Challenges in Medium Voltage Microgrids Case Study: Alcântara Launch Center

In this paper, some challenges in microgrids $(\mu \text{Grid})$ are presented and discussed, which arise from the modification of the electrical system circuit when a $\mu \text{Grid}$ is operating isolated from the main grid, specifically because the distribution network becomes a circuit in ungrounded delta, and the microgrid power sources have low short-circuit capacity. The main problems discussed are the non-detection of ground overcurrent in an earth fault event, the unbalance between voltages measured by voltage transformers (VTs) connected between phases-to-earth, and the phenomenon of ferroresonance. These problems directly influence the coordination of the electrical protection, component integrity, and synchronism check between different power sources of the $\mu \text{Grid}$ . The microgrid at the Alcântara Launch Center (ALC) in Alcântara, Maranhão, Brazil, was the case study where the problems have been observed, and the proposed solution was validated, which were based on a study of protection, parameterization of protection relays and damping resistors.