中壓補償電網(wǎng)發(fā)生間歇性接地故障的檢測畢業(yè)論文外文翻譯.doc

1、.翻譯部分中文譯文中壓補償電網(wǎng)發(fā)生間歇性接地故障的檢測摘要從波蘭中壓配電網(wǎng)獲得的經(jīng)驗表明，當(dāng)?shù)嘏袛嚅g歇性接地故障的標(biāo)準(zhǔn)是不可靠的，造成這種情況的原因有兩個：一是電網(wǎng)缺乏穩(wěn)定性，二是測量信號的功率總是會降到保護啟動時的功率值以下。本文提出了一種新的基于小波分析理論的自適應(yīng)算法，它可以檢測到發(fā)生間歇性接地故障時測量信號的具體動態(tài)過程。并且通過EMTP程序包產(chǎn)生的信號對該算法進行了模擬分析。緒論一般而言，波蘭的中壓配電網(wǎng)中性點是經(jīng)消弧線圈接地運行的，以此補償短路電容電流。它主要用于農(nóng)村地區(qū)，線路為架空線路。這種電網(wǎng)的特點是發(fā)生接地故障的概率很大，占了所有記錄故障的90%多。由于接地點相對較高的過渡電

2、阻，以及降水、風(fēng)力、高低溫的影響，會導(dǎo)致線路的連續(xù)性被破壞，從而導(dǎo)致接地故障的發(fā)生。這些故障的特點是使得故障檢測與定位變得困難。在討論故障類型時，下面的故障類型可能會遇到： 具有高過渡電阻的電阻性故障， 互感器發(fā)生短路， 被周期性和非周期性破壞的故障。實際故障中，可能會表現(xiàn)出上面所列的其中一個或者所有的類型。本文只針對間歇性故障期間自動保護單元的運行情況進行分析。為了評價保護的可操作性，故障時發(fā)出的測量信號的大小和類型是確定的。能夠表明網(wǎng)絡(luò)中發(fā)生間歇性接地故障的最重要的信號是零序電壓，其值通常是通過增加相電壓的瞬時值來找出。故障定位可以通過以下幾種標(biāo)準(zhǔn)來找出： 零序電流， 零序電流和零序電壓產(chǎn)

3、生的功率， 零序電壓和零序電流之間的相位差， 零序?qū)Ъ{，或者它的有功電導(dǎo)與無功電納。然而，上述所列的標(biāo)準(zhǔn)在間歇性接地故障發(fā)生時通常是不可行的。網(wǎng)絡(luò)模型為了模擬和研究間歇性接地故障中的故障現(xiàn)象，本文建立了一個典型的中壓對稱電網(wǎng)，如圖1所示。圖1 中壓電網(wǎng)圖應(yīng)用EMTP/ATP程序包對故障進行模擬仿真，仿真參數(shù)選擇如表1所示：表1 模擬15KV網(wǎng)絡(luò)的參數(shù)電網(wǎng)電容電流101，3A故障線電容電流10，6A補償程度+15%過渡電阻2模型中假設(shè)故障發(fā)生在一條線路上，其對地電容電流為10，6A，帶負(fù)荷150KW?？紤]以下故障類型：A類型永久性故障，B類型間歇性故障，持續(xù)時間=10ms，暫停時間=10ms，C

4、類型間歇性故障，持續(xù)時間=10ms，暫停時間=100ms，D類型間歇性故障，持續(xù)時間=50ms，暫停時間=50ms，所有故障都是在線路1靠近總線處的始端被模擬的，并標(biāo)注出了如下量：網(wǎng)絡(luò)零序電壓，故障線路零序電流和非故障線路零序電流。實驗結(jié)果導(dǎo)納判據(jù)在第部分所列出的用于保護的判據(jù)中，可用于判斷間歇性接地故障這種“困難型”故障最有效的是零序?qū)Ъ{判據(jù)，或者根據(jù)它的組成部分：電導(dǎo)和電納。為了實現(xiàn)基于零序?qū)Ъ{的接地故障保護，本文運用了幅值比較（圖2中的CA1，CA2）。在這種最簡單的情況下，被比較的輸入信號是通過如下式子給出的： （1） （2） （3）系數(shù)，決定測量通道中處理信號的比值。圖2基于零序?qū)Ъ{

