ExportCableReliability
DescriptionofConcerns
May2017(updatedJuly2017)
ExportCableReliability–DescriptionofConcerns
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DISCLAIMER
ThisreporthasbeenwrittenbyTransmissionExcellenceLtdonbehalfoftheOffshoreWindProgrammeBoard(OWPB),withtheassistanceofanad-hocgroup(the“ExportCableReliabilityProject”)thatincludesrepresentativeofmostoftheUK’soffshorewindfarmdevelopersandallofthecompaniesthatowntheUK’soffshorewindexportcables(theoffshoretransmissionowners,orOFTOs).Whilsttheinformationcontainedinthisreporthasbeenpreparedandcollatedingoodfaith,theOWPBandtheauthorsmakenorepresentationorwarranty(expressorimplied)astotheaccuracyorcompletenessoftheinformationcontainedinthisreport(includinganyenclosuresandattachments)norshalltheybeliableforanylossordamage,whetherdirectorconsequential,arisingfromrelianceonthisreportbyanyperson.Inparticular,butwithoutlimitation,theOWPBandtheauthorsacceptnoresponsibilityfortheaccuracyandcompletenessofanycommentson,oropinionsregardingthefunctionalandtechnicalcapabilitiesofanyequipment,softwareorotherproductsmentionedinthereport.TheOWPBandtheauthorsarenotresponsibleinanywayinconnectionwitherroneousinformationordatacontainedorreferredtointhisdocument.Itisuptothosewhousetheinformationinthisreporttosatisfythemselvesastoitsaccuracy.Thisreportanditscontentsdonotconstituteprofessionaladvice.Specificadviceshouldbesoughtaboutyourspecificcircumstances.Thereporthasbeenproducedbytheauthorsbasedoninformationprovidedbyindustryparticipantsandhasnotbeensubjecttoindependentverification.TheOWPBandtheauthorsacceptnoresponsibilityfortheaccuracyandcompletenessofanycommentson,oropinionsregardingthefunctionalandtechnicalcapabilitiesof,anyproductsorservicesmentioned.Thereportisnotintendedtobeinstructional,ortorequireanyaffectedpartytobehaveinacertainway,ortoremovetherightofanysuchpartytotakeitsowncommercialdecisionsontheissuesdiscussedherein.Tothefullestextentpossible,theOWPBandtheauthorsdisclaimanyliabilityarisingoutoftheuseofthereport,includinganyactionordecisiontakenasaresultofsuchuse.
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TableofContents
DISCLAIMER..................................................................................................................................2
1 SUMMARY........................................................................................................................4
2 EXPORTCABLEFAILURERATE–UKEXPERIENCE............................................................5
3 CAUSEOFTHISHIGHFAILURERATE–UKEXPERIENCE..................................................6
4 OTHERRELEVANTEXPERIENCE........................................................................................7
5 EXPECTEDEXPORTCABLEFAILURERATE........................................................................8
6 COSTOFCABLEFAILURES................................................................................................9
7 SUGGESTEDACTIONSFORCOMPANIESORDERINGNEWCABLES...............................11
8 NEXTSTEPS.....................................................................................................................12
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1 SUMMARY
ThispreliminaryreportdescribestheUK’sexperienceofoperatinghighvoltage(³132kV)offshorewindfarmsubmarineexportcables.IntheUKallsuchexportlinksuseACcableswiththreepowercoresandatleastonefibreopticcorepackagedtogetherwithinonearmouredcable.TodatetheUKoffshorewindindustryhasexperiencedsevenpost-commissioningfailures(faultsorpre-emptiverepairs)onitsfleetofhighvoltageexportcables.Basedoninitialdetailsprovidedtousbytheownersofthesecables1,weunderstandthatsixofthesefailureswouldnothaveoccurredhadafibreopticcorenotbeenincludedwithinthepowercable.Inmostofthesecasesaninitialfailureinthefibreopticcoreappearstohavedevelopedsoastoaffectapowercore.Thereappeartobeavarietyofpossiblemechanismswhichcancausetheinitialfailureinthefibreopticcore,andavarietyofmechanismswherebythedamagemaypossiblyspreadtopowercores.TheauthorhasnotbeenabletoundertakeacomprehensivesurveyofcablefailuresoutsidetheUKoffshorewindsector,althoughtwofailuresontheGuernsey-Jerseycableandonefailureonanon-UKoffshorewindfarmcablearebelievedtobelinkedtofailuresinafibreopticcore.Uptotheendof2016thetotalexperience-baserepresentedbytheUK’sfleetofhigh-voltageoffshorewindexportcablestotalledover4,400km.years.Thesevenfailuresthatoccurred,therefore,representameantimebetweenfailuresof630km.years.Thiscompareswiththemeantimebetweenfailuresof1,400km.yearssuggestedbyCigreTechnicalBrochure379,whichhaspreviouslybeenthemainsourceofinformationonsubmarinecablereliability2.AnestimatehasbeenmadeofthecostoftheUK’shighvoltageexportcablefailures;thiscomprisesboththecostofrepairsandthecostoflostwindfarmproduction.Theestimatedtotalcostisabout£160m,ornearly£170kforeverykmofhighvoltageexportcablecurrentlyinservice.Thishighcostemphasisestheimportanceofeliminatingcables’vulnerabilitytofibreopticcorefailuresinfutureprojects.ThereportsetsoutthepositionofOFTOsandwindfarmdevelopersinrelationtohowbesttoensurethattherisksfacedbyfutureprojectsaresuitablymitigated.
