RETURNPATH(TWMR),ALASKA‐
SPECIFICDESIGN.............................................................................................................................................................26 C.4.3 BIPOLARHVDCINTERTIELINE,ALASKASPECIFICDESIGN...................................................................................29 C.4.4 CONCEPTUALDESIGNANALYSIS...................................................................................................................................32 C.4.5 MAINTENANCEMETHODS..............................................................................................................................................33
C.5 CONCEPTUALDESIGNANALYSIS...................................................................................................................35 C.5.1 STRUCTURALDESIGN......................................................................................................................................................35 C.5.2 FOUNDATIONDESIGN.....................................................................................................................................................35 C.5.3 ANALYSISOFTHERMOPROBEPERFORMANCE............................................................................................................35 C.5.4 ELECTRICALDESIGN.......................................................................................................................................................44
C.6 TESTINGOFOVERHEADDESIGNCONCEPTS............................................................................................49 C.6.1 TESTOBJECTIVES............................................................................................................................................................49 C.6.2 TESTSITE.........................................................................................................................................................................49 C.6.3 INSTALLATION..................................................................................................................................................................49 C.6.4 MONITORING....................................................................................................................................................................50
APPENDIXCATTACHMENTS...........................................................................................................................................63 ATTACHMENTC‐1:ZARLINGAEROCONSULTING(ZAE)THERMALANALYSISOFTHERMOPILE.....................................63 ATTACHMENTC‐2:ARCTICFOUNDATIONS,INC.(AFI)SHOPDRAWINGS............................................................................91
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LISTOFTABLES
TableC‐1 ConceptualDesignDataforConventionalACIntertieLine....................................................12
TableC‐2 ConceptualDesignDataforConventionallyBuiltMonopolarSWERHVDCIntertieLine..........................................................................................................................................................................15
TableC‐3 ConceptualDesignDataforConventionallyBuiltMonopolarHVDCwithMetallicReturn..........................................................................................................................................................................18
TableC‐4 ConceptualDesignDataforConventionallyBuiltBipolarHVDCIntertieLine...............21
TableC‐5 ConceptualDesignDataforAlaska‐SpecificMonopolarSWERHVDCIntertieLine....25
TableC‐6 ConceptualDesignDataforAlaska‐SpecificMonopolarMetallic‐ReturnIntertieLine28
TableC‐7 ConceptualDesignDataforAlaska‐SpecificBipolarHVDCIntertieLine..........................31
TableC‐8 SummaryofResultsfromThermoprobeModelingbyZAE....................................................37
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LISTOFFIGURES
FigureC‐1 TangentPoleforConventionalACIntertieLine..........................................................................11
FigureC‐2 ConventionalTangentPoleforMonopolarSWERHVDCIntertieLine..............................14
FigureC‐3 ConventionalTangentPoleforMonopolarHVDCwithMetallicReturn...........................17
FigureC‐4 ConventionalTangentPoleforBipolarHVDCIntertieLine...................................................20
FigureC‐5 Alaska‐SpecificTangentPoleforMonopolarSWERHVDCIntertieLine..........................24
FigureC‐6 Alaska‐SpecificTangentPoleforMonopolarMetallic‐ReturnIntertieLine....................27
FigureC‐7 Alaska‐SpecificTangentPoleforBipolarHVDCIntertieLine...............................................30
FigureC‐8 PrototypeMicro‐ThermopileTripodPoleFoundation............................................................38
FigureC‐9 ShopDrawingofPrototypeGFRPPoleBaseAdapterforMicro‐ThermopileFoundation(Sheet1of3)..............................................................................................................................................39
FigureC‐10 ShopDrawingofPrototypeGFRPPoleBaseAdapterforMicro‐ThermopileFoundation(Sheet2of3)..............................................................................................................................................40
FigureC‐11 ShopDrawingofPrototypeGFRPPoleBaseAdapterforMicro‐ThermopileFoundation(Sheet3of3)..............................................................................................................................................41
FigureC‐12 GalvanizedScrewAnchorswith8‐InchFlights...........................................................................43
FigureC‐13 TypicalBipolarHVDCTransmissionLineUsingSuspensionInsulators...........................45
FigureC‐14 TypicalTangentStructureUsingPostInsulators.......................................................................46
FigureC‐15 TypicalAngleStructureUsingSuspensionandPostInsulators...........................................47
FigureC‐16 TypicalTangentStructureUsingSuspensionandPostInsulators......................................48
FigureC‐17 InstallingMicro‐ThermopileforGuyAnchor...............................................................................51
FigureC‐18 SettingMicro‐ThermopileGuyAnchorwithSandSlurryBackfill.......................................52
FigureC‐19 InstallingMicro‐ThermopileforGuyAnchor...............................................................................53
FigureC‐20 Micro‐ThermopilesStagedatFairbanksTestSiteforInstallationofPrototypeFoundations..........................................................................................................................................................................54
FigureC‐21 Micro‐ThermopileTripodforPrototypePoleFoundation.....................................................55
FigureC‐22 InstallingHelicalScrewAnchorforGuyAnchor.........................................................................56
FigureC‐23 GuyAttachedtoMicro‐ThermopileFoundation.........................................................................57
FigureC‐24 AssemblingthePrototypeGFRPPoleSplice.................................................................................58
FigureC‐25 InstalledGFRPPole,Micro‐Thermopiles,andAdapterPlate.................................................59
FigureC‐26 PrototypeGFRPPoleFoundationDuringInstallation..............................................................60
FigureC‐27 PrototypePoleattheFairbanksTestSite......................................................................................61
FigureC‐28 PrototypePoleattheFairbanksTestSite......................................................................................62
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C.1 INTRODUCTION
Theconceptualoverheadtransmissionlinedesignalternativespresentedinthisappendixrequiredconsiderationofsite‐specificconditions,codes,utilityandlenderrequirements,constructionmethodologies,standarddesignpractices,andprojecteconomics.
Twoconceptualdesignapproachesforoverheadhigh‐voltagedirectcurrent(HVDC)intertieshavebeenevaluated,eachwithacapacitytosupply1megawatt(MW)at50kilovolts(kV)DC:(1)U.S.DepartmentofAgriculture(USDA)RuralUtilitiesService(RUS)designapproach,modifiedforHVDCinterties;and(2)Alaska‐specificdesignapproachforHVDCinterties.Eachisdescribedbelow.
C.1.1 RuralUtilitiesService(RUS)DesignApproach,ModifiedforHVDCInterties
ThefirstconceptualdesignapproachisbasedontheuseofstructuresthatareconstructedinaccordancewiththeRUSstandardpracticesforconventional12.4/24.9kilovolt(kV)alternatingcurrent(AC)distributionlines.29TheseRUSstandardpracticesarecurrentlyusedtodevelopACintertiesthroughoutAlaskaandarewidelyacceptedbytheutilityindustry.HVDCtransmissionrequiresfewerconductorsthanAC,resultinginreducedloadsonthesupportingstructures.Asaresult,theconceptualdesignsdevelopedwiththeRUSapproachhavelongerrulingspansthantypicalAClines.ThisresultsinfewertransmissionstructuresfortheHVDCintertieandanassociatedcomparativereductioninconstructioncost.
C.1.2 Alaska‐specificDesignApproachforHVDCInterties
ThesecondconceptualdesignapproachtakesthelogisticandtechnicalchallengesofconstructioninruralAlaskaintoconsiderationandfocusesonmethodstoreduceconstructioncostswithoutcompromisingperformanceorlong‐termmaintainability.Thisdesignapproachincorporatescost‐savingfeaturesmadepossiblethroughHVDC‐specificdesignalternatives,materials,andconstructionmethods.DesignfeaturesofthisconceptincludetheuseofguyedcompositestructurestoallowsignificantlylongerrulingspansthanispossiblewithRUSstandardpractice.Thereducednumberofstructures,lesscostlyfoundations,andreducednumberofconductorsallresultinadditionalsavingscomparedwithintertiesbuilttoRUSstandardpractices.
ThefollowingthreeHVDCtransmissioncircuitconfigurationsareconsideredforeachoftheHVDCconceptualdesignapproaches:
● Monopolarsingle‐wiretransmissionwithearth‐returnpath(SWER);
● Monopolartwo‐wiretransmissionwithmetallicconductor‐returnpath(TWMR);
● Bipolartwo‐wiretransmission.
Schematicfiguresareprovidedinthisappendixforeachoftheseconceptualdesigns.Detailedreportsthataddressvarioustechnicalaspectsoftheassumedconditionsandloadingsusedtodeveloptheseconceptualdesignsareprovidedasattachmentstothisappendix.
29 Inthisreport,theterm“RUSstandardpractice”referstooverheadintertielinedesignsbasedonthemethodsandmaterials
presentedinRUSdesignmanualsfortransmissionanddistributionlineconstruction,includingbutnotlimitedto:REA,1982,RUS,1998,2002,2003a,2003b,2003c,and2009.
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C.2 DESIGNCRITERIAFOROVERHEADINTERTIELINES
ThefollowingdesigncriteriahasbeendevelopedasabasisfortheconceptualdesignoftheHVDCoverheadintertielines.
C.2.1 GeotechnicalConditions
Basedontheanalysisdescribedbelow,conceptualfoundationdesignalternativesforaguyedpoleutilizethreethermoprobemicropilesforthepolebaseandhelicalanchorsfortheguys.TheconceptualfoundationdesignalternativesarepresentedonFiguresC‐9throughC‐11.Theoverheadsystemtestsiteincludesinstallationofbothoftheseprototypefoundations,aswellasthermoprobemicropilesandscrewanchorstorestraintheguywires.
PolarconsultcontractedwithGolderAssociates,Inc.(Golder)toidentifyandcharacterizethemostcommongeotechnicalconditionsthatposethegreatesttechnicalandeconomicchallengesforruralAlaskaoverheadintertielinesascurrentlydesigned.
Insummary,GolderidentifiedthreeconceptualgeotechnicalconditionsrepresentingthegreatesteconomicchallengeforruralAlaskaoverheadinterties.Thesearesummarizedbelow.
Profile“A”:Icy,“warm”permafrostcomprisedprimarilyoflow‐plasticitymineralsiltbelowanactivelayerwithhigherorganiccontent.Thepermafrosttemperatureintheupper15feetbeneaththeactivelayerwouldhaveamaximumtemperature(occurringinlateautumn)of31.0to31.5°F.Theactivelayerisassumedtobeapproximately3.5feetthick,consistingoforganicsoilsandsurfacepeat.Surfacevegetationintheprojectfootprintisassumedtoremainundisturbedbylineconstruction.ThisprofileisintendedtorepresentagenericgeotechnicalprofileinthelowerYukonandKuskokwimareas.
Profile“B”:Warmanddegradingpermafrost,primarilylow‐tomoderate‐plasticitymineralsiltwithelevatedporewatersalinity.Taliksorthinunbondedsoillayersmaybepresentinthefrozensoilmatrixwithin15to20feetbelowgrade.Temperaturesareexpectedtoaverage31.5to31.8°Fintheuppermost15feetbelowtheactivelayer.Degradingpermafrostconditionsareexpectedbelowtheactivelayerinsomeareasalongtheintertiealignment.Surfacevegetationintheprojectfootprintisassumedtoremainundisturbedbylineconstruction.ThisprofileisintendedtorepresentagenericgeotechnicalprofilealongcoastalareasofwesternAlaska.
Profile“C”:Thawedorunfrozenmineralsoil,generallysandywithsiltcontentsof20%to40%totaldryweight.Highlydegradedpermafrostwithsignificantthawedzonesispresentbelowtheactivelayer.Soilmoisturecontentsrepresentsaturatedconditionsandnosignificantporewatersalinityispresent.Ahigherorganiccontentactivelayerispresent,withgrasses,brush,andtreesforvegetation.Theactivelayerisapproximately5feet.ThisprofileisintendedtorepresentagenericgeotechnicalprofilealongthepermafrostmarginininteriorAlaskaorinlandareaswithsignificantpermafrostdegradation.
C.2.2 EnvironmentalLoads
Thefollowingloadingswereanalyzedforeachconceptualdesign:
Case1:NationalElectricalSafetyCode(NESC)250B=½inchofice,4poundspersquarefoot(psf)wind.
Case2:NESC250C=noice,120mphwind.
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Case3:NESC250D=¼inchofice,80mphwind.
Case4:Highice=1inchice,nowind,30degreesFahrenheit(°F).
Case5:Noiceorwind.
TheseloadcasesareconsideredsufficientformanyruralAlaskaoverheadintertieapplications.Specificlocationsmaybesubjecttohigherand/orlowerwindand/oriceloadings.30Exceptwherespecificallystatedotherwise,eachoftheconceptualdesignspresentedinthissectioncomplywiththemoststringentoftheseloadconditions.
30 Section4.6ofthePhaseIFinalReportprovidesasummaryofenvironmentalloadingsaroundAlaska(Polarconsult,2009)
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C.3 CONCEPTUALDESIGNOFOVERHEADHVDCTRANSMISSION,RUSSTANDARDPRACTICE
Theconceptualdesignsofoverheadintertielinespresentedinthissectionhavebeendevelopedtotakeadvantageofthefollowingfactors:
● Alaskacontractors,linecrews,andutilitylinepersonnelarefamiliarwithRUSstandardpracticematerials,designs,andconstructionpractices,thustheywillbemorefamiliarwiththetechniquesandproceduresforbuilding,maintaining,andrepairingtheselines.
● AlaskaalreadyhasmanymilesofRUSstandard‐practicedistributionandtransmissionlinesbuiltandinservicethroughoutthestate.Utilitiesunderstandtheperformancerecordandissueswiththistypeoflineconstruction.
● Utilitylenders,whichincludesRUS,understandandacceptRUSstandardconstructionpractice,whichcansimplifyobtainingfundsforconstructingnewinterties.
Totakeadvantageofthesefactors,conceptualdesignforHVDCpreservedRUSstandardpracticeconstructiontotheextentpossible,modifyingthepoletopassemblytoaccommodatetheconductor(s),insulator(s),andclearancesforHVDCoperation.TherulingspanisalsoincreasedtotakeadvantageofthefewerwiresandreducedstructureloadsassociatedwiththeHVDCcircuitconfigurations.
StructuralanalysisofconventionaloverheadHVDCtransmissionstructures(adaptedfromRUSstandardpractice)wasperformedbyPolarconsult.Aconceptualdesignsummaryispresentedinthefollowingsectionsforeachlineconfiguration.
C.3.1 ConventionalACIntertieDesign
ConventionalACintertiedesignsforlow‐power(under1MW)ruralAlaskaACintertielinesareconsideredinthisstudyforthefollowingreasons:
1. ThemajorityofexistingruralAlaskaintertiesarebuiltperRUSstandardpractice.Thus,thisconventionalACoverheadlineconfigurationisthebaselineforcomparisonsofcapitalcost,electricalefficiency,andothermetricsbywhichtheHVDCintertiesystemsareevaluatedinthisreport.
2. TheRUSstandardpracticeconstructionthatisusedformostACintertielinesinruralAlaskahasbeenusedinthisreportasthebasisforconceptualdesignofconventionallybuiltHVDCintertielines.
MostruralAlaskaACintertielinesaredesignedandconstructedperRUSstandardpractice,whichtypicallyusesdirect‐burialcantileveredwoodpoles.31Manyintertielines,suchasthoseintheYukon‐Kuskokwimregion,cannotusedirect‐burialcantileveredwoodpoledesignsduetotheadversegeotechnicalconditions.Intheseproblemareas,thewoodpoleiscommonlyattachedtoasteelpiledriventoadepthofasmuchas40feettoprovideanadequatefoundationforthecantileveredpole.Thewoodpolesaretypically35to45feetinlength,dependingonthesiteconditionsandlinedesign.
ThepolessupportastandardRUStangentpole‐topassemblyaspresentedonFigureC‐1.TheconceptualdesigndataforthistypeoflineconstructionisprovidedinTableC‐1.
31 SeeRUS,1998;RUS,2005.
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Figure C-1 Tangent Pole for Conventional AC Intertie Line
ImageCredit:RUS,1998
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Table C-1 Conceptual Design Data for Conventional AC Intertie Line
I. GENERAL INFORMATION
PROJECT: CONCEPTUAL 1 MW HVDC LINESUMMARY OF CONCEPTUAL DESIGN DATA LINE IDENTIFICATION: VOLTAGE:
RUS STD. AC CONSTRUCTION 14.4 / 24.9 KV AC
THREE‐PHASE 14.4 / 24.9 Kv AC INTERTIE TYPE
STANDARD RUS CONSTRUCTION THREE PHASE AC DIST LINE < 1 MW
TYPE OF TANGENT STRUCTURE: BASE POLE:
WOOD POLE 35 FT CLASS 1
DESIGNED BY: POLARCONSULT ALASKA (CONCEPT DESIGN)
II. CONDUCTOR DATA TRANSMISSION COMMON NEUTRAL
SIZE: 1/0 (raven) 1/0 (raven)
STRANDING: 6/1 6/1
MATERIAL: ACSR ACSR
DIAMETER (IN): 0.398 0.398
WEIGHT (LBS/FT): 0.145 0.145
RATED STRENGTH (LBS): 4,380 4,380
III. DESIGN LOADS
NESC LOADING DISTRICT: HEAVY TRANSMISSION (LBS/FT) COMMON NEUTRAL (LBS/FT)
a. ICE (IN.): (vertical) 0.5 in. radial 0.5 in. radial
b. WIND ON ICED COND (PSF): (transverse) 4.0 psf 4.0 psf
c. CONSTANT K: (resultant + K) 0.3 psf 0.3 psf
EXTREME ICE (NO WIND): (vertical) 1.0 in. radial 1.0 in. radial
EXTREME WIND (NO ICE): (transverse) 120 mph 30.6 psf 120 mph 30.6 psf
EXTREME ICE + WIND:
ICE: (vertical) 0.25 in. radial 0.25 in. radial
WIND: (transverse) 80 mph 13.6 psf 80 mph 13.6 psf
IV. SAG & TENSION DATA
RULING SPAN: 250 ft.
SOURCE OF SAG/TENSION DATA: SOUTHWIRE SAG10 TRANSMISSION COMMON NEUTRAL
TENSIONS (% RATED STRENGTH) INITIAL FINAL INITIAL FINAL
NESC a. UNLOADED TEMP: 60 F lbs: 1,333 642 1,333 642
30% 15% 30% 15%
NESC b. LOADED TEMP: 0 F lbs: 2,190 2,190
50% 50%
MAXIMUM ICE TEMP: 30 F lbs: 2,488 2,488
HIGH WIND (NO ICE) TEMP: 60 F lbs: 1,875 1,875
UNLOADED LOW TEMPERATUR TEMP: ‐20 F lbs: 1,868 1,868
SAGS (FT)
NESC DISTRICT LOADED TEMP: 0 F 3.61 3.61
UNLOADED HIGH TEMP TEMP: 212 F 3.56 3.56
MAXIMUM ICE TEMP: 30 F 5.93 5.93
LOADED 1/2" ICE, NO WIND TEMP: 32 F 3.73 3.73
V. CLEARANCES
MINIMUM CLEARANCES TO BE MAINTAINED AT: EXTREME ICE LOADING
CLEARANCES IN FEET RAILROADS ROADS CULTIVATED AREAS (REMOTE AREAS) ADD'L ALLOWANCE
TRANSMISSION CLR. TO GROUND NA 21.2 21.2 5.0
VI. RIGHT OF WAY
WIDTH: 30 FT. AT EXTREME WIND, FINAL SAG, AREAS WITH TYP. STRUCTURES ADJ. TO ROW
WIDTH: 35 FT. AT EXTREME WIND, FINAL SAG, CLEARANCE TO VEGETATION AT LINE ELEV.
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C.3.2 MonopolarSingle‐WireTransmissionwithEarth‐ReturnPath(SWER),ConventionallyBuilt
TheRUSstandardpracticeforanAClineconstruction(FigureC‐2)canbeadaptedforamonopolarSWERHVDCline.Thenecessarychangesarelistedbelow:
● Eliminationofthefour(orthree)conductors,insulators,andthecross‐armassembly.
● Additionofasingleconductorratedforthestructuralloadsandelectricalrequirementsoftheline.Aluminumconductorsteelreinforced(ACSR)4/0Penguinwasselectedfortheconceptualdesign.
● Addasinglelinepostinsulatorratedfornominal50kVDCandthestructuralloadsfromtheconductors.A115kVACNGKpolymerlinepostinsulator(#L4‐SN321‐15U)wasselectedfortheconceptualdesign.32
● Increasetherulingspanbetweenthepolesfrom250feet(typicalforAClines)to500feet.
Atangentpole‐topassemblyforaconventionallybuiltmonopolarHVDCSWERintertieisshownonFigureC‐2.TheconceptualdesigndataforthistypeoflineconstructionisprovidedinTableC‐2.
32 TheinsulatordesignisconsideredconservativeandisanticipatedtobeadequateformostregionsofAlaska.Insulatorsrated
atalowervoltagemaybeappropriateforsomeintertielines.
