电容器组单相断线故障继电保护拒动行为分析

Behavior analysis for relay protection during single-phase wire-breaking fault of capacitor bank

不平衡电压保护是隔离电容器不对称故障的有效手段,该保护的设计建立在电容器故障时中性点电压漂移的基础上。工程实践表明,在单星形不接地电容器组发生单相断线时,该原理会导致电容器保护拒动。为解决此问题,通过理论分析,指出传统的电容器不平衡电压保护存在不能反映单星形不接地电容器组断线故障的原理性缺陷;而后基于单星形不接地电容器组发生断线故障时存在负序电流的特点,提出负序电流的保护方案。理论分析表明,该方案可以防止电容器发生断线故障时保护出现拒动现象。

The unbalanced voltage protection is designed based on the voltage drift of neutral point during capacitor faults to effectively isolate the asymmetric faults of capacitor,but it may refuse to act when the single-phase wire-breaking fault happens in the ungrounded star-connecting capacitor bank,which is pointed out by the theoretical analysis in principle.As there is negative-sequence current in such case,the negative-sequence current protection is proposed to prevent the improper behaviour of unbalanced voltage protection,which is verified by theoretical analysis.