Impact of GIS Configuration and Trapped Charge Effects on Very Fast Transient Overvoltage in 400 kV Systems using ATP-EMTP

This paper deals with the very fast transient over-voltage (VFTO) in a 400 kV Gas insulated substation (GIS), with a special focus on the influence of GIS configurations and trapped charge on this overvoltage. Using an operational UK substation, the impact of GIS components configuration on VFTO magnitudes and their distribution within the substation has been analysed using ATP-EMTP. Comprehensive simulations have been considered where the influence of bushings, busbars, disconnectors, and elbows on transient voltage behaviour have been covered. The results indicate that both configuration and trapped charge significantly impact the VFTO peak. Increasing trapped charge level result in a peak value increase of up to 36 %. For a given trapped charge level, the voltage peak value is greatly influenced by the selected configuration, with the worst-case scenario observed in changes to the capacitive voltage transformer parameters. These findings can aid in developing improved insulation coordination and optimised GIS designs for enhanced reliability in UK substations.