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Figure C-2 Conventional Tangent Pole for Monopolar SWER HVDC Intertie Line
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Table C-2 Conceptual Design Data for Conventionally Built Monopolar SWER HVDC Intertie Line
I. GENERAL INFORMATION
PROJECT: CONCEPTUAL 1 MW HVDC LINESUMMARY OF CONCEPTUAL DESIGN DATA LINE IDENTIFICATION: VOLTAGE:
RUS STD. AS HVDC SWER 50 KV HVDC
MONOPOLAR HVDC OVERHEAD INTERTIE, SWER CIRCUIT TYPE
STANDARD RUS CONSTRUCTION MONOPOLAR HVDC SWER
TYPE OF TANGENT STRUCTURE: BASE POLE:
WOOD POLE 35 FT CLASS 1
DESIGNED BY: POLARCONSULT ALASKA (CONCEPT DESIGN)
II. CONDUCTOR DATA TRANSMISSION COMMON NEUTRAL
SIZE: 4/0 'PENGUIN' (NONE)
STRANDING: 6/1
MATERIAL: ACSR
DIAMETER (IN): 0.563
WEIGHT (LBS/FT): 0.291
RATED STRENGTH (LBS): 8,350
III. DESIGN LOADS
NESC LOADING DISTRICT: HEAVY TRANSMISSION (LBS/FT) COMMON NEUTRAL (LBS/FT)
a. ICE (IN.): (vertical) 0.5 in. radial (NONE)
b. WIND ON ICED COND (PSF): (transverse) 4.0 psf
c. CONSTANT K: (resultant + K) 0.3 psf
EXTREME ICE (NO WIND): (vertical) 1.0 in. radial
EXTREME WIND (NO ICE): (transverse) 120 mph 31.1 psf
EXTREME ICE + WIND:
ICE: (vertical) 0.25 in. radial
WIND: (transverse) 80 mph 13.8 psf
IV. SAG & TENSION DATA
RULING SPAN: 500 ft.
SOURCE OF SAG/TENSION DATA: SOUTHWIRE SAG10 TRANSMISSION COMMON NEUTRAL
TENSIONS (% RATED STRENGTH) INITIAL FINAL INITIAL FINAL
NESC a. UNLOADED TEMP: 60 F lbs: 1,999 1,142 (NONE)
24% 14%
NESC b. LOADED TEMP: 0 F lbs: 4,175
50%
MAXIMUM ICE TEMP: 30 F lbs: 4,982
HIGH WIND (NO ICE) TEMP: 60 F lbs: 3,915
UNLOADED LOW TEMPERATUR TEMP: ‐20 F lbs: 3,013
SAGS (FT)
NESC DISTRICT LOADED TEMP: 0 F 9.71
UNLOADED HIGH TEMP TEMP: 212 F 11.32
MAXIMUM ICE TEMP: 30 F 14.06
LOADED 1/2" ICE, NO WIND TEMP: 32 F 10.44
V. CLEARANCES
MINIMUM CLEARANCES TO BE MAINTAINED AT: EXTREME ICE LOADING
CLEARANCES IN FEET RAILROADS ROADS CULTIVATED AREAS (REMOTE AREAS) ADD'L ALLOWANCE
TRANSMISSION CLR. TO GROUND NA 21.7 21.7 5.0
VI. RIGHT OF WAY
WIDTH: 40 FT. AT EXTREME WIND, FINAL SAG, AREAS WITH TYP. STRUCTURES ADJ. TO ROW
WIDTH: 45 FT. AT EXTREME WIND, FINAL SAG, CLEARANCE TO VEGETATION AT LINE ELEV.
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C.3.3 MonopolarTwo‐WireTransmissionwithMetallicConductor‐ReturnPath(TWMR),ConventionallyBuilt
ThestandardRUSdesignforanAClinecanbeadaptedforamonopolarHVDClinewithmetallicreturn.Necessaryadaptationsarelistedbelow:
● Eliminatethefour(orthree)conductors,insulators,andthecross‐armassembly.
● Increasetherulingspanfortheintertielinefromatypical250feetupto500feet.
● Addonecantileveredlinepostinsulatorratedfornominal50kVDCandthestructuralloadsfromtheconductors.115kVACNGKpolymerlinepostinsulators(#L4‐SN321‐23)wereselectedfortheconceptualdesign.
● Addoneoffsetneutralbracketforthemetallicreturnconductor.
● Addtwoconductorsratedforthestructuralloadsandelectricalrequirementsoftheline.ACSR4/0Penguinwasselectedfortheconceptualdesignforbothhigh‐voltageconductors.
Atangentpole‐topassemblyforthisconceptualdesignisshownonFigureC‐3.TheconceptualdesigndataforthistypeoflineconstructionisprovidedinTableC‐3.
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Figure C-3 Conventional Tangent Pole for Monopolar HVDC with Metallic Return
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Table C-3 Conceptual Design Data for Conventionally Built Monopolar HVDC with Metallic Return
I. GENERAL INFORMATION
PROJECT: CONCEPTUAL 1 MW HVDC LINESUMMARY OF CONCEPTUAL DESIGN DATA LINE IDENTIFICATION: VOLTAGE:
RUS STD. AS HVDC TWMR 50 KV HVDC
MONOPOLAR HVDC INTERTIE ‐ TWMR CIRCUIT TYPE
(METALLIC RETURN) MONOPOLAR HVDC ‐ METALLIC RETURN
STANDARD RUS CONSTRUCTION TYPE OF TANGENT STRUCTURE: BASE POLE:
WOOD POLE 45 FT CLASS 1
DESIGNED BY: POLARCONSULT ALASKA (CONCEPT DESIGN)
II. CONDUCTOR DATA TRANSMISSION COMMON NEUTRAL
SIZE: 4/0 'PENGUIN' 4/0 'PENGUIN'
STRANDING: 6/1 6/1
MATERIAL: ACSR ACSR
DIAMETER (IN): 0.563 0.563
WEIGHT (LBS/FT): 0.291 0.291
RATED STRENGTH (LBS): 8,350 8,350
III. DESIGN LOADS
NESC LOADING DISTRICT: HEAVY TRANSMISSION (LBS/FT) COMMON NEUTRAL (LBS/FT)
a. ICE (IN.): (vertical) 0.5 in. radial 0.5 in. radial
b. WIND ON ICED COND (PSF): (transverse) 4.0 psf 4.0 psf
c. CONSTANT K: (resultant + K) 0.3 psf 0.3 psf
EXTREME ICE (NO WIND): (vertical) 1.0 in. radial 1.0 in. radial
EXTREME WIND (NO ICE): (transverse) 120 mph 32.2 psf 120 mph 32.2 psf
EXTREME ICE + WIND:
ICE: (vertical) 0.25 in. radial 0.25 in. radial
WIND: (transverse) 80 mph 14.3 psf 80 mph 14.3 psf
IV. SAG & TENSION DATA
RULING SPAN: 500 ft.
SOURCE OF SAG/TENSION DATA: SOUTHWIRE SAG10 TRANSMISSION COMMON NEUTRAL
TENSIONS (% RATED STRENGTH) INITIAL FINAL INITIAL FINAL
NESC a. UNLOADED TEMP: 60 F lbs: 1,999 1,142 1,999 1,142
24% 14% 24% 14%
NESC b. LOADED TEMP: 0 F lbs: 4,175 4,175
50% 50%
MAXIMUM ICE TEMP: 30 F lbs: 4,982 4,982
HIGH WIND (NO ICE) TEMP: 60 F lbs: 3,983 3,983
UNLOADED LOW TEMPERATUR TEMP: ‐20 F lbs: 3,013 3,013
SAGS (FT)
NESC DISTRICT LOADED TEMP: 0 F 9.71 9.71
UNLOADED HIGH TEMP TEMP: 212 F 11.32 11.32
MAXIMUM ICE TEMP: 30 F 14.06 14.06
LOADED 1/2" ICE, NO WIND TEMP: 32 F 10.44 10.44
V. CLEARANCES
MINIMUM CLEARANCES TO BE MAINTAINED AT: EXTREME ICE LOADING
CLEARANCES IN FEET RAILROADS ROADS CULTIVATED AREAS (REMOTE AREAS) ADD'L ALLOWANCE
TRANSMISSION CLR. TO GROUND NA 21.7 21.7 5.0
VI. RIGHT OF WAY
WIDTH: 50 FT. AT EXTREME WIND, FINAL SAG, AREAS WITH TYP. STRUCTURES ADJ. TO ROW
WIDTH: 45 FT. AT EXTREME WIND, FINAL SAG, CLEARANCE TO VEGETATION AT LINE ELEV.
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C.3.4 BipolarTwo‐WireTransmission,ConventionallyBuilt
ThestandardRUSdesignforanAClinecanbeadaptedforabipolarHVDCline.Necessaryadaptationsarelistedbelow:
● Eliminatethefour(orthree)conductors,insulators,andthecross‐armassembly.
● Increasetherulingspanfortheintertielinefromatypical250feetupto500feet.
● Addtwocantileveredpostinsulatorsratedfornominal50kVDCandthestructuralloadsfromtheconductors.A115kVACNGKpolymerlinepostinsulator(#L4‐SN321‐15U)wasselectedfortheconceptualdesign.
● Addtwoconductorsratedforthestructuralloadsandelectricalrequirementsoftheline.ACSR4/0Penguinwasselectedfortheconceptualdesignforboththehigh‐voltageandmetallic‐returnconductors.
Atangentpole‐topassemblyforthisconceptualdesignisshownonFigureC‐4.TheconceptualdesigndataforthistypeoflineconstructionisprovidedinTableC‐4.
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Figure C-4 Conventional Tangent Pole for Bipolar HVDC Intertie Line
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Table C-4 Conceptual Design Data for Conventionally Built Bipolar HVDC Intertie Line
I. GENERAL INFORMATION
PROJECT: CONCEPTUAL 2 MW HVDC LINESUMMARY OF CONCEPTUAL DESIGN DATA LINE IDENTIFICATION: VOLTAGE:
RUS STD. AS BIPOLAR HVDC +/‐ 50 KV HVDC
BIPOLAR HVDC INTERTIE TYPE
STANDARD RUS CONSTRUCTION BIPOLAR HVDC
TYPE OF TANGENT STRUCTURE: BASE POLE:
WOOD POLE 40 FT CLASS 1
DESIGNED BY: POLARCONSULT ALASKA (CONCEPT DESIGN)
II. CONDUCTOR DATA TRANSMISSION + 50 kVDC TRANSMISSION ‐ 50 kVDC
SIZE: 4/0 'PENGUIN' 4/0 'PENGUIN'
STRANDING: 6/1 6/1
MATERIAL: ACSR ACSR
DIAMETER (IN): 0.563 0.563
WEIGHT (LBS/FT): 0.291 0.291
RATED STRENGTH (LBS): 8,350 8,350
III. DESIGN LOADS
NESC LOADING DISTRICT: HEAVY TRANSMISSION (LBS/FT) TRANSMISSION (LBS/FT)
a. ICE (IN.): (vertical) 0.5 in. radial 0.5 in. radial
b. WIND ON ICED COND (PSF): (transverse) 4.0 psf 4.0 psf
c. CONSTANT K: (resultant + K) 0.3 psf 0.3 psf
EXTREME ICE (NO WIND): (vertical) 1.0 in. radial 1.0 in. radial
EXTREME WIND (NO ICE): (transverse) 120 mph 31.2 psf 120 mph 31.2 psf
EXTREME ICE + WIND:
ICE: (vertical) 0.25 in. radial 0.25 in. radial
WIND: (transverse) 80 mph 13.9 psf 80 mph 13.9 psf
IV. SAG & TENSION DATA
RULING SPAN: 500 ft.
SOURCE OF SAG/TENSION DATA: SOUTHWIRE SAG10 TRANSMISSION TRANSMISSION
TENSIONS (% RATED STRENGTH) INITIAL FINAL INITIAL FINAL
NESC a. UNLOADED TEMP: 60 F lbs: 1,999 1,142 1,999 1,142
24% 14% 24% 14%
NESC b. LOADED TEMP: 0 F lbs: 4,175 4,175
50% 50%
MAXIMUM ICE TEMP: 30 F lbs: 4,982 4,982
HIGH WIND (NO ICE) TEMP: 60 F lbs: 3,922 3,922
UNLOADED LOW TEMPERATUR TEMP: ‐20 F lbs: 3,013 3,013
SAGS (FT)
NESC DISTRICT LOADED TEMP: 0 F 9.71 9.71
UNLOADED HIGH TEMP TEMP: 212 F 11.32 11.32
MAXIMUM ICE TEMP: 30 F 14.06 14.06
LOADED 1/2" ICE, NO WIND TEMP: 32 F 10.44 10.44
V. CLEARANCES
MINIMUM CLEARANCES TO BE MAINTAINED AT: EXTREME ICE LOADING
CLEARANCES IN FEET RAILROADS ROADS CULTIVATED AREAS (REMOTE AREAS) ADD'L ALLOWANCE
TRANSMISSION CLR. TO GROUND NA 21.7 21.7 5.0
VI. RIGHT OF WAY
WIDTH: 50 FT. AT EXTREME WIND, FINAL SAG, AREAS WITH TYP. STRUCTURES ADJ. TO ROW
WIDTH: 45 FT. AT EXTREME WIND, FINAL SAG, CLEARANCE TO VEGETATION AT LINE ELEV.
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C.4 CONCEPTUALDESIGNOFOVERHEADHVDCTRANSMISSION,ALASKA‐SPECIFICMETHODS
TheconceptualdesignsofoverheadintertielinespresentedinthissectionhavebeendevelopedtoreduceconstructioncostsonruralAlaskainterties.Costreductionisachievedthroughspecialattentiontothefactorslistedbelow.
● Minimizingtherelianceonheavyequipmentthatmustbemobilizedtoaconstructionsite.Iflighterequipmentorlocalequipmentcanbeusedforconstruction,mobilizationcostswillbeless,reducingprojectcosts.
● Maximizingtheflexibilityinconstructionmethodsandseasons.Bydesigningfortheuseofsmallerequipment,greateruseofhelicoptersforconstructionsupport,andsimilartechniques,all‐seasonconstructionbecomespossible,creatingnewopportunitiestoincreaseutilizationofequipment,increasecompetitionforlineconstructionprojects,andreduceprojectcosts.
Thesefactorshavebeenincorporatedintotheconceptualdesignelementslistedbelow.
● Useoftallerstructuresandlongerspans.BecauseHVDCcircuitsrequireonlyoneortwowires,theycanutilizelongerspansthanacomparablethree‐orfour‐wireACcircuit.Increasingspansreducesthenumberofstructuresandfoundationsforagivenlengthofoverheadline,whichreducescosts.Withthisapproach,tallerstructuresareneededtomaintainrequiredclearancesbetweentheconductorandtheground.
● Useofglass‐fiber‐reinforcedpolymer(GFRP)polesinsteadofwoodorsteelpoles.GFRPpoleshavebeenusedforover50yearsinelectricutilityapplications33buthavelittletonohistoryinAlaska’selectricutilityindustry.GFRPpolesarelighterthanwoodorsteelpolessotheycanbetransportedbyasmallhelicoptersuchasaHughes500orBellUH‐1“Huey.”Theyarealsorot‐resistantanddonotleachtoxicpreservativesintothesoilsaroundthepole.ThePhaseIIprojectincludeddemonstrationofafield‐friendlyspliceforGFRPpoles,whichpermitstallpolestobeshippedinpartsandassembledinthefield.ThissplicecanalsobeusedforfieldrepairofdamagedGFRPpoles.
● Useofguyedstructuresinareaswheregeotechnicalconditionspreventcantileveredpolesfrombeingdirectlyburiedinthesoil.Acceptedpracticeforsuchconditionsistodriveasteelpileupto40feetdeepandthenfastenawoodpoletothesteelpile.Installingthesteelpilerequiresmobilizingacraneorotherheavyequipmenttotheprojectsite.Aguyedstructurecanbeinstalledinsuchconditionswithamuchsmallerbasefoundation,astheguyscarrymostofthemoment,andthestructurebasemostlycarriescompressiveloads.
ThefollowingsectionsdescribeconceptualdesignsusingtheseAlaska‐specificmethodsforthefollowingtypesofHVDCcircuits:
● MonopolarSWER;
● MonopolarTWMR;
● Bipolartwo‐wiretransmission.
Inallcases,theconceptualdesignspresentedinthefollowingsectionscomplywiththedesigncriteria,loadfactors,andstrengthfactorssetforthinSectionC.2ofthisappendixandbyRUS.34
33Ibrahim,2000.34 RUS,2009
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C.4.1 MonopolarSingle‐WireTransmissionwithEarth‐ReturnPath(SWER,Alaska‐SpecificDesign
TheAlaska‐specificconceptualdesignforamonopolarHVDClineconsistsofthefollowingelements:
● Single19#10Alumoweldconductorinstalledatarulingspanof1,000feet.
● Asinglelinepostinsulatorratedfornominal50kVDCandthestructuralloadsfromtheconductors.A115kVACNGKpolymerlinepostinsulator(#L4‐SN321‐15U)wasselectedfortheconceptualdesign.35
● A14‐inch‐diameter,0.375‐inchwall,50‐foot‐tallGFRPpole.Thispolecanbeincreasedto70feetifneededwithoutmodificationforspansupto1,500feetorforincreasedgroundorterrainclearances.
● Fourguysattachedtothepoletopinstalledata45‐degreeangletotheconductoranda45‐degreeangletoground.
● Guyanchorsconsistingoftwoflightsof8‐inchscrewanchorsdriven10to15feetintotheground.
● Apolebasefoundationconsistingofthree1½‐inchby25‐footthermoprobemicropilesinstalledtoadepthof20feet.Theremaining5feetserveasthethermoproberadiator.
Atangentpole‐topassemblyforthismonopolarHVDCSWERintertieconceptualdesignisshownonFigureC‐5.TheconceptualdesigndataforthistypeoflineconstructionisprovidedinTableC‐5.
35 TheinsulatordesignisconsideredconservativeandisanticipatedtobeadequateformostregionsofAlaska.Insulatorsrated
atalowervoltagemaybeappropriateforsomeintertielines.
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Figure C-5 Alaska-Specific Tangent Pole for Monopolar SWER HVDC Intertie Line
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Table C-5 Conceptual Design Data for Alaska-Specific Monopolar SWER HVDC Intertie Line
I. GENERAL INFORMATION
PROJECT: CONCEPTUAL 1 MW HVDC LINESUMMARY OF CONCEPTUAL DESIGN DATA LINE IDENTIFICATION: VOLTAGE:
AK SPECIFIC HVDC SWER DES. 50 KV HVDC
MONOPOLAR HVDC OVERHEAD INTERTIE, SWER CIRCUIT TYPE
ALASKA‐SPECIFIC CONSTRUCTION MONOPOLAR HVDC SWER
TYPE OF TANGENT STRUCTURE: BASE POLE:
GUYED FRP POLE 45 FT FRP POLE
DESIGNED BY: POLARCONSULT ALASKA (CONCEPT DESIGN)
II. CONDUCTOR DATA TRANSMISSION COMMON NEUTRAL
SIZE: 19#10 ALUMOWELD (NONE)
STRANDING: 19#10
MATERIAL: ALUMOWELD
DIAMETER (IN): 0.509
WEIGHT (LBS/FT): 0.449
RATED STRENGTH (LBS): 27,190
III. DESIGN LOADS
NESC LOADING DISTRICT: HEAVY TRANSMISSION (LBS/FT) COMMON NEUTRAL (LBS/FT)
a. ICE (IN.): (vertical) 0.5 in. radial (NONE)
b. WIND ON ICED COND (PSF): (transverse) 4.0 psf
c. CONSTANT K: (resultant + K) 0.3 psf
EXTREME ICE (NO WIND): (vertical) 1.0 in. radial
EXTREME WIND (NO ICE): (transverse) 120 mph 32.2 psf
EXTREME ICE + WIND:
ICE: (vertical) 0.25 in. radial
WIND: (transverse) 80 mph 14.3 psf
IV. SAG & TENSION DATA
RULING SPAN: 1,000 ft.
