Comprehensive coordination of combined directional overcurrent and distance relays considering miscoordination reduction

This paper presents a novel approach to solve the miscoordination problem of combined directional overcurrent and distance relays in transmission and subtransmission systems. In order to reduce relays miscoordinations, a general objective function is presented to find optimum directional overcurrent relays time setting multipliers, characteristics, and pickup currents by optimization algorithms. In previous researches, different approaches have been presented but they cannot find a reliable solution to avoid from having negative discrimination times between the backup and main relay (miscoordination), which means operation of the backup relay before the main relay. Using proposed approach, not only the number of miscoordinations can be greatly decreased but also the positive discrimination times can be minimized. The proposed method is tested on 9-bus and 39-bus test system. Genetic algorithm and human behavior-based optimization are used as optimization tools to find optimum settings. The results indicate that the proposed approach is capable of solving the miscoordination problem, in addition to minimization of discrimination and relay operation times compared with previous approaches.