Impact of evolving fault on fault phase selector based on differential superimposed phase currents

Evolving fault adversely affects the performance of the fault phase selector based on the differential superimposed phase currents (DSIPC), which is widely used in practical relay. It is because that this phase selector is designed only for simple fault, whereas the evolving fault is more complex in nature, comprising primary fault and secondary fault. In order to analyze the impact of the evolving fault on this phase selector, two new concepts are proposed, namely, the secondary fault network and the secondary fault component. The later is just the superimposed current utilized by the phase selector after evolving fault occurs. With the secondary fault network and secondary fault component, the performance of the phase selector under evolving fault is studied deeply. Analysis results show that source condition, fault type, fault position and fault resistance might cause the phase selector operates incorrectly.