局部放電檢測原理

ReviewofLecture51.MechanismsofDielectric

AgingbyPD2.ProcessofDielectric

AgingbyPD3.TheInfluenceFactorsonAgingRate4.PD

EvaluationApproachesContents:Electricalagingisatypeofdielectricdeteriorationunderthelong-termelectricalfieldandduetothefactofpartialdischarges.DefinitionofElectricalAging:精品資料1ReviewofLecture5Damageofinternaldischargetopolymerandoil-paperbranchedtypebrushtypetree精品資料2ReviewofLecture5TheInfluenceFactorsonAgingRateElectricalfieldstressVoltagefrequencySituationofcavityandgascontentsinsideTemperatureandhumidityMechanicalforce精品資料3ReviewofLecture5Estimationbythebasicparameters(1)Apparentcharge,qa(2)Dischargeenergyandpower,WandP(3)Thephaseangleofpulses(4)UiandUeEstimationbythedistribution(statistical)graphs精品資料4Lecture6PrinciplesofElectricalDischargeDetection局部(júbù)放電檢測的基本原理精品資料5Contents1.TheBasicDiagramofERA2.TheDetectionImpedance3.TheAmplificationofImpulses4.DetectionSensitivity5.ImpulseResolution6.Calibration脈沖電流法基本原理檢測(jiǎncè)阻抗脈沖(màichōng)放大檢測靈敏度脈沖分辨率放電量標定精品資料61.TheBasicDiagramofERA1.Ahigh-voltagesourcee,freeofdischarge.2.Asamplecxaffectedbydischarges.3.AnimpedanceZd4.AcouplingcapacitanceCk6.AnamplifierA7.AnobservationunitO高壓電源，無局放試品檢測(jiǎncè)阻抗耦合電容(diànróng)放大器觀測單元Δu5.AprotectingimpedanceZm保護阻抗，低通濾波精品資料71.TheBasicDiagramofERATwoconnectingmethods(thelocationofZdincircuit):1.InserieswiththesampleCx-Seriescircuit.2.InserieswiththecouplingcapacitorCk-Parallelcircuit.SeriescircuitParallelcircuit串聯(lián)(chuànlián)回路并聯(lián)(bìnglián)回路精品資料82.TheDetectionImpedanceFunctions:(1)totransfertheimpulsecurrentintovoltageand(2)tosuppresstheinterferencesofpowerfrequencyandharmonicfromsource.RCcircuitRLCcircuit取得局部放電所產(chǎn)生(chǎnshēng)的高頻脈沖信號抑制試驗電壓的工頻及其諧波的低頻(dīpín)信號精品資料92.1theRCcircuit2.TheDetectionImpedanceDischargeextinguishes,CddischargesviaRdCt，Tunedcapacitance調(diào)諧電容Dampingconstant衰減常數(shù)精品資料102.TheDetectionImpedanceFrequencyspectrumofRCcircuitIfconsideringtherisingedgeofimpulseFT3dB精品資料11(1)Theheightoftheimpulseisproportionaltothemagnitudeqofthedischarges.(2)Cd↘→Δudm↗→sensitivity

↗.檢測阻抗上的脈沖高度(gāodù)與放電量q成正比一定(yīdìng)的q下，減小Cd可以增大Δudm,提高靈敏度(3)AcouplingcapacitanceCkisneeded,substitutingarbitrarycapacitanceforCkresultsinaverysmallΔudm

→sensitivity↘.耦合電容是必須的，采用雜散電容替代Ck導致測量得到的脈沖幅值會變得非常小,降低靈敏度2.TheDetectionImpedanceSomeconclusionsofRCcircuit:精品資料122.TheDetectionImpedance(4)TheheightoftheimpulseisindependentofRd.however,R↘→

αd

↗,theimpulsebecomesosharpandwillnotbeamplifiedfullyinsomeamplifier,whichresultinsmallerimpulseamplitude→sensitivity↘.測量得到脈沖高度雖然與Rd無關(wúguān)，但降低Rd會使得脈沖下降變快，頻譜變寬，對放大器要求高，降低靈敏度.(5)TheimpulsesdetectedbyRCcircuitisunidirectionalandone-to-onecorrespondingtodischarge,αd

↗→resolution↗RC上的脈沖(màichōng)與放電脈沖(màichōng)一一對應，脈沖(màichōng)持續(xù)時間短分辨率越高精品資料132.TheDetectionImpedance(6)Theintegralofud(t)withrespecttotisindependentonαf.Anintegratedcircuitisconvenienceforobservationofq.

e.g.lowerfrequencyamplifierUd(t)對時間的積分與上升沿無關，與q成正比，因此適合采用積分式電路觀測(guāncè)q，比如采用低頻放大器.精品資料14tud(t)2.TheDetectionImpedance2.2theRLCcircuitLRCcircuitTheimpulseisanattenuatedoscillationwiththesamecrestvoltageaswithanRCcircuit.衰減振蕩波，同RC回路峰值(fēnɡzhí)相等DampingconstantOscillatingangularfrequency衰減系數(shù)振蕩(zhèndàng)角頻率ba精品資料152.TheDetectionImpedanceab精品資料162.TheDetectionImpedanceSomeconclusionsofRLCcircuit:(1)Theheightoftheimpulseisproportionaltothemagnitudeqofthedischarges.脈沖高度(gāodù)仍然與放電量大小成正比(2)ThemaximumofUd(w)occursatω=ωd

