基于零序电流投影系数的小电阻接地系统高阻接地故障保护

High Resistance Ground Fault Protection of Low Resistance Grounding System Based on Zero Sequence Current Projection Coefficient

小电阻接地系统可以有效抑制过电压,快速切除故障。随着电缆网规模的日益扩大,越来越多的大中城市开始使用该种接地方式。但现阶段采用的零序过电流保护启动门槛值较高,高阻接地故障时将拒动。分析了接地故障时中性点零序电流与各出线零序电流的关系,发现故障出线零序电流略大于中性点零序电流且二者近似反向,而健全出线零序电流远小于中性点零序电流且相位差约为90°,提出一种利用出线零序电流在中性点零序电流上投影系数大小的小电阻接地系统接地故障保护方法,可显著提高高阻接地时的保护灵敏度。仿真结果验证了方法的正确性及有效性。

Low-resistance grounding system can effectively suppress overvoltage and quickly remove faults.With the increasing scale of cable networks,more and more large and medium-sized cities begin to use this grounding mode.However,the currently used start-up threshold of zero-sequence over-current protection is high,and the protection would refuse to operate at high-resistance grounding fault.This paper analyzes the relationship between the zero-sequence currents on neutral point and on line during grounding fault.It is found that the zero-sequence current of faulty line is slightly larger than neutral zero-sequence current and they are approximately reversed to each other in phase position.The zero-sequence current in healthy line is much smaller than the neutral zero-sequence current,and their phase difference is about 90°.A grounding fault protection method using the zero-sequence current projection coefficient of the line on neutral point is proposed,to significantly improve sensitivity of protection in high-resistance grounding fault.Simulation results verify correctness and effectiveness of the proposed method.