5、接地故障保護的等效模型這種接地故障保護取決于零序?qū)Ъ{模塊，通過比較和信號來實現(xiàn)。這種比較發(fā)生在幅值比較模塊CA1中，保護動作的條件是： （4）也就是說，安裝在第i條線路上的保護裝置的運行范圍是由導(dǎo)納矢量圖的末端決定的，其值滿足如下條件： （5）圖3中給出了這種保護的啟動響應(yīng)，這是一個光滑的導(dǎo)納弧線，覆蓋了所有的象限。保護運行的補充條件是要有合適的電壓零序分量，在這個解決方法里，啟動單元是幅值比較模塊CA2，它將信號和啟動信號相比較，判據(jù)如下： （6）其中是預(yù)定的啟動值，根據(jù)它就可以區(qū)分接地故障狀態(tài)與正常運行狀態(tài)。圖3基于導(dǎo)納的接地故障保護啟動響應(yīng)圖4給出了線路1發(fā)生永久性故障（A類型）時故障線

6、路的零序電流、非故障線路零序電流、零序電壓以及故障線路的零序?qū)Ъ{和非故障線路零序?qū)Ъ{。圖4線路1發(fā)生永久性故障故障線路零序?qū)Ъ{要比非故障線路的高出許多倍，故根據(jù)標(biāo)準(zhǔn)（4）來區(qū)分故障線路是可行的。對于中斷頻率相對較高的間歇性故障（B類型），也有類似的情況，相應(yīng)的運行結(jié)果如圖5所示。故障產(chǎn)生的暫態(tài)量衰減完之后，零序電壓依然接近永久性故障的零序電壓值，而且故障線路的零序?qū)Ъ{明顯高于非故障線路，并一直持續(xù)這種狀態(tài)。圖5線路1發(fā)生B類型間歇性接地故障圖6線路1發(fā)生C類型間歇性接地故障圖7線路1發(fā)生D類型間歇性接地故障當(dāng)故障間的暫停時間較長時（如C類型和D類型中的），區(qū)分短路線路就比較困難了。這種故障的運

7、行結(jié)果如圖6和圖7所示。整個故障期間零序電壓（與啟動信號成比例）一直保持較高的幅值。由于故障消失瞬間產(chǎn)生的電壓暫態(tài)量衰減較低，所以故障檢測不會很難。但區(qū)分故障線路時就比較困難，因為故障點循環(huán)電弧在電網(wǎng)中產(chǎn)生的暫態(tài)量，會導(dǎo)致故障線路導(dǎo)納周期性地降至非故障線路導(dǎo)納值。C類型和D類型故障均涉及到此問題。在這種情況下，基于零序?qū)Ъ{的保護方法就變得不合適了。而采用小波分析，尤其是多分辨率分解測量信號會更加合適。多分辨率小波分析小波分析的主要工具是多分辨率分解測量信號，它是通過設(shè)置多級波形附加過濾器（高通波形和低通尺度函數(shù)）實現(xiàn)的。這種可分解波形的計算程序叫Mallut算法。產(chǎn)生多分辨信號的迭代過程以波形

8、信號分解樹的形式給出，如圖8所示。迭代中的每一步，被分析信號都是經(jīng)過過濾的。迭代次數(shù)沒有限制，圖8中假設(shè)為n次。每次迭代結(jié)果包含兩部分：高頻成分和被分析信號的低頻成分，其中高頻成分在迭代期間不再需要被過濾，所以信號的分解過程就是一種多層次的迭代過程，是通過低通濾波通道實現(xiàn)的，而且連續(xù)的近似與連續(xù)的分解有關(guān)。當(dāng)選擇母小波來分析圖5、6、7中的測量信號時，“光滑型”小波（如Morlet小波）是分析信號頻譜較好的解決方案，即“光滑型”小波沿頻率軸有著較好的頻率定位，而對于沿時間軸的，選擇連續(xù)型小波（如Haar小波）會好一些。查閱了諸多小波類型的性能概要之后，筆者得出一個結(jié)論：Haar小波的性能最能滿

