基于故障暂态行波高低频能量比值的交流输电线路快速保护方案

Fast Protection Scheme for AC Transmission Lines Based on Ratio of High and Low Frequency Energy of Transient Traveling Waves

新能源电力系统中大量电力电子装置的应用使得基于工频量的保护方案难以适用,暂态量保护方案的优势更加凸显。现有暂态量保护存在阈值整定困难、区内末端高阻故障情况下容易拒动的问题。针对以上问题,该文首先分析了线路不同位置发生故障时行波的传输路径,推导了电压行波的表达式,明确了不同位置发生故障时行波的频率分布规律。在此基础上,采用时频分析能力更好的小波包变换提取故障暂态特征,并在暂态能量中引入频率信息以放大高频分量的影响,增大区内、外故障时高低频暂态能量的分布差异,进而提出利用高低频能量比值进行区内外故障识别的新方案。新方案无需复杂的阈值设置,采用高低频能量比值方式削弱了过渡电阻和故障距离对保护判据的影响,最后基于PSCAD/EMTDC仿真验证了新方案的有效性和可行性。

The application of a large number of power electronic devices in the new energy power system makes it difficult to apply the protection schemes based on the power frequency,which highlights the advantages of the transient protection scheme.The existing transient protections have the problems of difficult threshold setting and easy refusal to operate in the case of high-resistance faults at the end of the zone.In response to the above problems,this paper firstly analyzes the transmission paths of the traveling waves when faults occur at different positions of the line.The expression of the voltage traveling waves is deduced,and their frequency distributions at different positions are clarified.On this basis,the wavelet packet transform with a better time-frequency analysis capability is used to extract the transient features of faults,and the frequency information is introduced into the transient energy to amplify the influence of high-frequency components.The high and low frequency transients are increased during the internal and external faults.According to the distribution difference of state energy,a new scheme is proposed to use the ratio of high and low frequency energy to identify the faults inside and outside the area.The new scheme adopts the ratio of high and low frequency energy to weaken the influence of the transition resistance and the fault distance on the protection criterion without complicated threshold setting.Finally,the effectiveness and feasibility of the new scheme are verified based on the PSCAD/EMTDC simulation.