Charging-Transient Based SLG Fault Location in Neutral-Unearthed Distribution System

The neutral point in medium voltage distribution system is mainly non-effectively earthed in China. The important characteristics of this system are the fault-phase voltage decreasing and the un-fault-phase voltage increasing when SLG (Single-Line-to-Ground) fault happened. Due to the existing of line capacitance, the transient progress of un-fault-phase voltage increasing can be regard as a charge transient and the progress of fault phase voltage decreasing can be regard as a discharge transient. By circuit analyzing found that the charge transient has the more obvious characteristics. Using the voltage and current waveform information recorded by the fault recorder installed in the substation. Using FFT(Fast Fourier Transform) to analyze the transient signal spectrum and identify the charge frequency, then use the "Morlet Wavelet" to extract the charge signal. After that we can calculate the fault distance. This method is proved by MATLAB simulation analysis.