变压器中性点间隙零序过流保护改进

Improved Protection on Zero Sequence Overcurrent in Transformers Neutral Point Gap

为了限制短路电流和满足继电保护整定需要,在220 k V变压器中性点装设放电间隙作为过电压保护。通过两起主变间隙保护动作事故,分析得出间隙击穿的原因是在单线带双变终端变电站中,线路发生单相接地故障时,零序暂态过电压会经终端站反射叠加,在变压器高频振荡作用下传导到不接地变压器中性点上形成过电压,导致间隙击穿事故。据此可在二次和系统管理方面采取措施,避免主变压器在中性点未出现危险过电压时间隙击穿导致主变跳闸,有效减少事故范围。

To limit short-circuit current and meet the requirement of setting of relay protection, discharge gap is arranged in the neutral point of transformers as overvoltage protection. Two faults of several main transformers trip- ping-out were analyzed and the resuhs revealed that when the single-phase grounding fault happened in a single with double terminal substation, the terminal reflection stack of zero sequence transient overvohage under the impact of high frequency oscillation was conducted to the no-grounding transformer neutral point to form overvoltage, callsing the gap breakdown. It can be inferred that measures can be taken in protection and system management aspects to avoid main transformer triping caused by gap breakdown when the main transformer neutral point is not in danger of overvoltage and thus reduce the range of accident.