Comparative Study of Optimal Relay Coordination with Current and Voltage-based Relay in Distributed Generation Systems

With the increased penetration of distributed generators (DGs) in the distribution system, the protection schemes based on standard inverse time characteristics are unsuitable as DGs alter the power flow from unidirectional to bidirectional and change the fault current level depending upon the operating mode of the microgrid. All of these result in the need for directional elements and communication links for proper coordination, which increase the cost and complication of the protection scheme. In this paper, the study of optimal relay coordination in a DG-based system is performed with user-defined characteristics, which is a logarithmic function of fault voltage and has a grading of relays independent of operating modes of the microgrid. Further, the performance of the voltage-based relay in terms of optimal settings and total operating time is compared to the conventional overcurrent relay. The optimal solution to the relay coordination problem is determined by a genetic algorithm (GA) and simulated annealing (SA), and the results of both the methods were compared for the user-defined and the standard relay characteristics.