Analysis of the Impact on the Grounding System in 110 kV Grid during Bottom-up Network Restoration

The purpose of this research is to study how the grounding on the high voltage end (110 kV) is impacted during a bottom-up network restoration process in different islanding configurations. The majorly used grounding method in high voltage grids in Germany and Central Europe is resonant grounding. So, during the investigation, it is analyzed what key factors affect the existing conventional grounding design. The influence of the short circuit contribution from the renewable energy resources, the variable grid size and the transformer grounding at the high voltage side of the distribution transformer are taken into consideration. The variation of the earth-fault residual current in the under- and over- compensation zone for 110 kV is studied during the different grid configuration, and the Petersen coil is designed in such way that the compensation requirement is satisfied, and the safety and the security can be achieved during the ground-fault scenario. In this way, the grid can be operated under the ground fault condition in each island grid configuration as well as grid connected mode. At the end of the research, the suitable and selective compensation region is established, and an automated tuning of the coil selection is specified as an option to support automated bottom-up restoration, which will be useful for the distribution system operators to design the grounding protection system considering the bottom-up network restoration.