Study On Fault Line Selection Method Of Small Current Grounding System Based On Extension Theory

There are two ways of grounding method of Power Systems, namely, direct grounding method of the neutral point and non-grounding of neutral point. Distribution networks of 6 ~ 66kV use small current grounding and the neutral point is not directly grounded, when the single-phase grounding fault occurs, grounding fault current is very small, including the Neutral mode, the resonant grounding method (also called the neutral grounding via arc suppression coil), Neutral Grounding Resistors. A commonly used neutral grounding method in mine power supply system is neutral grounding via arc suppression coil, and the selection faults reasons is also analyzed. In this paper, the in-depth research of single phase grounding steady state and transient state characteristics of small current grounding system and its fault characteristics law are described, summed up the difficulties and problems of the small current grounding fault selection; and wavelet theory, the wavelet packet theory, the optimal wavelet packet basis search algorithm are described in detail; also the nature of mathematical morphology, pattern spectrum of the basic theory is introduced in detail. The advantages and disadvantages of commonly used filtering method are analyzed; the paper presents a filter based on M-band wavelet filter combination, namely: firstly the improved function of fundamental frequency used to filter fundamental frequency information, and then use the M-band wavelet filter based on the information filtering method; and gives a typical analysis of the signal filtering. According to the characteristics and rules of single-phase ground fault, two methods are proposed based on the amount of transient fault line selection method, namely: adaptive and relative energy line selection method based on wavelet packet spectrum coefficients, the fault line method based on the pattern spectrum. And the simulation results of this analysis of two methods were proposed to verify the feasibility of the method. By analyzing the defects of the commonly used single criterion for fault line selection, a theory put forward based on the integration of extension fusion method of fault line selection algorithm. That is: relative energy adaptive fault line selection method based on wavelet packet decomposition coefficient, intelligent integration of fault line selection method based on the shape spectrum and extension theory. And define the extension theory based fusion algorithm of intelligent fault line selection method and the selection function of the relative ratio of line selection weight coefficient, the simulation verify the feasibility of the methods.