Optimal coordination of directional overcurrent relays considering two-level fault current due to the operation of remote side relay

Abstract

Overcurrent relays are widely used for the protection of distribution and sub-transmission networks. The network topology change is one of the issues that affects the coordination of directional overcurrent relays (DOCR) in the meshed network. Faster operation of relay on one side of the line respect to the relay on the other side of the line, causes the network topology change during fault, and leads to a change in the short-circuit current (SCC) passing through the other side relay and it’s backup relay. In this case, the coordination between the main and the backup relays can be disturbed due to a change in the SCC passing through them. Previous studies use the highest SCC between the SCC before topology change and the SCC after topology change in coordination of relays to overcome this issue. In this paper, a new DOCR coordination method based on the dynamic model of DOCR is presented to consider the effect of network topology change during the short circuit. The new method is formulated as a linear programming (LP) problem. Efficiency of the proposed method in comparison to conventional methods is illustrated by implementing on two sample networks, 8 bus network and IEEE 30 bus network.