基于小波变换的直流系统接地故障检测中小波基的选择与比较

直流系统接地故障检测中常用的低频信号注入法容易受到各支路电缆中存在的对地电容的影响,在其基础上比较了基于复值小波变换和Morlet小波变换的检测方法,它们可以有效地克服对地电容的影响.当接地故障发生后,向直流系统正负母线注入低频正弦电压信号,利用套在各支路的电流互感器检测出支路中的低频电流信号,通过小波变换算法从中提取出与注入信号同频的正弦电流信号,计算出该电流信号中的阻性分量即可求得该支路的接地电阻值,从而可以判断出故障支路.经过MATLAB仿真分析,比较这两种方法,证明他们在对地大电容情况下都可以准确提取出低频电流相量特征,正确判断出故障支路.

Comparison and Selection in Detection of DC System Grounding Fault Based on Different Wavelets

The method of low frequency signal injection, which is usually used to detect DC system grounding fault, is easily influenced by the capacitors betwee n ground and each branch. This paper compares two detection methods based on dam ped complex wavelet transform and Morlet wavelet transform respectively.They can eliminate the influence of direct earth capacitance efficiently. When the groun ding fault occurs, the sine voltage signal with low frequency is injected into t he positive bus and the negative bus. The current signal existing in each branch is detected by the current transformer that is installed on the branch. The com plex wavelet transform algorithm extracts the sine current signal that has the s ame frequency with the injected signal from each branch current. Then the value of the resistance current that is included in the extracted current can be calcu lated to get the value of each branch's insulating resistance. At last the fault ing branch will be found. The result of simulation by MATLAB proved that compari ng the two methods, they can both get the phasor character of the low frequency current exactly in the case of high direct earth capacitance and the faulting br anch will be found accurately.