SOURCE OF SAG/TENSION DATA: SOUTHWIRE SAG10 TRANSMISSION COMMON NEUTRAL
TENSIONS (% RATED STRENGTH) INITIAL FINAL INITIAL FINAL
NESC a. UNLOADED TEMP: 60 F lbs: 8,071 6,798 (NONE)
30% 25%
NESC b. LOADED TEMP: 0 F lbs: 11,246
41%
MAXIMUM ICE TEMP: 30 F lbs: 12,637
HIGH WIND (NO ICE) TEMP: 60 F lbs: 10,075
UNLOADED LOW TEMPERATUR TEMP: ‐20 F lbs: 9,736
SAGS (FT)
NESC DISTRICT LOADED TEMP: 0 F 15.97
UNLOADED HIGH TEMP TEMP: 212 F 13.73
MAXIMUM ICE TEMP: 30 F 23.85
LOADED 1/2" ICE, NO WIND TEMP: 32 F 15.02
V. CLEARANCES
MINIMUM CLEARANCES TO BE MAINTAINED AT: EXTREME ICE LOADING
CLEARANCES IN FEET RAILROADS ROADS CULTIVATED AREAS (REMOTE AREAS) ADD'L ALLOWANCE
TRANSMISSION CLR. TO GROUND NA 21.7 21.7 5.0
VI. RIGHT OF WAY
WIDTH: 60 FT. AT EXTREME WIND, FINAL SAG, AREAS WITH TYP. STRUCTURES ADJ. TO ROW
WIDTH: 70 FT. FOOTPRINT OF 4‐GUYED STRUCTURE, GUYS AT 45 DEGREES TO LINE
WIDTH: 95 FT. FOOTPRINT OF 4‐GUYED STRUCTURE, GUYS IN LINE AND NORMAL TO CONDUCTOR.
WIDTH: 55 FT. AT EXTREME WIND, FINAL SAG, CLEARANCE TO VEGETATION AT LINE ELEV.
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C.4.2 MonopolarTwo‐WireTransmissionwithMetallicConductor‐ReturnPath(TWMR),Alaska‐SpecificDesign
TheAlaska‐specificconceptualdesignforamonopolarHVDCline(FigureC‐6)canbeadaptedforatwo‐wiremonopolarHVDClinewithmetallicreturn.Thenecessarychangesarelistedbelow:
● IncreasetheGFRPpoleheightfrom50feetto65feet.NochangeisneededinthepolesectionormaterialundertheloadcaseslistedinSectionC.2.
● Additionofasecond19#10Alumoweldconductorsupportedbyanoffsetbracket15feetbelowthetopofthepole.Atthisattachmentpoint,thissecondconductorwillhaveadequateclearancefromtheguys,ground,andthehigh‐voltageconductorunderallloadconditionslistedinSectionC.2ofthisappendix.
● Maintaintherulingspanat1,000feet.
Atangentpole‐topassemblyforaconventionallybuilttwo‐wiremonopolarHVDCintertieisshownonFigureC‐6.TheconceptualdesigndataforthistypeoflineconstructionisprovidedinTableC‐6.
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Figure C-6 Alaska-Specific Tangent Pole for Monopolar Metallic-Return Intertie Line
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Table C-6 Conceptual Design Data for Alaska-Specific Monopolar Metallic-Return Intertie Line
I. GENERAL INFORMATION
PROJECT: CONCEPTUAL 1 MW HVDC LINESUMMARY OF CONCEPTUAL DESIGN DATA LINE IDENTIFICATION: VOLTAGE:
AK SPECIFIC HVDC SWER DES. 50 KV HVDC
MONOPOLAR HVDC OVERHEAD INTERTIE TMWR CIRCUIT TYPE
(METALLIC RETURN) MONOPOLAR HVDC WITH METALLIC RETURN
ALASKA‐SPECIFIC CONSTRUCTION TYPE OF TANGENT STRUCTURE: BASE POLE:
GUYED FRP POLE 65 FT FRP POLE
DESIGNED BY: POLARCONSULT ALASKA (CONCEPT DESIGN)
II. CONDUCTOR DATA TRANSMISSION COMMON NEUTRAL
SIZE: 19#10 ALUMOWELD 19#10 ALUMOWELD
STRANDING: 19#10 19#10
MATERIAL: ALUMOWELD ALUMOWELD
DIAMETER (IN): 0.509 0.509
WEIGHT (LBS/FT): 0.449 0.449
RATED STRENGTH (LBS): 27,190 27,190
III. DESIGN LOADS
NESC LOADING DISTRICT: HEAVY TRANSMISSION (LBS/FT) COMMON NEUTRAL (LBS/FT)
a. ICE (IN.): (vertical) 0.5 in. radial 0.5 in. radial
b. WIND ON ICED COND (PSF): (transverse) 4.0 psf 4.0 psf
c. CONSTANT K: (resultant + K) 0.3 psf 0.3 psf
EXTREME ICE (NO WIND): (vertical) 1.0 in. radial 1.0 in. radial
EXTREME WIND (NO ICE): (transverse) 120 mph 34.0 psf 120 mph 34.0 psf
EXTREME ICE + WIND:
ICE: (vertical) 0.25 in. radial 0.3 in. radial
WIND: (transverse) 80 mph 15.1 psf 80 mph 15.1 psf
IV. SAG & TENSION DATA
RULING SPAN: 1,000 ft.
SOURCE OF SAG/TENSION DATA: SOUTHWIRE SAG10 TRANSMISSION COMMON NEUTRAL
TENSIONS (% RATED STRENGTH) INITIAL FINAL INITIAL FINAL
NESC a. UNLOADED TEMP: 60 F lbs: 8,071 6,798 8,071 6,798
30% 25% 30% 25%
NESC b. LOADED TEMP: 0 F lbs: 11,246 11,246
41% 41%
MAXIMUM ICE TEMP: 30 F lbs: 12,637 12,637
HIGH WIND (NO ICE) TEMP: 60 F lbs: 10,075 10,075
UNLOADED LOW TEMPERATUR TEMP: ‐20 F lbs: 9,736 9,736
SAGS (FT)
NESC DISTRICT LOADED TEMP: 0 F 15.97 15.97
UNLOADED HIGH TEMP TEMP: 212 F 13.73 13.73
MAXIMUM ICE TEMP: 30 F 23.85 23.85
LOADED 1/2" ICE, NO WIND TEMP: 32 F 15.02 15.02
V. CLEARANCES
MINIMUM CLEARANCES TO BE MAINTAINED AT: EXTREME ICE LOADING
CLEARANCES IN FEET RAILROADS ROADS CULTIVATED AREAS (REMOTE AREAS) ADD'L ALLOWANCE
TRANSMISSION CLR. TO GROUND NA 21.7 21.7 5.0
VI. RIGHT OF WAY
WIDTH: 60 FT. FOR EXTREME WIND, FINAL SAG, AREAS WITH TYP. STRUCTURES ADJ. TO ROW
WIDTH: 100 FT. FOOTPRINT OF 4‐GUYED STRUCTURE, GUYS AT 45 DEGREES TO LINE
WIDTH: 135 FT. FOOTPRINT OF 4‐GUYED STRUCTURE, GUYS IN LINE AND NORMAL TO CONDUCTOR.
WIDTH: 60 FT. FOR EXTREME WIND, FINAL SAG, CLEARANCE TO VEGETATION AT LINE ELEV.
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C.4.3 BipolarHVDCIntertieLine,AlaskaSpecificDesign
TheAlaska‐specificconceptualdesignforamonopolarHVDCline(FigureC‐7)canbeadaptedforatwo‐wirebipolarHVDCline.Thenecessarychangesarelistedbelow:
● IncreasetheGFRPpoleheightfrom50feetto55feet.Nochangeisneededinthepolesectionormaterial.
● Eliminatethepost‐topinsulatorandaddtwo8‐foot‐longcross‐arms.APowertrusion#SH2096100Norequalwasselectedfortheconceptualdesign.
● Installtwosuspensioninsulatorsoffeachendofthecross‐arm.A115‐kVACNGKsuspensioninsulator#251‐SE510‐EEorequalwasselectedfortheconceptualdesign.
● Use19#10Alumoweldastheconductorforboththepositiveandnegativepolesofthecircuit.
● Maintainthesamespanlengthof1,000feet.
Atangentpole‐topassemblyforanAlaska‐specificbipolartwo‐wireHVDCintertieisshownonFigureC‐7.TheconceptualdesigndataforthistypeoflineconstructionisprovidedinTableC‐7.
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Figure C-7 Alaska-Specific Tangent Pole for Bipolar HVDC Intertie Line
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Table C-7 Conceptual Design Data for Alaska-Specific Bipolar HVDC Intertie Line
I. GENERAL INFORMATION
PROJECT: CONCEPTUAL 1 MW HVDC LINESUMMARY OF CONCEPTUAL DESIGN DATA LINE IDENTIFICATION: VOLTAGE:
AK SPECIFIC HVDC SWER DES. 50 KV HVDC
BIPOLAR HVDC INTERTIE TYPE
ALASKA‐SPECIFIC CONSTRUCTION BIPOLAR HVDC
TYPE OF TANGENT STRUCTURE: BASE POLE:
GUYED FRP POLE 55 FT FRP POLE
DESIGNED BY: POLARCONSULT ALASKA (CONCEPT DESIGN)
II. CONDUCTOR DATA TRANSMISSION COMMON NEUTRAL
SIZE: 19#10 ALUMOWELD 19#10 ALUMOWELD
STRANDING: 19#10 19#10
MATERIAL: ALUMOWELD ALUMOWELD
DIAMETER (IN): 0.509 0.509
WEIGHT (LBS/FT): 0.449 0.449
RATED STRENGTH (LBS): 27,190 27,190
III. DESIGN LOADS
NESC LOADING DISTRICT: HEAVY TRANSMISSION (LBS/FT) COMMON NEUTRAL (LBS/FT)
a. ICE (IN.): (vertical) 0.5 in. radial 0.5 in. radial
b. WIND ON ICED COND (PSF): (transverse) 4.0 psf 4.0 psf
c. CONSTANT K: (resultant + K) 0.3 psf 0.3 psf
EXTREME ICE (NO WIND): (vertical) 1.0 in. radial 1.0 in. radial
EXTREME WIND (NO ICE): (transverse) 120 mph 32.3 psf 120 mph 32.3 psf
EXTREME ICE + WIND:
ICE: (vertical) 0.25 in. radial 0.3 in. radial
WIND: (transverse) 80 mph 14.3 psf 80 mph 14.3 psf
IV. SAG & TENSION DATA
RULING SPAN: 1,000 ft.
SOURCE OF SAG/TENSION DATA: SOUTHWIRE SAG10 TRANSMISSION COMMON NEUTRAL
TENSIONS (% RATED STRENGTH) INITIAL FINAL INITIAL FINAL
NESC a. UNLOADED TEMP: 60 F lbs: 8,071 6,798 8,071 6,798
30% 25% 30% 25%
NESC b. LOADED TEMP: 0 F lbs: 11,246 11,246
41% 41%
MAXIMUM ICE TEMP: 30 F lbs: 12,637 12,637
HIGH WIND (NO ICE) TEMP: 60 F lbs: 10,075 10,075
UNLOADED LOW TEMPERATUR TEMP: ‐20 F lbs: 9,736 9,736
SAGS (FT)
NESC DISTRICT LOADED TEMP: 0 F 15.97 15.97
UNLOADED HIGH TEMP TEMP: 212 F 13.73 13.73
MAXIMUM ICE TEMP: 30 F 23.85 23.85
LOADED 1/2" ICE, NO WIND TEMP: 32 F 15.02 15.02
V. CLEARANCES
MINIMUM CLEARANCES TO BE MAINTAINED AT: EXTREME ICE LOADING
CLEARANCES IN FEET RAILROADS ROADS CULTIVATED AREAS (REMOTE AREAS) ADD'L ALLOWANCE
TRANSMISSION CLR. TO GROUND NA 21.7 21.7 5.0
VI. RIGHT OF WAY
WIDTH: 60 FT. FOR EXTREME WIND, FINAL SAG, AREAS WITH TYP. STRUCTURES ADJ. TO ROW
WIDTH: 95 FT. FOOTPRINT OF 4‐GUYED STRUCTURE, GUYS AT 45 DEGREES TO LINE
WIDTH: 125 FT. FOOTPRINT OF 4‐GUYED STRUCTURE, GUYS IN LINE AND NORMAL TO CONDUCTOR.
WIDTH: 55 FT. FOR EXTREME WIND, FINAL SAG, CLEARANCE TO VEGETATION AT LINE ELEV.
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C.4.4 ConceptualDesignAnalysis
Theconceptualdesignofoverheadtransmissionstructuresandfoundationsconsideredmethodsforconstruction,long‐termoperation,maintenance,repair,andreplacementoftheHVDCtransmissioninfrastructure.
C.4.4.1 ConstructionMethods
Thecost‐reductionpotentialofHVDConruralAlaskaprojectsmayberealizedusingoptimizedconstructionmethods.
Theuseoflightweightoverheadstructuresandfoundationsallowssignificantlatitudefortheconstructionandmaintenanceofthelines.Theuseofhelicopterstostagethematerialsandconstructionequipmentbecomespossible.
ConventionalACtransmissionlineconstructionistypicallyperformedinthewintertosupporttheheavyequipmentrequiredforconstruction.Thisequipmentoftenincludeslargepile‐drivingordrillingmachinesthatcanonlybeoperatedonfrozenground.Theresultingwinterconstructionschedule,combinedwithsummermobilizationoftheequipment,contributessignificantlytothehighcostofACinterties.
ACtransmissionstructuresandfoundationsareusuallybasedonacantileverpoledesign.Forthelow‐strengthgeotechnicalconditionsfoundinmuchofruralAlaska,thisdesignapproachisinefficientcomparedtotheuseofaxiallyloadedguyedstructuresproposedintheHVDCconceptualdesign.
TheHVDCconstructionapproachcanutilizeHughes500orBellUH‐1typehelicopters,whicharecommonlyavailableinAlaska.Thesehelicoptershaveaslingcapacityofapproximately1,000and3,000pounds,respectively.TheHVDCcompositepolestructures,guywires,screwfoundations,thermoprobefoundations,andothertransmissioncomponentscanbereadilystagedbythesehelicopters.Installationequipmentandotherconstructiontoolsareavailableinsizesthatcanbeliftedbyhelicopter.
Inaddition,thisconstructionapproachinvolvestheuseoftracked,low‐ground‐pressurevehicleswithattachmentsoptimizedfortheinstallationoftheHVDCfoundationsanderectionofthecompositepolestructures.TheidealvehiclewouldbesimilartoahydraulicallydrivenBBCarrier.TheBBCarrierwasapredecessorofNodwelltrackedvehicles,butmuchsmaller36.Thehydraulicdrivesystemcanbeusedtopowerdrills,winches,spades,impactdrivers,andotheronboardequipmentusedforlineconstruction37.
C.4.4.2 RecommendedConstructionApproach
ThefollowingnarrativesetsforththegeneralconstructionapproachrecommendedfortheconceptualoverheadHVDCintertiedesignpresentedherein.Preferredconstructionmethodsforanyspecificintertiewilldifferfromthisapproachandwillaffectconstructioncosts.
1. Identifyandprocurepropertyrightstotheintertiealignment.Standardpracticesforthiseffortareappropriateandarenotduplicatedhere.
36 TheBBCarrierwasmanufacturedinthelate1950sandearly1960sbyBombardier.Itisnolongerinproductionandisquite
raretoday.Itfeaturedagrossvehicleweightofabout2,000pounds,apayloadcapacityofabout1,000pounds,andagroundpressureoflessthanonepsi.Itsdrivetrainusedaplanetarytransmission,maintainingpowertobothtracksduringturns,whichreducedthetendencyofthesevehiclestodamagefragiletundravegetation.
37 A20,000to30,000‐ft‐lbhydraulicimpactdriverheadonasmallboomwouldbeusefulfordrivingfoundationscrewanchors.
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2. Sendanengineeringcrewandsurveypartytosurveythelineanddeterminepolelocationsinthefield.Surveyingandpreliminarylinedesignmaybecompletedbeforehandbyremotemethods(e.g.,lightdetectionandranging[LIDAR]survey).Theengineeringcrewwillconductgeotechnicaltestingateachpolesitetodeterminethetypeoffoundationrequired.Asappropriate,theengineeringcrewmayadjustpolelocationsbasedonencounteredconditions.
3. Orderandshipmaterialstotheprojectsite.Dependingontheproject,oneorbothvillageswillbeusedasthebaseofoperations.Itmaybecost‐effectivetopreassemblepoleorfoundationunitspriortoshippingtothesite.
4. Prepareandinstallpolefoundations.Dependingontheproject,polefoundationsmaybeshippedreadytoinstallormayrequiresomeassemblyinthevillage.Oncereadytodeploytothefield,thefoundationsforeachpole(polebaseandthreeguyfoundations)willbeairliftedtothepolesitebyhelicopter.Asmalllow‐ground‐pressurevehiclewillbeusedtoinstallthefoundations.Dependingontheterrain,thisstagemayoccurduringthelatewinterorsummermonths.Thegroundvehiclewillremaininthefield,andpersonnelandconsumableswillbetransportedtothevehicledailybyair.Thiswillreducetransittimes.
5. Prepareandassemblepoles.Thiswilloccurinoneorbothvillagesandmayincludesplicingthepoles,attachingthepoletopandbasehardware,attachingthepostinsulatorandstringingblocks,andattachingtheguywiresandhardware.Anassembledpolewillbepackagedinamannersuitableforairliftandclearlylabeledsoitisdeployedtotheproperfoundation.
6. Poleinstallation.Eachassembledpolewillbeairliftedbyhelicoptertothepole'sfoundation.Thepolewillbespottedonthegroundbythehelicopterandagroundcrew.ThegroundcrewwilluseanA‐frameandtheirsmall,low‐ground‐pressurevehicletoerectthepoleusingtwooftheguyanchorsashoistpoints.Alternatively,thehelicoptercouldbeusedforfastererectingandsecuringofthepole.Oncethepoleiserected,plumbed,andguystensioned,thecrewwilldrivetothenextfoundationsite.Dependingonhelicopterlogistics,itmaybecost‐effectivetoemploytwogroundcrewsforthisactivity.Groundcrewsandconsumableswillbemobilizedtothelinedailybyhelicopter.
7. Stringingandsettingtheconductor.Thestringinglinewillbedeployedbyhelicopter.Onceinplace,theconductorwillbestagedbyhelicopteranddeployedbygroundcrews.AHughes‐500canliftapproximately2,000feetofconductoratatime.Oncetheconductorisstrung,groundcrewswillascendeachpoletoset,tension,andfixtheconductor.Armorwrapandvibrationdamperswillbeinstalledatthistime.
C.4.5 MaintenanceMethods
Thissectiondiscussestheconceptualmaintenanceandrepairmethodsthatareappropriateforthelong‐span,tall‐poleHVDCSWERoverheadintertie.Whilesometopicsmaybegenerallyapplicabletothemaintenanceandrepairofoverheadinterties,thisdiscussionfocusesonandisspecifictothisparticularintertiedesignconcept.
Fiberglasspolescannotbeclimbedusingthespur‐and‐beltmethodcommonlyemployedtoclimbwoodpoles.Instead,apulleyandcableorropesystemwouldbeanintegralpartofthefiberglasspole.Thepulleywouldbeinstalledinthepoletop,andthecablewouldtraveldownthepoleinterior.Thelinecrewisenvisionedtouseaharnessandwinchapparatustoattachtothepoleapparatusandusethissystemtoliftalinemantothepoletopformaintenance.
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Thisapproachoffersseveraladvantagescomparedwithconventionalpoleclimbingmethods.
● Theequipmentandinherentsafetyoftheapproachenableslessexperiencedcrewstoascendthepoles.
● Pole‐topmaintenanceiseasierorpossibleduringcolderweatheroradverseconditions.
● Ascent,descent,andtop‐siteworkisfasterbecausethecrewisnotasfatigued.
● Workislessphysicallydemanding,reducingthelikelihoodoffatigue‐relatedaccidents.
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C.5 CONCEPTUALDESIGNANALYSIS
Themajorityofthedesignanalysisfortheoverheadtransmissionconceptspresentedinthisstudyfollowsestablisheddesignpracticesthatarefoundinindustryliterature.38ThissectiondiscussesspecificaspectsoftheconceptualdesignofHVDCsystemsthatareuniquetoAlaskaandwarrantmoredetaileddiscussion.
C.5.1 StructuralDesign
PolarconsultcontractedwithLineDesignEngineering,Inc.(LDE)forassistanceinthestructuralandcodeanalysisofAlaska‐specificoverheadHVDCtransmissionstructuredesignconcepts.
C.5.2 FoundationDesign
PolarconsulttaskedGolderwithdevelopingconceptualfoundationdesignsfortherepresentativesoilsandgeotechnicalconditionsdiscussedinthisreport.Golderproposedthreefoundationdesignconceptsthatprovideeconomicalfoundationoptionsforsupportingguyedpowerpolesintherepresentativegeotechnicalconditions.Thesearesummarizedbelow.
● Passivelycooledthermoprobemicropiles,installedunderthepoletoreceivecompressiveloads.ArcticFoundations,Inc.(AFI)wasidentifiedasanexperiencedmanufacturerofsuchfoundationsystems.
● Small‐diameterhelicalanchors,installedunderthepoletoreceivecompressiveloadsorinstalledattheguystoreceivetensionloads.Thermopilescouldbeinstalledadjacenttotheseanchorstodecreasetemperaturesinthebearingsoils,whichwillincreasetheanchorstrength.
● Smaller‐diameter(4‐to6‐inch)verticalpilesforbothpolesandguys,installedwithimpacthammersusingsmallertrackedrigs.Thermopilescouldbeinstalledadjacenttotheseanchorstodecreasetemperaturesinthebearingsoilsandincreasepilestrength.
