Review: Methods for relay coordination

Reliability of the power system degrades with abnormal operating condition of the protective system caused due to overvoltage, under-frequency, overload etc. which may leads to interruption of the supply, and may damage equipment's connected to the system. To maintain system stability and reliability it is necessary to have a protective system which operates as quickly as possible, isolates smallest part of the system under fault. For this purpose it is necessary to have coordination between the protective devices to assure safe operation. This paper represents the relay coordination of distribution system with and without penetration of distributed generators due to increase in the interest in distributed generation by renewable energy sources. Directional overcurrent relaying, which is simple and economic, is commonly used as primary protection in distribution and sub transmission system and secondary protection in transmission system. This inclusion of DG may cause false tripping in feeders, increasing or decreasing short circuit levels, bidirectional power flow in case of radial distribution system, so to find the optimal solution of relay coordination problem there are different optimization methods. In this paper review of the methods like Genetic algorithm, Linear programming, Particle swarm optimization and Hybrid PSO is presented. Out of these methods hybrid PSO gives better solution with less iterations as compared to Genetic algorithm, Linear programming. In Hybrid PSO, TMS is considered as continuous parameter and current setting as discrete parameter. TMS is calculated by linear programming at the end of each iteration of PSO optimization algorithm.