WG031113 High Temperature Conductor.docx
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WG031113 High Temperature Conductor.docx
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WG031113HighTemperatureConductor
CONSIDERATIONSRELATINGTOTHEUSEOFHIGHTEMPERATURECONDUCTORS.
CompiledbyR.Stephen
CigreWG03;WG12-1;WG11-3
1Introduction
Inmanycountries,newpowerlineshavenotbeenbuiltformanyyearsandtheabilityofobtainingrightofwaysisbecomingmoreandmoredifficult.Nevertheless,overthesametimeperiod,manysuchcountrieshavealsoexperiencedasmallbutsteadyincreaseinthepowerconsumption.Itisthusbecomingnecessarytoupratethethermalpowertransfercapacity.Oneofthewaysinwhichthiscanbeachievedisbyreconductoring.Thiscanbeperformedbyeitherusingconductorslargerthanatpresentorconductorswiththesamediameter.
Increasingthethermalratingofanexistinglinebyuseofareplacementconductorlargerthantheoriginal(havinglowerresistance),willincreasebothtransverseiceandwindloadsandtensionloadsonexistingstructures.Alargerconventionalconductorimposinggreaterloadsontheexistingstructuresmayreducethereliabilityoftheexistinglineunlessthestructuresarereinforced.
Increasingthethermalratingofanexistinglinebyuseofareplacementconductorhavingnearlythesamediameterastheoriginalconductorbutcapableofoperationathighertemperature(withinexistingsagclearanceandloss-of-strengthconstraints)mayavoidtheneedforextensivereinforcementofsuspensionstructures.Thereareseveraldifferenttypesofhightemperature,lowsagconductorsthatcanbeusedtoincreasethethermalratingofexistinglineswithaminimumofstructuralreinforcement.
Themostattractivechoiceofreplacementconductordependsonthedesignconditionsoftheexistingline.Allarepotentiallyasolutionwhenthelinethermalratingistobeincreasedbymorethan50%.
Thisreportdescribesthetypesofcommerciallyavailable,triedandtestedhightemperatureconductorthatare(atthetimeofwriting)inusearoundtheworld.Inadditionitdescribestheeffectoftheseconductorsoninsulators.Italsodescribesthetypesoffittingsthatareusedontheseconductorsworldwide.
ThisreportisaresultofextensiveworkundertakeninCigreworkinggroupsWG12(electricalaspects),WG03(insulators),andWG11(mechanicalaspectofconductorsincludingfittings).
2TypesofhightemperatureconductorsRef[7]
“HighTemperatureConductor”isdefinedasaconductorthatisdesignedforapplicationswherecontinuousoperationisabout100°Cortheconductorisdesignedtooperateinemergencyconditionsabove150°C.ThetypesofconductorthatareatpresentcommerciallyavailablearebrieflydescribedinTABLEI
ACSS
AluminiumConductor,SteelSupported
(1)
(2)
ACSS/TW
CompactAluminiumConductor,SteelSupported
(1)
(2)
ACCR
AluminiumConductor,CompositeReinforced
GZTACSR
GapTypeUltraThermalResistantAluminiumAlloy,SteelReinforced
KTACSR
HighStrengthThermalResistantAluminiumAlloyConductor,SteelReinforced
(1)
TACSR
ThermalResistantAluminiumAlloyConductor,SteelReinforced
(1)
XTACIR
ExtraThermalResistantAluminiumAlloyConductor,InvarReinforced
ZTACSR
UltraThermalResistantAluminiumAlloyConductor,SteelReinforced
(1)
ZTACIR(3)
UltraThermalResistantAluminiumAlloyConductor,InvarReinforced
TABLEI.Differenttypesofhightemperatureconductors
(1)Additionalsufficesareallowedtodescribethetypeofcore(e.g.ACSS/GA)
(2)OriginallyknownasSSAC
(3)CouldalsobeknownasSTACIR
2.1Conductormaterials.
Theseconductors,designedforhightemperatureoperation,consistofvariouscombinationsofthealuminiumandsteelwirematerialslistedinTABLEII.
Zinc-5%AluminiumMischmetalcoatedsteelwireiscapableofoperationathighertemperaturesthannormalgalvanisedsteelwire(i.e.250ºCinsteadof200ºC).Invarsteelwirehasanotablylowerrateofthermalexpansionwhencomparedtoordinarygalvanisedsteelcorewirebuthassomewhatlowertensilestrengthandmodulus.
TypeofAluminium
Conductivity
(%IACS)
Min.Tensile
Strength
(MPa)
AllowableOperating
Temperature(ºC)
Continuous
Emergency*
HardDrawn
1350-H19
(HAL)
61.2
159-200
90
120
HighStrengthThermalresistantAluminiumAlloy
KTAL
60
225-252
150
180
ThermalResistant
TAL
60
159-176
150
180
ExtraThermal
Resistant
ZTAL
60
159-176
210
240
FullyAnnealed
1350-0
63
59–97
200–250**
250**
TABLEII.CharacteristicsofAluminiumandHighTemperatureAluminiumAlloyWires.
*Emergencyoperatingtemperatureisnotwelldefinedbutitisgenerallyagreedthattheemergencytemperatureshouldnotapplyformorethan10hoursperyear.
**Fullyannealedaluminiumstrandscanoperateattemperaturesinexcessof250oCbutarenormallylimitedtolowertemperaturesbecauseofconcernsaboutconnectorsandsteelcorewirecoatings.