Existingconventionalfoundationmethodsweremaintainedforconventionalintertielineconstruction.Thisconsistsofeitherdirectburialofawoodpoleinsuitablesoilsorfasteningawoodpoletoadrivensteelpileinthemoredifficultgeotechnicalconditions.
Forguyedpowerpoles,asetofthree1½‐inch‐diameterthermoprobemicropilesinstalledtoadepthof20feetwitha5‐footradiatorsectionabovegroundareusedastheconceptualdesignforthepolebase,andhelicalanchorsareusedastheconceptualdesignforthepoleguys.
C.5.3 AnalysisofThermoprobePerformance
PolarconsultcontractedwithZarlingAeroEngineers(ZAE)tomodeltheseasonalthermalperformanceofapassivecoolingelementsuchasathermoprobemicropile.ZAEmodeledawarmpermafrostconditionanalogoustoGolder’sgeotechnicalProfile“C”usingthickandthinorganiclayersandcurrentclimatedataformarginalpermafrostintheFairbanksarea.Thermoprobeswiththermalconductancesof1.0Britishthermalunit(Btu)/hr‐ft‐°Fand2.0Btu/hr‐ft‐°Fwereconsidered.39ZAEalsoevaluatedtheeffectofplacinga4‐inch‐thicklayerofrigidinsulationonthegroundsurfacewithin4feetofthethermoprobe.
38RepresentativepublicationsincludeRUS,2001;RUS,2003a;RUS,2009;Naidu,1996;KZK,2006;Skrotzki,1980;Southwire,2008;andThrash,2007.39The1.5‐inch‐diameter,25‐foot‐longthermoprobesinstalledattheFairbanksTestSite(seeSectionC.6ofthisappendix)haveanestimatedthermalconductanceof0.3Btu/hr‐ft‐°F(AFI,2011).
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ZAErepeatedthisanalysiswithwarmerclimateconditionstoforecasttheperformanceofthethermoprobesunderawarmingclimateinthe2060to2069decade.TheresultsoftheseanalysesaresummarizedinTableC‐8.ZAE’stechnicalanalysisandreportisincludedasAttachmentC‐1tothisappendix.
TableC‐8presentsthefollowingmodelresultsthatdirectlypertaintothestructuralperformanceofthethermoprobes:
1. Maximumdepthoftheactivelayer(occursinlatefall).Thisdefineshowmuchoftheupperportionofthethermoprobeisinthawed,structurallyweaksoilsthatprovidedlimitedlateralsupporttothethermopile.Forstructuralanalysis,thisportionofthethermoprobeisassumedtobeanunsupportedcolumnthatmustbestiffenoughtotransfercompressiveloadsfromthetopofthethermoprobedowntothepermafrostregionwithoutbuckling.
2. Averagemaximumtemperatureofthepermafrost1footfromthethermopileinearlyfall(maximumannualtemperature).Thisdefinestheminimumstrengthofthesoilaroundthethermoprobeandthebearingstrengthofthethermopiletoresistbothcompressiveandtensionloads.
TheresultsofZAE’sanalysis(TableC‐8)areexplainedbelow.Itisimportanttoemphasizethattheseresultsarespecifictothesoilparameters,thermoprobeperformance,andclimateconditionsmodeled.Othermodelinputsmayproducesignificantlydifferentresults.
1. Underthegeotechnicalconditionsmodeled,a4‐inchlayerofrigidfoaminsulationinstalledatthesurfaceandextendingradiallyoutfromthethermoprobefor4feetcanreducethemaximumdepthoftheactivelayerby1to2feet.Duetothemodeststructuralbenefit,expectedcost,anddifficultyofinstallingandmaintainingsuchaninsulationassembly,thisinsulationelementisnotincludedintheconceptualfoundationdesigns.
2. Underallgeotechnicalconditionsmodeled,thethermoprobelowersthesoiltemperatureimmediatelysurroundingthethermoprobethroughouttheyear.Thiseffectismostpronouncedduringthewintermonthswhenthethermoprobeisextractingheatfromthesoilandcoolsthesoilbyupto5°Fsurroundingthethermoprobe.Thiscoldbulbpersiststhroughthesummer,resultinginanend‐of‐summerresidualthermalanomalyofafew1/10ths°Finthesoilsurroundingthethermoprobe.Thisresultsignificantlyenhancesthecompressiveandtensioncapacityofthethermoprobeduringthewinterandspringmonthsandproducesalesser(anddecreasing)enhancementthroughthesummerandintofall.Thethermoprobeimmediatelystartscoolingthesurroundingsoilsuponthereturnoffreezingnighttimeconditionsinthelatefall.
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Table C-8 Summary of Results from Thermoprobe Modeling by ZAE
Thermoprobeconductance=1.0Btu/hr‐ft‐°F Thermoprobeconductance=2.0Btu/hr‐ft‐°F ThinOrganicLayer ThickOrganicLayer ThinOrganicLayer ThickOrganicLayer
ExistingClimateConditions (Fairbanks,1971–2000)
4”SurfaceInsulation
NoSurfaceInsulation
4”SurfaceInsulation
NoSurfaceInsulation
4”SurfaceInsulation
NoSurfaceInsulation
4”SurfaceInsulation
NoSurfaceInsulation
Maximumdepthofactivelayerwithoutthermoprobe(atthermoprobe)1 6.5feet 3feet 6.5feet 3feet
Maximumdepthofactivelayerwiththermoprobe(atthermoprobe) 5.1feet 6.5feet <1foot 3feet 5feet 6.0feet <1foot 3feet
Averageearlywintersoiltemperatureonefootfromthermoprobe 30°F 30°F 30°F 30°F 28°F 28°F 28°F 28°F
Endofsummer/earlyfalltemperaturesonefootfromthermoprobe 30‐35°F 30‐35°F 30‐32°F 30‐34°F 30‐35°F 30‐35°F 29‐33°F 29‐34°F
Projected2060‐2069ClimateConditionsforFairbanks(+2.7°Fincreaseinannualmeantemperature)
Maximumdepthofactivelayerwithoutthermoprobe(atthermoprobe)1 8feet 8feet 3.5feet 3.5feet NA NA NA NA
Maximumdepthofactivelayerwiththermoprobe(atthermoprobe) 6.5feet 7.5feet 1foot 3.5feet NA NA NA NA
Averageearlywintersoiltemperatureonefootfromthermoprobe 31°F 31°F 31.5°F 31.5°F NA NA NA NA
Endofsummer/earlyfalltemperaturesonefootfromthermoprobe 31‐37°F 31‐37°F 31‐34°F 31‐35°F NA NA NA NA
SeethefullZAEreport,AttachmentC‐1tothisappendix,formoredetailedinformation. 1 Temperatureat11feetfromthermoprobe,whichisthelimitofthemodelgraphicsinthereport.NA: Notanalyzed.
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C.5.3.1 ThermoprobeConceptualDesign
AFIdevelopedconceptualthermopiledesignsbasedonthestructuralloadsgivenfortheAlaska‐specificintertiestructures.ThedesignandfabricationsheetsfortheAFIthermopileareincludedasAttachmentC‐2.
Polefoundationsusingeitherasingle3‐inchthermopileorasetofthree1½‐inchthermopilesarebothpractical.1½‐inchthermopilescanbeinstalledbysmallerequipmentthana3‐inchpile,althoughthematerialcostandinstallationtimewillbothbesomewhathigherthanforasingle3‐inchthermopile.Onsomeprojects,theuseofsmallerequipmentisexpectedtoresultinsufficientsavingsinspiteoftheincreasedmaterialandlaborcosts.
FiguresC‐9throughC‐11presenttheadapterplatedevelopedtomateaGFRPpoletothree1½‐inchthermopiles.FigureC‐8belowshowstheprototypeinstallationofthispolefoundationdesigninstalledatthefoundationtestsiteinFairbanks.TheFairbankstestingisdescribedingreaterdetailinSectionC.6ofthisappendix.
Figure C-8 Prototype Micro-Thermopile Tripod Pole Foundation
Fairbanks,Alaska.Polarconsult,2011
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Figure C-9 Shop Drawing of Prototype GFRP Pole Base Adapter for Micro-Thermopile Foundation (Sheet 1 of 3)
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Figure C-10 Shop Drawing of Prototype GFRP Pole Base Adapter for Micro-Thermopile Foundation (Sheet 2 of 3)
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Figure C-11 Shop Drawing of Prototype GFRP Pole Base Adapter for Micro-Thermopile Foundation (Sheet 3 of 3)
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C.5.3.2 ScrewAnchorConceptualDesign
BasedontheconceptualdesignanalysispreparedbyGolder,screwanchorsfittedwithtwoflightsof8‐inchhelicesanddriventoadepthof10to15feetbelowthegroundsurfacewillbesuitableforanchoringmostguys.IntheconceptualsoilspresentedbyGolder,theseanchorscanbeinstalledwithatorqueof10,000to15,000foot‐pounds.Guysatanglestructuresordeadendsmayrequiretwoormoreanchors.RepresentativescrewanchorsareshownonFigureC‐12.
Figure C-12 Galvanized Screw Anchors with 8-Inch Flights
Palletofgalvanizedscrewanchorswith8‐inchflights.SimilaranchorsaresuitableforrestrainingguysforAlaska‐specifictransmissionstructuresinmanychallengingsoils.(Polarconsult,2011;PhotographcourtesyofAlaska
FoundationTechnology,Inc.)
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C.5.4 ElectricalDesign
C.5.4.1 Conductor
A1‐MWtransmissioncapacityat50kVDCequatestoanominalpeakampacityof20amperes.Overloadorfaultconditionsarehigher.TheeconomicallyallowableconductorlossesontheHVDClineweresetat3%lossesat100%nominalcapacity.Fora25‐mile,1‐MW,two‐wiremonopolarintertie,thisisapproximatelyequivalentto1.5ohmsperconductor‐mile.TherequiredconductorresistanceisthesameforamonopolarSWERtransmissioncircuit,providedthatthegroundinggridsandearthreturnpathwayhaveatotalresistanceequaltoorlessthan37.5ohms.
Thestructuralrequirementsoftheconductorarepartofalargertechnicalandeconomicanalysisoftheoverheadsystemdesign.ForruralAlaskaintertielines,longerspansandfewerfoundationswillgenerallyresultinloweroverallcapitalcosts.Thisdesigndecisioncallsforstrongerconductorstowithstandthehigherstressesfromenvironmentalloadsandtallerpolestomaintaingroundclearancesundermaximumsagconditions.
ForconventionallybuiltHVDCintertiedesignconcepts,thesedesignconsiderationsresultedintheselectionofa4/0ACSRPenguinconductorforallHVDCcircuitconfigurations.
ForAlaska‐specificHVDCintertiedesignconcepts,thesedesignconsiderationsresultedintheselectionofa19#10AlumoweldconductorforallHVDCcircuitconfigurations.
C.5.4.2 Insulators
InsulatorsinDCapplicationsaremoresusceptiblethanACinsulatorstotheaccumulationofcontaminationontheinsulatorsheds.Thisisduetothepresenceofastaticelectricfieldaroundthehigh‐voltageconductor,whichattractschargedparticlestowardtheconductor.ThisattractionofchargedparticlesresultsinmoreparticleslandingonandcontaminatingtheinsulatorthanoccursoncomparableACsystems.ThisisbecausethealternatingelectricfieldaroundanACconductordoesnotimpartanetattractiontochargedparticles.
Periodicrainsandotherweathereventscandislodgetheseparticlesfromtheinsulatorsheds.Variousspecialcoatingscanalsohelptorepelparticles.Iftheinsulatorprovidesasufficientlylongleakagepathtoaccommodatetheaccumulatedcontamination,thennoactionisrequired.Insomeclimates,itisnecessarytowashtheinsulatorsperiodically.Thiscanbedonefromsuitablyequippedhelicoptersorlinetrucks.
OnmostruralAlaskaintertielines,washinginsulatorswouldbecostprohibitive,andwhenpossible,theinsulatorsshouldbedesignedtowithstandlong‐termaccumulationofcontamination.DesignguidanceforHVDCinsulatorsindicatethatinsulatorsratedfor34.5to42kVACserviceareadequatefor50kVDC,dependingonthedegreeofenvironmentalcontaminationandself‐cleaningconditionsthatexistalongtheintertieroute.40
DuetothewiderangeofenvironmentalconditionspresentinAlaska,averyconservativeconceptualinsulatordesignhasbeenadoptedtoprovideasubstantialallowanceforinsulatorcontamination.Indiscussionswithinsulatormanufacturers,insulatorsratedfor115kVAChavebeenselectedfortheconceptualdesign.Thisprovidesaleakagepathlengththatismorethan2.7timesthepublishedguidanceforHVDCtransmissioninsulators.Specificprojectsmaybeabletorealizesomecostsavingsbyusing
40Arrillaga,1998.Page256‐257.
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lower‐voltageinsulatorsiftheyaredistantfromcoastalregions(saltspray),activerivers(blowingdust),glaciers(blowingdust),aridregions(lackofcleansingrains),andsimilargeographicorclimaticcharacteristics.
MostHVDClinesarebipolarsystemswithtwohigh‐voltageconductors(FigureC‐13).Atypicaleconomicdesignsolutionforatwo‐conductoroverheadintertielineusessuspensioninsulators.InamonopolarSWERoverheadsystem,themosteconomicaldesigncallsforalinepostinsulatoratopasinglestructure.
Figure C-13 Typical Bipolar HVDC Transmission Line Using Suspension Insulators
HVDCcrossover,NorthDakota.Source:http://upload.wikimedia.org/wikipedia/commons/b/ba/HVDC_Crossover_North‐Dakota.jpg.
Atthespans,voltages,andenvironmentalloadsconsideredforthisapplication,acompositelinepostwitha3.5‐inch‐diameterpultrudedfiberglasscoreandsiliconeshedsarenecessarytowithstandthevertical,lateral,andlongitudinalmechanicalloadsplacedontheinsulator.Aninsulatorsuchaspartno.L4‐SN321‐15UmanufacturedbyNGK,Inc.orsimilarproductsaresuitableforthisapplication.Certainloadconditions,suchasunbalancedsheddingof1‐inchradialiceona1,000‐footspan,exceedtheratedstructuralcapacityofthisinsulator.
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Forspecificprojects,thislimitationcanbeaddressedinseveralways(e.g.,lessstringentdesignloads,reducedinsulatormargin,shorterspans,etc.).Manufacturersaredevelopingstrongerlinepostinsulators(4.0‐and4.5‐inchcores)thatwillbeadequateforallloadcombinationsconsideredinthisstudy.Itisestimatedthatthesewillbecommerciallyavailableby2014orthereafter.
Alternateinsulatorconfigurationscanalsobeusedtocircumventthestructurallimitationsofexistinglinepostinsulators.FiguresC‐14throughC‐16presenttwopotentialinsulatorconfigurationsthatusesuspensioninsulatorstoreducetheloadingsonalinepostinsulator.Theseconfigurationscanbeadaptedforuseonanyoftheconceptualoverheaddesignspresentedinthisappendix.Suspensioninsulatorsarelesscostlythanthelinepostinsulators;however,thesemorecomplicatedassemblieswillrequiremorelabortoinstall.
Figure C-14 Typical Tangent Structure Using Post Insulators
CantileveredwoodpoletangentstructureforanACtransmissionline.Postinsulatorsareusedtocarryallthree‐phaseconductors.Thepost‐topinsulatorcarrieslongitudinalandlateralforcesinbending,andthetwosideinsulatorscarryverticalandlongitudinalforcesinbending.TheseapplicationsaresimilartothoseshownonFigureC‐3andFigureC‐4.
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Figure C-15 Typical Angle Structure Using Suspension and Post Insulators
GuyedsteelpoleanglestructureforanACtransmissionline.Suspensioninsulatorsareusedtocarrytheconductortension,andapostinsulatorisusedtoholdtheconductoroffofthesupportstructure.Availablepostinsulatorsarenotstrongenoughtobeusedasapost‐topinsulator(asonFigureC‐4orC‐14)inthistypeofapplication.(Polarconsult,
2012)
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Figure C-16 Typical Tangent Structure Using Suspension and Post Insulators
Cantileveredwoodpoletangentstructurefora115kVACtransmissionline.Notetheuseofasuspensioninsulatorintensionandpostinsulatorincompressiontocarrytheweightoftheconductor.Thebaseofthepostinsulatorishingedtoallowsomelongitudinalmovementoftheconductor.Thepostinsulatoralsocarriesmostofthelateralwindloadsontheconductor.Thisinsulatorconfigurationcanbeusedforsingle‐ordouble‐wireHVDCcircuitconfigurations.Aback
guycouldbeusedtoreducethenetmomentonthepoleandfoundation.(Polarconsult,2012)
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C.6 TESTINGOFOVERHEADDESIGNCONCEPTS
Mostelementsoftheconceptualoverheaddesignsdescribedinthisappendixutilizecommerciallyavailableandacceptedmaterials,designs,andconstructionmethods.CertaincomponentsoftheconceptualdesignspresentedinSectionC.5representinnovationsinoverheadlinedesignthatdonothaveaprovenrecordwithintheutilityindustry.Inordertoevaluatetheperformanceofthesecomponents,theywereinstalledatatestsiteinFairbanks,Alaska.ThissectiondescribestheobjectivesandinstallationoftheFairbanksTestSite.
C.6.1 TestObjectives
TheprimarytestobjectivesoftheFairbanksTestSitearelistedbelow.
1. Demonstrateperformanceandassemblytimeofaspliceforaconstant‐sectionGFRPutilitypole.
2. Demonstrateinstallationandperformanceofmicro‐thermopilepolefoundations.
3. Demonstrateinstallationandperformanceofmicro‐thermopileguyanchors.
4. Demonstrateinstallationandperformanceofscrewguyanchors.
5. DemonstratetheinstallationandperformanceoftheoverallguyedGFRPpolestructure.
C.6.2 TestSite
ThetestsiteislocatedonprivatepropertyoffFarmer’sLoopRoadnorthofCreamers’FieldinFairbanks.Thesiteconsistsofwarmice‐richsiltypermafrostsoils.Thesitehasanorganiclayerconsistingofdeciduousshrubsandblackspruce.Peatwaspresentatdepthsof1to5feetbelowgroundsurface.TheactivelayerinSeptemberextendedtoadepthof3feet,withstandingwaterencounteredwithinthevegetativematnearthesurface.
Geotechnicalconditionsatthesitearecharacteristicofmarginalwarmpermafrostconditions,generallyconsistentwithconceptualgeotechnicalprofile“C”developedbyGolderanddescribedinSectionCofthisappendix.
C.6.3 Installation
Keyitemsinstalledatthetestsitearedescribedinthissection.
C.6.3.1 SoilTemperatureProbes
Thesitehastwosoiltemperaturemonitoringprobes.Eachprobeisa¾‐inchPVCpipeinsertedintoadrillholethatextendsto25feetbelowgrade.Oneholeislocatedadjacent(1.0footaway)tothemicro‐thermopiletripodpolefoundationandwillbeusedtomonitorthethermaleffectsofthethermopilesandvegetationclearing.Thesecondholeislocatedapproximately50feetawayinanundisturbedblacksprucestandandwillbeusedtocollectbaselinesoiltemperaturedata.
C.6.3.2 Glass‐Fiber‐ReinforcedPolymer(GFRP)Pole
Thesitehasone60‐foot‐tallguyedglass‐fiber‐reinforcedpolymer(GFRP)pole.TheGFRPpolehasaroundsection,is12inchesindiameter,andhasa0.5‐inchwall.TheGFRPpoleismanufacturedbyPowertrusions,Inc.TheGFRPpoleconsistsofa40‐footand20‐footsectionconnectedbyafullmoment‐carryingslip‐onexternalsplice.Thesplicedoesnotrequireanyglueorsolventtodevelopbearingormomentcapacity.Bearingiscarriedbyphysicalcontactofthebutt‐endsofthepolesegments.Momentis
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carriedthroughmechanicalcontactbetweenthepoleandsplicewalls.Thespliceisheldinplaceby#14¼‐inch‐diameterx1½‐inch‐longzincplatedTekshexwasherheadscrewsdrivenaroundtheperimeterofthespliceintoeachpolesegment.ThepoleattheFairbankssiteisincompression.Powerlinepolessubjecttoupliftwouldneedtodesignthespliceconnectionfortensionloads.
C.6.3.3 GFRPPoleFoundation
TheGFRPpolefoundationisamicro‐thermopiletripodwithanadapterpiecetofitthepoleontothemicro‐thermopiles.ShopdrawingsoftheadapterpiecearepresentedonFigureC‐9throughC‐11.Theadapterpiece:
● Featuresanintegralhingeassemblytoraiseorlowerpolesinthefield,
● Providesgeneroustolerancesforbatteranglesandplacementofthemicro‐thermopiles,and
● Providesfullflexibilityinorientationofthehingeanglerelativetothetripodangle(sothepolecanberaisedorloweredinlinewithaguyanchorregardlessofhowthepolefoundationmicro‐thermopilesareoriented.
