发电机高压厂变低压侧分支零序过流保护改进方案

Improvement Scheme for Zero-sequence Overcurrent Protection of the Low-voltage Side Branch of a Generator High-voltage Plant Substation

由于单相接地故障时,电容电流较大,发电机高压厂变低压侧广泛采用低阻接地方式。高压厂变低压侧零序过流保护常规做法仅引入中性点侧零序电流,无法准确判断故障点位置,从而导致第一时限需要闭锁厂用电切换,复归前第二时限无法启动厂用电切换。通过再引入低压分支侧零序电流,改进保护逻辑,可以准确判断故障点位置,第一时限对应故障点在分支断路器下游,动作于跳分支断路器并闭锁厂用电切换,而无需考虑后续启动厂用电切换;第二时限对应故障点在高压厂变低压绕组和低压分支,动作于全停并启动厂用电切换。

Due to the large capacitance current during single-phase ground fault,the low-resistance grounding method is widely used on the low-voltage side of high-voltage plant transformers of generators.The conventional practice of zero-sequence overcurrent protection on the low-voltage side of high-voltage plant transformers only introduces zero-sequence current on the neutral side,which cannot accurately determine the location of the fault point,resulting in the first time limit to block the plant power switching and the second time limit to start the plant power switching before reversion.By re-introducing the zero sequence current on the LV branch side and improving the protection logic,the location of the fault point can be accurately judged.The first time limit corresponds to the fault point downstream of the branch circuit breaker,and the action is to jump the branch circuit breaker and block the plant power switch,without considering the subsequent start of the plant power switch;the second time limit corresponds to the fault point in the LV winding and LV branch of the HV plant,and the action is to make a full stop and start the plant power switch.