Optimal coordination of distance and overcurrent relays considering a non‐standard tripping characteristic for distance relays

Abstract

The aim of relay coordination is to obtain the optimal relay settings which result in minimum operating times of the relays, satisfying selectivity constraints. In combined coordination of distance and directional overcurrent relays (D&DOCRs), operating times of the second zone of distance relays ( T Z2 ) are typically increased in order to satisfy the selectivity constraints. In this study, a new operating characteristic (OPC) for distance relays is proposed which decreases T Z2 s. In the proposed OPC, the common characteristic for the second zone is divided into two sections: the first section protects the main line beyond the first zone with delay time T Z2n1 and the second one protects 50% of the adjacent line with delay time T Z2n2 . A new formulation is then proposed for the non-linear problem of D&DOCRs coordination based on the proposed OPC. The presented method is tested on three test systems: namely, the 8-bus, the IEEE 14-bus, and the IEEE 30-bus test systems. The simulation results show that the method can be used to achieve a faster protection especially when robust coordination is desired.