小电阻接地系统两点接地时保护误动浅析

Analysis of relay misoperation in two-point grounding fault of small resistance grounding system

某钢铁厂原料区域10 kV配电系统采用小电阻接地,在运行过程中发生电缆A、B相两点接地事故,造成上级主变中性点保护先于电缆零序保护出口跳闸。通过故障发生时系统的正序、负序、零序等值回路分析与计算,对故障时的电流大小及方向进行定量分析,找出保护越级动作的原因,提出一种通过修改上下级保护定值的方法解决保护误动问题,并针对保护调整后与一次系统设备配合的合理性进行了分析。

The 10 kV power system in the raw material area of an iron and steel plant adopts a small resistance grounding system.In the process of operation,the two-point grounding accident of phase A and B of the cable occurs,which causes the neutral point protection of the transformer tripping before the zero sequence protection of the cable.Through the analysis and calculation of the positive,negative and zero sequence equivalent circuit of the system at the time of fault occurrence,this paper makes quantitative analysis on the magnitude and direction of the current,finds out the cause of the protection over grade action,puts forward a method to solve the problem of protection over grade action by modifying the setting value of the upper and lower level protection,and analyzes the rationality of the coordination with the primary system equipment after the protection adjustment.