基于特征能量函数的故障暂态量时频特征分析

Time-frequency characteristic analysis on fault transient quantity based on characteristic energy function

基于故障暂态分量的线路保护不受系统震荡、过渡电阻等因素的影响,可满足超高压系统对保护速动性的要求。由于线路边界效应,线路在发生区内、外故障时,保护安装处的电流互感器TA检测到的故障电流中高频电流分量的含量会有所不同,差异集中体现在100 k Hz左右。首先采用模量变换对三相故障电流进行解耦处理,紧接着采用Db4正交基小波对模分量进行离散小波变换,最后基于小波能量理论,构造了特征能量函数来检测这一差异,提取出线路发生区内、外故障时暂态分量的时频特征,为基于故障暂态分量的线路保护提供新判据。在PSCAD/EMTDC中搭建模型,结果表明,该算法能快速提取出线路故障时暂态分量的时频特征,并能正确反应出线路的区内、外故障,同时实现故障测距。

Line protection based on transient components is not affected by system oscillation,transition resistance,and other factors,so it can meet the requirements of EHV system for protection speed. Because of the line boundary effect,the content of high frequency current component detected by TA at the protection installation will be different when the internal and external fault occurs in the line,and the frequency difference is concentrated at about 100 k Hz. Firstly,the modulus transform is adopted to decouple three-phase fault current; followed by discrete wavelet transform based on Db4 orthonormal basis wavelet; at last,the characteristic energy function based on wavelet energy theory is constructed to detect the difference. The time-frequency characteristics of internal and external fault are extracted,which provides a new criterion for line protection based on fault transient components.Based on the model built on PSCAD/EMTDC,the results show that the algorithm can quickly extract the time-frequency characteristics of transient components of transmission line fault, which can correctly reflect the line faults both internal and external,and realize fault location at the same time.