1 As part of a later stage in the examination of these faults,we hope to arrange for the root cause analysis documentspreparedafterforeachofthesefailuretobereviewedbyanexperttocheckforcommonalitiesandtoverifytheapparentcommonroleofthefibreopticcore.
2 Both the number from Cigre and the number calculated fromUK export-cable experience suffer from being based onrelatively small sample sizes. Although neither number has strong statistical support, the UK number at least has theadvantageofbeingsolelybasedonrelevantcabletypes.
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2 EXPORTCABLEFAILURERATE–UKEXPERIENCE
AninvestigationhasbeenundertakenintothereliabilityofthehighvoltageexportcablesusedtoconnectUKoffshorewindfarmstotheonshoregrid.Thishasexaminedcablefailuresthatmetthefollowingsetofcriteria:
i) Thefailedcablewasathree-coreACsubmarinecableoperatingatanominalvoltageof132kVorhigher3.
ii) ThepurposeofthefailedcablewastoconnectaUKoffshorewindfarmtothegrid.
iii) Thefailedcablehadbeencommissionedandwasinnormalservicewhenthefailureoccurred.Theresultspresentedinthisdocumentthereforeexcludedamageduringconstructionthatrequiredthecabletoberepairedbeforeitcouldbeputintoservice4.Theresultsalsoexcludecaseswhereacablesufferedknownmechanicaldamageduringinstallationbut,asamatterofconvenience,thecablewastemporarilyputintoservicependingrepair.
iv) Thefailurethataffectedthecablemightbeeitherafault(shortcircuit),or
apre-plannedrepairtothecablewheretheownerbelievesthatafaultislikelytodevelop.Ineithercasetheaffectedcablewillbecut,thefaulty(orsuspect)partremoved,andareplacementlengthofsparecablejointedintoplace.
TheinvestigationfoundatotalofsevencablefailuresfromNovember2011todatethatmetthecriteriasetoutabove.Inaddition,atleasttwosituationsexistintheUKwhereanexportcable,whichremainsinservice,isexhibitingsymptomsthatsuggestthatafaultmaydevelop.Discussionswithalimitednumberofnon-UKcableownerssuggestthatasimilarsituationmayexistonatleastoneexportcableoutsideoftheUK.Uptotheendof2016thetotalexperience-baserepresentedbytheUK’sfleetofhigh-voltageoffshorewindexportcablestotalledover4,400km.years.Thesevenfailuresthatoccurred,therefore,representameantimebetweenfailuresofjustunder630km.years.Readersshouldnotethat–liketheCigredatadiscussedinSection5below–thismeantimebetweenfailuresnumberisbasedonalimitedsamplesizewiththefaultsbeingconcentratedonafewprojects.Thismeansthatunusuallygoodorbadresultsfromahandfulofprojectscaneasilybiastheresultsupordown.
3Noattempthasbeenmadetoexaminetheperformanceof lowervoltagethreecoreACcablessuchasthe33kVcableswidelyusedwithinoffshorewindfarms.Differencesinownershipmeanthatadifferentorganisationalapproachmayberequiredifitisdesiredtoextendtheworkdescribedinthisreporttoencompasssuchcables.