C.6.3.4 Guys
TheGFRPpoleissecuredbyfour3/8‐inchextra‐high‐strength(EHS)guylinessetat90degreestoeachotherand45degreestoground.Theguysandguyhardwareisconventional.AFUTEKmodelLSB4000loadcellisriggedintooneguywireoneachaxistomeasureguywiretension.
C.6.3.5 GuyAnchors
FourdifferentguyanchorsareinstalledattheFairbankssite.
1. A25‐foot‐longby1½‐inch‐diametermicro‐thermopile,installedata45‐degreeangletothegroundsurface(directlyin‐linewiththeguy).Thisanchorresistsguytensionsolelywithskinfriction.Theanchorisinstalledwiththetop5feetabovegroundastheradiatorsection.
2. A25‐foot‐longby1½‐inch‐diametermicro‐thermopile,installedata70‐degreeangletothegroundsurface.Thisreducedanglefromverticaliseasiertoinstallbutplacesamomentonthemicro‐thermopile.
3. Astandard8‐inchdouble‐flightscrewanchor.Thescrewanchorwasdriven15feetbelowgroundsurfaceata45‐degreeangle,placingtheanchorflightsapproximately10feetbelowgrade.
4. Astandard6‐inchswampanchor.Theswampanchorisscrewedintothesoilbyadriverodthatisthenwithdrawn.Theanchorattachestotheguywireviaagroundcable.Thistypeofanchorislesssusceptibletofrostheavethanthethreeotheranchorsdescribedabove.
C.6.4 Monitoring
Polarconsultwillcontinuetomonitortheinstallationatthetestsiteforperformance.
1. Monitorseasonalfluctuationsinsoilthermalprofilestoestablishbaselinethermalprofilesandtheperformanceofthemicro‐thermopiles.
2. Monitorguywiretensionsanddifferentialelevationsofguywiresandpolefoundationtoidentifycreepinthefoundations.
3. MonitorperformanceoftheGFRPpoleandsplice.
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Figure C-17 Installing Micro-Thermopile for Guy Anchor
ContractorGeoTekAlaska,Inc.drillingaholeforinstallationofamicro‐thermopileata45‐degreebatterangleusingaGeoProbe8040seriesdrillrig.Themicro‐thermopilewillserveasaguyanchorfortheprototypeguyedGFRPpole
installationattheFairbanksTestSite.(Polarconsult,2011).
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Figure C-18 Setting Micro-Thermopile Guy Anchor with Sand Slurry Backfill
Settingmicro‐thermopileguyanchorwithasandslurry.(Polarconsult,2011)
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Figure C-19 Installing Micro-Thermopile for Guy Anchor
ContractorGeoTekAlaska,Inc.drillingaholeforinstallationofamicro‐thermopileata45‐degreebatterangleusingaGeoProbe8040seriesdrillrig.Themicro‐thermopilewillserveasaguyanchorfortheprototypeguyedGFRPpole
installationattheFairbanksTestSite.(Polarconsult,2011).
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Figure C-20 Micro-Thermopiles Staged at Fairbanks Test Site for Installation of Prototype Foundations
1½‐inch‐diameterby25‐foot‐longmicro‐thermopilesusedforpolebaseandguyanchorsystemsforaprototypeguyedGFRPpoleinstalledattheFairbanksTestSite.Threemicro‐thermopilesareusedatthepolebase,andoneeachfortwo
ofthefourguyanchors.(Polarconsult,2011)
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Figure C-21 Micro-Thermopile Tripod for Prototype Pole Foundation
Micro‐thermopiletripodforprototypepolefoundation.Thefourthpipeatleftisasoiltemperaturemonitoringwellthatisusedtomonitorthethermal‐affectedzonearoundthethermopiles.Thereisasecondsoiltemperaturemonitoringprobelocatedapproximately40feetfromthepolebase(notshowninphoto)thatisusedtoestablishthebaseline
thermalprofileofthesite.(Polarconsult,2011)
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Figure C-22 Installing Helical Screw Anchor for Guy Anchor
ContractorCityElectric,Inc.installingahelicalscrewanchorwithtwo8‐inchflights.Theanchorwasdriven15feetintothegroundata45‐degreebatterangle.Theanchorwillbeusedtosecureoneofthefourguysontheprototype
GFRPpoleinstalledattheFairbanksTestSite.(Polaconsult,2011)
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Figure C-23 Guy Attached to Micro-Thermopile Foundation
GuywiresupportingtheinstalledprototypeGFRPpoleattheFairbanksTestSite.Theguyanchorisamicro‐thermopileinstalledata20‐degreebatterangle.Thisguywireincludesaloadcelltomonitorguywiretension.Theloadcellreaderisattachedtothecellandisvisibleinthephoto(blackandyellowdevicebelowtheguywire).Polarconsult,2011.)
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Figure C-24 Assembling the Prototype GFRP Pole Splice
ContractorCityElectric,Inc.installingthefieldsplicefortheprototypeGFRPpole.40‐footand20‐footGFRPpolesegmentsweresplicedtocreatethe60‐footpoleerectedatthesite.Thespliceslidesoverthepolesegmentsandcarriesmomentthroughcontactbetweenthepoleandsplicewalls.Verticalloadsarecarriedthroughthebuttendsofthepolesegments.Noglueoradhesiveisnecessaryforthesplicetodevelopthefullmechanicalstrengthofthepole.Thescrews
servetopreventdifferentialmovementbetweenthepoleandsplice.(Polarconsult,2011)
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Figure C-25 Installed GFRP Pole, Micro-Thermopiles, and Adapter Plate
DetailofprototypeGFRPpolebaseattheFairbanksTestSite.Thecustom‐designedbaseplateaccommodatesthevariableangleandlocationofthethreemicro‐thermopilesandincludesahingesothepolecanbeloweredifneeded.Thebaseplateallowsforadjustmentofthehingeorientationduringinstallationsoaguyanchorcanbeusedtowinch
thepoledown.(Polarconsult,2011)
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Figure C-26 Prototype GFRP Pole Foundation During Installation
DetailofprototypeGFRPpolebaseattheFairbanksTestSite.Theadapterplatewasadjustedduringinstallationsothehingeisorientedinlinewiththeguyanchorinthedistance(orangeflagging).Thisallowsuseoftheguyanchorto
lowerthepolewithawinchifneeded.(Polarconsult,2011)
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Figure C-27 Prototype Pole at the Fairbanks Test Site
ViewoftheprototypeguyedGFRPpoleinstalledattheFairbanksTestSite.Thisphotographistakenatadistanceofapproximately200yardsfromthe60‐foottallpole.(Polarconsult,2011)
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Figure C-28 Prototype Pole at the Fairbanks Test Site
ViewoftheprototypeguyedGFRPpoleinstalledattheFairbanksTestSite.Thisphotographistakenatadistanceofapproximately25yardsfromthe60‐foottallpole.Thefourguysandthepolesplicearevisibleinthisphotograph
(Polarconsult,2011)
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APPENDIXCATTACHMENTS
AttachmentC‐1:ZarlingAeroConsulting(ZAE)ThermalAnalysisofThermopile
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APPENDIXD
CONCEPTUALDESIGNFORSUBMARINECABLES
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TABLEOFCONTENTS
APPENDIXDATTACHMENT...............................................................................................................................................5 ATTACHMENTD‐1:CABLETRICITYHVDCTRANSMISSIONSYSTEMSFORRURALALASKAAPPLICATIONSDCPOWERCABLES
FOR1–5MWCONVERTERS............................................................................................................................................5
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APPENDIXDATTACHMENT
AttachmentD‐1:CabletricityHVDCTransmissionSystemsforRuralAlaskaApplicationsDC
PowerCablesfor1–5MWConverters
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APPENDIXE
SWERCIRCUITSANDHVDCSYSTEMGROUNDING
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TABLEOFCONTENTS
E.1 SINGLE‐WIREEARTHRETURN(SWER)CIRCUITS...................................................................................7
E.2 SYSTEMGROUNDING.............................................................................................................................................7
APPENDIXEATTACHMENTS.............................................................................................................................................9 ATTACHMENTE‐1:HVDCGROUNDELECTRODEOVERVIEW...................................................................................................9 ATTACHMENTE‐2:GROUNDINGSTATIONFIGURE...................................................................................................................25
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LISTOFFIGURES
FigureE‐1 GroundingStation....................................................................................................................................27
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E.1 SINGLE‐WIREEARTHRETURN(SWER)CIRCUITS
Themosteconomicalapplicationsoflow‐powerhigh‐voltagedirectcurrent(HVDC)systemsinAlaskawillusemonopolarcircuitswithsingle‐wireearthreturn(SWER).AlaskahasadoptedtheNationalElectricSafetyCode(NESC)toregulatethedesignandinstallationofutilitygradeelectricsystems.TheNESCdoesnotallowtheuseofSWERcircuits.Thisruleisbasedonconsiderationsoflifesafety(avoidanceofsteppotentialhazards)andeconomics,asDCSWERcircuitscancauseacceleratedcorrosionofnearbyburiedmetalinfrastructuresuchaspipelines.
SWERcircuitsaresuccessfullyusedonACandDCcircuitsinmanyinternationaljurisdictions.InmanyruralAlaskaapplications,theuseofHVDCSWERcircuitsisasafeandappropriatetechnologythatcansavesignificantcosts.ThereisaprocesstoobtainwaiverstotheNESCrulesthatwillpermittheinstallationofSWERcircuits.TwoACSWERsystemsbuiltinthe1980ssuccessfullyobtainedsuchwaivers.
PolarconsultsubcontractedwiththeManitobaHVDCResearchCentre(MHRC)topreparealetterreportsummarizingthetechnicalandcodeissuesassociatedwiththeappropriateuseofSWERcircuits.ThatreportisincludedasAttachmentE‐1tothisappendix.
E.2 SYSTEMGROUNDING
Aconceptualdesignforalow‐powerHVDCgroundingstationsuitableforusewiththeproposedHVDCtransmissionsystemisincludedintheattachmenttothisappendix.
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APPENDIXEATTACHMENTS
AttachmentE‐1:HVDCGroundElectrodeOverview
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AttachmentE‐2:GroundingStationFigure
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Figure E-1 Grounding Station
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APPENDIXF
HVDCPOWERCONVERTERDEVELOPMENT
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TABLEOFCONTENTS
F.1 CONVERTERDEVELOPMENT.............................................................................................................................7 F.1.1 INTRODUCTION..................................................................................................................................................................7 F.1.2 CONVERTERSIZINGANALYSIS........................................................................................................................................7 F.1.3 CONVERTERTESTRESULTS...........................................................................................................................................10
F.1.3.1 FiberOpticTriggeringSysteminHigh‐VoltageTank..............................................................10 F.1.3.2 IGBTSwitchesinHigh‐VoltageTank...............................................................................................10
APPENDIXFATTACHMENTS...........................................................................................................................................13 ATTACHMENTF‐1:PPSHVDCPOWERCONVERTERREPORT...............................................................................................13
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LISTOFFIGURES
FigureF‐1 TypicalLoadDurationProfileforanAlaskaVillage....................................................................8
FigureF‐2 PeakLoadsinAlaskaVillages(2007–2009).................................................................................9
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F.1 CONVERTERDEVELOPMENT
F.1.1 Introduction
Thehigh‐voltagedirectcurrent(HVDC)converterdevelopedunderthisprojectisa1‐megawatt(MW)powerconvertercapableofbidirectionalpowerconversionbetweenthree‐phase480voltsalternatingcurrent(VAC)and50kilovolts(kV)HVDC.TheconvertercapacityisappropriatetosupplytheelectricalneedsofmostAlaskavillages.Incontrast,existingHVDCpowerconvertersystemsareonlycosteffectiveatmuchlargertransmissioncapacities,startingatapproximately50MWandextendingupto1,000sofMWsofcapacity.
MultipleHVDCconverterscanbe“paralleled”toachievehigherpowertransmissioncapacitieswhereneeded.BasedonPhaseIIdevelopmentwork,thepriceofacommerciallyproduced1‐MWHVDCpowerconverterisestimatedtobe$250,000.Atleasttwo1‐MWconvertersareneededforacomplete1‐MWHVDCtransmissionsystem.
ThisappendixpresentsPrincetonPowerSystems,Inc.’s(PPS’s)finaldeliverablesforconverterspecification,design,andtestplanunderPhaseIIoftheHVDCtechnologydevelopmentprogram(AttachmentF‐1).
PPShassuccessfullydemonstratedoperationoftheprototypeconvertersatthefull50kVDCandpowerflowinbothinverter(HVDCtoAC)modeandrectifier(ACtoHVDC)modeinacontrolledtestfacilitysetting.Thesetestingeffortsvalidatethedesignandbasicfunctionalityoftheconverter.
Inthecourseoftesting,PPSidentifiedtwohardwareproblemsthatpreventedfull‐powertestingoftheprototypeconverters.PPShasinvestigatedtheseproblemsandidentifiedtheactionsnecessarytocorrectbothproblems.TheproblemsandsolutionsarediscussedinAttachmentF‐1tothisappendix.
PPSiscontinuingtoworkonthehardwaremodificationsneededtocorrectthepriortechnicalproblems.Duetothelonglead‐timetoobtainsuitablereplacementinsulatedgatebipolartransistor(IGBT)switches,theconvertermodificationsandtestingarenotexpectedtobecompleteduntillate2012.PPSwillissueasupplementalreportdetailingtheresultsoffinalPhaseIItestingwhentestingiscompleted.ThissupplementalreportandthefullyoperationalconverterswillbePPS’sfinaldeliverableunderPhaseIIofthisresearchanddevelopment(R&D)project.
F.1.2 ConverterSizingAnalysis
TheelectricalloadcharacteristicsofruralAlaskancommunitiesthatarethetargetofthisprojectwereevaluated.ThecapacityoftheHVDCintertiesystemwasbasedonthelikelypeakloadsandloaddurationprofilesoftheselectedcommunities.
Thedurationofpeakloadsprovidesaneconomicbasisfordesigncapacityoftheintertie.Ingeneral,theintertieisdesignedtominimizethelinelossesatpeakloads.TheloaddurationprofileforHooperBayispresentedonFigureF‐1.ThisprofileisrepresentativeofruralAlaskancommunitieswithapeakloadof760kW,andwillgenerallyapplytoothercommunities.Somecommunities,suchasthosewithfishprocessors,willhaveloadprofilesdifferentthanthatshownonFigureF‐1.
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Figure F-1 Typical Load Duration Profile for an Alaska Village
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Polarconsult,201241
ThepeakloadsofruralAlaskacommunitiesparticipatinginthePowerCostEqualization(PCE)programwerereviewedtodeterminetheappropriatepowercapacityfortheHVDCintertiesconsideredforthisstudy.ThedistributionofpeakloadsispresentedonFigureF‐2.
Basedonthisanalysis,a1‐MWpowerintertieisanappropriateconceptualcapacityforthemajorityofruralAlaskainterties.Formaximumreliabilityandflexibility,thepowerconverterspecificationscallfora1‐MWunitcomprisedoftwo500‐kWmodulesoperatinginparallel.Theconvertermodulescanbeconnectedtooperateinparallel,thusprovidingadditionalcapacityuptoafewMWswherenecessary.IntertiesdesignedformorethanafewMWsmaywarrantreevaluationoftheACinterfacevoltage(480volts[V]forthe500‐kWpowerconvertermodule).
41DatageneratedforHooperBayusingtheAlaskaVillageElectricLoadCalculator(NREL,2005)
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Figure F-2 Peak Loads in Alaska Villages (2007 – 2009)
0
1000
2000
3000
4000
5000
Point L
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arville
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d (
kW)
(2) 1 MW HVDC CONVERTERS USED FOR BIPOLAR INTERTIE, ADEQUATE FOR 82% OF COMMUNITIES.
1 MW HVDC CONVERTER, ADEQUATE FOR 76% OF COMMUNITIES.
1 MW HVDC CONVERTER WITH 500KW MODULE FAILURE, ADEQUATE FOR 60% OF COMMUNITIES.
Source: 2009 Power Cost Equalization Data, Alaska Energy Authority
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F.1.3 ConverterTestResults
Inthecourseoftestingtheprototypeconverters,PPShassuccessfullydemonstratedoperationatthefull50kVDCandpowerflowinbothinverter(HVDCtoAC)modeandrectifier(ACtoHVDC)mode.Inthecourseoftesting,PPSidentifiedtwohardwareproblemsthatpreventedcompletionofPhaseIItestingoftheprototypeconverters,includingdemonstrationoffullpoweroperation.PPShasinvestigatedtheseproblemsandidentifiedtheactionsnecessarytocorrectbothproblems.Theproblemsandsolutionsaresummarizedbelow.
F.1.3.1 FiberOpticTriggeringSysteminHigh‐VoltageTank
Afiberopticnetworkisusedtotriggerthesolid‐stateIGBTswitchesinsidethehigh‐voltagetank.Testingrevealedproblemswiththetriggeringtimingandreliabilityofthistriggeringsystem.Investigationdeterminedthatthelensesusedinthefiberopticsystemexhibitexcessivelyhighsignalloss,causingtheobservedtimingandreliabilityissues.PPShasidentifiedandtesteddifferentlensesandisproceedingtoreplacethelensesinbothprototypeconvertermodulestosolvethisproblem.
F.1.3.2 IGBTSwitchesinHigh‐VoltageTank
TheIGBTswitchesinthehigh‐voltagetankwerefoundtoenterthermalrunawaywhentheprototypeconverterisoperatedatlow‐powerlevelsininverter(HVDCtoAC)mode.Investigationhasdeterminedthattheseswitchesdonotperforminaccordancewiththemanufacturer’sspecifications.Consultationswiththemanufacturerhasnotproducedanacceptableremedy,andPPShasconcludedthattheseIGBTscannotbeusedforthisapplication.PPShasidentifiedalternateIGBTsthatmeetthetechnicalandeconomiccriteriaofthisproject,andisproceedingtoupgradetheconverterswiththeseswitches.Becausetheswitchesoperateatadifferentvoltagethantheoriginalswitchesandhaveadifferentformfactor,redesignofthehigh‐voltagestageboardsisnecessary.
Becauseofthehardwareproblemsidentified,PPShasnotyetcompletedconvertertesting.FinaltestingispendingreceiptofnewIGBTs.
FigureF‐3showsasimplifiedschematicillustratingthecurrentdevelopmentstatusoftheconverter’sbasicfunctionalmodes.
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Figure F-3 Simplified Schematic Illustrating Technical Progress
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APPENDIXFATTACHMENTS
AttachmentF‐1:PPSHVDCPowerConverterReport
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APPENDIXG
HVDCSYSTEMPROTECTION,CONTROLS,ANDCOMMUNICATIONS
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TABLEOFCONTENTS
G.1 INTRODUCTION........................................................................................................................................................7 G.1.1 POINT‐TO‐POINTSYSTEMS.............................................................................................................................................7 G.1.2 MULTITERMINALHVDC(MTDC)SYSTEMS...............................................................................................................7
G.2 PROTECTIVEHARDWARE...................................................................................................................................7
G.3 COMMUNICATIONS.................................................................................................................................................7 G.3.1 FAULTDETECTION............................................................................................................................................................8 G.3.2 INFRASTRUCTURE..............................................................................................................................................................8
G.4 OVERHEADINTERTIECOMMUNICATIONOPTIONS................................................................................9 G.4.1 OPTICALGROUNDWIRE..................................................................................................................................................9 G.4.2 POWERLINECARRIER......................................................................................................................................................9 G.4.3 WRAPPEDFIBER‐OPTICCABLE......................................................................................................................................9 G.4.4 SEPARATETELECOMUNDERBUILD................................................................................................................................9
G.5 UNDERGROUNDCABLEINTERTIEOPTIONS..............................................................................................9
G.6 SUBMARINECABLEINTERTIEOPTIONS....................................................................................................10
G.7 BROADBANDINTEGRATION............................................................................................................................10
APPENDIXGATTACHMENTS...........................................................................................................................................11 ATTACHMENTG‐1:MHRCTASK3,HVDCSTATIONHARDWARERECOMMENDATIONS..................................................11 ATTACHMENTG‐2:MHRCTASK2,MULTI‐TERMINALHVDCTECHNICALREVIEW........................................................25 ATTACHMENTG‐3:MHRCTASK5,CARRIERCOMMUNICATIONS........................................................................................45
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LISTOFTABLES
TableG‐1 CommunicationsOptionswithHVDCInterties.........................................................................G‐8
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G.1 INTRODUCTION
Thisappendixdiscusseselectricalprotection,controls,andcommunicationsrequirementsneededtooperatethehigh‐voltagedirectcurrent(HVDC)systemsdiscussedinthisreport.Therearecertainminimumprotection,control,andcommunicationprovisionsrequiredofanyHVDCsystem.
