基于小波变换的直流线路行波保护采样数值稳定性研究

Study on numerical sampling stability of traveling wave protection based on wavelet transform

高压直流输电系统由于输送容量大,输电距离远,在我国电力系统中起到越来越重要的作用。一旦直流输电线路发生故障,快速准确识别故障具有极其重要的意义。对小波变换的直流输电线路行波保护方案进行了研究,发现在10 kHz的采样率下,对同一行波不同的采样,可导致小波变换模极大值的波动范围达7倍以上,意味着采用离散采样进行保护整定有严重的数值稳定性问题。提出了多重采样方法,以采样重数为表征指标,获得了小波变换方法故障指标数值波动的可能范围,分析了数值波动概率分布情况,并获得了过渡电阻值对故障指标波动范围的影响。该研究方法和结论对于实际工程中的行波保护整定,具有较重要的参考意义。

HVDC plays the more and more important role in China's power system because of its large transmission capacity and long transmission distance.Once the fault occurs in DC transmission line,it is very important to identify the fault quickly and accurately.In this paper,the traveling wave protection scheme of DC transmission line based on wavelet transform is studied systematically.It is found that the sampling range of the same traveling wave can cause the fluctuation range of the modulus maximum of the wavelet transform to be more than 7 times under the sampling rate of 10 kHz,which means that the discrete sampling protection setting has serious numerical stability.This paper proposes a multiple sampling method.Taking the sampling weight as the characterization index,the possible range of wavelet transform fault index numerical wave is obtained,and the probability distribution of the wave value is analyzed.On this basis,the influence of the transition resistance value on the fluctuation range of the fault index is obtained.The research methods and conclusions of this paper have important reference significance for the traveling wave protection setting in practical engineering.