Improvement of Robust Coordination of Distance and Overcurrent Relays by Selecting Appropriate Performance Characteristics of Overcurrent Relays using Hybrid Algorithm of Genetic and Linear Programming

In transmission and sub-transmission systems, distance and overcurrent relays have a vital role in protection of transmission lines. Power systems have different topological uncertainties such as planned or unplanned line outages. Such uncertainties affect network impedance matrix, and the distribution and amplitude of fault currents through the relays leads to changes in the coefficients of coordination constraints. Therefore, mal-operation of relays and non-selective operation of protection system may occur. In order to have a robust coordination, coordination constraints from different topologies must be taken into account in the coordination problem. In such conditions, in order to satisfy all constraints, operating time of relays increases. In this paper, the selection of appropriate characteristic among standard characteristics for overcurrent relays is proposed to reduce the operating time of relays despite the existence of robust coordination. The proposed approach is tested on an 8-bus and the IEEE 14-bus test systems. Simulation results show that, by applying the proposed method to the coordination problem of distance and overcurrent relays, the operating time of relays, while maintaining their correct operation of relays, is significantly reduced, despite the network restructuring.