Optimal Coordination of Directional Overcurrent Relays using Particle Swarm Optimization Technique

Abstract- The main function of the protective devices in the power system is to detect and remove the selected faulty parts as fast as possible. Directional over current relays are commonly used for the protection of interconnected sub transmission systems, distribution systems, or as a secondary protection of transmission systems. For the systems having more than one source connected, that is meshed or looped networks, directional over current relays become the suitable choice for better selectivity, since directional relays operate only when the fault current flows in the specific tripping direction desired. The most vital task when installing directional relays on the system is selecting their suitable current and time settings such that their fundamental protective functions are met under the requirements of sensitivity, selectivity, reliability and speed. The problem of setting Directional Over Current Relay(DOCR) is a highly constrained optimization problem that has been solved as a linear programming problem. The calculation of the time dial setting (TDS) and pick up current (IP) setting of the relays is the core of the coordination. This paper calculates the TDS by choosing one of the available pick up current settings as the predetermined value. The simplex two phase method is used to determine the optional TDS of the relays. Improvement in the solution is brought by using the particle swarm optimization technique to the co-ordination problem for reaching the global optimum value with less computational time. Sample 3 bus and 8 bus systems are utilized for comparing the results obtained by PSO with that of the simplex method. The optimization method used in the recent times minimizes the operating time of the relays much, when compared to the other methods. This method also enhances quicker solution of coordination process.