考虑波速特性的小波变换模极大值法的电力电缆局部放电定位研究

PD Location Method of Power Cable Based on Wavelet Transform Modulus Maxima Considering Wave Characteristics

电力电缆局部放电的有效检测和精确定位对于保障城市配电网系统的安全可靠供电具有重要意义。首先,通过在实验室搭建10 k V振荡波检测系统对一条497 m长缺陷电缆进行局部放电检测试验,并分析了局部放电信号在电缆中的传播特性;其次,通过比较不同时域定位方法的定位精度,提出采用小波变换模极大值法与自相关方法的联合定位方法以减小定位误差。此外,为了降低波速不定性对局部放电定位精度的影响,对试品电缆的波速特性进行了测量,并提出利用局部放电信号小波变换各尺度中心频率对应的波速进行定位计算,由于各尺度下频率分量较为集中,降低了由于波速不定性带来的定位误差。试验结果表明,振荡波电压能够有效激发局部放电的产生,所提定位方法具有较高的定位精度,满足工程需要。

The efficiency detection and precision location of partial discharge in power cable are of great signification to the safety and reliability of the urban distribution network. In this paper, an oscillating waveform test system for 10 k V cable which was used for the PD testing of a 497 meters long cable with defects was established in the laboratory. The propagation characteristics of partial discharge signal in power cable ware analyzed. By comparing the PD location precision of different TDR methods, a method which combined the wavelet transform modulus maximal method and self-correlation method was proposed. In order to reduce the PD location errors caused by velocity ambiguity of PD signal, the velocity characteristics of the test cable were measured in the laboratory. Then the central frequency at each wavelet scale and the corresponding velocity was calculated. After that, the calculated velocity was used for the location of PDs. Due to the frequency component at each scale is relatively concentrated, the location errors caused by velocity ambiguity are reduced. At last, experimental results shown that oscillating voltage can effectively excite the generation of partial discharge and the location method proposed in this paper is a valid method for PD location with sufficient accuracy and reliability which fully meets the project need.