Analysis of the influence to fault detecting of DC system from distributed capacitance

Inject signal is the most popular method used for fault detecting in the DC system. However, it usually misjudges faults due to the existence of distributed capacitance in substations. In this paper, the EHV substation secondary cable laying is considered, and typical capacitance and resistance values of secondary cable to the ground are used. We analyse the influence of distributed capacitance on fault detection when the injected signal is a low-frequency square wave. And then the integral method based on the inject signal is proposed, which can distinguish fault branches from non-fault branches. Furthermore, the influence of the time constant and injected signal frequency is discussed.