Initssimplestform,theprotection,controls,andcommunicationsprovisionsmaybemanuallyoperated.Thisapproachissimplertomanageandlesscostlytoinstallandmaintainthanfullyautomatedsystems,butisgenerallylimitedtopoint‐to‐pointinterties.
Theprotection,controls,andcommunicationsneedsofmorecomplexmultiterminalHVDC(MTDC)systemsrequirestheuseofautomatedcontrolsforoperation.Therequirementforautomatedcapabilitiesaremorecostlyandcomplicatedtooperate.
G.1.1 Point‐to‐PointSystems
ManyruralHVDCintertiesmaybenefitfromapoint‐to‐pointHVDCsystem.Low‐power(<1MW)point‐to‐pointmonopolarHVDCsystemscanautomaticallyregulatepowerflowovertheHVDCsystembymonitoringtheHVDCvoltage.Nocommunicationsbetweentheconvertersareneededtoachievethisbasicpowertransferfunction.Existingcommercialtelecommunicationsnetworksinthecommunitiescanbeusedtoprovidesomedegreeofmonitoringandcontrolfunction.
G.1.2 MultiterminalHVDC(MTDC)Systems
MTDCnetworksbydefinitionhavemorethantwoHVDCconverterstationsconnectedtoagivenHVDCline.EachoftheconverterstationsiscapableofaddingorsubtractingpowerfromtheHVDCline.
MTDCnetworksareprojectedtobethelowestcostintertiesolutionformanyoftheruralenergynetworksunderconsideration.Theseregionsincludeinterconnectionofseveralsoutheastcommunities,theadjacentcommunitiesintheYukon‐KuskokwimDelta,andothersintheBristolBayarea.Accordingly,thetechnicalfeasibilityofMTDCnetworksisofparticularinterestforAlaska’sutilityindustry.
G.2 PROTECTIVEHARDWARE
RecommendationspreparedbytheManitobaHVDCResearchCentre(MHRC)discussthegeneralDC‐sideHVDCconverterstationhardwarenecessaryforbasicoperationandprotectionoftheHVDCsystem.ThisinformationispresentedinAttachmentG‐1tothisappendixandistitled“TechnicalNoteonHVDCStationHardware.”
ProtectiveAC‐sidehardwarewillincludefusesorbreakers,disconnects,andcontrolsasneededtointegratewiththelocalgeneratingplant.Project‐specificdesignisnecessaryastheseinterfacescanrangefrombasicandmanuallyoperatedtohighlyintegratedandautomated,dependingontheneedsoftheparticularapplication.ThepowerconvertersdevelopedbyPPSsupportstandardcommunicationprotocolstoallowintegrationwithoverallcontrolsystems.
G.3 COMMUNICATIONS
Communicationsareusedformonitoringofconverterstationstatus,economicdispatchofdistributedgenerationassets,faultdetectionontheHVDCnetwork,andrelatedutilityfunctions.Systemsoftenincludededicatedvoiceanddatacircuitstofacilitatecommunicationsbetweendifferentpartsoftheutilitytransmissionnetwork.
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G.3.1 FaultDetection
WithoutdifferentialcurrentmonitoringbetweentheHVDCconverterstations,ifthetotalcurrentintotheHVDCsystem(faultcurrent+loadcurrent)islessthantheratedsystemcurrent(20amperesfora1‐MWintertie),therectifyingconverterwillnotbeabletodistinguishthefaultloadfromanormalloadandwillcontinuetoinputpowerintotheHVDClinetomaintaintheHVDCvoltage.Ifthefaultcurrentishighenoughtoexceedthecapacityoftherectifyingconverter,thentheconverterwilltripandannounceafault.
Theresultisthatalowimpedancefaultcangenerallybedetectedbytheanomalouslyhighpowerdraw,whereasahighimpedancefaultcanremainundetectedindefinitelywiththisscheme.Timelydetectionandcorrectionisthereforedesirablewherepractical.
ACsystemsexperiencesimilarproblemsdetectinghighimpedancefaults,sothistypeofriskisnotwithoutprecedentonutilitysystems.Theremotenessandlackofpeopleinthevicinityofthesetransmissionlinesisafactorthatshouldbeconsideredwhenutilitiesevaluatethisrisk.Aproject‐specificanalysisshouldbeconductedforeveryintertietoevaluatethecostoffaultdetectioncapabilitiesagainsttherisksassociatedwithundetectedfaults.
Detectionofpersistenthighimpedancefaultsrequires,ataminimum,slow‐speedcommunicationbetweentheconverterstationsanddifferentialcurrentmonitoring.Ifthefaultimpedanceissohighthatthefaultcurrentisbelowtheerrorofthedifferentialcurrentdetectionmethod(ascouldbethecaseforadownedconductorlyingonice,forexample),thefaultmayremainunnoticedevenwiththisdetectionregimeinplace.Theonlypracticalwaytoidentifysuchfaultsisbyphysicalinspectionoftheintertieline.FaultdetectionisdiscussedintheMHRCTechnicalNoteonHVDCStationHardwareRecommendationsincludedasAttachmentG‐1tothisappendix.
G.3.2 Infrastructure
AllremoteAlaskacommunitieshaveaccesstobasictelephoneserviceandbroadbandinternetservice.Ataminimum,theseservicesareprovidedthroughgeosynchronoussatelliteplatforms.Dependingontheprojectlocation,communitiesmaybeservedbyexistingmicrowaverelaysystems,copperwirenetworks,fiber‐opticnetworks,oracombinationofthese.
Theslowestcommunicationoptionavailablestatewideisgeosynchronoussatellite‐basedcommunicationswithaninherentlatencyofatleast250millisecondsforone‐waycommunications.Thislatencyarisesfromthetraveltimeforasignaltoreachtheorbitingsatelliteandreturntoearth.SignalprocessingattheEarthstationsoraboardthesatelliteaddtothislatency.
Thiscommunicationsmethodwouldbesufficientforabasicdifferentialcurrentmonitoringprotocolandforcertainsupervisorycontrolanddataacquisition(SCADA)functionsforanHVDCintertie.
Optionsforintegrateddedicatedcommunicationscircuitsarediscussedin‘TechnicalNoteonCarrierCommunications,”preparedbyMHRC,includedasAttachmentG‐3tothisappendix.
Thecost‐effectivenessofsuchoptionswilldependonthetypeofHVDCintertie,andonthespecificconfigurationoftheHVDCline.TableG‐1summarizesthethreebasicHVDCintertieconfigurationsandpotentiallysuitablecommunicationstechnologiesforeach.
Table G-1 Communications Options with HVDC Interties
Intertie Type Communications Option
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Overhead Conductor Optical Ground Wire (OPGW) Carrier
Wrapped fiber-optic cable Separate telecom underbuild
Underground Cable Separate fiber-optic cable in same trench Fiber-optic circuit bundled into power cable
Submarine Cable Fiber-optic cable in conductor tube Fiber-optic cable in armor strand
G.4 OVERHEADINTERTIECOMMUNICATIONOPTIONS
G.4.1 OpticalGroundWire
Opticalgroundwire(OPGW)isatypeofelectricalconductorthathasaluminumconductorstrandssurroundingastainless‐steeltubeattheconductor’score.Opticalfibersareroutedthroughthestainless‐steeltube.OPGWiscommonlyusedasanoverheadgroundingwireonACtransmissiontowersforlightningprotection.
Dependingontheapplication,OPGWmaybesuitableforuseasthecurrent‐carryingconductoronanHVDCtransmissionline.Onepotentiallysignificantdrawbackwouldbetheincreasedcomplexityofrepairingconductorbreaksduetothestainless‐steeltubeandopticalfibers.Theneedforspeciallytrainedpersonnelandequipmenttorepairthistypeofconductorcouldsignificantlydelaytherepairofaconductorbreak,reducingthereliabilityofthetransmissionline.
TheMHRCTechnicalNoteincludedasAttachmentG‐3tothisappendixdiscussesOPGWapplicationsinmoredetail.
G.4.2 PowerLineCarrier
Powerlinecarrier(PLC)isameansofusingacurrent‐carryingconductorinanintertiecircuittocarryadatasignalaswell.Acoilisusedtomagneticallyinduceadatawaveformontotheconductor,andasecondcoilisusedtoreceivethewaveform.PLCsystemshavebeenimplementedonHVDCcircuitsandarediscussedintheMHRCTechnicalNoteinAttachmentG‐3.
G.4.3 WrappedFiber‐OpticCable
Opticalfiberpackagesareavailablethatcanbewrappedoveramessengerwire,suchasthepowerconductor.Therearetwopotentialdrawbackswiththisoption.Thefirstisthattheopticalfibercablewouldincreasethewindexposureandicingsurfaceoftheconductor,increasingenvironmentalloadingsontheoverheadsystem.Thesecondisthatthepresenceoftheopticalfibercablewouldcomplicatetherepairofbrokenconductors.
G.4.4 SeparateTelecomUnderbuild
DependingonthetypeofoverheadlineconstructionusedfortheHVDCintertieline,aconventionaltelecommunicationsunderbuildmaybeappropriate.Thiscouldusefiberorcopperdependingonthespecificcircumstances.
G.5 UNDERGROUNDCABLEINTERTIEOPTIONS
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ThemoststraightforwardmeansofaddingcommunicationstoanundergroundcableHVDCintertieistoincludeaseparatefiber‐opticorcoppercable.Fiberopticswouldbepreferredifasingle‐wireearthreturn(SWER)circuitisused,asitwouldnotpickupthereturncurrent.Conventionaldesignandconstructionpracticesaresuitableforinstallationofco‐locatedundergroundcommunicationandpowercables.
G.6 SUBMARINECABLEINTERTIEOPTIONS
Therearethreegeneraloptionsforbundlingtelecommunicationswithsubmarinepowercables.Allthreeutilizefiberoptics,andareacceptedpracticeforsubmarinepowerand/ortelecommunicationcables.Thesemethodsare:
● Replacingoneormoreofthearmorwiresonthesubmarinecablewithahollowstainless‐steeltubeandroutingopticalfibersthroughthetube(s).
● Utilizingahollowcoppertubeasthecurrent‐carryingconductorandroutingopticalfiberswithinthecoppertube.Thisisacommoncableconstructionontransoceanicfiber‐opticcables.
● Insertingastainless‐steeltubebetweentwolayersofthesubmarinecable,typicallybetweentheleadsheath(ifsoequipped)andthepolyethyleneoutercablejacket.Opticalfibersareroutedthroughthistube.
G.7 BROADBANDINTEGRATION
ThereisanopportunitytointegratebroadbandcommunicationswithcertainHVDCintertieprojects.Wherefeasible,combiningpowerandtelecommunicationsconnectivityintoasingleprojectcansignificantlyincreasethebenefitsofanintertieprojectanddeliverbothcapabilitiesatalowercostthanpossiblethroughindividualprojects.
Thisopportunityisparticularlypromisingforundergroundandsubmarinecableapplications.Inmanyapplications,theincrementalcostofincludingafiberopticbundlewitheitherpowercableisexpectedtobemodestcomparedtotheresultingbenefits.AttachmentD‐1discussesthisopportunityinthecontextofsubmarinecables.
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APPENDIXGATTACHMENTS
AttachmentG‐1:MHRCTask3,HVDCStationHardwareRecommendations
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AttachmentG‐2:MHRCTask2,Multi‐TerminalHVDCTechnicalReview
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AttachmentG‐3:MHRCTask5,CarrierCommunications
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APPENDIXH
CANDIDATEHVDCSYSTEMDEMONSTRATIONPROJECTS
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TABLEOFCONTENTS
H.1 INTRODUCTION........................................................................................................................................................7
H.2 DEMONSTRATIONPROJECTOBJECTIVES.....................................................................................................7
H.3 CRITERIAFORDEMONSTRATIONPROJECTSITES...................................................................................8
H.4 POTENTIALDEMONSTRATIONPROJECTS.................................................................................................10 H.4.1 SUMMARYOFPROJECTSCONSIDERED.........................................................................................................................10 H.4.2 HVDCDEMONSTRATIONPROJECTSONEXISTINGACDISTRIBUTIONLINES.......................................................12
H.4.2.1 DillinghamtoAleknagikACLineConversion(DemonstrationOnly)...............................12 H.4.2.2 EurekaACLineConversion(DemonstrationOnly)..................................................................12 H.4.2.3 HopeSubstationtoHopeACLineConversion(DemonstrationOnly).............................12 H.4.2.4 Homer–SeldoviaACLineConversion(DemonstrationOnly)............................................13
H.4.3 HVDCDEMONSTRATIONPROJECTSONNEWACDISTRIBUTIONLINEEXTENSIONS.........................................13 H.4.3.1 GVEAPhillipsRoadLineExtension..................................................................................................14 H.4.3.2 GVEACummingsRoadLineExtension...........................................................................................14 H.4.3.3 MEAtoIndependenceMineLineExtension.................................................................................14
H.4.4 HVDCINTERTIEPROJECTS...........................................................................................................................................15 H.4.4.1 BarrowtoAtqasukHVDCIntertie.....................................................................................................15 H.4.4.2 NometoTellerandBrevigMissionHVDCIntertie....................................................................15 H.4.4.3 PilgrimHotSpringstoNomeHVDCIntertie................................................................................15 H.4.4.4 St.Michaels–StebbinsHVDCIntertie.............................................................................................16 H.4.4.5 St.Mary’stoMountainVillageHVDCIntertie..............................................................................16 H.4.4.6 DillinghamtoManokotakHVDCIntertie.......................................................................................16 H.4.4.7 NewStuyahok–EkwokHVDCIntertie...........................................................................................16 H.4.4.8 Kodiak–OuzinkieHVDCIntertie......................................................................................................16 H.4.4.9 Green’sCreektoHoonahHVDCIntertie........................................................................................17 H.4.4.10 PetersburgtoKakeHVDCIntertie....................................................................................................17 H.4.4.11 GustavustoGlacierBayNationalParkIntertie(HVDCDemonstrationOnly)..............17
H.4.5 PROJECTMAPS.................................................................................................................................................................18
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LISTOFTABLES
TableH‐1 TypesofHVDCDemonstrationProjectsandFactorsforEach................................................9
TableH‐2 PotentialHVDCDemonstrationProjects........................................................................................10
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LISTOFFIGURES
FigureH‐1 LocationMapforPotentialDemonstrationProjectSites........................................................11
FigureH‐2 VicinityMapforDemonstrationProjectsnearDillingham.....................................................18
FigureH‐3 VicinityMapforEurekaACLineConversion................................................................................19
FigureH‐4 VicinityMapforHopeACLineConversion...................................................................................20
FigureH‐5 VicinityMapforSeldoviaACLineConversion.............................................................................21
FigureH‐6 VicinityMapforDeltaJunctionACLineExtension....................................................................22
FigureH‐7 VicinityMapforDeltanaACLineExtension.................................................................................23
FigureH‐8 VicinityMapforIndependenceMineACLineExtension.........................................................24
FigureH‐9 VicinityMapforBarrow–AtqasukHVDCIntertie.....................................................................25
FigureH‐10 VicinityMapforDemonstrationProjectsnearNome...............................................................26
FigureH‐11 VicinityMapforSt.Michaels–StebbinsHVDCIntertie...........................................................27
FigureH‐12 VicinityMapforSt.Mary’s–MountainVillageHVDCIntertie..............................................28
FigureH‐13 VicinityMapforNewStuyahok–EkwokHVDCIntertie..........................................................29
FigureH‐14 VicinityMapforKodiak–OuzinkieHVDCIntertie.....................................................................30
FigureH‐15 VicinityMapforGustavusandHoonahHVDCInterties...........................................................31
FigureH‐16 VicinityMapforKake–PetersburgHVDCIntertie....................................................................31
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H.1 INTRODUCTION
Thisreportincludestheevaluationofpotentialprojectsfordemonstrationofthehigh‐voltagedirectcurrent(HVDC)technologyinPhaseIII.Thiseffortconsistedofthefollowingmajoractivities:
● Definingtheprimaryobjectivesofademonstrationproject;
● Definingthekeycriteriaforcandidateprojects;
● Identifyingpotentialintertieprojects;
● Contactinglocalstakeholderstogatherinformationaboutthoseprojects;and
● EvaluatingtheprojectsforsuitabilityasademonstrationofthisHVDCtechnology.
Thisappendixsummarizesandpresentsthefindingsfromtheseactivities.Aspecificsitehasnotbeenselectedforademonstrationprojectatthistime.Polarconsultwillcontinuetoworkwiththevariousprojectstakeholderstoidentifyaspecificdemonstrationprojectinthefuture.
H.2 DEMONSTRATIONPROJECTOBJECTIVES
PolarconsultworkedwiththeStakeholder’sAdvisoryGroup(SAG),individualstakeholders,Polarconsultsubcontractors,andotherinterestedentitiesoverthecourseofPhaseIItorefinetheobjectivesofthePhaseIIIdemonstrationprojectfortheproposedHVDCsystem.
Definingtheseobjectiveswasamajortopicofdiscussionatthe2ndSAGMeeting,heldinAnchorageonJanuary14,2011.AseriesofconferencecallswereheldwithmembersoftheSAGinJanuaryandFebruary2011torefinetheobjectivesofthedemonstrationprojectandthecandidatesitesidentifiedbyPolarconsult.
Theseeffortsestablishedthefollowingaskeyobjectivesofthedemonstrationproject:
● FacilitateexpeditiousadvancementoftheproposedHVDCsystem.Ademonstrationprojectthatcannotbeimplementedforyearsduetoprohibitivecost,regulatoryimpediments,orsimilarfactorscouldundulydelaycommercialacceptanceofthesystemandwidespreaddeploymentinAlaska.
● Demonstratetostakeholders(Alaskautilities,policymakers,regulators,etc.)thattheHVDCconverterisfunctional,robust,andpracticalunderthelogistical,electrical,andenvironmentaloperatingconditionstypicalofruralAlaskaapplications.
● Demonstratethatinnovativeaspectsofthetransmissionlineconstruction,suchasuseofsingle‐wireearthreturn(SWER)circuitsinpermafrostregions,newoverheadlinedesignsormaterials,andsimilarsystemelementsarereliable,cost‐effective,andappropriateforruralAlaskaintertieapplications.
OneofthekeyinsightsprovidedbytheSAGwasthatthecommercializationplanfortheproposedsystem,includingthedemonstrationphase,shouldbedesignedinameasuredmannerthatincrementallydemonstratesandprovesupthevarioustechnicalaspectsofthesystem.Itwassuggestedthatasingleoverlyambitiousdemonstrationprojectthatfeaturesseveralinnovativetechnologiesincreasestheriskthatanyonenoncriticaltechnicalfailuremaybecomeinterpretedasafailureoftheoverallsystem.
ThegoalofPhaseIIIwillincludefulltestingoftheconvertersystem,includingthemanufacturerandthird‐partyfunctional,compliance,andperformancetestingneededtomovetheconvertertechnology
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fromadvancedprototypestoacommercialproduct.PhaseIIIwillalsoincludeafullscalefielddemonstrationoftheHVDCtechnologyonautilitysysteminAlaska.Thespecificprojectdetailsaredependantonthecandidatelocationselectedfortheintertie.PhaseIIIisintendedtobethefinalproof‐of‐conceptproject,tobefollowedbycommercialdeploymentofthesystem.
H.3 CRITERIAFORDEMONSTRATIONPROJECTSITES
PhaseIIIdemonstrationswillpresentafullyfunctionalreal‐worldHVDCtransmissionlineusingtheconvertertechnologydevelopedinthisproject.AvailableinventoriesofAlaskaintertiecandidatesarepresentedinDistributingAlaska’sPower(WHPacific,2008)andRuralAlaskaElectricUtilityIntertiesSurvey(Neubauer,1997).
Polarconsultconductedanextensivereviewofpotentialcandidatedemonstrationprojects,startingfromtheseresourcesandothercurrentinformation.Theresultinglistofpotentialdemonstrationprojectsisnotcomprehensive,astherearenumerousopportunitiesforruralAlaskapowerinterties,butitdoesprovidearepresentativeselectionofgeographicandtechnicalcriteriafordemonstrationsites.Threetypesofdemonstrationprojectswereconsidered,listedbelow.KeyfactorsaboutthesuitabilityofthesetypesofprojectsaresummarizedinTableH‐1.
1. NewRuralAlaskaHVDCIntertie.ThisoptionwouldbeafullyfunctionalHVDCintertiedemonstration.ItwouldconsistofbuildinganewintertiebetweentwoAlaskavillages,orpossiblybetweenalargergridandavillage.
2. NewACDistributionLineExtensionOperatedasHVDCforTrialPeriod.Thisoptionwouldbeanewalternatingcurrent(AC)distributionlineextensionfromanexistingsystemtoanewarea.ThelineextensionwouldbeoperatedasanHVDClineforthedemonstrationperiod,andthenconvertedtoACafterthedemonstrationprojectconcluded.
3. ExistingACDistributionLineExtension,ConvertedtoHVDCforDemonstrationThenSwitchedBacktoAC.ThisoptionwouldconvertanexistingACdistributionlinetoHVDCforthedemonstrationproject.ThelinewouldbeconvertedbacktoACafterthedemonstrationprojectconcluded.