4Thehighlevelofinsuranceclaimsarisingfromsubmarinecabledamageduringload-out,laying,burial,orfromotherwindfarmconstructionactivities,hasbeenpubliclydocumentedbyseveral insurancecompanies.Suchsourcestypicallyshowcablesrepresentingaboutthreequartersofallclaimsonawindfarm’sconstructionallrisks(CAR)insurance.
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3 CAUSEOFTHISHIGHFAILURERATE–UKEXPERIENCE
Allthree-coreACcablesusedbyoffshorewindfarmscontainatleastonefibreopticcore(seefigure1).Figure1:(Left)crosssectionofatypical3-coresubmarinecableshowingtwopowercoresandthefibreopticcore.(Right)closeupofthefibreopticcore.Thisshowsopticalfibres(brightlycolouredstandsemergingfromcable),themetaltubeenclosingthefibres(thesilvercirclearoundthefibres),armouring(thethickersilverstandsaroundthemetaltube–notpresentinallfibreopticscores),andtheanti-corrosionsheath(thickblackplasticaroundthearmourlayer).Inthisdesignthefibreopticcoreisheldinplacebyamouldedplasticinsertwhichfillstheintersticesbetweenthepowercoresandthearmouring.Accordingtoinformationprovidedbythecableowners,sixofthesevencablefailuresreferredtoinSection2involvedfailureswithinthefibreopticcore.Thesefailuresinthefibreopticcoreeitherdevelopedtoaffectapowercore(themorecommonsituation),oranoutageofthepowercoreswasrequiredtorepairthefibres(lesscommon).Wherefailuresinthefibreopticcorehavedevelopedandaffectedapowercore,thedamagetothecablecausedbytheeventualshortcircuitmaymakeitdifficulttoestablishanyrootcause,andtherootcausesofthefailuresinthefibreopticcoresappeartovarybetweencases.Nevertheless,afewpointsaboutthefibreopticcorearerelevant:
i) Thefibreopticcoreismuchsmallerandlighterthanthepowercoreswithinthesamecable.Itisthereforemorevulnerabletobeingdamagedduringtheassemblyofthecablewherelargerandheaviercableelementsareinmotionaroundit.
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ii) Thefibreopticcoreisexposedtoa50Hzmagneticfieldfromtheadjacent
powercores.Thefibreopticcoresusedinsubmarinecablealwaysincludeametallictubetopreventseawaterfromreachingtheopticalfibresthemselves,andthemagneticfieldsthatthefibreopticcoreisexposedtocancausecurrentsandvoltagestobeinducedonthismetallictube,especiallyiffaultsortransientscausethemagneticfieldstobeunusuallystrong.(Forthecabledesignshowninfigure1above,thetubeismadefromstainlesssteelandissurroundedbyarmourwires;theseincreasemechanicalstrengthbutcanalsocarryaninducedelectricalcurrent).
iii) Despitethefactthatitmaybeexposedtosignificantcurrentsandvoltages,thedesignandtestingofthefibreopticcoreisfocussedontheopticalcharacteristicsoftheopticalfibresthatitcontains–notonitsabilitytowithstanditselectricalserviceconditions.Indeedwithsomedesignstheelectricalconditionofthefibreopticcoreisinherentlydifficulttomeasure,evenwhilethecableisstillinthefactory.
Althoughthelevelofdamagefromshortcircuitsoftenmakesdiagnosisdifficult,analysisbycableownerssuggeststhatthemechanismsbywhichafailureinafibreopticcorecouldaffecttheadjacentpowercore(s)alsovarybetweencases.Mechanismsinvolvingelectricaldischarge,overheatingandelectrochemicaleffects(corrosion)havebeensuggestedinvariouscasesandallneedtobefurtherinvestigatedandunderstood.ThereareseveraltypesoffibreopticcorepresentacrosstheUKexportcablefleet.Thefaultsthathaveoccurredhaveaffectedmorethanonetypeoffibreopticcore.Althoughsometypesoffibrecorehavenotyetbeenaffected,thelimitedamountofdataavailablemeansthatitisnotpossibletobeconfidentthatthesetypesdonotsharesomeorallofthesamevulnerabilitiesasthosetypesthathavealreadyexperiencedfailures.Whilethereismuchuncertaintyabouttheexactmechanismsandrisks,theanalysisundertakenbythecableownershighlightonekeypoint:ifthefibreopticcorehadnotbeenpresentinsidethepowercablethenthefailurewouldnothaveoccurred.Thisanalysissuggeststhatthefibreopticcoremaybeaweakpointforthewholepowercable:relativetothepowercoresitissmaller,lighter,haslimitedelectricalwithstandcapabilities,andissubjecttolittleornoelectricaltesting.Yetthepresenceofthefibreopticcoremayincreasethevulnerabilityofthewholecabletofullelectricalfailure.
