小电阻接地系统高阻接地故障反时限零序过电流保护

Zero-sequence Inverse-time Overcurrent Protection Against High-impedance Grounding Fault in Low-resistance Grounding System

目前小电阻接地系统接地保护主要采用零序过电流保护,其保护动作值较高,但发生高阻接地故障时保护装置容易拒动。结合反时限过电流保护的特点,在分析小电阻接地系统单相高阻接地故障零序电流分布特征以及零序电压与零序电流关系的基础上,提出了一种新型的反时限零序过电流保护方法。通过各出线保护间的时间配合可使保护装置的启动电流定值无需躲过本线路的最大电容电流,并且通过构造修正系数来提高高阻接地故障时检测到的等效零序电流的大小,从而提高高阻接地故障保护能力,消除因电流互感器测量误差而造成的拒动问题。

Zero-sequence overcurrent protection currently prevalent in low-resistance grounding systems has a high value of protection action.Hence when systems encounter high-impedance grounding faults,the protection devices are prone to defying activation.In considerations of characteristics of inverse time limit overcurrent protection,distribution of zero-sequence current with high-impedance fault,and relationship between zero-sequence voltage and current,a novel method of zero-sequence inverse-time overcurrent protection is proposed.Through time coordination among each outgoing line protection,starting current setting of the protection device is exempt from avoiding the maximum capacitive current of the line.Moreover,the introduction of a correction factor facilitates increase in the determined value of equivalent zero-sequence current upon the occurrence of high-impedance ground fault.As a result,the improvement in protection against high-impedance grounding faults can be achieved,and the problem of defying activation caused by measurement error of current transformer can be addressed.