電氣工程與自動化外文翻譯---中壓補償電網發(fā)生間歇性接地故障的檢測（英文）

1、Paper accepted for presentation at 2003 IEEE Bologna PowerTech Conference, June 23-26, Bologna, Italy Detection of the Intermittent Earth Faults in Compensated MV Network Jozef Lorenc', Kazimierz Musierowicz“, Andr

2、zej Kwapisz“ Abstract - The experience acquired from the Polish medium voltage power distribution networks shows the nnreliability of the localization criterions applied to the intermittent earth faults. It results

3、 fmm 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 adaptive algorithm based on the wavelet analysis enabling detec

4、tion 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. INTRODUCTION In general, th

5、e MV distribution networks in Poland 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 line

6、s are the overhead ones. Such networks are characterized by large number of the earth faults exceeding 90% of all recorded faults. Due to the relatively high cross resistance at the defect's location (RF) as well

7、 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. Characteristics of these fau

8、lts makes impossible the detection and localization of such disturbance [3]. The following fault types can be encountered to the discussed faults group: - - - An actual fault can show either one or all of the

9、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

10、which can occur 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 a

11、dding the instant values of phase voltages. The criterion value of the fault localization can he: - zero current component, b resistance faults of high cross resistance , RF, break in the live wire short circuit on

12、 the receiver side, faults being broken cyclically and non-cyclically. - power of the zero current component, b, and zero voltage component, UO, phase shift angle between the zero current and voltage components, z

13、ero admittance component, YO, or its components: active Go or reactive Bo. However, the criterion values as listed above are often - - unreliable when the intermittent earth fault occurs. 11. MODEL OF NETWORK For mo

14、deling 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. I FLg.1. Medium v

15、oltage network scheme The faults were modeled and simulated using the EMTP/ATP program package. Chosen parameters of network 'assumed for simulation purposes are shown in Table 1. r.mm I MODEUED 15 KV NETWORK P

16、ARAMErrr(S Network capacity current b Fault line capacity cnnent la^ 1 101,3A I 10,6A Decompensation level I +IS% Cmss resistance RP Inn The work has been supported by the State Committee for Scientific Resear

17、ch (DS.-41- 612) and Famework Programme 5 (FP5). *'The authors are from Poznan University of rechnoiagy; jo2ef.lorenc@'put.poznan.pl kazimie~.musiemwici@pnl.poznan.pl andrzej.kwapisr@ajax.epe.put.pznan.pl

18、In the model the assumption was made that the faults occur in a line with to-ground-capacitive current of 10,6 A and a moderated power load of 150 kW. The following fault types have been considered: 0-7803-7967-5/03/$

19、17.00 02003 IEEE I I I i Time (mr) Ag.1 ht-nent earth fault ( D-type) in line 1 A discrimination of the short-circuited line in case when the pause between successive faults is relatively long (long time t, - C an

20、d 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 voltage zero component (to which the start-up signal S ,is proportional) remains at

21、 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 ar

22、ise with 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

23、 undamaged line admittance level. It refers to both the C-type and D-type faults. In such a case, an improper operation of the admittance criterion-related protection can be expected. Better opportunities open when u

24、sing the wavelet expansions [2], [4], 1.51, especially the multi-resolution decomposition [6] of the measuring signals (WD). Iv. MULTI-RFSOLUTION WAVELET ANALYSIS A main tool of the wavelet analysis in the proposed ap

25、plication 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

26、leading to the decomposition is called the Mallut algorithm [l]. The iteration process of creating the multi-resolution signal representation can he presented in the form of the wavelet signal decomposition tree as s

27、hown 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 results in both: the high-frequency component call

28、ed U 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 f

29、orm of the multilevel iterative process carried out on the low-pas filtration channel, and the successive approximations are subject to the successive decomposition. When choosing the mother wavelet for analys

30、is of measuring signals shown in figures 5,6 and 7, the known rule has been taken into account the 'smooth - shape' wavelets (the Morlet's wavelet, for example) are of better resolution when analysing th

31、e 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

32、along 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

33、application, regarding both the metrological aspects as the speed of real-time calculations carried out in protections. The basic Haar's wavelet is defined as follows: 1 f o r O < f < + If/@)= -1 for+-<

34、;t-<I ( 7 )1 0 for other f and generates a set of wavelets with elements as 1f/,,(t)=2~““~(2-“t-n) form,n= ..., -2,-l,O, 1,2, .. . ( 8 )Advantage of the vm function in proposed application is their good localizati