,andthesignalmustbeamplifiedbytheamplifierthathaveabandwidthbeingequalto,orlargerthanthatofthesignal.需選用中心頻帶范圍等于ωd或者稍寬一些的放大器，可以對信號(xìnhào)中大部分能量進行放大(3)ThemaximumsensitivitycanbeobtainedwhenCd≈0andCk>>Cd靈敏度最大的條件為Cd≈0及Ck>>Cd

精品資料173.TheAmplificationofImpulses(1)wide-bandandlow-frequencyamplifier3.1Classificationofamplifier(2)tuningamplifierfa1(lowerlimitfrequency):kHz3dBfa2(upperlimitfrequency):MHz(wide-band),100~300kHz(low-frequency)

Narrowband:

Δfisabout10kHz,f0isadjustable,Medianband:

Δfisabout100kHz.窄頻帶(píndài)中頻帶(píndài)寬頻帶和低頻放大調(diào)諧放大器精品資料183.TheAmplificationofImpulses(1)AfterRCCircuitAmplifier:anidealamplifierandalowpassfilter理想(lǐxiǎng)放大器+低通濾波器3.2Characteristicsofamplifier精品資料193.TheAmplificationofImpulses(1)(2)Wide-bandamplifierlow-frequencyamplifierIntegralamplifier!精品資料203.TheAmplificationofImpulses(2)AfterRLCCircuitFrequencyselectingamplifier:anidealamplifierandatuningcircuit調(diào)諧(tiáoxié)放大器(1)α

a>αd:αresponse

(2)α

a<αd:βresponseαresponse

βresponse

精品資料214.DetectionSensitivitySensitivity:Thesmallestpartialdischargethatcanbeobservedforacertainsignal-to-noiseratio(SNR≧2).靈敏度：在保證一定的信噪比條件下，所能檢測到的最小視在放電(fàngdiàn)電荷大小Noisesources:fromtheamplifierfromthecircuit.噪聲(zàoshēng)來源放大器測試回路SNR=Us/Un≧2精品資料224.DetectionSensitivity4.1Sensitivitybyamplifiernoise以放大器噪聲(zàoshēng)決定檢測靈敏度signal精品資料234.DetectionSensitivity4.2SensitivitybycircuitnoiseTheeffectivevoltageofthenoiseoverthedetectionresistor:K-Boltzmann’sconstantCt-thecapacitancebetweenAandBT-theabsolutetemperatureABTheamplitudeofnoiseisabout2.5timesaslargeasUeff噪聲(zàoshēng)的幅值是其有效值的約2.5倍，因此噪聲(zàoshēng)的幅值Un為檢測阻抗電阻器上的噪聲(zàoshēng)電壓有效值精品資料244.DetectionSensitivityqsdeterminedbyamplifier(qAs)noiseislargerthanthatofbycircuitnoise(qCs)以測試回路(huílù)噪聲決定的檢測靈敏度要比以放大器噪聲決定的檢測靈敏度高ByamplifierBycircuitThecircuitnoiseisstepped-upbyatransformerandaddedtotheamplifier1:N用變壓器將回路噪聲(zàoshēng)升高至超過放大器噪聲(zàoshēng)精品資料255.ImpulseResolutionThedegreetowhichtheimpulsescanbeseparatedisgivenbytheresolution,whichisdefinedasthenumberofimpulsesthatcanbedistinguishedinonequadrantofa50Hzsinewave.theresolutionofthedetectioncircuit脈沖(màichōng)分辨率是指在50Hz正弦波的一個象限內(nèi)，能分辨的脈沖(màichōng)數(shù)。ImpulseresolutiondependentsontheresolutionoftheoscilloscopescreenTheresolutionoftheamplifier檢測(jiǎncè)單元分辨率放大器分辨率示波器分辨率脈沖分辨率取決于精品資料265.ImpulseResolution5.1theresolutionofthedetectioncircuit(1)RCcircuitDampingconstant衰減常數(shù)Timeconstant時間常數(shù)(shíjiānchánɡshù)Inordertobeseenseparated,theimpulsesmustrecurafteratimeintervalwhichis1.5to3timesthetimeconstantτdoftheimpulses.為了使各個脈沖(màichōng)能充分分辨，脈沖(màichōng)必須經(jīng)過約1.5~3倍的時間常數(shù)τd，精品資料275.ImpulseResolution(2)RLCcircuitDampingconstant衰減常數(shù)Timeconstant時間常數(shù)(shíjiānchánɡshù)精品資料285.ImpulseResolution5.2theresolutionoftheamplifierTheresolutionofamplifierdependsonitsbandwidthΔf放大器的分辨率取決于它的頻帶寬度Δf(1)Tuningamplifier(2)wide-bandorlowfrequencyamplifier精品資料295.3theresolutionoftheoscilloscopescreen示波器屏幕(píngmù)分辨率5.ImpulseResolutionTheminimumthicknessoftheluminouslineonanormaloscilloscopescreenisabout0.2mm示波器上可分辨(fēnbiàn)的發(fā)光線最小寬度約為0.2mmIfthescreenhasawidthof100mm,itcanresolveamaximumof500linesorimpulses.Twoquadrantsofthe50Hzsinewaveusuallyaredisplayedoverthefullwidthofthescreen.Consequently,amaximumof250impulsesperquadrantcanberesolved.屏幕寬度為100mm,可分辨最多500個脈沖，100mm為2個象限的寬度，因此分辨率為500/2=250精品資料305.4thetotalresolution5.ImpulseResolutiondetectioncircuit(1)RCcircuit(2)RLCcircuitamplifier(1)Tuningamplifier(2)wide-bandorlowfrequencyamplifieroscilloscopescreenrtotalisdeterminedbythesmallestone!總的分辨率由最小的一個(yīɡè)決定精品資料316.Ca