9、足應(yīng)用的要求，可以把計量學(xué)視為運行在保護方面的實時計量速度?；镜腍aar小波定義如下： （7）產(chǎn)生一系列小波，其成分為： （8）函數(shù)的優(yōu)點是定位效果好，通過函數(shù)不連續(xù)性有利于任意精度的定位來獲得時間上的無限精確定位，函數(shù)擴展被定義為Haar小波集。Haar縮放函數(shù)是通過如下關(guān)系式給出： （9）測量信號多級分解的實現(xiàn)過程的特點是計算效率高。Haar小波的應(yīng)用結(jié)果里，每一級的分解被限定在平均值（低通濾波器）的計算和差值（高通濾波器）的計算。平均值比較粗略（近似）而差值比較精確（詳細(xì)）。圖8信號小波分解樹測量信號的分解和間歇性接地故障時故障線路的辨別為了辨別故障時的故障線路，第部分應(yīng)用了分解測量信

10、號的迭代方法，并分析了故障線路零序電流和非故障線路零序電流。圖9中給出了B、C、D類型間歇性接地故障產(chǎn)生的信號的6級分解過程，其結(jié)果是采用基本Haar小波分析得到的，采樣頻率為10KHz。圖形中可以很明顯的看出不同頻率范圍內(nèi)信號的特點、幅值和在時間軸上的位置，同時，d1、d2、d3級別上相應(yīng)的衰減現(xiàn)象也清晰可見。在較高的分解級d4、d5、d6上，衰減現(xiàn)象期間的定位變得要么不那么明顯（非故障線路），要么很明顯（故障線路），這是區(qū)分故障線路的基礎(chǔ)，即從非故障線路中區(qū)分出故障線路。信號中斷瞬間會產(chǎn)生很明顯的“尖峰”，導(dǎo)致信號平均值遠(yuǎn)低于峰值。在d4、d5、d6級中含有高頻成分，與絕對平均值成正比，在

11、寬為N的窗口中計算出的第K個值由下式給出： （10）假設(shè)間歇性接地故障期間短路線路的辨別是通過比較C和實現(xiàn)的，前者是絕對瞬間值與絕對平均值的比，后者是絕對瞬間值與啟動值的比。 （11）圖10 B類型間歇性故障時非故障線路零序電流的5級分解圖11 C類型間歇性故障時故障線路零序電流的5級分解圖12 C類型間歇性故障時非故障線路零序電流的5級分解圖13 D類型間歇性故障時故障線路零序電流的5級分解圖14 D類型間歇性故障時非故障線路零序電流的5級分解圖15間歇性接地故障線路信號的分解算法當(dāng)保護符合條件（11）時，如果存在零序電壓（OS1=1），即接地故障依然存在，且任何關(guān)掉導(dǎo)納保護（OS2=0）的

12、脈沖都沒有發(fā)出，那么斷路器就會跳開。圖15給出了間歇性接地故障線路信號的分解算法。圖16是一種自適應(yīng)接地故障保護的模塊圖，它是傳統(tǒng)導(dǎo)納保護的擴展，基本補償模塊是WD模塊和PAC比較器，前者用于測量信號的多級分解，后者用于執(zhí)行線路分解算法。圖16自適應(yīng)接地故障保護模塊圖由于保護采用了這種邏輯結(jié)構(gòu)，WD和PAC模塊便可以增加故障切除的可靠性，而依靠傳統(tǒng)的保護標(biāo)準(zhǔn)是無法實現(xiàn)可靠保護的。總結(jié)以上關(guān)于間歇性接地故障的和測量信號表明傳統(tǒng)的故障保護裝置在故障保護及故障線路確定方面存在一些問題，當(dāng)故障暫停時間超過10毫秒時選線難度會增加。因為這種暫停有可能發(fā)生在對稱中壓配電網(wǎng)，會導(dǎo)致一些非中斷型接地故障，所以

