Optimal Coordination of Directional Overcurrent Relay using Water Evaporation Optimization Algorithm

Abstract

In modern power system, protection devices play an important role. The protection in the network is provided by combined operation of relays, breakers etc. Two types of relays, primary and backup relays are installed for increasing the reliability of power system which should have a coordinated operation time to provide a reliable protection and to avoid unnecessary tripping of relays thereby reducing the total operational time of relays.. The relay operation requires TMS, PSM and pickup current settings. The aim of optimal coordination of Directional Overcurrent Relays is to maintain a certain time gap called coordinated time interval between the operation of primary and backup relays for preventing any malfunction and unnecessary tripping of relays and to obtain the optimal settings of relays so that the overall tripping time of all the primary relays is minimized. Thus, obtaining the Time Multiplier Setting (TMS), Plug Setting Multiplier (PSM) and pickup current settings for minimizing the operating time of relays while adhering to various boundary constraints and coordination become a highly constrained problem. The water evaporation optimization algorithm uses the water molecules as the algorithm individuals which gives the fast and more accurate results due to its global and local search ability in two different phases of evaporation. The mentioned formulation is proposed to be realized with the water evaporation optimization technique. The problem formulation is divided into two sections: (1) Continuous settings optimization and (2) discrete settings optimization. This problem of continuous and discrete coordination of directional overcurrent relay is validated by implementing through the standard IEEE 8 bus and 9 bus systems.