TALandZTALaluminiumwireshaveessentiallythesameconductivityandtensilestrengthasordinaryelectricalconductorgradealuminiumwirebutcanoperatecontinuouslyattemperaturesupto150ºCand210ºC,respectively,withoutanylossoftensilestrengthovertime.Fullyannealedaluminiumwiresarechemicallyidenticaltoordinaryharddrawnaluminium,havemuchreducedtensilestrength,andcanoperateindefinitelyattemperaturesevenhigherthan250ºCwithoutanychangeinmechanicalorelectricalproperties.
Forthepurposeofthisbrochure,whereaconductorconstructionreferredtocouldbemadeupusingeithertheZTALortheTALalloy,itisdescribedas(Z)TAL.
Min.TensileStrength(MPa)
ModulusofElasticity(GPa)
Coef.ofLinearExpansion
(x10-6)
Galv.SteelHS
Galv.SteelEHS
1230-1320
1765
206
11.5
Alum.Clad(AC)20.3%I.A.C.S.
1103-1344
162
13.0
Zinc-5%Al.Mischmetal
Standard
HS
1380-1450
1520-1620
206(Initial)
186(Final)
11.5
Galv.Invar
Alloy
1030-1080
162
2.8-3.6
TABLEIII.CharacteristicsofSteelCoreWiresforuseinoverheadconductor.
ThedifferenttypesofconductorandcorematerialsusedinhightemperatureconductorsareshowninTABLEIV.
CoreMaterial
AluminiumAlloy
Metalmatrixcomposite
Galvanisedsteel
Aluminiumcladsteel
Galvanisedinvarsteel
Aluminiumcladinvarsteel
TA1(60TA1)
ACCR
TACSR
TACSR/AC
KTA1
KTACSR
KTACSR/AC
ZTA1(UTA1)
ZTACSR
GZTACSR
ZTACSR/AC
ZTACIR
XTA1
XTACIR
1350-0
ACSS/GA
ACSS/AW
TABLEIV.conductortypesrelatingtocoreandconductormaterial
2.2Hightemperatureconductorconstructions.
TACSRand(Z)TACIRarestrandedinthesamefashionasordinaryACSR.Theirelectricalandmechanicalpropertiesaresimplytheresultoftheircompositealuminiumandsteelwireproperties.
ACSScanbestrandedusingeitherroundortrapezoidalshapedaluminiumwires.Ineitherdesign,theconductordependsprimarilyonthesteelcorewiresformechanicalstrength.
TheuniqueinstalledpropertiesofG(Z)TACSRaretheresultofbothitswirepropertiesanditsconstruction.Theinnermostlayerof(Z)TALwiresistrapezoidalandasmallgaptothecoreislefttoallowinstallationwithtensionappliedtothesteelcoreonly.
2.2.1(Z)TACSR
(Z)TACSRhasthesameconstructionasconventionalACSR,withgalvanisedsteelwiresforthecoreand(Z)TALwires(heatresistantaluminiumalloywireswithzirconiumadded)surroundingthem.TABLEIIIshowsbasiccharacteristicsof(Z)TALwires.
FIGUREI.crosssectionoftacsrconductor
(Z)TACSRconductoris,inalmostallrespects,identicaltoconventionalACSRconductors.Thealuminiumalloyusedin(Z)TACSRhasaslightlyhigherelectricalresistivitythanstandardhard-drawnaluminium,butinallotherrespectsthetwoconductorsarealmostidentical.Unliketheconductorsdescribedbelow,(Z)TACSRisnot,bydesign,alow-sagconductor.IthasthesamethermalelongationbehaviorasACSR.Themainadvantageof(Z)TACSRisthatitsaluminiumalloywiresdonotannealattemperaturesupto150oCforTALand210oCforZTAL(Temperaturesabove100oCwouldcauseannealingofthealuminiumstrandsinstandardACSR.
(Z)TACSRcanthereforebeusedtouprateexistinglineswheresomeadditionalclearanceisavailable.Steel-coredconductors(andothernon-homogeneousconductors)havewhatisknownasa“knee-point.”Thisisatemperatureabovewhichthehigherthermalexpansionrateofaluminiumcausesallthestressoftheconductortobebornebythesteelcore.Beyondthisknee-pointtemperature,therefore,theconductorexperiencesasagincreaseduetotheexpansionofsteelalone.Thisnewexpansioncoefficientwillbelowerthanthatfortheconductoratlowertemperatures,resultinginrelativelylowsagincreaseswhenoperatedathightemperature.StandardACSRexhibitsthisproperty,butusuallyatatemperaturebeyondtheannealinglimit.TheTALalloyofTACSRallowsthisbehaviortobeexploited.AtpresentTACSRiscurrentlyusedinplaceofconventionalACSRinmorethan70%ofthetransmissionlinesinJapan.
2.2.2G(Z)TACSR
Gaptypeconductor[1]hasauniqueconstruction.Thereissmallgapbetweenthesteelcoreandinnermostshapedaluminiumlayer,inordertoallowtheconductortobetensionedonthesteelcoreonly.Thiseffectivelyfixestheconductor’sknee-pointtotheerectiontemperature,allowingthelow-sagpropertiesofthesteelcoretobeexploitedoveragreatertemperaturerange.Thegapisfilledwithheatresistantgrease(filler),toreducefrictionbetweenthesteelcoreandaluminiumlayer,andtopreventwaterpenetration.
FIGUREII.-Cross-sectionofGTACSRconductor
.
Duringinstallation[13]ofG(Z)TACSR,thealuminiumlayersofconductormustbede-stranded,exposingthesteelcore,whichcanthenbegrippedbyacome-alongclamp.Theconductoristhensaggedonthesteelcore,andaftercompre
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