optimal adjustment of dualsetting overcurrent relays in inverter-based microgrids

Increasing the penetration of distributed generation (dg) systems in power systems has many advantages, but it also has problems, including interference with the proper functioning of the protection systems. this problem is severe in microgrid systems that contain many dgs. overcurrent relays are one of the most critical protection equipment of protection systems. the dg sources significantly change the characteristics of fault currents and the protection designs as well as the coordination of overcurrent relays. this paper proposes a coordination method for directional overcurrent relays with dual adjustment to resolve the interference problem in the protection system of a microgrid in the presence of distributed generation sources based on the electronic power converter (inverter). this is done by considering the curve of different standard characteristics according to the iec60255 standard in two operating modes, the grid-connected and islanded. a genetic optimization algorithm is used to reduce the total operating time of the relays. the simulation results verify the effectiveness of the proposed coordination method. the results show that the protection coordination scheme with dual adjustment relays and the use of combined characteristic curves can significantly reduce the operating time of the total relays.