Fault protection solutions appropriately used for ungrounded low-voltage AC microgrids

This paper proposes possible fault protection solutions for an ungrounded AC microgrid (MG) based on a review on existing microgrid protection solutions in recent years. A generalized fault protection system of ungrounded low-voltage (LV) AC microgrids is divided into six individual protection zones including: (i) protection of distributed generators (DGs) and energy storage devices; (ii) protection of isolation and distribution transformers; (iii) protection of power converters; (iv) protection of inverter-based DG and rotating-based DG branches; (v) protection of load branches; and (vi) protection of AC trunk lines and common buses. Advantages and shortcomings of available fault protection schemes for each different MG protection zone are analysed in the paper.