一起35 kV单相接地故障引起接地变跳闸的事故分析

Analysis on the Tripping Accident of Grounding Transformer Caused by a 35 kV Single-Phase Grounding Fault

研究了某220 kV变电站内发生的一起因单相接地故障引起35 kV接地变保护动作,致使接地变开关分闸的事件。通过现场情况调查和查阅故障录波数据,采用电路理论和相量分析法,结合理论分析与实践验证,对该事件进行了调查分析,明确了事件发生的原因是因配网用户采用变压器的高压侧为“Y”型接线方式,且其中性点直接接地,为接地零序电流提供了通路,导致了这起事件。说明用户侧变压器一次侧的接线方式会对电网侧的中性点不接地系统造成影响,从而影响电网的可靠性,需要引起重视。

The paper analyzes an event of the 35 kV grounding transformer protection action which contributes to grounding transformer switch tripping when a single-phase grounding fault occurs in the 220 kV substation. After field investigation and fault recording data research, the authors apply electric circuit theory and phasor analysis method to investigate the event. The reason for the tripping accident is that distribution network users employ “Y” type connection mode on HV side of the transformer with neutral directly grounding which provides circuit for grounding zero sequence current and causes this accident. According to the analysis, it is found that the primary side connection mode of user-side transformers can affect grid-side neutral point ungrounded system, lowering the reliability of the power grid.Therefore, attention should be paid to it.