超高压线路差动保护的高阻接地故障拒动分析及改进措施

Research and improvement of differential protection failure for EHV line high resistance grounding fault

500kV超高压线路高阻接地时,初始阶段故障电流突变量很小,主保护有可能拒动.随着接地故障电阻变小,故障电流增大后由后备保护动作切除,而后备保护较长时间切除故障可能影响电网稳定.介绍"7·10"500kV花博甲线高阻接地故障差动保护拒动事件,分析不同运行方式对两侧故障电气量的影响,总结现有差动保护启动判据的缺陷,并提出采用近故障侧保护装置启动判据、负序电压启动判据等改进措施,有效提高了高阻接地时差动保护的动作可靠性.

When high-resistance grounding fault occurs in 500 kV EHV line, the sudden change of fault current is not significant at the initial stage, so main protection may refuse to operate. As the grounding resistance decreases and the fault current increases, the fault can be cleared by the back-up protection action, which may impact the power grid stability seriously. A differential protection failure event was introduced in this paper, which occurred on Hua-Bo 500 kV line in Guangzhou province on July 10. The effect of operation modes on fault characteristics at both terminals was analyzed. Based on the deep research of existing differential protection methods, the improvement measures including the near fault terminal characteristics criterion and negative sequence voltage criterion was presented. They can highly improve the reliability of differential protection operation, especially when high impedance grounding fault occurs.