Bat Algorithm for Optimal Coordination of Directional Overcurrent Relay System

Abstract

In the field of modern power system, protection devices attains a powerful role. The performance of any protection network is the result of combined operation of relays, breakers etc. Two types of relays, primary and backup relays are installed for increasing the reliability of power system. A primary relay is setup for the fast response of any faulty condition. If it fails, then backup relay perform the same task after some time gap. This simultaneous operation of primary and backup relays require some attention for preventing any malfunction occurring due to improper time gap between them. Due to this, it becomes a highly constrained optimization problem and structure of large power system increases its non-linearity. This dissertation presents a technique for estimating the optimal settings of relays which in turn provide the faster operating time for primary relays and suitable coordination time interval for the backup relay effective operation. The settings for relay operation includes TMS, PSM and pickup current settings. A very popular swarm based meta-heuristic Bat Algorithm (BA) is implemented for the calculation of optimal solution. This coordination problem is divided in to two categories: (I) Continuous settings optimization for TMS and pickup current, (II) Mixed integer settings optimization for TMS and PSM. For first category conventional form of bat algorithm and binary version of BA for second category is utilized. The IEEE 8 bus system with and without external grid is used to validate the proposed technique. The techniques based on bat behavior proves to generate optimal solution providing better convergence rate.