Research On Fault Line Selection In Small Current Grounded System Based On Evidence Theory

Neutral ineffectively earthed systems include neutral unearthed, neutral earthed by high resistance and neutral resonance earthed systems. Thus the fault line selection for the single-phase grounding fault has always been an important subject.Rapid and accurate detecting of fault line is the guarantee for power system safety operation.Two aspects of research works to solve this problem have been done in this thesis:(1) D-S evidence theory was used in this article to fuse different fault line selection methods into compositive index for improving fault line judging ability. The fault characteristics of distribution network single phase grounding fault was analyzed. Related concepts of evidence theory, establishment of identificate framwork and construction of credit assignment were described in detail. Accordin to the characteristics of fault transient information, DP6 orthogonal wavelet basis function was selected for extracting the fault transient information effectively. Fault measures was established based on line selecting criterion, synthesized using evidence theory combination rule and fault line selecting based on line selecting decision.(2) Because the traditional D-S evidence theory did not consider credibility and correlation of evidence during evidende combination, there existed problem absolutely and empirically. To overcome the poor veracity of grounded fault line selection in small current grounded system, which induced by the reliability of symptom and the correlation symptom terms, a novel fault line selection method is proposed based on improved D-S evidence theory in the paper. Firstly, the fault line selection model is established based on traditional D-S evidence theory. Secondly, the effective measuring for the reliability of symptom and the correlation symptom terms is solved by information entropy and information energy. Finally, the novel method is verified by an actual example.