Grounding Fault Protection with Phase Current Difference for Ineffectively Earthed Power Systems

Ground fault current is very small in ineffectively earthed power systems, and it is difficult to detect the fault line. Traditional fault detection methods based on zero sequence current are difficult to satisfy the requirement of distribution automation (DA). In order to improve it, the grounding fault protection scheme with phase current sampled value difference is presented in this paper. The grounding fault can be detected by comparing the current variation difference between faulted and sound phases. If the difference is larger than a threshold, grounding fault is occurred in the tested feeder. EMPT simulation and experiment results show that the proposed method can correctly detect all kinds of faults with high reliability. It can be carried out easily in FTU and satisfy the requirement of distribution automation.