Grounding the AC Microgrid

Grounding strategy of an AC microgrid affects its line-to-ground fault response, personnel/equipment safety, service continuity, insulation requirements, and protection criteria. Therefore, a comprehensive knowledge of the available grounding strategies and their effects is essential for design and operation of the microgrid components and especially its protection. In this paper, characteristics of different AC distribution system grounding devices and grounding configurations are investigated. Subsequently, AC microgrid grounding requirements and issues are identified based on the unique characteristics and constraints of microgrids. The results of the aforementioned investigations are used to identify the best grounding strategies, i.e., grounding configurations, transformer connection types, and grounding devices, for the AC microgrid. The study results indicate that the four-wire multi-grounded configuration is the most suitable choice for the majority of microgrids, especially in North America. The $Yg/\Delta$ and Yg/Yg transformers are identified as the most appropriate choices for DER interface to the four-wire multi-grounded microgrid. Besides, low-reactance and low-resistance grounding devices are recommended for the DER interface transformers.