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Table H-1 Types of HVDC Demonstration Projects and Factors for Each
Projects
Factors
Permanent HVDC Intertie Between Two Alaska
Villages
(Operate as HVDC)
AC Distribution System Extension
(Operate as HVDC, then convert to AC)
Existing AC Distribution Line
(Convert to HVDC, then revert to AC)
Function Intertie limited to power transmission (no services along intertie route)
Power Capacity
Peak load limited to 500 kW (to utilize existing prototype converters)
Cost & Length Intertie length of 10+ miles
to achieve cost savings over an AC intertie
Minimize intertie length (to maintain affordable budget and help avoid funding delays)
Schedule
3 to 5+ years
Requires (design, permitting, right-of-way,
funding, etc.)
1-3+ years
(May require right-of-way acquisition, design, permitting,
funding, etc.)
+/- 1 year
(Existing right-of-way, should require fewer permits and design,
funding, etc.)
Benefits
1. HVDC demonstration.
2. New intertie lowers utility costs to both communities.
1. HVDC demonstration.
2. Utility/public receive an AC line extension.
1. HVDC demonstration only. Hosting utility incurs costs and customers incur
service interruptions.
Organizational Complexity
Two utilities involved, may require RCA involvement and regulatory oversight.
Single utility involvement (to reduce interconnection or
regulatory issues).
Single utility involvement (to reduce interconnection or
regulatory issues).
Technical
Intertie connections at 480-V bus of existing
power plants.
Intertie connections at distribution voltage. Step
up/down transformers required.
Intertie connections at distribution voltage. Step
up/down transformers required.
kW:kilowatt
RCA:RegulatoryCommissionofAlaska
V:volt
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H.4 POTENTIALDEMONSTRATIONPROJECTS
H.4.1 SummaryofProjectsConsidered
TheintertiesprojectsreviewedbyPolarconsultarelistedbycategoryinTableH‐2andshownonFigureH‐1.Moredetailedinformationandpreliminarymapsofpotentialintertieroutesareprovidedonthefollowingpages.
Table H-2 Potential HVDC Demonstration Projects
RuralAlaskaMicrogrids MajorAlaskaGrids
New HVDC Intertie
Build as HVDC; keep as HVDC after demonstration.
Barrow – Atqasuk (NSB) Pilgrim Hot Springs – Nome (NJUS)St. Mary’s – Mountain Village – Pilot
Station (AVEC) Dillingham – Manokotak (NEC) New Stukahok – Ekwok (AVEC) Kodiak – Ouzinkie (KEA - OED)
Kake – Petersburg (IPEC/SEAPA)
Hoonah – Green’s Creek (IPEC/ AEL&P)
AC Line Extension
Build as HVDC; convert to AC after demonstration.
Gustavus – Glacier Bay Nat’l Park (GEC)
Delta Junction (GVEA) Deltana (GVEA)
Independence Mine (MEA)
Existing AC Line Demonstration
Convert to HVDC; revert to AC after demonstration.
Dillingham – Aleknagik (NEC) Glennallen – Eureka (CVEA) Canyon Creek – Hope (CEA)
Homer – Seldovia (HEA)
AcronymsandAbbreviations:
NEC NushagakElectricCooperative,Inc.
NSB NorthSlopeBorough
NJUS NomeJointUtilityService
IPEC InsidePassageElectricCooperative,Inc.
SEAPA SoutheastAlaskaPowerAgency
GEC GustavusElectricCompany
AVEC AlaskaVillageelectricCooperative,Inc.
CEA ChugachElectricAssociation,Inc.
HEA HomerElectricAssociation,Inc.
CVEA CopperValleyElectricAssociation,Inc.
KEA KodiakElectricAssociation,Inc.
OED CityofOuzinkieElectricDepartment
MEA MatanuskaElectricAssociation,Inc.
GVEA GoldenValleyElectricAssociation,Inc.
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Figure H-1 Location Map for Potential Demonstration Project Sites
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H.4.2 HVDCDemonstrationProjectsonExistingACDistributionLines
ThissectionprovidesoverviewsofpotentialHVDCdemonstrationprojectsthatwouldbeimplementedonexistingACdistributionlines.TheAClinewouldbeconvertedtoHVDCserviceforthedemonstrationproject,andaftertheHVDCdemonstrationiscompleted,thelinewouldberevertedtoACservice.Thecandidateintertiesareorganizedgeographically,movingfromnorthwesttosoutheast.
H.4.2.1 DillinghamtoAleknagikACLineConversion(DemonstrationOnly)
Thisisanexisting,approximately25‐mile‐long,three‐phaseACintertiethatprovideselectricservicetoAleknagikfromNushagakElectricCooperative’sdieselgeneratorsinDillingham(FigureH‐2).ThelineisunderstoodtobeofstandardRuralUtilitiesService(RUS)construction,insulatedto34.5kilovolts(kV)butoperatedasa7.2/12.4‐kVintertie.ThisexistinglinewouldbeconvertedtoHVDCoperationforademonstrationperiod,andthenrevertedtonormalACoperationafterthedemonstrationiscompleted.
TheloadinAleknagikisnotknown.Ifitexceeds500kilovolt‐amperes(kVA),theneitheradditionalintertiecapacityordieselgeneratorsinAleknagikwouldberequired.
Theexistinginsulatorsontheintertieshouldbesufficientforserviceat50kVDC.Becausethelineisinsulatedat34.5kV(approximatelyequalto60kVDC),theremaybeissueswithbuildupofcontaminationunderastaticDCelectricfieldleadingtoarcingovertheinsulators.Ifthisbecameanissue,theinsulatorswouldneedtobecleaned.AnalysisiswarrantedtoseeiftheHVDCintertievoltageshouldbereducedtoavoidthisproblem.VoltagereductionwouldalsodecreasethepowerthroughputcapabilityoftheHVDCconverters.
H.4.2.2 EurekaACLineConversion(DemonstrationOnly)
Thisisanexisting,approximately50‐mile‐long,single‐phase,14.4‐kVdistributionlineownedandoperatedbyCopperValleyElectricAssociation,Inc.(CVEA)servingthecommunitiesandresidentswestofGlennallen,Alaska(FigureH‐3).ThedemonstrationprojectwouldconsistofconvertingasegmentofthislinetoHVDCoperationforthedemonstrationperiod,thenconvertingitbacktoACoperation.
ThegeotechnicalconditionsalongthislinearebelievedtobefavorablefortestingaSWERconfigurationinpermafrostsoilsalthoughanappropriatelinesegmentwouldneedtobeidentifiedforSWERoperation.
ThepeakloadontheHVDCsegmentofthelinewoulddependonwherethedemonstrationwouldtakeplacealongtheline.Apeakloadof167kVAorlesswouldbepreferredtoallowuseofthe500‐kVAprototypeconverters.
PreliminarydiscussionswereheldwithCVEAinFebruary2011regardingthisdemonstrationproject.Aspecificsitewasnotidentified,butCVEAwasgenerallysupportiveofhostingtheHVDCdemonstrationproject,providedthatitdidnotdamageutilityassetsornegativelyimpactcustomersandwasrevenue‐neutraltotheutility(Botulinski,privateconversation,2011).
H.4.2.3 HopeSubstationtoHopeACLineConversion(DemonstrationOnly)
Thisisanexisting,approximately20‐mile‐long,singlephase,14.4‐kVdistributionlineownedandoperatedbyChugachElectricAssociation,Inc.(CEA)servingthecommunityofHopeonTurnagainArmnearAnchorage(FigureH‐4).Hopehasapeakloadofapproximately300kilowatts(kW).CEAisplanningamultipartupgradeofthislinetoaddressreliabilityissues.Thefirstpartofthisupgradeprojectwouldrebuildandrelocateapproximately4milesoftheintertiestartingattheHopeSubstationneartheHope
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JunctionontheSewardHighway.CEAestimatesthatthisprojectwouldbereadyforconstructionin2013(Jenkins,privateconversation,2011).Thedemonstrationprojectwouldcoordinatewiththelineupgrade.
Thedemonstrationprojectwouldrequiretransformersoneitherendofthedemonstrationsegmenttoconvertbetween14.4kVandthe480‐VACinterfaceofthepowerconverters.Inaddition,becausethe14.4‐kVlineissinglephase,theconvertercapacitywouldbereducedbyapproximately1/3to167kVA.ThiscouldbeaddressedeitherwithincreasedconvertercapacityoroccasionaloperationoftheexistingdieselgeneratorinHopetomeetpeakloads.
CEAissupportiveofhostingtheHVDCdemonstrationproject,providedthatitdidnotdamageutilityassetsornegativelyimpactcustomersandwasrevenue‐neutraltotheutility.Whilethisintertieappearstechnicallyfeasible,lesscomplicatedHVDCdemonstrationprojectslikelyexistwithinthestate.
H.4.2.4 Homer–SeldoviaACLineConversion(DemonstrationOnly)
ThisisanexistingdistributionlineownedandoperatedbyHomerElectricAssociation,Inc.(HEA),servingthecommunitiesonthesouthsideofKatchemakBayfromHalibutCovetoSeldovia.Thelineisthree‐phase,24.9‐kVACstartinginHomer.ItcrossesKatchemakBaywitha4.5‐mile‐longcableinstalledin2001,andthencontinuesasanoverheadlinetothesouthbaycommunities(FigureH‐5).TheoverheadlineisacombinationofconventionalRUSconstructionandtreecable.Loadonthisdistributioncircuitisapproximately1,100kVA(McDonough,privateconversation,2011).
TheconceptforthisdemonstrationprojectwouldbetooperatetheexistingsubmarinecableasanHVDCcableforthedemonstrationproject.Therearetwochallengeswiththisconcept:
1. Thepeakloadonthecircuitisapproximatelytwicethecapacityoftheprototypeconverters.ThiswillrequireloadsharingbetweenHEAthroughtheHVDClinkanddieselsonthesouthsideofthecable.Thisisnotatechnicalchallenge;however,itwillresultinsignificantcoststhatthedemonstrationprojectbudgetwouldneedtoabsorb.500kWofcontinuousdieselgenerationfora6‐monthdemonstrationperiodwouldcostapproximately$700,000.Abetteralternativeatthispricemaybetobuildtwomore500kWconvertermodules,increasingtheHVDCintertiecapacityto1,000kW.
2. Theexistingsubmarinecableisonlyratedfor24.9kVAC.Thisisapproximatelyequalto43kVDC,lessthanthenominalHVDCsystemvoltageof50kV.Twopossibleremediesexistforthis.IfHEAcanbeassuredthatthecablewilloperateat50kVDCwithoutilleffect,thenthedemonstrationprojectcouldproceed.GiventhatcablesaretypicallysubjectedtoDCvoltagesontheorderof50to100kVduringacceptancetests,itseemslikelythatthiswouldbepossible.Thenatureoftheseassuranceshasnotbeendefined.ThesecondremedyistodecreasetheoperatingvoltageoftheHVDCintertie.PPShasindicatedthattheconvertersoftwarecanbeprogrammedtoreducetheDCvoltage;however,thiswilldecreasethepowerratingoftheconverters.Loweringthevoltagefrom50to40kVwouldlowerthepowerratingofaconvertermodulefromapproximately500to400kVA.
HEAissupportiveofhostingtheHVDCdemonstrationproject,providedthatitdidnotdamageutilityassetsornegativelyimpactcustomersandwasrevenue‐neutraltotheutility.Whilethisintertieappearstechnicallyfeasible,lesscomplicatedHVDCdemonstrationprojectslikelyexistwithinthestate.
H.4.3 HVDCDemonstrationProjectsonNewACDistributionLineExtensions
ThissectionprovidesoverviewsofpotentialHVDCdemonstrationprojectsthatwouldbeimplementedonpurpose‐builtACdistributionlineextensions.AftertheHVDCdemonstrationiscompleted,thelinewouldbeconvertedtoACserviceandwouldbealastingbenefittotheutilityandnewlyservedcustomers.Thecandidateintertiesareorganizedgeographically,movingnorthwesttosoutheast.
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H.4.3.1 GVEAPhillipsRoadLineExtension
Thisprojectwouldbeanapproximately1.75‐milesingle‐phaseoverheaddistributionextensiontoserveseveralresidencesattheendofPhillipsRoadinDeltaJunction,withintheGoldenValleyElectricAssociation,Inc.(GVEA)servicearea(FigureH‐6).ThelineextensionwouldbebuiltasastandardACdistributionline,operatedasanHVDCintertiefordemonstrationpurposes,andthenturnedovertoGVEAforsubsequentoperationasanACdistributionline.
GVEAandtheresidencesattheendofthelinewouldbothlikelycontributefundsorin‐kindservicestothelineextension.Totalcontributionisestimatedat$50,000,andthelinebuild,excludinganycostsassociatedwiththeHVDCdemonstration,isbudgetedat$140,000.Aright‐of‐waywouldneedtobeobtainedfortheproject,whichwouldtakeanestimated6to12months.
TheprojectislocatedincloseproximitytotheTrans‐AlaskaPipelineSystem,andassuchwouldlikelynotbesuitablefordemonstrationofSWERoperation.Thepeakloadoftheresidencesattheendofthelineislikelylessthantheapproximately167‐kVAcapacityofthe500‐kWprototypeconvertersinsingle‐phaseoperation.
GVEAisverysupportiveofhostingtheHVDCdemonstrationproject,providedthatitdidnotdamageutilityassetsornegativelyimpactcustomersandwasrevenue‐neutraltotheutility,beyondthein‐kindconstructioncontributionsthatGVEAofferedforthelineextension(Wright,privateconversation,2011).
H.4.3.2 GVEACummingsRoadLineExtension
Thisprojectwouldbeanapproximately4‐to6‐milesingle‐phaseoverheaddistributionextensiontoserveseveralresidencesattheendofCummingsRoadinDeltana,withintheGVEAservicearea(FigureH‐7).ThelineextensionwouldbebuiltasastandardACdistributionline,operatedasanHVDCintertiefordemonstrationpurposes,andthenturnedovertoGVEAforsubsequentoperationasanACdistributionline.
GVEAandtheresidencesattheendofthelinewouldbothlikelycontributefundsorin‐kindservicestothelineextension.Totalcontributionisestimatedat$60,000,andthelinebuild,excludinganycostsassociatedwiththeHVDCdemonstration,isbudgetedat$560,000.Aright‐of‐waywouldneedtobeobtainedfortheproject,whichwouldtakeanestimated6to12months.
Thepeakloadoftheresidencesattheendofthelineislikelylessthantheapproximately167‐kVAcapacityofthe500‐kWprototypeconvertersinsingle‐phaseoperation.
GVEAisverysupportiveofhostingtheHVDCdemonstrationproject,providedthatitdidnotdamageutilityassetsornegativelyimpactcustomersandwasrevenue‐neutraltotheutility,beyondthein‐kindconstructioncontributionsthatGVEAofferedforthelineextension(Wright,2011).
H.4.3.3 MEAtoIndependenceMineLineExtension
Thisprojectwouldbeanapproximately5.5‐mileundergroundACdistributionlinefromtheendofMatanuskaElectricAssociation,Inc.(MEA)’sexistingHatcherPassdistributionlineuptotheIndependenceMineStateHistoricalPark(StatePark)(FigureH‐8).ThelinewouldbebuiltasanACdistributionfeeder,operatedasanHVDClineforthedemonstrationproject,andthenrevertedtoACoperation.
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Easementsforthefirstapproximately2milesofthelineextensionarependingfromtheAlaskaDepartmentofNaturalResources(ADNR)andMatanuska‐SusitnaBorough(MSB)foraproposedhydroelectricprojectlocatedalongtheroute.42Neweasementswouldberequiredfortheremainingapproximately3.5milestotheStatePark.TheintertiewouldeliminatetheneedfordieselgenerationattheStateParkduringthesummermonths.ThehydroelectricprojectdeveloperandADNRDivisionofParksandRecreationbothmaysupportthisprojectwithmatchingfunds.
Whencontactedregardingthisproject,theStateParkwassupportive(Biessel,privateconversation,2011).Threeprivateentitieslocatedneartheparkexpressednointerestinconnectingtotheline.Whencontactedregardingthisproject,MEAexpressedconcernsaboutitsstaffavailabilitytosupportthisproject(Kuhn,privateconversation,2011).
H.4.4 HVDCIntertieProjects
ThissectionprovidesoverviewsofpotentialHVDCintertiesbetweenruralAlaskacommunities.Theintertiesareorganizedgeographically,startinginthenorthwestandmovingtothesoutheast.
H.4.4.1 BarrowtoAtqasukHVDCIntertie
This75‐mile‐longoverlandintertiewouldconnectAtqasuk,whichuseshigh‐costdieselforelectricity,toBarrow,whichgenerateselectricityfromlow‐costnaturalgas(FigureH‐9).ThisprojectcouldincludeconversionofAtqasuktoelectricheatingtoachievegreaterbenefits.TheNorthSlopeBoroughiscurrentlystudyingthisintertie.IftheHVDCtechnologyiscommerciallyavailableinatimelymanner,itcouldbeusedonthisintertie.Ifitisnot,theintertiewouldbebuiltasathree‐phaseACline.
H.4.4.2 NometoTellerandBrevigMissionHVDCIntertie
Thisapproximately75‐mile‐longoverlandintertiewouldconnectTellerandBrevigMission—whichbothgenerateelectricitywithdieselfuel—toNome,whichgenerateselectricityfromdieselandsomewind(FigureH‐10).TheAlaskaVillageElectricCooperative,Inc.(AVEC)recentlybuiltanintertiebetweenTellerandBrevigMission.IfthePilgrimHotSpringsgeothermalresourceisdevelopedandislargeenoughtosupplyNomeaswellasTellerandBrevigMission,itcouldsignificantlyreduceelectriccostsinthesevillages.
H.4.4.3 PilgrimHotSpringstoNomeHVDCIntertie
ThegeothermalresourceatPilgrimHotSpringscouldprovideelectricityforNome.Oneofthechallengeswiththisrenewableenergyconceptisthecostoftheapproximately60‐miletransmissionlinebetweenPilgrimHotSpringsandNome(FigureH‐10).UsingthisHVDCtechnologycouldreducethecostsofthisintertie,improvingprojecteconomics.OnepotentialhurdleforthisdemonstrationprojectcandidateisthatthePilgrimHotSpringsresourcehasbeententativelyestimatedat5megawatts(MW).Thisislargerthanthecapacityoftheprototypeconverters,andapproximatelyten500‐kWconverterswouldbeneededateachendoftheintertie.PPShasindicatedthatparallelingthismanyconverterstogetheristechnicallyfeasiblebutthisfunctionhasnotbeenverifiedatthistime.ACEPisassessingthegeothermalresourceatPilgrimHotSprings,whichwillhelpdeterminehowmuchpowercanbederivedfromtheresource(Mager,privateconversation,2011).
42ThedeveloperofthishydroelectricprojectisanaffiliatedinterestofPolarconsultAlaska,Inc.
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H.4.4.4 St.Michaels–StebbinsHVDCIntertie
Thisapproximately10‐mile‐longoverlandintertiewouldconnectSt.MichaelsandStebbins,twovillagesservedbytheAVEC,allowingAVECtoeconomizebyconsolidatingbulkfuelandgenerationassetsandoperationsatonevillage(FigureH‐11).Thereisgoodmarineaccesstobothvillages.TherelativelyshortdistanceofthisintertiereducesthesavingsofanHVDCintertiecomparedwithanACintertie.
H.4.4.5 St.Mary’stoMountainVillageHVDCIntertie
Thisapproximately26‐mile‐longoverlandintertiewouldconnectSt.Mary’sandMountainVillageontheYukonRiver,allowingAVECtoeconomizebyconsolidatingbulkfuelandgenerationassetsandoperationsatonevillage(FigureH‐12).Thereisgoodaccesstobothvillages,andanexistingroadbetweenthemwouldfacilitateconstructionoftheoverheadintertie.
H.4.4.6 DillinghamtoManokotakHVDCIntertie
Thisapproximately20‐mile‐longintertiewouldconnectManokotaktoDillingham(FigureH‐2).ThisintertiewouldallowtheDillinghamandManokotakelectricutilitiestoconsolidateoperations,loweringcostsinManokotak,andimprovingtheeconomiesofscaleforbothutilities.Inaddition,Dillinghamiscurrentlystudyingtwohydroelectricresources,LakeGrantandLakeElva,whichwouldprovidestable,low‐costelectricity.Iftheseprojectsarebuilt,ratesinManokotakwouldbesignificantlyreducedwiththisintertie.AnintertiebetweenManokotakandDillinghamhasbeenstudiedinthepast(Polarconsult,1986)buthasnotbeenconstructed.TheproposedHVDCtechnologycouldreducecostsfortheintertie,improvingprojecteconomics.
