非晶合金铁芯Word格式.docx
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rioFreireI
IDepartamentodeEngenhariaElé
trica,UniversidadeFederaldeCampinaGrande-UFCG,RuaAprí
gioVeloso,882,CEP58429-900,CampinaGrande,PB,Brasil
IICompanhiadeEnergiaElé
tricadoEstadodeTocantins,Palmas,TO,Brasil
ABSTRACT
Inthispaperarepresentedsomeconsiderationsabouttheperformanceofsinglewireearthreturnamorphousalloycoretransformersincomparisonwithconventionalsiliconsteelsheetscorestransformersusedinruralelectricenergydistributionnetwork.Ithasbeenrecognizedthatamorphousmetalcoretransformersimproveelectricalpowerdistributionefficiencybyreducingtransformercorelosses.Thisreductionisduetosomeelectromagneticpropertiesoftheamorphousalloyssuchas:
highmagneticpermeability,highresistivity,andlowcoercivity.Experimentalresultsobtainedwithsomesingle-phase,60
Hz,5
kVAamorphouscoretransformersinstalledinaruralareaelectricdistributionsysteminNorthernBrazilhavebeenconfirmingtheirsuperiorperformanceincomparisontoidenticalnominalratedtransformersbuiltwithconventionalsiliconsteelcores,particularlywithregardtotheexcitationpowerandtotheno-loadlosses.
Keywords:
amorphousalloy,corelosses,energyefficiency,transformer
1.Introduction
Singlewireearthreturn(SWER)coretransformersarecharacterizedbyhavingonlyonebushingonthehighvoltagesideandtwoormorebushingsonthelowvoltageside.Generally,thesetransformersaredesignedandconstructedtobeusedinruralelectricitydistribution.UsuallySWERcoretransformersarelow-costequipmentandhaveapparentpowerof5,10and15
kVA.
Thedistributionofelectricitypowerinruralareashasgenerallyhighcostofoperationfortheconcessionarycompaniesduetotheseasonalityoftheirloads.Undertheseconditions,thelossesinthecoresofthetransformersmanufacturedwithconventionalgrainorientedsiliconsteelbecomesignificantwhenthesetransformersoperateinconditionsoflightloadornoload.Insuchcircumstances,partofthetotalcurrentabsorbedbytheelectricsystemisusedinthemagnetizingcoretransformersprocess.However,theselossescanbereduced,whichcanbeachievedbyreplacingtheconventionalbytransformersforamorphousmetal-basedtransformers,becauseithasbeenrecognizedthatamorphousmetalcoretransformersimproveelectricalpowerdistributionefficiencybyreducingexcitationcurrentandcorelosses1.Thisreductionisduetosomeelectromagneticpropertiesoftheamorphousalloyssuchas:
highmagneticpermeability,highresistivity,andlowcoactivity2.
InthispaperarepresentedsomeexperimentalresultsobtainedwithSWER,60
kVAamorphouscoretransformersinstalledinaruralareaelectricdistributionsystem,distant50
kmfromPalmas(capitalofthestateofTocantins),locatedintheAmazonregionofBrazil.
Fromtheseresultsitcanbeobservedthesuperiorperformanceofamorphouscoretransformersincomparisontoidenticaltransformersmanufacturedwithconventionalcold-rolledgrain-oriented(CRGO)siliconsteelcores,particularlywithregardtotheexcitationcurrentandtotheno-loadlosses.Beforebeinginstalled,alltransformersweresubmittedtotestasstatedatBrazilianStandards.
2.FromAcademicResearchtoElectricDistributionSystems
Chronologically,thedevelopmentofamorphousalloyspotentiallyapplicableintransformercoresbeganin1975.However,theintroductionofthesematerialsinthemarketonlyhappenedin1976,withthefirstamorphousmetaldistributiontransformer(AMDT),builtatMIT'
sLincolnLaboratory(USA).Inthatopportunity,a30
kVAtransformerprototype,withanamorphousmaterialcore,wascomparedtoaconventionalsiliconsteelcoretransformerofequalnominalratedpower.Oncethecomparativetestswerecarriedout,theresultsobtainedwerefavorabletoAMDT,particularlyintheaspectsrelativetothelossesandtheexcitationcurrent:
therewasareductionof60%inthetotallosses(87.5%inthecorelossesand21%inthecopperlosses)andtheexcitationcurrentwasreducedfrom2.5to0.12
A.However,inwhatconcernstheweight,AMDTpresentedanincreaseof15%incomparisontotheconventionalsiliconsteelcoretransformer3.
Intheearly1980'
s,EPRI(ElectricPowerResearchInstitute,USA)andGeneralElectriclaunchedaprojectinwhich25unitsofpre-prototype25
kVA,15
kVamorphousmetalcoredistributiontransformers(AMDT)weretestedfortwoyears,followedbydesigningandtesting1000unitsofthesamesizeAMDTsontheirdistributionsystems.Thepurposeofthefieldtrialwastoconferthelong-termstabilityofcorelossinamorphousmetaltransformersunderactualoperationconditions.Tenyearslater,therewasanestimated60000to70000
AMDTinstalledthroughouttheworld.
