Lessons Learned on Protection Coordination Considerations Within Inverter-Based Microgrids

A microgrid is a collection of interconnected loads and distributed energy resources (DER) within clearly defined electrical boundaries that act as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in both grid-connected and island-mode. One of the main drivers for Microgrids is it provide opportunities for system reliability and resilience. The operational mode and types of generation sources of the DERs within the Microgrid, and the existing distribution protection schemes; amongst others, presents challenges to Microgrid protection. For a Microgrid to be reliable and resilient, a robust, sensitive, selective, dependable and reliable protection scheme is required; to effectively respond to various Microgrid operational modes. This paper summarizes the lessons learned from protection coordination and design implemented within two utility service territories - an urban network system and a residential radial neighborhood. The investigation assesses the viability of various protection schemes. Protection response has been reviewed with respect to real world application; including, benefits and limitations of selectivity, sensitivity and reliability.