小电流接地故障熄弧后电气量对暂态选线方法的影响

Influences of Electrical Quantities on Transient Line Selection Methods after Arc Extinction under Small Current Grounding Fault

为提高小电流接地故障选线准确率,部分选线装置使用故障全过程电气量。对间歇性接地故障而言,故障全过程电气量包括熄弧后暂态信息,而熄弧后与燃弧期间暂态特征的差异及对暂态选线方法的影响尚不明确。本文根据覆盖故障全过程的小电流接地故障暂态等值电路,分析故障点工频电流熄弧后母线零序电压、故障线路和健全线路暂态零序电流特征,以及熄弧后暂态量对暂态选线方法可靠性的影响。研究发现,不接地系统熄弧后暂态电气量主谐振频率小于10 Hz,谐振接地系统熄弧后暂态电气量主谐振频率略高于工频;熄弧后暂态电气量极可能使暂态幅值比较法误选为健全线路,同时使极性比较法、功率方向法误报为母线接地故障。最后仿真验证了所提结论的正确性。

To improve the line selection accuracy under small current grounding fault,some line selection devices use the electrical quantities during the whole fault process.For an intermittent grounding fault,these quantities include the transient information after the arc extinction.However,the differences in transient characteristics before and after the arc extinction and their influences on the transient line selection methods are still uncertain.In this paper,according to the transient equivalent circuit under small current grounding fault that covers the whole fault process,the characteristics of zero-sequence voltage of the busbar and the transient zero-sequence current of the fault and healthy lines after the arc extinction of power frequency current at the fault point are analyzed,and influences of transient electrical quantities after arc extinction on the reliability of the transient line selection methods are also explored.It is found that the main resonance frequency of transient electrical quantities in an isolated neutral system after the arc extinction is less than ten Hzs,and the main resonance frequency of transient electrical quantities in a resonant grounding system after the arc extinction is slightly higher than the power frequency.After the arc extinction,the transient electrical quantities are very likely to make the transient amplitude comparison method mistakenly select a healthy line,while making the polarity comparison method and power direction method mistakenly report a busbar grounding fault.Finally,the digital simulations verify the conclusions.