Analysis and Countermeasures of Single-phase Disconnection Fault in Low Resistance Grounding System

Low resistance grounding system is very common in urban medium voltage distribution networks,and there is usually no relay protection against disconnection fault in these systems.When such faults occur,these are always found by the users first.And there is delay for power supply companies to deal with this type of fault.Through the analysis of the impact of single-phase disconnection on high-voltage and low-voltage sides of transformers on the users,this paper calculates the zero sequence and negative sequence components after the fault and proves the relay protection of overcurrent and zero sequence current in the existing distribution networks is difficult to respond to this kind of fault.In addition,it proposes the ways of improvement in detecting faults by means of zero sequence and negative sequence components.