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2
WindingD.C.
resistance
measurement
TomeasureD.C.resistanceofHVandLVwindingsatwindingendbyHS305,Thetestresultoferror:
phase<
4%,line<
2%.
K=(Rmax-Rmin.)/Rave.
Kistheunbalancedrateofthree-phaseDCresistance.
3
Measurementof
insulation
resistance
Transformerenclosureshouldbewellgrounded,thentomeasureinsulationresistance。
BymeasurementmeterZC11D-5,2500V.(HV:
>
1000MΩ;
LV:
50MΩ)
Connectiondiagramofinsulationresistancemeasurementisasfollowing:
4
A.C.voltage
withstandtest
Appliedvoltagewithstandtestuses50Hzsine-wavesingle-phaseA.C.voltage,testedwindingoftransformerisshortedandenergized,theothernon-testedwindingsareshortedgrounding,alsothecore,clampandtankaregrounded.Thistestisconsideredtobequalified,ifthereisnodischarge,breakdownandnosuddendecreaseoftestingvoltage.Thetestingvoltagesare:
HV&
neutral-38kV60s,LV-3kV60s.(13.8KV/0.4KV)
neutral-50kV60s,LV-3kV60s.(22KV/0.4KV)
5
Inducewithstandvoltage
1、inducewithstandvoltage
Thewiringdiagramofinducewithstandvoltagetestisasfollowing:
L.Vacsurgemagnetism,HVsideisopen-circuit.
Wiringdiagramisfollowing:
H.Vinducewithstandvoltage:
(13.8kV×
2;
22kV×
2)
Use50kVA、200Hzgeneratorsetthree-phaseoutputtoL.Vwindingoftestedtransformer.H.Vtappositionisat3step,Testlastsfor30s(Formula:
testtime=120*50/200=30s).Thistestisconsideredtobequalifiedifthereisnofollowingsituation----current-increasing,difficultytoapplyvoltage,dischargeandbreakdownandotherabnormalsituation.
t=120*fr/f
t:
testtime
fr:
ratedfrequency
f:
testfrequency
6
no-loadlossand
no-loadcurrent
ThetestedtransformerisenergizedatLVsideby200kVAthreephasebooster.
Applythe400VvoltagefromL.Vsidetosurgemagnestim,MeasuretheI0andP0’.Aftercorrection,I0%andP0shouldmeettherequirementsoftechnicalspecification(13.8kV/0.4kV:
≤1.15kW;
22kV/0.4kV:
≤1.35kW).Duringthetest,HVsideisopen-circuit,neutralpointisearthed.
Po=Po’(1+d)
Po:
no-loadlossafterrevised.
Po’:
measuredno-loadloss
d=(Uavevalue-Uvirtualvalue)/Uavevalue
7
Measurementofshort-circuitimpedanceandon-loadloss
Accordingtorequirementsofthestandard,theloadlossandimpedanceatratedstep,shouldbemeasured.ThemeasurementshouldbeconductedbetweenHVandLVwindingswithHVenergizedandLVshort-circuit.Atratedstep,themeasurementvalueshouldbeaccordingtothetechnicalrequirement(13.8kV/0.4kV:
≤5.3kW;
≤5.41kW).
Thepowersupplyforthistestisfrom200kVAgeneratorunitandtransmitstotestedtransformerinputtermina
P115℃=(Pk-Pr)/K+Pr*K
P115℃:
loadlossat115℃Pk:
measuredloadlossPr:
resistancelossK:
temperaturecoefficient
P115℃:
loadlossat115℃
Pk:
measuredloadloss
Pr:
resistanceloss
K:
8
Measurementofpartialdischarge
Appliedvoltagephasetophaseis1.8Ur(Urisratedvoltage),anddurationofvoltageapplicationis30s.Thenreducingthevoltagephasetophaseto1.3Uratholdingthesupply,lasts3min;
Inthecourse,measuringpartialdischarge.
Ⅰ.Thetestcircuitforthreephasethransformerpartialdischargetest.
1----LVwinding2----HVwinding3----MeasurementintrumentS----Switch
Ⅱ.Themethodofapplingvoltageis9diagram.
9Diagramthemethodofapplingvoltageforthepartialdischarge.
9
soundlevel
Duringtest,HVtapchangershouldbeatratedstep,ApplyingratedvoltageandratedfrequencyatLVside.Thesoundpressurelevelshouldbemeasuredatspecifiedlinewhichis1mfromreferenceradiatingsurface.Distancebetweentwoadjacentmeasuringpointsshouldbelessthan1m.
Beforeandaftersoundleveltest,backgroundsoundlevelalsoshouldbemeasured.Atlasttocorrectandcalculatethemeasureddataaccordingtostandards,theresultshouldmeetthecustomer’srequirement:
<
47dB.
10
Lightningimpulsetest
Thenegativefull-wavelightningimpulsetestsofHV,LVterminalareasfollowing:
Full-wave:
1.2±
30%/50±
20%μs,HV(peak):
95kV(13.8KV/0.4KV)LV(peak):
125kV(22KV/0.4KV)
Testprocedureisasfollowing:
Negativefull-waveimpulseatfirstreduced50%voltage;
Negativefull-waveimpulseatthirdratedvoltage.Duringtest,there’snoabnormalsoundandthewaveshapewillnotbeabnormal,Thistestisconsideredtobequalified.
11
temperaturerise
Temperaturetest(typetest)1.Technicaltestrequirement:
Temperatureriseofwinding:
100KTestsupply:
200KVA,50Hzthreephaseboober
Thewindingstemperature-risewerecalculatedbytheformula△θ’c=△θc[1+(△θe/△θc)1.25]0.8usingtheresultobtainedbytwoseparatetemperature-rise;
thefirsttestwithonluno-loadloss,thesecondtestwithonlyloadloss.
Firsttest
Thehigh-voltagewindingofthetransformerwasop-circuitedandthelow-voltagewindingwassuppliedattheratedvoltage(400V);
thesesupplywereapplieduntilthesteady-stateconditionwasreached.
Then,resistanceofwindingsweremeasuredindirectcurrent(seegraphics)inordertodeterminetheirtemperature-risebyresistancevariationmethod.
Secondtest
Thelow-voltagewindingofthetransformerwasshort-circuitedandthehigh-voltagewindingwassuppliedatatastvoltagetoallowtheratedcurrent(13.8kV/0.4kV:
26.36A;
16.53A)topassthroughthehigh-voltagewinding;
thesesupplywasapplieduntilthesteady-stateconditionwasreached.
Then,resistancesofwindingsweremeasuredindirectcurrentinordertodeterminetheirtemperature-rise△θcbyresistancevariationmethod.