Coordination of Protection Devices in Microgrids

In this paper, some challenges in microgrids $(\mu \text{Grid}$ , which arise from the limitation of protection devices, such as the point of common coupling (PCC) switch and relays of Medium Voltage (MV) circuit breaker, are presented and discussed. These challenges directly influence the coordination of the electrical protection and the functionality of the $\mu \text{Grid}$ especially during transition between operation modes (on-grid to off-grid and vice-versa). Those limitations were observed in the $\mu \text{Grid}$ at the Alcântara Launch Center (ALC), Maranhão, Brazil. The solutions were based on guaranteeing flexibility to the protection coordination for different voltage transient levels, using single-phase, three-phase positive, negative and zero sequence voltage protections. In addition, to ensure black start functionality, a logic was implemented to inhibit tripping by undervoltage and by negative sequence overvoltage, both due the electrical transients that appear during that $\mu \text{Grid}$ starting. The applied solutions were validated and presented satisfactory results.