A new protection scheme for boundary load switch in distribution networks

A new protection scheme for boundary load switch, implemented by using only transient zero-mode current, is proposed in the paper. For neutral indirectly grounded system, the traditional boundary load switch, which is based on power frequency components, is difficult to determine the direction of single-phase-to-earth fault. In this paper, the transient zero-mode current has been analyzed for single-phase-to-earth fault in neutral indirectly grounded system. It concludes that there is significant difference in magnitude of transient currents between the load side fault and source side fault. Load side fault and source side fault can be distinguished by comparing the magnitude of measured transient zero-mode current with the setting threshold. The simulation tests associated with the typical distribution system in EMTP-ATP validate the protection scheme and algorithm for boundary load switch can work properly.