| Neutral insulated or Peterson coil earthed power network is widely used in China's 6～66kV distribution networks. It can play an important role in improving power supply reliability of distribution networks. But when single phase grounding fault occurs in this kind of network, the faulty line detection is very difficult to be realized because of the low fault current. In order to solve this problem, many researches are carried out mainly in two fields. One is to improve the precision and sensibility of detecting elements, and the other is to adopt mathematical methods or tools to analyze original fault information in different ways ,so as to find new faulty line detection theory. Great achievements are made after researches of many decades, a lot of kinds of detecting elements and faulty line detection theories are brought forward, but there is no perfect solution till now.In this background , this paper comprehensively expatiated the basal theoretics of small current grounding power system and detailedly described the characteristics of steady and transient state of single phase grounding fault occur in it. Also, this paper introducted every aspects of faulty line detection technology and commented on the strengths and weakness of each theory. And then ,a simulation model based on PSB toolbox of MATLAB Simulink is established ,which is referring to the Yangjiaping power supply bureau distribution networks.Aim at the faulty line detection theory based on wavelet packets ,which is the most popular topic of faulty line detection research nowadays, an improved faulty line detection method is proposed in this paper by applying both the wavelet packets technology and the correlation analysis technology of digital signal processing. Firstly, each line's transient zero sequence current, which appears in the small current neutral grounding power system when a single phase grounding fault occurring, is decomposed to obtain the suitable outputs of specific frequency bands. And the characteristic frequency band of each line, in which the transient capacity current is most concentrated, is chosen out adaptively according to the view of maximum energy. Secondly, the correlation analysis between each line's waveform of wavelet packets decomposition coefficient corresponding to its characteristic frequency band is carried out, so as to acquire the correlation matrix and then get each line's integrated correlation coefficient. Finally, the result of faulty line detection is obtained, which is arranged by the size of the prob- abilities to occur the grounding fault. Large numbers of MATLAB simulation result showed that this method based on correlation analysis of wavelet packet muti-frequency had ameliorated the existent faulty line detection technology based on the first semi-wave method or on the traditional wavelet packets method. It had made great progress in enhancing the accuracy of faulty line detection.But many experiences showed that there is no single faulty line detection method suitable for all kings of practial situation. So this paper introduced information fosion technology to folly make use of all the steady-state and transient-state information of sing-phase-to-earth fault current and proposed a multi-criterion fosion faulty line detection method. Large numbers of MATLAB simulation result showed that this method based on information fosion technology had integrated many useful faulty line detection method and can exert the excellences of each one, enlarge the range of right estimation for faulty line. It has more strong adaptability and fault tolerant capability than the single method, and made more progress in enhancing the accuracy of faulty line detection. It ensured the reliability of faulty line detection and has great perspective in the future.
|
PDF Full Text Request