Research on Detection Method of High-Impedance Grounding Fault for The Grounding Transformer

In the distribution power grid with neutral point grounded through low-resistance, the zero-sequence relay of the grounding transformer can act on any grounding fault in the grid, which is the backup protection for all the feeders on the same bus, and as a result, when the zero-sequence relay of the grounding transformer acts, the circuit breaker of the bus bar should be tripped, which may increase the risk of power loss of the whole bus bar. In the fact, if a grounding fault occurs only at the grounding transformer, only the circuit breaker of the grounding transformer itself is necessary to be tripped. In this paper, a detection method for the in-area grounding fault of the grounding transformer based on zero-sequence power is proposed, which can distinguish in-area grounding faults from the out-area ones of the grounding transformer. With the relay based on the method, only the breaker of the grounding transformer itself will be tripped when an in-area grounding fault occurs, and the operation mode of the distribution power grid can be switched manually after the fault isolation, to avoid the tripping of the whole bus bar. In this way, the risk of power loss of the whole bus bar can be reduced, and the reliability of power supply can be increased.