局部放電檢測原理

1、1Review of Lecture 51. Mechanisms of Dielectric Aging by PD2. Process of Dielectric Aging by PD3. The Influence Factors on Aging Rate4. PD Evaluation ApproachesContents: Electrical aging is a type of dielectric deterioration under the long-term electrical field and due to the fact of partial dischar

2、ges.Definition of Electrical Aging :2Review of Lecture 5Damage of internal discharge to polymer and oil-paperbranched type brush type tree 3Review of Lecture 5The Influence Factors on Aging Rate d c b a HV e 4Review of Lecture 5Estimation by the basic parameters(1) Apparent charge, qa(2) Discharge e

3、nergy and power, W and P(3) The phase angle of pulses (4) Ui and Ue Estimation by the distribution (statistical) graphstqa(t)qitiui00.0020.0040.0060.0080.0100.0120.0140.0160.0180.020-0.500.55Lecture 6 Principles of Electrical Discharge Detection局部放電檢測的基本原理61. The Basic Diagram of ERA2. The Detection

4、 Impedance3. The Amplification of Impulses4. Detection Sensitivity5. Impulse Resolution6. Calibration7CxZdZmeCkoA1. The Basic Diagram of ERA1. A high-voltage source e, free of discharge.2. A sample cx affected by discharges.3. An impedance Zd4. A coupling capacitance Ck6. An amplifier A7. An observa

5、tion unit O高壓電源，無局放試品檢測阻抗耦合電容放大器觀測單元ui5. A protecting impedance Zm保護阻抗，低通濾波81. The Basic Diagram of ERACxZdZmeCkoACxZdZmeCkoATwo connecting methods (the location of Zd in circuit):1. In series with the sample Cx- Series circuit.2. In series with the coupling capacitor Ck- Parallel circuit.Series cir

6、cuitParallel circuit串聯(lián)回路并聯(lián)回路92. The Detection ImpedanceFunctions:(1) to transfer the impulse current into voltage and(2) to suppress the interferences of power frequency and harmonic from source.CdRdCdRdCdLdRdCdLdRd取得局部放電所產(chǎn)生的高頻脈沖信號抑制試驗電壓的工頻及其諧波的低頻信號102.1 the RC circuit2. The Detection ImpedanceCdRdC

7、kCxABu/dkdkxCCCCCqudkkdmCCCuudkkdkdkxCCCCCCCCqxkddCCCCq)1 ( )1 (kdxdvCCCCCvdmCquduDischarge extinguishes, Cd discharges via Rdddtdmtdmdeueutu/)(dkxkxddtdRCCCCCRC )(Ct，Tuned capacitance調(diào)諧電容tvddeCqtu)()/(1tddCRDamping constant 衰減常數(shù)112. The Detection Impedancedmu)(tudt2/122)()(dvdCqUFrequency spectrum

8、of RC circuittvddeCqtu)(If considering the rising edge of impulse )(/11)1 ()(/ttfdvtddfddeeCqeutuFTfUdm2dmU)(),(fUUddh2df,tdhCR1tddCRf2123dB12(1)The height of the impulse is proportional to the magnitude q of the discharges.(2) Cd ud m sensitivity .檢測阻抗上的脈沖高度與放電量q成正比一定的q下，減小Cd可以增大udm ,提高靈敏度xkdddmCCC

9、Cqu)1 ( (3)A coupling capacitance Ck is needed, substituting arbitrary capacitance for Ck results in a very small udm sensitivity.耦合電容是必須的，采用雜散電容替代Ck導(dǎo)致測量得到的脈沖幅值會變得非常小,降低靈敏度2. The Detection ImpedanceSome conclusions of RC circuit:132. The Detection ImpedancedU)(tudt(4) The height of the impulse is in

