Effect of electrode surface roughness and dielectric coating on breakdown characteristics of high pressure CO2 and N2 in a quasi-uniform electric field

SF₆ gas has excellent dielectric strength and interrupting capability and is used in various applications such as gas insulated switchgear (GIS) in substations. However, since SF₆ has a high global warming potential (GWP), it is imperative to reduce its use and develop recovery technology for its reuse. This paper examined the potential of alternative insulating gases for GIS, determining experimentally the ac and lightning impulse breakdown characteristics of CO₂ and N₂ gases, which have little environmental impact, in a quasi-uniform electric field. The effect of electrode surface roughness is greater in N₂ than in CO₂. The impulse ratio in a quasi-uniform electric field was smaller in N₂ than in CO₂ at low pressure, but this reversed when the pressure reached 1.2 MPa. The dielectric strength of an electrode with a dielectric coating was approximately equal to that of a specular-finish bare electrode in either CO₂ or N₂ when an ac voltage was applied. When lightning impulse voltage was applied, a significant improvement of dielectric strength was observed if a dielectric coating was applied to the electrode considered to be the initial electron source.