Abstract: Distributed generation is local generation near local load that feeds the local load. This local load and local generation form a grid known as microgrid. Microgrid operates in two modes 1) islanded mode 2) grid connected mode. Protection scheme used in the islanded mode is not used in the grid connected mode because of threshold settings. Main three instability problems occur in the interconnected power system are Frequency, Voltage and Angle. This paper deals with the design of an adaptive frequency relay, which is used to protect the distributed generation against frequency variations in grid connected mode as well as in islanded mode. It is also used to detect islanding condition of the system. The modeling is done in MATLAB/SIMULINK environment.

Keywords: Distributed generation, Adaptive frequency relay, Phase locked loop (PLL)