小电流接地故障无功功率分析及选线新方法

Reactive power analysis and novel faulty selection method in resonant grounding system

对于谐振接地系统的单相接地故障,由于现场普遍存在电压互感器(PT)和电流互感器(CT)极性反接的现象,当仅仅利用故障的暂态无功功率方向进行选线时极易发生误选。分析了PT、CT极性反接对故障暂态和工频无功功率的影响,提出一种利用故障的工频无功功率对暂态无功功率进行修正再选线的新方法。即:修正后的暂态无功功率为负值的线路为故障线路,如果所有出线修正后的暂态无功功率都是正值则为母线接地。该方法可以忽略PT和CT的极性反接影响,扩大了选线适用范围。仿真和现场的数据证明了该方法的可行性。

Because of the incorrect polarity connection of voltage transformer and current transformer in field, faulty feeder selection based on transient reactive power direction leads to wrong easily when there is a single-phase earth fault in resonant grounding system. In this paper, the effect of the incorrect polarity connection of voltage transformer and current transformer on transient reactive power and power-frequency reactive power is analyzed. A novel method using the power-frequency reactive power to correct the transient reactive power for faulty feeder selection is proposed. The faulty feeder is the one which the corrected transient reactive power is negative. If all of the corrected transient reactive powers are positive, it is bus fault. The proposed method is independent of polarity connection of voltage transformer and current transformer, which enlarges the selection scope. The feasibility of the new method is verified by digital simulation and field fault data.