H.4.4.7 NewStuyahok–EkwokHVDCIntertie
Thisapproximately8‐mileoverlandintertiewouldconnectthesetwoAVECvillages,allowingAVECtoeconomizebyconsolidatingbulkfuelandgenerationassetsandoperationsatonevillage(FigureH‐13).TherelativelyshortdistanceofthisintertiereducesthesavingsofanHVDCintertiecomparedwithaconventionalACintertie.
H.4.4.8 Kodiak–OuzinkieHVDCIntertie
Thisapproximately8‐mile‐longsubmarinecableintertiewouldconnectOuzinkiewiththeKodiakElectricAssociation,Inc.(KEA)grid(FigureH‐14).Ouzinkiegenerateselectricitywithacombinationofhydroanddiesel.KEAgenerateselectricityfromacombinationofhydro,wind,anddiesel.DuetothedifferentgenerationsourcesandeconomyofscaleontheKEAsystem,KEA’selectricratesaresignificantlylowerthanOuzinkie’s.TheintertiewouldbenefitKEAbyincreasingloadandwouldbenefitOuzinkiebyreducingrates.KEAandOuzinkiehavealreadystudiedanoverlandintertiewithashortACcablecrossingofNarrowStrait(Dryden&Larue,2011).Theestimatedcostsoftheshortcablecrossingareasignificantportionofthetotalprojectcost,inpartduetothemobilizationcostsofspecializedequipmentforcableinstallation.Itmaybemorecost‐effectivetoinstallasubmarineHVDCcablefortheentireroute.
ThisintertieappearstobeasuitablecandidateforanHVDCdemonstrationproject.TheeconomicbenefitstoOuzinkieappeartobesignificant(Totemoff,privateconversation,2011).AsubmarineHVDCcableusingthetechnologydevelopedinthisprojectappearstobealessexpensiveoptionthantheoverhead/cablecrossingoption.Ouzinkie’speakloadisapproximately400kW,withinthecapacityoftheprototypeconverters.Furtherconversationswiththeprojectstakeholdersarewarranted.
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H.4.4.9 Green’sCreektoHoonahHVDCIntertie
This26‐mile‐longsubmarineintertiewouldconnectHoonahtoAlaskaElectricLightandPowerCompany(AEL&P)’sJuneaupowergrid,providinglower‐costpowertoHoonah(FigureH‐15).TheintertieisagoodlengthforHVDCandwouldprovideaclearbenefittoHoonah.Theintertiehasbeenunderconsiderationforseveralyears,andsignificantengineeringstudieshavealreadybeencompleted.TheintertieisuneconomicusingACtransmissionorexistingHVDCtechnology.TheproposedHVDCtechnologycouldreducecostsfortheintertie,improvingprojecteconomics.
H.4.4.10 PetersburgtoKakeHVDCIntertie
Thisapproximately60‐mile‐longsubmarineandoverlandintertiewouldconnectKakewiththePetersburg‐Ketchikangrid(FigureH‐16).TheintertiewouldallowKaketoconvertfromhigh‐costdieselelectricitytolow‐costhydroelectricity,andwouldbepartoftheproposedsoutheastintertiegrid.UsingHVDCcouldreducecostsbyallowinglongerspans,buriedcable,orincreaseduseofsubmarinecable.Whilea1‐MWmonopolarHVDCintertiewouldbesufficienttoserveKake,futureextensionofthesoutheastintertietoSitkaordevelopmentofnearbyhydropowerresourcescouldincreasetheloadonthisintertietotensofmegawatts.
H.4.4.11 GustavustoGlacierBayNationalParkIntertie(HVDCDemonstrationOnly)
Withthecompletionofthe800‐kWFallsCreekHydroelectricProjectin2009,Gustavusnowhasexcesshydropower.TheheadquartersofGlacierBayNationalPark,locatedapproximately5to10milesfromGustavus,continuestorelyondieselgenerationforelectricity(FigureH‐15).ConnectingtheparkheadquarterswithGustavuswouldallowtheParktoreducefuelconsumptionandoperatingcostsandwouldallowGustavustoincreaseitsratebaseandpowersales,loweringoverallrates.AburiedHVDCcablewouldbepreferabletooverheadAClinesinthepark,whereaestheticsareamajorfactor.Duetotherelativelyshortlength,anHVDCintertiemaynotbecost‐effectivecomparedtoanACintertie.
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H.4.5 ProjectMaps
Figure H-2 Vicinity Map for Demonstration Projects near Dillingham
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Figure H-3 Vicinity Map for Eureka AC Line Conversion
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Figure H-4 Vicinity Map for Hope AC Line Conversion
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Figure H-5 Vicinity Map for Seldovia AC Line Conversion
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Figure H-6 Vicinity Map for Delta Junction AC Line Extension
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Figure H-7 Vicinity Map for Deltana AC Line Extension
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Figure H-8 Vicinity Map for Independence Mine AC Line Extension
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Figure H-9 Vicinity Map for Barrow – Atqasuk HVDC Intertie
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Figure H-10 Vicinity Map for Demonstration Projects near Nome
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Figure H-11 Vicinity Map for St. Michaels – Stebbins HVDC Intertie
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Figure H-12 Vicinity Map for St. Mary’s – Mountain Village HVDC Intertie
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Figure H-13 Vicinity Map for New Stuyahok – Ekwok HVDC Intertie
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Figure H-14 Vicinity Map for Kodiak – Ouzinkie HVDC Intertie
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Figure H-15 Vicinity Map for Gustavus and Hoonah HVDC Interties
Figure H-16 Vicinity Map for Kake – Petersburg HVDC Intertie
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APPENDIXI
STAKEHOLDERADVISORYGROUPINVOLVEMENTANDMEETINGS
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TABLEOFCONTENTS
I.1 INTRODUCTION........................................................................................................................................................7
I.2 LISTOFSAGMEMBERS.........................................................................................................................................8
I.3 SUMMARYOFSAGROLEANDPOLICIES.......................................................................................................9 I.3.1 POLICIESANDPROCEDURES............................................................................................................................................9
I.3.1.1 Formation......................................................................................................................................................9 I.3.1.2 ScheduledMeetings...................................................................................................................................9 I.3.1.3 Organization.................................................................................................................................................9 I.3.1.4 Communication...........................................................................................................................................9 I.3.1.5 Termination................................................................................................................................................11
I.4 STAKEHOLDERADVISORYGROUP(SAG)MEETINGPRESENTATIONMATERIALS.................12 I.4.1 SAGMEETING#1–FAIRBANKS,ALASKA(APRIL27,2010)................................................................................12 I.4.2 SAGMEETING#2–ANCHORAGE,ALASKA(JANUARY14,2011)........................................................................32 I.4.3 SAGMEETING#3–ANCHORAGE,ALASKA(OCTOBER25,2011).......................................................................53
I.5 HANDOUTSFROMOTHERMEETINGSCONDUCTEDDURINGTHEPROJECT...........................105 I.5.1 SOUTHEASTCONFERENCEMID‐SESSIONSUMMIT–JUNEAU,ALASKA(MARCH2,2010)............................107 I.5.2 EMERGINGENERGYTECHNOLOGYFORUM–JUNEAU,ALASKA(FEBRUARY14,2011).................................113 I.5.3 BROWN‐BAGWORKSESSION–ANCHORAGE,ALASKA(AUGUST29,2011)...................................................125 I.5.4 HVDCCONVERTERDEMONSTRATION–LAWRENCEVILLE,NEWJERSEY(NOVEMBER14,2011).............145
I.6 ADDITIONALMEETINGS.................................................................................................................................151
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LISTOFTABLES
TableI‐1 ListofSAGMembers.................................................................................................................................8
TableI‐2 SummaryofCorrespondencewithSAGMembers......................................................................10
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I.1 INTRODUCTION
ThisappendixprovidesthefollowingdetailedinformationregardingtheStakeholdersAdvisoryGroup(SAG)formedforPhaseIIoftheHigh‐VoltageDirectCurrent(HVDC)DevelopmentProgram:
● ListofSAGmembers;
● SummaryofSAGroleandpolicies;
● SummaryofkeyinformalcorrespondencebetweenSAGmembersandPolarconsultoverthecourseoftheproject;
● HandoutsandtranscriptsfromthethreeSAGmeetings;and
● Handoutsfromothermeetingsandoutreachactivitiesconductedoverthecourseoftheproject.
Meetingtranscriptsareavailableseparately.
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I.2 LISTOFSAGMEMBERS
Table I-1 List of SAG Members
Company First Name Last Name Position
Denali Commission Denali Daniels SAG Chair Alaska Center for Energy and Power (ACEP) Gwen Holdmann ACEP Director Alaska Center for Energy and Power (ACEP) Jason Meyer ACEP Project Manager Alaska Center for Energy and Power (ACEP) Brent Sheets SAG Member Polarconsult Alaska, Inc. Joel Groves Project Manager Polarconsult Alaska, Inc. Earle Ausman President Polarconsult Alaska, Inc. David Ausman Vice President Princeton Power Systems, Inc. (PPS) Darren Hammell Executive Vice President Alaska Department of Labor (AKDOL) Daniel Greiner Alt. SAG Member Alaska Department of Labor (AKDOL) Alvin Nagel SAG Member Alaska Division of Community and Regional Affairs (DCRA) Percy Frisby SAG Member Alaska Energy Authority (AEA) David Lockhard SAG Member Alaska Power & Telephone Company (APT) Bob Grimm SAG Member Alaska Power Association (APA) Marilyn Leland SAG Member Alaska Village Electric Cooperative, Inc. (AVEC) Meera Kohler SAG Member Alaska Village Electric Cooperative, Inc. (AVEC) Brent Petrie Alt. SAG Member Bering Straits Native Corporation (BSNC) Jerald Brown SAG Member Bethel Electric Utility (BEC) Bob Charles SAG Member Copper Valley Electric Association (CVEA) Robert Wilkinson SAG Member Dillingham Nels Andersen SAG Member Golden Valley Electric Association, Inc. (GVEA) Brian Newton SAG Member Homer Electric Association, Inc. (HEA) Brad Janorschke SAG Member Inside Passage Electric Cooperative (IPEC) Jodi Mitchell SAG Member Institute of Northern Engineering (INE, UAF) Ron Johnson SAG Member Kodiak Electric Association, Inc. (KEA) Darron Scott SAG Member Kotzebue Electric Association, Inc. (KoEA) Brad Reeve SAG Member Matanuska Electric Association (MEA) Joe Griffith SAG Member Matanuska Electric Association (MEA) Trivia Singaraju Alt. SAG Member Naknek Electric Association, Inc. (NEA) Donna Vukich SAG Member Nat’l. Rural Electric Cooperative Association (NRECA) Tom Lovas SAG Member Nome Chamber of Commerce (NCC) Mitch Erickson SAG Member Nome Joint Utilities (NJUS) John Handeland SAG Member North Slope Borough (NSB) Kent Grinage SAG Member Northwest Arctic Borough (NWAB) Ingemar Mathiasson SAG Member Nushagak Electric Association Mike Favors SAG Member Nuvista Light and Power, Inc. (NLP) Bob Charles SAG Member Southeast Conference (SEC) Robert Venables Alt. SAG Member Southeast Conference (SEC) Shelly Wright SAG Member Southwest Alaska Municipal Conference (SWAMC) Andy Varner SAG Member U.S. Department of Agriculture (USDA) Rural Utilities Service (RUS) Eric Marchegiani SAG Member University of Alaska Fairbanks (UAF) Richard Wies SAG Member
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I.3 SUMMARYOFSAGROLEANDPOLICIES
I.3.1 PoliciesandProcedures
TheSAGisanadvisorybodycomprisedofrepresentativesofAlaska’sruralelectricutilityindustryandrelatedprofessionals.ThepurposeoftheSAGistoprovidecomments,feedback,review,andrecommendationstotheHVDCDevelopmentProgram,awardedbytheDenaliCommission(Commission),managedbytheAlaskaCenterforEnergyandPower(ACEP),andcontractedtoPolarconsultAlaska,Inc.(Polarconsult).
I.3.1.1 Formation
TomaintainindependenceoftheSAG,ACEPidentifiedmembersforparticipation,withconsiderationofrecommendationsfromPolarconsultandtheDenaliCommission.AfinalcandidatelistwassentoutforcommenttoPolarconsultandforwardedforapprovaltotheDenaliCommission.
I.3.1.2 ScheduledMeetings
PerthescopeofworkunderUAF–PolarconsultContract#10‐0055,theSAGformallyconvenedthreetimesoverthecourseoftheHVDCProject.Perthescopeofworkandbudget,thecostofconveningthesemeetingswastheresponsibilityofPolarconsult.Fundingformembertravelandparticipationcostswasnotprovided.Themeetingswereconvenedinamannerconducivetoremoteparticipationofmembers.ThemeetingdateswereApril28,2010;December1,2010;andJuly15,2011.
TheagendaforthesemeetingswassetbyACEP,withinputfromPolarconsultandtheDenaliCommissionandfinalapprovalbytheDenaliCommission.
I.3.1.3 Organization
TheSAGshallconsistoftheChair(theDenaliCommission)andmembers.TomaintainequalityontheSAG,individualorganizationsmayholdonlyonememberposition.Upto30SAGmemberswillbeallowed,thefinalnumberdeterminedbasedonthelevelofinterest.Ifatanytimeoverthecourseoftheprojectoneofthemembersresignsorisnolongeractive,ACEPwillinviteanotherindividualtofillthisposition,withtheapprovaloftheDenaliCommission.Membersmaydesignateproxiesfromwithintheirorganizationtoattendmeetings.
ACEPencouragesorganizationsandindividualsnotselectedfortheSAGtoparticipateinformallyinthisproject.Publiccommentisalwayswelcomeandane‐maillistandforumwillbemadeavailableontheACEPprojectwebsite.
I.3.1.4 Communication
Atcertainprojectmilestones,oruponrecommendationfromACEP,Polarconsultshallsolicitcomments,review,andrecommendationstotheHVDCprogram.AllformalcommunicationbetweenPolarconsultandtheSAGshallbethroughtheChair,withinclusionofACEP.PolarconsultisfreetocontactthewholeSAGformallyorcontactindividualSAGmembersinformally,astheneedarises.AllinformalcommunicationwillnotrepresenttheadviceorrecommendationsoftheSAG.Intheinterestsofpromotingmaximumfeedbackfromtheindustry,confidentialcommunicationswillbeacceptedwherethereisademonstratedneedtomaintainconfidentiality.
TableI‐2providesasummaryofcorrespondencewithSAGmembersrelatedtothisproject.
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Table I-2 Summary of Correspondence with SAG Members
Date SAG Member Participants Subject Summary
Jan.–Feb. 2010 MEA
Trivi Singaraju (MEA) Gary Kuhn (MEA)
Joel Groves (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
Jan.–Feb. 2010 CVEA Chris Botulinski (CVEA)
Earle Ausman (Polarconsult) Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
Jan.–March 2010
At Large Citizen
Nels Anderson Earle Ausman (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
Jan.–March 2010 CEA
Ed Jenkin (CEA) Dave Ausman (Polarconsult) Joel Groves (Polarconsult)
Earle Ausman (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
Jan.–March 2010 HEA
Brad Zubeck (HEA) Kathy McDonough (HEA) Joel Groves (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
May–June 2010 NWAB Ingemar Mathiasson (NWAB)
Earle Ausman (Polarconsult)
International examples of
electric codes
Mr. Mathiasson used his contacts in Sweden to request examples of international electric codes with
regard to SWER circuits, HVDC, and related rural electric issues.
July–October
2010 AVEC
Brent Petrie (AVEC) Bill Thomson (AVEC) Mark Tietzel (AVEC)
Joel Groves (Polarconsult) Earle Ausman (Polarconsult)
HVDC Converter Specification
Discussions and comments from AVEC on draft specification for
HVDC power converter.
July–October
2010 UAF/ACEP
Richard Wies (UAF) Jason Meyer (ACEP)
Joel Groves (Polarconsult) Earle Ausman (Polarconsult)
HVDC Converter Specification
Discussions and comments from AVEC on draft specification for
HVDC power converter.
August 2010 AVEC Mark Teitzel (AVEC) Joel Groves (Polarconsult)
Conceptual Design of
Overhead Line
Request for examples of environmental loadings used on
previous AVEC interties, performance of these projects.
September 2010 IPEC Peter Bibb (IPEC)
Joel Groves (Polarconsult) Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
October–November
2010 GVEA
Mike Wright (GVEA) Searl Burnett (GVEA)
Earle Ausman (Polarconsult)
Conceptual Design of
Overhead Line
Site visit to review design, performance, and failure modes of
guyed Y and X towers on transmission lines between
Fairbanks and Healy.
November 2010 AVEC
Brent Petrie (AVEC) Joel Groves (Polarconsult)
Earle Ausman (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
December 2010 SEC
Shelly Wright (SEC) Robert Venables (SEC)
Joel Groves (Polarconsult) Earle Ausman (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
January 2011 APT
Bob Grimm (APT) Earle Ausman (Polarconsult) Joel Groves (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
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Date SAG Member Participants Subject Summary
January 2011 NWAB
Ingemar Mathiasson (NWAB) Brent Petrie (AVEC)
Joel Groves (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
January 2011 RUS Eric Marchegiani (RUS)
Joel Groves (Polarconsult) Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
January 2011 Multiple Multiple SAG Members Demonstration
Project Sites
Teleconference with SAG members on HVDC demonstration project
sites.
January–March 2011 GVEA
Mike Wright (GVEA) Joel Groves (Polarconsult)
Earle Ausman (Polarconsult)
Demonstration Project Sites
Discussing potential HVDC demonstration project sites.
March 2011 AVEC
Bill Thomson (AVEC) Joel Groves (Polarconsult)
Earle Ausman (Polarconsult) Randy Wachal (MHRC)
HVDC Controls and integration
Discussions among Polarconsult, Manitoba, and AVEC on system controls and integration needs.
May–June 2011 CVEA
Chris Botulinski (CVEA) Earle Ausman (Polarconsult) Joel Groves (Polarconsult)
HVDC Test Site Discussions looking for a test site for HVDC pole and foundations.
June 2011 UAF
Richard Wies (UAF) Jason Meyer (ACEP)
Joel Groves (Polarconsult) Earle Ausman (Polarconsult)
Examples of cold regions design for overhead HVDC
Visit of Chinese delegation regarding design of HVDC line across the
Tibetan Plateau.
June–July 2011 GVEA
Mike Wright (GVEA) Joel Groves (Polarconsult)
Earle Ausman (Polarconsult) HVDC Test Site Discussions looking for a test site for
HVDC pole and foundations
July 2011 AKDOL
Al Nagel (AKDOL) Dave Greiner (AKDOL) Randy Wachal (MHRC)
Joel Groves (Polarconsult)
SWER circuit safety.
Discussions with Alaska Department of Labor regarding HVDC SWER
circuits and soliciting comments on the SWER analysis prepared by
Manitoba.
November 2011 AVEC Pam Lyons (AVEC)
Joel Groves (Polarconsult) Converter
Shipping Cost
AVEC assistance on obtaining shipping costs to move prototype
converters to Alaska.
Nov, 2011 – Jan 2012 AVEC
Meera Kohler (AVEC) Mark Tietzel (AVEC) Brent Petrie (AVEC)
Joel Groves (Polarconsult)
Cost data for past AC projects
Discussions from November 2011 through January 2012 regarding details of cost data for remote
Alaska AC intertie projects built over the past decade.
December 2011 AKDOL
Al Nagel (AKDOL), Dave Greiner (AKDOL), Jason
Meyer (ACEP), Joel Groves (Polarconsult)
SWER circuit safety.
Discussions with Alaska Department of Labor regarding HVDC SWER
circuits and NESC code.
I.3.1.5 Termination
TheSAGshallbeformallyterminatedupontheendoftheprojectissuedfromtheDenaliCommission.
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I.4 STAKEHOLDERADVISORYGROUP(SAG)MEETINGPRESENTATIONMATERIALS
I.4.1 SagMeeting#1–Fairbanks,Alaska(April27,2010)
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I.4.2 SAGMeeting#2–Anchorage,Alaska(January14,2011)
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I.4.3 SAGMeeting#3–Anchorage,Alaska(October25,2011)
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I.5 HANDOUTSFROMOTHERMEETINGSCONDUCTEDDURINGTHEPROJECT
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I.5.1 SoutheastConferenceMid‐SessionSummit–Juneau,Alaska(March2,2010)
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I.5.2 EmergingEnergyTechnologyForum–Juneau,Alaska(February14,2011)
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I.5.3 Brown‐BagWorkSession–Anchorage,Alaska(August29,2011)
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I.5.4 HVDCConverterDemonstration–Lawrenceville,NewJersey(November14,2011)
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I.6 ADDITIONALMEETINGS
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ThefollowingadditionalmeetingswereheldduringthecourseofthisprojectregardingaHVDCtransmissionsysteminruralAlaska.
● SoutheastConferenceMid‐SessionSummit–Juneau,Alaska(MARCH2,2010)
● EmergingEnergyTechnologyForum–Juneau,Alaska(February14,2011)
● Brown‐BagWorkSession–Anchorage,Alaska(August29,2011)
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APPENDIXJ
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