适用于多端直流电网的电压极性比较式行波保护方案

Traveling Wave Protection Scheme of Voltage Polarity Comparison Formula for Multi-terminal DC Power Network

相较于在直流线路两端配置限流电抗器,多端直流电网(multi-terminal DC power grid,MTDC)在换流站出口安装限流电抗器可在抑制短路电流的前提下减少经济性投资。针对此类拓扑结构下基于边界效应的直流线路保护不再适用的问题,该文分析了多端柔直电网线路故障下行波复杂的折反射现象,推导了线路发生区内外故障时,两端保护安装处测量到的前两个电压行波的表达式,揭示了区内外故障时线路两端的电压行波的极性特征,在此基础上提出了基于电压极性比较的行波保护方案。该方案无需考虑阈值设定和采样不同步的影响,能够可靠识别出区内外故障。最后,基于PSCAD/EMTDC仿真平台,验证了该保护方案的有效性。

Compared with the configuration at the both terminals of the DC lines,installing the current-limited reactors at the port of the converter station in the multi-terminal DC power grid(MTDC) can reduce the economic investment on the premise of restraining the short-circuited current.Aiming at such problem that the conventional DC line protections based on boundary effects are no longer applicable under the similar conditions,the complex refraction and reflection phenomena of the traveling waves under the faults of the MTDC are analyzed in this paper.And when the internal and external faults occur,the expressions of the first two voltage traveling waves measured at the relay locations of each line are deduced.The polarity characteristics of the voltage traveling waves at both ends of the line are revealed in case of the internal and external faults.On this basis,a traveling wave protection scheme based on the voltage polarity comparison is proposed.Without necessarily considering the influence of the threshold setting and the sampling asynchrony,this scheme is able to reliably identify the internal and external faults.Finally,the effectiveness of the protection scheme is verified through the PSCAD/EMTDC simulation platform.