4 OTHERRELEVANTEXPERIENCE
TheauthorsareawareofafewfailuresofsimilarhighvoltagethreecoreACcablesoutsideoftheUKoffshorewindindustry,thoughwedonothaveaccesstoacomprehensivelistoffailuresortheircauses.
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TheGuernsey-Jersey90kVcablehassufferedtwofailureswhichtheownerhaspubliclystated5wererelatedtoanissuewithinthefibreopticcore.Theseare:
i) Afaultonthecablein2012
ii) Apre-emptiverepairin2015.Inthiscaseforensicanalysisofthereplacedsectionofcableshowedthat“thepowercablewouldinevitablyhavefailedwithinaveryshortperiodoftime”hadthepre-emptiverepairnotbeenundertaken.
Theauthorsarealsoawareofatleastonenon-UKoffshorewindfarmexportcablewhereafaulthasbeenlinkedtoanissuewiththefibreopticcore.
5 EXPECTEDEXPORTCABLEFAILURERATE
Priortotheworkundertakenforthisreport,estimatesofthereliabilityofsubmarinecablestypicallyreferencedCigreTechnicalBrochure379(TB-379):“UpdateofServiceExperienceofHVUndergroundandSubmarineCableSystems”.Thepartofthisreportthatdealswithsubmarinecablesmadeuseofsubmarinecablefailuredatafrom32sources,coveringtheperiodfrom1990to2005.ThemostrelevantreliabilitydataprovidedbyTB-379isameantimebetweenfailuresofover1400km.yearsforthecategoryof“ACXLPE6cables”,withthebulkofthesefailuresbeingexternal(i.e.thecablebeinghitbyananchor,trawlboardorsimilar).UnfortunatelytheACXLPEcablescategoryusedbyCigreisextremelybroad,encompassingmanytypesofcablethatareirrelevantforUKoffshorewindapplications:
i) Nearlyhalfofthecablesinthiscategoryareatvoltagesbetween60kVand
110kV,makingtheirrelevancefortheUKfleetofcablesat132kVandabovequestionable.
ii) Athirdofallthecablesinthecategoryaresingle-core,andsoimmunetotheproblemsdescribedinSection3,whichareuniquetothreecorecables.AllwindfarmACcablesareofthethreecoretype.
iii) NoinformationisprovidedregardingwhetherthethreecorecablesinCigre’sdatasetincludefibreopticcoresornot(showinghowthisissuewasnotconsideredrelevantforreliabilityuntilrecently).
iv) Noinformationisprovidedregardingwhetherthecableisburiedornot.It
seemslikelythatmostoftheexternalfaultsindicatedbyCigreoriginatefromunburiedcablesections,andthatCigre’smeantimebetweenfailureswouldbemuchhigherifallofthecablesintheirdatasetwereburied,asUKwindfarmcablesare.
5SeetheannualreportofGuernseyElectricity,March2015.6CrossLinkedPolyethylene
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Despitethe“ACXLPE”categorybeingextremelybroad,thedatasetavailabletoCigrewasnotparticularlylarge:evenin2005,whenthefleetstudiedbyCigrewouldhavebeenatitslargest,thedatasetfor“ACXLPE”cableswasnotsignificantlylargerthanthecurrentUKoffshorewindhighvoltageexportcablefleet.This,presumably,iswhythewritersofTB-379wereunabletoprovidemoredetailedbreakdowns.Cigrehasrecentlyestablishedaworkinggroup(B1.57)whichaimstoupdateTB-379,andUKcableownersareurgedtocontributetoitswork.Thisgroupisnotexpectedtoissueitsfinalreportuntil2018:inthemeantimepartiesseekingstatisticaldataonexportcablereliabilitywillstillneedtoreferenceTB-379,butshouldconsidercombiningthiswithnewerdataknowntobedirectlyrelevanttowindfarmexportcables–suchastheUKexportcableexperiencesetoutinSection2above.
