The Application Research Of Multifractal And Wavelet To Select Fault Line In Neutral Un-Direct Ground System

The single phase fault line selection of neutral un-direct grounding system is still a problem in Power System now. The way used of steady signals is often unreliable because of faint permanent grounding current and unstable arc. Recently algorithm of utilizing the transient signal construct criterion becomes the researching focus. The multi-fractal spectrum which is used to deal with the discontinuous, weak and non-stationary fault signals can well analysis the process about the neutral un-direct grounding system in single phase fault transient and extract fault features. So multi-fractal combined with wavelet is used to research selecting fault line in the paper. This combination can better solve the problem of the fault line selection of neutral un-direct grounding system in single phase fault.Firstly, home principles and methods as well as abroad ones on the fault line selection of neutral un-direct grounding system in single phase fault are summed up, overview and analysis in this paper. Secondly, wavelet theory, fractal theory and the relationship between them are described in detail to provide the theoretical basis for the combination of multi-fractal and wavelet, which deal with the fault line selection of neutral un-direct grounding system in single phase fault. And then comprehensive analysis of the multi-fractal is made. The application about wavelet transform modulus maxima and the improved wavelet coefficient moment algorithm, which is on this basis, in the multi-fractal spectrum makes multi-fractal spectrum inherit the merits of wavelet transform and react sensitively to the singularity of the signal. Then fault about single phase grounding is analyzed from two sides of steady fault and transient fault. The analysis shows that after grounding fault there is zero transient sequence current in the line, and the current direction of fault line is opposite to the sound line, and the zero transient current of fault line is greater than any other sound line. Finally, a 35kV distribution lines simulation model is established by PSCAD/EMTDC4.02 simulation software, through the comparison about multi-fractal spectrum of the overall zero sequence current, the paper obtains a new line selection criterion of neutral un-direct grounding system in single phase fault criteria based on multi-fractal spectrum. In order to comprehensive test the feasibility of the criterion and fully consider the impact of earth mode, path resistance and inception angles, a large number of typical examples are used to authenticate the criterion. The results shows that the line selection method based on multi-fractal spectrum is not effected by the grounding method, transition resistance and initial current angle, and have high reliability and strong anti-interference ability, can accurately select the fault line.