Protection Scheme for Island Operated Medium-Voltage Microgrid

Abstract

During island operation, high fault currents from the utility grid are not present. Also, most of the distributed generation units that are connected to microgrid, are likely to be inverter interfaced and have limited fault current feeding capabilities. Due to that, during microgrid island operation, conventional distribution system protection schemes which assume a single path for the fault current and a high fault current level when compared to the load current, can be less efficient, may have slower fault clearing time and be less sensitive and selective. Several solutions have been proposed and many of the proposed solutions rely on the use of high-speed communication links to send tripping or blocking signals between relays. This paper proposes a new protection scheme, including both short-circuit and earth-fault protection, for island operated medium-voltage distribution network (microgrid) having multiple protection zones without the need for high-speed communication. The proposed protection scheme is not dependent from fault current contribution of the units and takes into account and is selective with low-voltage-ride-through curves of the units.