The Analysis Of Transient Simulation Based On Small Current Netural Grounding System And The Application Of Wave-Let Theory

The single phase-to-grounding fault frequently occurs in neutral ungrounded system. The fault line must be found to avoid a phase-to-phase fault .In this paper, firstly, the condition on single phase-to-grounding fault occurring in neutral ungrounded system are discussed and then the main troubles in choosing fault line are pointed out. Further, the methods are proposed to compare and summarize for choosing fault line and detecting distance in neutral ungrounded system. Subsequently, the characteristics of zero sequence current and transient courses are introduced and analyzed. Since that the choosing line hardware for the neutral ungrounded system has just passed part of the dynamic simulative test, MATLAB software was chosen to do a lot of simulative tests on single phase-to-grounding fault. And the simulative sampling ratio is almost the same as the hardware's. Because there is a low wave filter in the hardware, I choose the db15 wave-let to carry out the multidimensional decomposition on the sample by the method of one dimension discrete wavelet in order to obtain low frequency signal including the high frequency transient information on single phase-to -grounding fault. Then I analyze the information continuously by wave algorithm. Plenty of experiments show that the fault line can be accurately chosen and the high frequency of transient signals can be precisely identified with the real part , imaginary part and module of wavelet transform. Therefore it proves the feasibility of the hardware.