Surface Charging Characteristics of a Real-Sized DC GIS Insulator in Pressurized Clean Air as a Feasible SF₆ Alternative

To assess the feasibility of clean air as an insulation medium in DC gas-insulated switchgear (GIS), the surface charge accumulation, a recognized pivotal concern, was examined both within clean air and SF₆, employing a real-sized insulator. The results indicate that the charge speckles tend to manifest in clean air, while the uniform charge distributions observed in both gases seem quite similar. Evidently, clean air at a pressure of 0.6 MPa is superior to SF₆ with equivalent insulation performance. With an increase in pressure, the formation of charge speckles was suppressed, while the uniform charging enhanced, a trend found to be mirrored in simulation results. Meanwhile, it was discerned that surface roughness of the conductor bears relevance to the formation of charge speckles, an effect that becomes particularly pronounced in clean air. Finally, an exploration into the influence of shielding structures on surface charge was conducted. The utilization of a shielding cover eventually yields higher but more uniform surface charge densities. The findings in this paper provide important guidance for the development of DC GIS using pressurized clean air.