Protection and Dynamic Analysis during Bottom-Up Restoration Process in MV/LV Microgrids

In this research, the authors analyze the protection behavior during power system restoration. The bottom-up network restoration is done with the help of a black-start unit and concludes with a biogas plant taking over the island. The focus of this paper is to evaluate the behavior of protection devices, and to check their selectivity, sensitivity and speed during different network restoration stages. The research is done in two parts: In study case I, a protection investigation is performed based on a short-circuit analysis of the complete microgrid. In study case II, the dynamic behavior of the power plant along with the voltage and frequency protection of distributed energy resources is considered. At the end of the investigation, recommendations for the restoration process in islanding grids are given with regards to the protection concept considering system stability to support automated bottom-up restoration. The results are useful for distribution system operators to design their protection concepts for their grid operation in more flexible ways especially considering islanded operations.