InBrazil,thefirststudiesandexperimentaltestshadtheirorigininlaboratoriesofsomedifferentinstitutions,intheearly1990'
s4,passing,soonafter,toassemblybyindustrialmanufacturers5.
3.ExperimentalProcedure
In
Figure
1
areshownsomeunitsof5
kVASWERtransformerswithamorphousalloycore(Fe78B13Si9)manufacturedbyBrazilianindustriesITB.Seventeenofthesetransformersweresubmittedtoopencircuitandshortcircuittestsinthelaboratoryofthefactory,inJanuary2009.
Thefollowingarelistedthemainelectriccharacteristicsoftransformersundertest:
•Ratedpower
kVA
=
5;
•Phases
1;
•Frequency
60
Hz;
•Highvoltageside(kV):
20.90to18.19;
•Lowvoltageside(V):
440/220;
•Ratedcurrentinhighvoltageside:
0.25
A;
•Ratedcurrentinlowvoltageside:
11.36
•Subtractivepolarity.
AllroutinetestscarriedoutinaccordancewithspecificBrazilianStandards.Butbecausethemaininterestisdirectlyrelatedtotheenergyefficiencyinthispaperareonlypresentedtwotests:
no-loadandshortcircuit.
4.Results
Table
arepresentedthecomparativevaluesconcerninglossesandexcitationcurrentinsingle-phase5
kVAtransformerswithmaximumtension24.2and36.2
kV,accordingtoBrazilianStandardNBR54406.
Theno-loadlossesandtheexcitationcurrentmeasurementswereperformedatnominalfrequency,applyingratedvoltagetothelowvoltagewindingandleavingthehighvoltageinopencircuit,asrequiredbyBrazilianStandardNBR53567.
2
arepresentedingraphform,theresultsofcomparativetestsbetweenseventeentransformerswithamorphousalloycoreandseventeentransformerswithCRGOsiliconsteelcore,allwiththesamenominalpowerrating(5
kVA).
5.Discussion
Sincetheexcitationcurrentissmall,theJoulelossesinthewindingsarenegligible;
thelossesresultingfromtheprocessofmagnetizationanddemagnetizationofthecorearesignificant.Inanalyticalterms,theselossesarecharacterizedashysteresis,eddycurrentsandanomalouslosses.
Thehysteresislossisdirectlyproportionaltothefrequencyofsupplyvoltageandeddycurrentlossisdirectlyproportionaltothesquareofthefrequencyofthesource.Thisisthereasonwhythistestshouldbeconductedatnominalfrequency.
Physically,thereasonfortheexcitationcurrentissmallcomparedtothenominalcurrentofthewinding,duetothefactthattheno-loadtransformercanberepresentedbyahigh-impedanceloadwithrespecttothepowersupply.Andthisimpedancewillbegreaterthelargerthemagneticpermeabilityandelectricalresistivityofcorematerial.
InthespecificcaseofamorphousFe78B13Si9
usedinthecoresoftransformersthesevaluesarehigherthanthevaluesforGOFeSialloysusedinconventionaltransformers.Therefore,themaximumrelativemagneticpermeabilityofamorphousFe78B13Si9,60
Hz,isaround70000,whilethevalueofthisquantityfortheGOFeSiat60
Hz,isaround40000.SincethevalueoftheelectricalresistivityofamorphousFe78B13Si9
isbetween130to135
µ
Ω.m,whilethevalueofthismagnitudefortheGOFeSiisaround10to47
Ω.m.Notethatthehighvalueofrelativepermeabilityprovidesabettermagneticcouplingandthehighvalueofelectricalresistivityresultsinsmallereddycurrentlossesinthecore.
NotealsothatalthoughbothtransformershavevaluesofexcitationcurrentandloadlossvaluesbelowtheBrazilianStandardNBR
5440recommended,itappearsthatthevaluesoftheexcitationcurrent(0.13
A)andno-loadlosses(8
W)fortransformerswithamorphouscoretransformersarelowerthanvaluesoftheconventionaltransformers,thatare0.36
Aand36
W,respectively.
Themeasurementofshortcircuitlosseswasperformedatnominalfrequency,connectingthehighvoltageterminalstothesourceandatthesametimekeepingthelowvoltagewindingsshort-circuited,asshowninFigure
3.
arepresentedthecomparativevaluesconcerningshort-circuittestinsingle-phase5
kV,accordingtoBrazilianStandardNBR
54406.
Ascanbeseenin
2,therearevirtuallynodifferencesbetweenthevaluesobtainedinshort-circuittestforbothtypesoftransformers.This,infact,wasexpected,sincetheactivelossesrelatetotheJouleeffectinthewindingsandhasnodependenceonthemagneticmaterialcoreandshort-circuitcurrentdependsontheimpedanceofashortcircuit.
Aftersubmittedtoroutinetestsinthelaboratory,theseventeen5
kVASWERamorphouscoretransformerswereinstalledinaruralareaelectricdistributionsysteminNorthernBrazil,