Abstract
Microgrids are small-scale electric energy systems that operate in parallel with the main grid (grid-connected mode) or completely isolated (island mode) and can seamlessly transition between both modes. The design of protection systems for microgrids can be challenging due to changing operating conditions and system topology. Grid-connected and island modes yield different fault current magnitudes and directions. This paper presents a case study of a protection and relaying scheme of an industry-grade real-world microgrid. Mathematical analysis and simulations were completed to quantify the magnitudes and directions of the fault currents in grid-connected and island modes. Other protective elements such as sync checks and under/over voltage were utilized to ensure smooth operation. Using industry-grade relays, a protection scheme was developed to ensure proper operation.