一起用户专用变压器中性点接地引起零序保护误动事件分析

Analysis of Zero-sequence Protection Malfunction Caused by Neutral Grounding of User Specific Transformer

220kV琴韵站发生多次两回20kV电缆馈线同时跳闸故障。从分析20kV电缆馈线同时跳闸的保护动作情况及故障录波出发,利用电压电流相量分析法,分析其原因是非故障线路存在用户专用变压器高压侧中性点直接接地。运用RTDS(real time digital simulator)系统仿真验证了系统发生接地故障时,非故障线路用户专用变压器高压侧中性点直接接地,会使故障线路零序电流幅值比理论计算值偏大,非故障线路三相电流相位偏向一侧,导致非故障线路零序保护误动作。

The problem of simultaneous trip of two 20kV cable feeders has occurred many times in the 220kV Qin Yun substation. Based on the analysis of the protection action and fault recording of 20kV cable feeders simultaneously and using the voltage and current phasor analysis method,this paper analyzes and concludes that the cause of the fault is the direct grounding of the neutral point of user specific transformer’s high voltage side in non-fault line. The RTDS system is used to simulate and verify that when a grounding fault occurs in the system,the direct grounding of neutral point on high voltage side of user specific transformer will cause the amplitude of zero-sequence fault current of fault line to be larger than theoretical calculation value,and the phase of non-fault line three-phase phase to be biased to one side,resulting in the protection malfunction of zero sequence protection action for non-fault line.