13、應(yīng)該研究可消除這種故障的新型保護方法。分析了間歇性故障的例子之后，可以很容易地看出多級小波分解能夠明顯地區(qū)分信號特點。所有的例子表明，在較低的分解級上（d1，d2，d3），來自故障線路和非故障線路的原始信號的擾動似乎很明顯。在較高的分解級上（d4，d5，d6），故障信號和非故障信號的圖像有著明顯的不同，從而可以區(qū)分出故障線路并消除故障。英文原文Detection of the Intermittent Earth Faultsin Compensated MV NetworkAbstract The experience acquired from the Polish medium volt

14、age power distribution networks shows the unreliability of the localization criterions applied to the intermittent earth faults. It results from the lack of stability and low power level of the measuring signals falling often down below the protection's start-up level. In the paper, a new adapti

15、ve algorithm based on the wavelet analysis enabling detection of specific dynamics of the measuring signal during intermittent earth faults is presented.The algorithm was analyzed utilizing the signals generated in the EMTP program package.I. INTRODUCTIONIn general, the MV distribution networks in P

16、oland operate with the neutral point grounded through the coil to compensate the capacitive short circuit current to the earth. It refers mainly to the rural area networks where the lines are the overhead ones. Such networks are characterized by large number of the earth faults exceeding 90% of all

17、recorded faults. Due to the relatively high cross resistance at the defect's location () as well as to the effects of the weather phenomena such as discharges, gusts of wind, high and low temperatures resulting in the rupture of the line conductors continuity, the earth faults occur.Characterist

18、ics of these faults makes impossible the detection and localization of such disturbance. The following fault types can be encountered to the discussed faults group: - resistance faults of high cross resistance, - break in the live wire short circuit on the receiver side, - faults being broken cyclic

19、ally and non-cyclically.An actual fault can show either one or all of the listed features. In the paper, the analysis is limited to the automatic protective units operation during intermittent faults.To assess the protection's operability,the levels and features of measuring signals which can oc

20、cur during the fault are to be identified.The most important signal indicating occurrence of the intermittent earth fault in the network is a zero-voltage component the values of which is often found by adding the instant values of phase voltages.The criterion value of the fault localization can he:

21、 - zero current component,- power of the zero current component, and zero voltage component, - phase shift angle between the zero current and voltage components, - , or its components: active zero admittance component,or reactive,. However, the criterion values as listed above are often unreliable w

22、hen the intermittent earth fault occurs. MODEL OF NETWORKFor modeling and studies of the earth fault phenomena accompanying the intermittent earth faults,a typical medium voltage balanced network has been chosen. The scheme of modeled network is shown in Fig.1.FLg.1. Medium voltage network schemeThe

23、 faults were modeled and simulated using the EMTP/ATP program package. Chosen parameters of network assumed for simulation purposes are shown in Table 1. TABLE 1MODEUED 15 KV NETWORK PARAMETERS電網(wǎng)電容電流101，3A故障線電容電流10，6A補償程度+15%過渡電阻2In the model the assumption was made that the faults occur in a line w

24、ith to-ground-capacitive current of 10,6 A and a moderated power load of 150 kW. The following fault types have been considered:-A-type - continuous fault, -B-type - intermittent fault of =l0ms duration time,=l0ms pause time, -C-type - intermittent fault of =l0ms duration time,=l00ms pause time, -D-

25、type - intermittent fault of =50ms duration time,=50ms pause time. All faults have been modelled at the beginning of the line 1,adjacent to the bus bars.The following magnitudes have been registered: network voltage zero component, ,as well as the zero component current of the damaged line,and that