10、dependent of Rd. however, R d , the impulse become so sharp and will not be amplified fully in some amplifier, which result in smaller impulse amplitude sensitivity.測量得到脈沖高度雖然與Rd無關(guān)，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.)/(1tddCRxkdddmCCCCqu)1 ( (5)The impulses detected by RC circuit is unidirectional an

11、d one-to- one corresponding to discharge, d resolutionRC上的脈沖與放電脈沖一一對應(yīng)，脈沖持續(xù)時間短分辨率越高142. The Detection ImpedancedU)(tudt )(/11)(ttfdvdfdeeCqtudvfdfdvdCqCqdttu11/11)(0(6) The integral of ud(t) with respect to t is independent on f. An integrated circuit is convenience for observation of q . e.g. lower

12、frequency amplifierUd(t)對時間的積分與上升沿?zé)o關(guān)，與q成正比，因此適合采用積分式電路觀測q，比如采用低頻放大器.15tud(t)2. The Detection Impedance2.2 the RLC circuitCdRdCkCxABLdLRC circuitduu)2/(1tddCRtddCL1The impulse is an attenuated oscillation with the same crest voltage as with an RC circuit. 衰減振蕩波，同RC回路峰值相等Damping constantOscillating an

13、gular frequency衰減系數(shù)振蕩角頻率)cos()(teCqtudtvddddcos)cos()/(11)(2tdtfdvdfdeteCqtu ba162. The Detection Impedancetud(t)a b 212222222122/dddddVdLRCqU dUd17)cos()(teCqtudtvdd)1 (kdxdvCCCCC2. The Detection ImpedanceSome conclusions of RLC circuit:(1)The height of the impulse is proportional to the magnitude

14、q of the discharges.脈沖高度仍然與放電量大小成正比(2)The maximum of Ud(w) occurs at =d , and the signal must be amplified by the amplifier that have a bandwidth being equal to, or larger than that of the signal. dUd需選用中心頻帶范圍等于d或者稍寬一些的放大器，可以對信號中大部分能量進行放大(3) The maximum sensitivity can be obtained when Cd0 and CkCd

15、靈敏度最大的條件為Cd0及CkCd 183. The Amplification of ImpulsesfA121fa1fa2fA121f0f(1)wide-band and low-frequency amplifier3.1 Classification of amplifier(2)tuning amplifierfa1(lower limit frequency): k Hz3dBfa2(upper limit frequency): MHz (wide-band), 100300kHz (low-frequency) Narrow band: f is about 10k Hz, f

16、0 is adjustable,Median band: f is about 100k Hz.窄頻帶中頻帶寬頻帶和低頻放大調(diào)諧放大器19CxZmeCkRaARdCaudAmplifierua3. The Amplification of Impulses(1)After RC CircuitAmplifier : an ideal amplifier and a low pass filter 理想放大器+低通濾波器tvddeCqtu)(22/1aaaafCRadttavadaeeCqAtu)(22)2/(1dtddfCRfA121fa1fa2aaaCRf212fUdm2dmU)(),(fU

17、Uddh2df,3.2 Characteristics of amplifier203. The Amplification of ImpulsesdaadttavadaeeCqAtu)(1)()(ttvaadeeCqAtu1/adttvdaeeCqAtuda(2)()(ttdavadaeeCqAtutdetaeuttaetdeWide-band amplifierlow-frequency amplifierdvdCqdttu0)(Integral amplifier!213. The Amplification of Impulses(2) After RLC CircuitCxZmeCk

18、RaGRdCaLaLdCdAmplifieruduaFrequency selecting amplifier : an ideal amplifier and a tuning circuit調(diào)諧放大器uatuat(1) a d: response (2) a d: response response response dUd224. Detection Sensitivity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電荷大小Noise sources:n from the amplifiern from the circuit.噪聲來源放大器測試回路4.724.734.74