6 COSTOFCABLEFAILURES
Theeconomicimpactofawindfarmexportcablefailurecanbeexaminedunderthefollowingcategories:
i) Thecostofrepairingthecable.
ii) Thecostoflostwindfarmproductionoveraperiodthatcanrangefromseveralweeks(forapre-emptiverepair)to3-5months7.foranunexpectedfault.
iii) Incaseswherethereisonlyasinglecableconnectinganoffshore
substation,thefailureofthiscablewillresultinthelossofallauxiliarypowertothewindturbines.Thisinturnwillleadtocostsfortheprovisionoftemporaryemergencygeneratorsand/orextramaintenancecostswhereturbinesareleftwithoutpowerforanextendedperiod.
Thecostofcablerepairincludespreciselocationofthefault;mobilisationofasuitablerepairvessel,equipmentandpersonnel;deburialofthefailedcable;removalofalengthofcable–oftenseveralhundredmeterslong–thatincludesthefaultlocation;jointinginalengthofsparecabletoreplacetheremovedsection;andreburyingorotherwiseprotectingtherepairedcable.Costswilldependonmarketconditionsandweatherconditionsduringtherepair,butcanbeextremelyhigh.Table1showsaselectionofpubliclydisclosedcablerepaircosts:
7TherepairtimesforthefoursubmarinecablefaultsindicatedbytheNGETC17documentare106days(3.5months),133days(4.4months),153days(5.0months)and105days(3.5months)
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Table1:PubliclydisclosedcablerepaircostsRepair
Cost Source
Guernsey-Jersey(2012) £8m BBCNews
Guernsey-Jersey(2015,pre-emptive) £5.3m Owners’annualreports
Moyle(2011-12),2repairs £15.5maverageperrepair
Owner’sannualreport
GwyntyMor(summer2015) £10.2m Ofgem(incomeadjustmentclaim)
GwyntyMor(2015-16) £14.2m Ofgem(incomeadjustmentclaim)
Thanet(2015) £11.7m Ofgem(incomeadjustmentclaim)
Excludingthesinglepre-emptiverepair,theaveragerepaircostfromthisdatasetis£12.5m.Thecostofapre-emptiverepairissubstantiallylessthanthecostofanunplannedrepair8.Inpractice,however,pre-emptiverepairsarefrequentlyimpossible:eitherbecausethecablegiveslittleornowarningoffailure,orbecause–giventhatthefailuremechanism(s)arestillpoorlyunderstood–theriskofunnecessarilyrepairingahealthycableisjudgedtobetoohigh.Asnotedabove,followinganunplannedfailureonaUKhighvoltageexportcablethetypicaltimerequiredtorepairthecableandreturnittoserviceis3-5monthsDuringthistimetheoutputofthewindfarmwillbecurtailed:
i) Ifthefailedcableistheonlyconnectiontoanoffshoresubstationthenalloftheoutputfromtheturbinesservedbythissubstationwillbelostuntiltherepairiscomplete.
ii) Iftherearetwo(ormore)cablesconnectinganoffshoresubstationthentheturbinesservedbythesubstationcancontinuetooperatewhilethefailedcableisrepaired,buttheiroutputwillberestrictedattimesofhighwind.
Basedontherepaircostsindicatedabove,theactualrepairtimesandsubstationconfigurations,andassumingthatexistingUKoffshorewindfarmshaveanaverageloadfactorof40%andatypicalincomeof£140/MWhr,aroughestimateofthetotalcosttotheindustryofthesevencablefailuresdescribedinSection2abovecanbecalculated.Theauthorestimatesthatthistotalcostisontheorderof£160m,roughlyequallysplitbetweenrepaircostsandthecostsoflostoffshorewindproduction.
8 Since Table 1 shows a cost for only one pre-emptive repair, we do not know if this £3.5m cost is typical or not.Nevertheless, it issomuch lowerthanthecosts fortheunplannedrepairsthat it issafetostatethatthecostofapre-emptiverepairwillbemuchlowerthanthatofanunplannedrepair.