26、of the undamaged line,. RESULTS OF EXPERMENTS - ADMTI'ANCE CRITERIONAmong the criterion values for protections as specified in section 1,for the 'difficult' fault cases such as intermittent earth ones, thc most effective is either the admittance,or one of its components: conductance,or s

27、usceptance,. To implement the admittance-type eaah fault protections,the amplitude comparators (CAI,CA2 in Fig 2) are used.In the simplest case,the input signals created according to the following rules are being compared: (1) (2) (3)The,and,coefficients determine the proportionality of the input si

28、gnal processing in the measuring paths.Fig.2. Admittance-type earth fault protection -equivalent schemeThe earth fault protection responding to the zero- admittance module compares the and signals.The comparison takes place within the amplitude comparator CA1. The protection in the i - th line acts

29、when (4)It means that the operation area of protection located in the i-th line is determined by the ends of admittance vectors of values meeting the condition: (5)In Fig.3,the start-up response of such a protection is shown.It is a plain-admittance curve including equally all quarters of the comple

30、x admittance plane. Supplementary clause of the protection operation is a proper level of voltage zero component. In such a solution,the start-up unit is the amplitude comparator CA2 in which thesignal level is compared to that of thestart-up signal level, according the the clause: (6)where theis th

31、e preset start-up value due to which the earth fault can be differentiated from the normal network operation.Fig3 Start-up response of the admittance-type earth-faul protenionIn Fig.4,the current zero components in the damaged line,and in the undamaged line, voltage zero component as well as zero-ad

32、mittances in the damaged line, and undamaged line, during continuous fault (A-type) in line 1 are presented.Fig.4 Continuous eanh fault (A-type) in line 1The zero admittance measured in the damaged line is some-fold higher than that in the undamaged line.Discrimination of damaged line according to c

33、riterion (4) should not pose the problems. Similar case is for an intermittent fault of relatively high interruption frequency (B-type), the corresponding runs of nalysed magnitudes are shown in Fig.5. After decay of the transient state resulting from the fault ocurrence,the zero voltage remains at

34、the level adjacent to the voltage during the continuous fault,and the admittance measured in the damaged line is all the time evidently higher than the admittance measured in the undamaged line.Rys.5.Intermittent earth fault (B-type) in line1Fig.6.Intermittent earth fault (C-type) in line1Fig.7.Inte

35、rmittent earth fault (D-type) in line1A discrimination of the short-circuited line in case when the pause between successive faults is relatively long (long time- C and D types) can he more difficult. The runs related to such faults are shown in figures 6 and 7. During entire duration of fault,the v

36、oltage zero component(to which the start-up signal is proportional) remains at the high level;it means that the fault detection should not be difficult due to the relatively low attenuation of the voltage transients after instantaneous disappearing of the fault.However, the problems could arise with

37、 damaged line discrimination.Due to the features of the transient process in the network resulting from the cyclic arc ignitions in the fault location, the damaged line admittance falls cyclically down to the undamaged line admittance level.It refers to both the C-type and D-type faults.In such a ca

38、se,an improper operation of the admittance criterion-related protection can be expected. Better opportunities open when using the wavelet expansions,especially the multi-resolution decomposition of the measuring signals (WD). MULTI-RFSOLUTION WAVELET ANALYSISA main tool of the wavelet analysis in th

39、e proposed application is the multi-resolution decomposition of measuring signals realized by the multistage set of the wavelet complementary filters(high-pass wavelets and low-pass scaling functions).The calculating procedure leading to the decomposition is called the Mallut algorithm.The iteration

40、 process of creating the multi-resolution signal representation can be presented in the form of the wavelet signal decomposition tree as shown in Fig.8.At any iterative step,the analysed signal is filtered.The number of iterative steps is unlimited;in Fig.8,n steps have been assumed.Each iteration r

