Protection of Distribution System Islands Fed by Inverter-Interfaced Sources

As the penetration of renewable energy resources increases, and standards evolve to accommodate it, it has become a distinct possibility that at least for some periods of times, islands sustained entirely by renewable resources may exist. Most common renewable resources connecting at distribution level may be photovoltaic solar and sometimes wind. These resources connect through inverters and their response to changes in system conditions, including faults, is completely governed by the inverter design and controls. Though many papers are written on microgrid protection, the scenario of 100% renewable fed islands has not been properly addressed from a protection viewpoint. This paper examines the operation of such islands at distribution voltage level, brings out design considerations of such islands, and analyzes protection principles in light of this unique configuration.