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7 SUGGESTEDACTIONSFORCOMPANIESORDERINGNEWCABLES
FromthecalculationdescribedinSection6above,thesevenfaultsthathaveoccurredtodatehaveresultedincoststhathavealreadyreachednearly£170kperkmofexportcable.Suchacostisasignificantpercentageofthecapitalcostofthesecables,implyingthatsignificantactionsandexpendituresmaybejustifiedonnewprojectsinordertoensurethatnewlyprocuredcablesdonotsufferfromthesameissues.Thisreportisnotintendedtobeinstructional,anddoesnotmakeanyrecommendationstotheprocurersofnewhighvoltageexportcables.HoweverwehavesummarisedbelowthetwomainopinionsexpressedbymembersoftheExportCableReliabilityProject,theindustrygroupcreatedbytheOWPBtoaidindiscussionsonthisissue.Whethertofolloweitheroftheseopinionsisadecisionforthereader.OFTOs’OpinionTheOffshoreTransmissionOwners(OFTOs),actingthroughtheirrepresentativebody,theElectricityNetworksAssociationOFTOForum,haveprovidedthefollowingstatement:
Integral FOC presents an inherent weakness where any single/ minor defectcaused during manufacture, load out, or installation leads to a power corefailure. This failure mode was not foreseen and is not identified in publiclyavailablefailurestatistics.NoFATorSATregimeisinplaceatpresenttoidentifythepresenceofdefectsimpactingtheFOC.IntheopinionoftheENAOFTOForumitisessentialthatFATandSATtestsareinplace to verify the integrity of 3-core AC transmission submarine cables withintegralfibreopticcable(s).UntilsuchtestsareinplacethereisariskoffuturefailuresrelatedtotheFOC,andthisriskshouldberecognisedbyallstakeholders.FOC=fibreopticcoreFAT=factoryacceptancetestSAT=siteacceptancetest
Generators’OpinionsWhilethereisnoequivalent“official”viewheldbygenerators,severalpersonsinvolvedinthedevelopmentofgeneratorconnectionshaveexpressedtheviewthatitisprematuretoconsiderremovingfibreopticcoresfrompowercables.Inparticular,therewereconcernsthatmovingthefibrecorefromtheexportcabletoacableofitsownwouldresultinunnecessarycostsandcouldintroducenewrisks–bothknownrisks(e.g.fibredamageduringinstallation)andunanticipatedrisks.Furthermoreremovingfibreopticcoresfrompowercablesmayreducedevelopers’abilitytoapplydynamicratings,atechniquewhichcanofferoverallcostreductions–particularlyasdistancesincrease–andwhichcanallowincreasedwindfarmoutputduringoutages.
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Ifadecisionismadetoretainafibrecoreinsidetheexportcable,however,greatcarewillberequiredinordertominimisetheriskofafailureinthefibrecore.Ithasbeensuggestedthatsometypesoffibreopticcoremaybeinherentlylessvulnerable,ortheirintegrationintotheoverallcabledesignmaybeimproved,anditmaybepossibleforbuyerstoassessorimprovethevulnerabilityofcabledesignsby:
i) Suitablyaddingtotheirtechnicalrequirements.Forinstance,cablebuyerscouldspecifymaximumcurrents/voltagesallowedonthefibrecore’smetallictubeundernormalandfault/transientconditions.
ii) Explicitlyspecifyingdesignsthatshouldreducefibrecorevulnerability.Forinstance,weunderstandthatconsiderationhasbeengiventospecifyinganoptimisedlocationforthefibrecorewithinthepowercableinordertominimiseitsexposuretoelectromagneticfields,andtospecifyingabalancedsetoffibreswithperiodicphaserotationwithrespecttothepowercores.
iii) Questioningmanufacturers(includingrequestsforinformationandvalidation
tests)onrelevantissues(forinstancethemagnitudeofinducedcurrentsandvoltagesundervariouscircumstances)beforeplacinganorder.
iv) Suitablymonitoringthemanufacturing(and/orinstallation)processes(i.e.
enhancedqualityassurance).
8 NEXTSTEPS
TheExportCableReliabilityprojecthasdevelopedaplanwhichwouldproduceadvicethatoffshorewinddeveloperscouldusewhenprocuringnewexportcablesforfutureprojects.Thiscouldinclude,forinstance:
i) Adviceonquestionsthatshouldberaisedwithcablemanufacturers.
ii) Adviceoncalculationmethodologiesthatcablemanufacturerswouldbeaskedtousewhenrespondingtosuchquestions.
iii) Adviceonadditionstodevelopers’technicalrequirements.
iv) Adviceontestsofthefibreopticcoresthatdevelopers,OFTO’sandgenerators
shouldaskcablemanufacturerstoundertake.Atanyearlystagewithinsuchfuturework,itwillbenecessarytocollectinformationoneachfault(throughquestionnairesand/orreviewofrootcauseanalysisreports)forreviewbyasingleexpertteamtocheckforcommonalitiesandtoverifytheroleofthefibreopticcore.Workisongoingonrefiningthisplanandobtainingfundingforitsexecution.
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