Impact of distributed generation on the blinding of an overcurrent relay in a distribution network

The increasing penetration of distributed generation poses significant challenges to existing protection systems. According to the Renewable Energy Sources Act, the installed capacity of photovoltaic (PV) systems in Germany must increase approximately four times. This paper examines the impact of PV penetration on the blinding of overcurrent protection within a 20 kV distribution grid in Southwest Germany. The analysis accounts for the PV penetration, fault impedance, changes in network topologies, and load variations. A dynamic model was developed to support this investigation. In addition, this study introduces a simple method to determine the share of PV in comparison to the rated transformer power at which blindness of overcurrent relays occurs. The results indicate that the fault resistance, load variations and topology can contribute to blinding of the protection system. Specifically, in the analyzed distribution network, fault resistances between 25 Ω and 30 Ω can cause blinding of the overcurrent relay with PV penetrations ranging from 1.5 to 5.5 times the installed PV capacity based on data from the grid operator in 2023.