零序导纳法接地选线保护原理

Principle of selective grounding fault protection based on zero sequence admittance

针对小电流接地电网单相接地故障选线及定位困难的状况,从分析中性点不接地或经消弧线圈电网故障前后各线路测量参数的思路出发,导出了在故障时测得的故障线路零序导纳与实际零序导纳不同、非故障线路与实际导纳相同的结论,对小电流故障进行接地选线。零序导纳法的关键是准确地测量线路的实际零序导纳,论文给出了几种能够获得线路实际零序导纳的方法。故障前后各线路的零序导纳用相同的硬件通道获得,自动地减小电压互感器TV、电流互感器TA误差的影响,选线原理具有较高的灵敏性和可靠性。通过记忆故障前各线路实际零序导纳,推导出故障点的计算公式,对故障予以定位。

Regarding to the difficulties of fault line selection and fault locating during single phase grounding fault of nondirectgrounded neutral system, the pre??and postfault parameters measured for each line inneutralpointungrounded power network or neutralpointgrounding power network through Petersen coil areanalyzed. It shows that the zerosequence admittance of the fault line would change while these of normal lines keep the same, which can be used for fault line selection at small current fault. The key point is to accuratelyacquire the practical zero sequence admittance. Several ways for measuring the admittance are given. The prefault admittance and postfault admittance are measured using the same HW channel to reduce the influence of PT and CT errors and obtain higher sensitivity and reliability. The practical zero sequence admittance of each line is stored and the algorithm for fault locating is derived.