41、esults in both:the high-frequency component called a detail (Di) which is no more filtered during successive iterative steps,and the low-frequency component(Ai) of analysed original signal S,called an app roximafion.Thus,the signal decomposition process has a form of the multilevel iterative process

42、 carried out on the low-pas filtration channel, and the successive approximations are subject to the successive decomposition.When choosing the mother wavelet for analysis of measuring signals shown in figures 5,6 and7,the known rule has been taken into account the 'smooth - shape' wavelets

43、(the Morlet's wavelet, for example) are of better resolution when analysing the signal frequency spectrum,i.e. they have better localization of frequency components along the frequency axis,while the discontinuously-shaped wavelets (the Haar's wavelet,for example) have better resolution alon

44、g the time axis.Referring to the overview of properties of many wavelets types,the Authors drew a conclusion that the Haar's wavelet's properties meet in the hest way the requirements of the considered application,regarding both the metrological aspects as the speed of real-time calculations

45、 carried out in protections. The basic Haar's wavelet is defined as follows:and generates a set of wavelets with elements as:Advantage of thefunction in proposed application is their good localization as for an infinitely precise localization in time is obtained enabling arbitrary accuracy of lo

46、calization of the function discontinuity (especially that of the step - see Figures 5 and 6), the function expansion being defined regarding the Haars wavelet set. The Haars scaling function is given by relationship:Presented realization of measuring signals multi-level decomposition is characterize

47、d by high calculation efficiency.In result of application of a simple Haars wavelet,decomposition at each level is limited to calculation of the average value ( low-pass filter) or of a difference ( high- pass filter).The average value is a rough representation(approximation) while the difference is

48、 a precise representation( a detail). Fig.8 Signal wavelet decomposition tree (WD)V. DECOMPOSITION OF MEASURTRING SIGNALS AND DAMAGED LINE DISCRIMINATION DURING INNTERMITIENT EARTH FAULTS To discriminate the line in which the earth fault occurred,the iterative method of measuring signals decompositi

49、on (WD) presented in section IV was applied.The zero current component measured in the short-circuited line,and healthy line,have been analysed.In figures 9 through 14,the six-level decomposition of signals obtained for considered B - C - and D - type intermittent faults are shown.The reported resul

50、ts have heen obtained using the basic Haars wavelet,at sampling frequency of 10kHz. In figures, the characteristic features of signal in various frequency ranges,their amplitudes and position on the time axis are evident,at the instants corresponding to the commutation phenomena is especially visibl

51、e at the dl,d2 and d3 levels. At higher decomposition levels,d4,d5,d6,localization during commutation phenomena become either less visible (in the undamaged line)or dominating (in the damaged line). Such a fact can form a basis for the damaged line discrimination i.e. for distinction of the latter f

52、rom the undamaged one. Occurrence of evident spikes at the signals discontinuity instants leads to the signal average value much lower than the peak value. At the d4,d5 and d6 levels along with the high frequency components,a run proportional to the absolute average value (). the k - th value of whi

53、ch calculated in the N-width window can he found from the relationship:is presented. It is assumed that the shorted lines discrimination during the intermittent earth is carried out by comparing the C ratio of the absolute instantaneous value and absolute average value to the start.up value of the r

54、atio:Fig.10. Five-level decomposition of currenf signal,Undamaged line, B-type intermittent faultRys.11. Five-level decomposition of current signal,damaged line, C-type intermittent faultFig.12. Five-level decomposition of currenf signal,Undamaged line, C-type intermittent faultRys.13. Five-level de

55、composition of current signal,damaged line, D-type intermittent faultRys.14. Five-level decomposition of current signal,undamaged line, D-type intermittent faultFig.15. Discrimination algorithm for line with intermittent fault to ground (PAC)When the protection meets the condition (1l), the breaker will open provided that the zero voltage component, ( =l),proving the existence of the eanh fault still remains,and any pulse (OS) switching off the admittance part of protection ( =0) was not sent out. The aleorithm representing the described idea of discrimination of t