中性点不接地系统铁磁谐振与单相接地辨识技术

Technique for Differentiation Between Ferroresonance and Single-phase-to-earth Fault in Isolated Neutral Point System

中性点不接地系统在电压互感器铁磁谐振的情况下可能出现零序电压长时间升高的现象,与单相接地故障现象类似。传统选线装置仅依靠零序电压和零序电流启动,不能有效辨识铁磁谐振,容易造成误动。重点分析了基频铁磁谐振的特征,详细对比了铁磁谐振与单相接地故障情况下三相电压及零序电压之间的差异,并在此基础上提出了基于零序电压和三相电压综合对比的铁磁谐振辨识技术。通过现场实际运行数据对该方法进行了验证,表明该方法能够有效提高选线装置的动作可靠性,满足实用要求。

Zero-sequence voltage will keep increasing when potential transformer ferroresonance occurs in an isolated neutral point system. Similar phenomenon happens during a single-phase-to-earth fault. An traditional line selection device starts when zero-sequence voltage and current exceed setting values, which is not effective for identification of ferroresonance and is apt to cause mis-operations. In the study, characteristics of fundamental frequency ferroresonance is emphatically analyzed and threephase voltages and zero-sequence voltage in case of both ferroresonance and single-phase-to-earth fault are compared in detail. On this basis, ferroresonance identification technique is proposed based on comprehensive comparison of zero-sequence voltage and three-phase voltage. Verification by field data reveals that the technique can effectively increase the reliability of line selection devices and therefore satisfy the requirements for practical implementation.