Hardware-in-the-Loop Testing of Direct Transfer Trip for Network Protector Units in the Presence of Distributed Energy Resources

This paper proposes a direct transfer trip (DTT) scheme for the protection of low voltage (LV) secondary spot networks. The conventional protection on secondary networks is based on network protector units (NPU). NPUs play a critical role in the effective isolation of faults by disconnecting the secondary side of service transformers and avoiding the flow of fault currents through alternative paths in LV spot networks. The proposed approach improves the performance of conventional NPU logic and addresses two major challenges. It is shown that the proposed approach can effectively isolate ground faults on the primary system for which the conventional NPUs can fail to detect when the service transformer has a Delta winding on the high voltage side. Moreover, the proposed approach can allow for the reverse power flow caused by the Distributed Energy Resources located in the secondary LV networks. The performance of the proposed approach is validated using a hardware-in-the-loop testbed that runs a LV spot network in Opal-RT real-time digital simulator.