19、4.754.764.77x 10-3-0.1-0.0500.050.1tUUsUnSNR=Us/Un 234. Detection Sensitivity4.1 Sensitivity by amplifier noise以放大器噪聲決定檢測靈敏度,)(tvddeCqtu)1 (kdxdvCCCCC)(tudA(f1,f2)vamCqAuZd2namuunvsuCq22NSvnsCuq2vsCq signalvamCqu244. Detection Sensitivity4.2 Sensitivity by circuit noiseThe effective voltage of the n

20、oise over the detection resistor:teffCKTUK-Boltzmanns constantCt-the capacitance between A and BT-the absolute temperatureCdRdCkCxABA BtnCKTU5 . 2The amplitude of noise is about 2.5 times as large as Ueff噪聲的幅值是其有效值的約2.5倍，因此噪聲的幅值Un為kxCCn/vnCKTnU) 1(5 . 2)/(kxkxtCCCCCdC)1 (kdxdvCCCCCvvsCKTnCq) 1(5 . 2

21、2vsCKTnq) 1(5vsCq 檢測阻抗電阻器上的噪聲電壓有效值254. Detection SensitivityvAsCqvCsCq)1 (kdxdvCCCCCqs determined by amplifier (qAs)noise is larger than that of by circuit noise(qCs)以測試回路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CxZmeCkRdACdBy amplifierBy circuitThe circuit noise is stepped-up by a transformer and added to the am

22、plifier1:N用變壓器將回路噪聲升高至超過放大器噪聲265. Impulse ResolutionThe degree to which the impulses can be separated is given by the resolution, which is defined as the number of impulses that can be distinguished in one quadrant of a 50Hz sine wave. uthe resolution of the detection circuit脈沖分辨率是指在50Hz正弦波的一個象限內(nèi)，能分

23、辨的脈沖數(shù)。Impulse resolution dependents onuthe resolution of the oscilloscope screenuThe resolution of the amplifier檢測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275. Impulse Resolution5.1 the resolution of the detection circuit(1) RC circuittvddeCqtu)(vCq)(tudttddCR)/(1tddCRDamping constant 衰減常數(shù)Time constant 時間常數(shù)In order

24、 to be seen separated, the impulses must recur after a time interval which is 1.5 to 3 times the time constant d of the impulses.為了使各個脈沖能充分分辨，脈沖必須經(jīng)過約1.53倍的時間常數(shù)d ，tddRCRt35 . 135 . 1Rtr/4501d3/4501tdCR6001285. Impulse Resolution(2) RLC circuit)cos()(teCqtudtvdd)2/(1tddCRDamping constant 衰減常數(shù)tddCR2Tim

25、e constant 時間常數(shù)dRt3tdCR6Rtr/4501tdCR6/4501tdCR12001295. Impulse Resolution5.2 the resolution of the amplifierfA121f0fThe resolution of amplifier depends on its bandwidthf放大器的分辨率取決于它的頻帶寬度f(1) Tuning amplifierfCRaaa12fftaR133Rtr/4501f1/4501200f(2) wide-band or low frequency amplifier221fCRaaaf21fftaR2

26、1233Rtr/4501f21/4501100ffA121fa1fa2aaaCRf212305.3 the resolution of the oscilloscope screen示波器屏幕分辨率5. Impulse ResolutionThe minimum thickness of the luminous line on a normal oscilloscope screen is about 0.2mm示波器上可分辨的發(fā)光線最小寬度約為0.2mmIf the screen has a width of 100mm, it can resolve a maximum of 500 l

27、ines or impulses. Two quadrants of the 50Hz sine wave usually are displayed over the full width of the screen. Consequently, a maximum of 250 impulses per quadrant can be resolved.5002 . 010025021500r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=250315.4 the total resolution5. Impulse Resolutiondetection circuit(1) RC circuitRtr/4501tdCR6001(2) RLC circuitRtr/4501tdCR12001amplifier(1) Tuning amplifier200fRtr/4501(2) wide-band or low frequency amplifierRtr/4501100foscilloscope screen250241500rrto