Research On Fault Line Detection For Single-Phase To Ground Faults In The Neutral Indirectly Grounded System Based On Transient Feature

Neutral indirectly grounded system, including Neutral non-grounded system and Petersen-coil grounded system, are widely used in MV distribution power system in China. The single-phase-to-ground fault happens most frequently in distribution network. There is no short circuit loop when single-phase-fault occurs, so the small current just follows into capacity ground. Due to the small fault current, unobvious fault features, the complex fault circumstances and the various system run mode, the problem of fault line detection hasn't be settled. Some limitations also exist in fault line detecting methods used in practice.For the sake of learning more efficient way to detect fault line, stable and transient features of single-phase-to-ground fault in neutral indirectly grounded system are deeply analyzed in this paper. There are many high frequency component features in transient fault zero sequence currents, and they could be used to detect fault line.This paper put forward a novel fault line detection method based on prony algorithm. Prony algorithm is a method in which a set of linear combination of exponential components were used to fit the uniformly-spaced sampling data, so the amplitude, phase, damping, and frequency of the signal can be analyzed. The method uses the prony method to analyze and transform the fault zero sequent current. Prony algorithm could be adopted to abstract the information about the harmonic component of fault zero sequence current by fit to a set of exponential components. It can abstract the harmonic components of zero currents self-adapting. Then the fault line could be detected by comparing the amplitude and phase of them. Theoretical analysis and simulation results show that the proposed method can detect the fault line reliably and exactly.The abrupt change and the transient features of zero currents are useful information for line detection. In this paper, the morphological filtering of mathematical morphology was used to filter the zero sequence current. Thesimulation results show that this method can enhance the abrupt change and transient features and weaken the stable feature. The fault features of zero sequent currents are more obvious after filtering, so it is beneficial to fault line detection.