Analysis of the calculation methods for shell circulating current and grounding current in 500 kV HGIS and the optimization of grounding scheme

The strong electromagnetic coupling between the wire and the shell of Hybrid Gas Insulated Switchgear (HGIS) will lead to a large induced current on the shell, which will further cause local heating of the outside shell. Moreover, the utilization of grounding wire to release this current may also lead to the problem of its heating and ground potential rise. This study is intended to further promote the calculation accuracy of the shell circulating current and grounding current of the 500 kV HGIS and also propose the proper grounding schemes. The simulation results show that the ground grid must be considered in the calculation model and the phase difference of the conductor current could be ignored when the three-phase spacing exceeded 7.5 m. Furthermore, the influences of shorting bars and ground grid on the simulation results were compared and analyzed, and the optimization of grounding scheme and corresponding suggestions were put forward. Generally, it was not recommended to erect shorting bars and auxiliary ground grids. But if the temperature rise exceeds the limit, the shorting bars can be added at the two ends of a HGIS branch and the auxiliary ground grid should be laid using materials with higher flow capacity.