基于谐波的低压配电干线中性线断线检测方法

三次谐波电流含量较大是目前低压配电系统负荷的普遍特征,利用这一特征,提出了在配电干线首端设置监测装置,对中性线断线故障进行检测的保护方法。其基本原理是通过检测线路首端三次谐波变化来判断是否发生中性线断线故障。仿真和实测分析表明:无论故障点以后的负荷是否平衡,当中性线断线时线路首端三次谐波均会呈现不同程度变化,故障点越接近线路首端,故障导致的三次谐波变化就越显著。对中性线断线故障时线路首端三次谐波和基波的突变规律,以及正常运行时,负荷三次谐波和基波的波动规律进行了研究和分析,获得了将故障和正常运行状态进行有效区分的故障判据和故障判别流程。利用实测负荷的波动数据进行仿真研究,验证了故障检测判据在负荷平衡和不平衡状态下对中性线断线故障判别的有效性。

A harmonic-based approach for open-neutral fault detection in low voltage systems

In low-voltage distribution system 3rd harmonic current content is big enough. It is a common characteristics. Through analyzing the characteristics of harmonic, a new open-neutral fault detection approach is proposed that monitoring device can be simply installed at feeder head. Main idea of the proposed approach is that the fault can be identified according to the 3rd harmonic variation measured at the feeder head. Simulation and experimental analysis shows that the 3rd harmonic current will show varying degrees of change at the feeder head when open neutral fault occurs, regardless of the load is balanced or unbalanced. The fault location is closer to feeder head indicates that the 3rd harmonic current change is more significant. This paper researches and analyzes the 3rd harmonic and fundamental currents sudden change method at feeder head when open-neutral fault happened, as well as 3rd harmonic and fundamental currents of load fluctuation method during normal operation. It obtains fault criterion and fault identification processes that can effectively distinguish between open-neutral fault and normal operation. The experimentally measured load fluctuation data for simulation study verifies the fault detection criterion is validity to open-neutral fault whenever in balanced and unbalanced load conditions.