A Shunt Current Limiting Method Based on Common Ground Electrode of Power Electronic Devices

For a DC system with a shared grounding electrode, when one DC system operates in a single pole ground mode and the other DC system is in a transition between single pole ground and single pole metal return mode, there will be shunt current flowing into the DC system in the transition state, posing a threat to station safety and causing pole shutdown due to overcurrent protection action of the station grounding network. This article first analyzes two operating modes of shared grounding electrodes, and concludes that the necessary condition for the inflow of shunt current into the grounding network within the station is the asymmetric operation of the DC system. Secondly, the principle of shunt current generation was analyzed, and existing measures to limit shunt current were summarized based on the generated principle. Furthermore, a current limiting method for installing a current limiter at the outlet of the grounding electrode bus is proposed. Finally, the working principle of current limiting and the working state of the DC system under different operation modes are analyzed, and the feasibility of the method is theoretically proved to limit the current of the grounding grid and the grounding electrode in the inflow station, so that the method can be extended to the scenario of the common grounding electrode of the multi-circuit DC system.