The effect of surface roughness on breakdown in Eco-friendly gas

SF6 gas has excellent insulation performance and stability, so it is widely used as an insulation material for high-voltage gas insulation systems of power equipment in the transmission and distribution industry. However, the GWP (Global Warming Potential) of SF6 gas is very high at 23,900, limiting its use in the power industry. Therefore, research has been conducted for a long time to reduce the amount of use or to find an alternative gas. Alternative gas candidates include CO2, N2, dry air gases and C5F10O and C6F12O. Among them, CO2 has a low GWP of 1 and a low boiling point, so it is easy to handle, and the arc extinguishing performance applied to GIS is relatively superior compared to other gases, and it can be mixed with O2 to improve insulation performance. Therefore, it is being actively considered as a promising alternative gas.In general, replacement gas has less than half the dielectric strength of SF6 gas, so the insulation distance between conductor and enclosure should be longer. In other words, the size of the enclosure that stores the gas is inevitably increased. However, due to cost and product size limitations, manufacturers are gaining insulation through activities such as increasing gas pressure or controlling other influencing factors. Since the critical electric field strength of the gas gap is expressed as the product of the gas pressure and the surface roughness, the surface roughness of the conductor under the ultra-high voltage condition is treated as an important factor affecting the insulation performance. Therefore, in order to secure sufficient insulation performance in eco-friendly products, it is necessary to check the insulation performance change according to the surface roughness and reflect this in the insulation design. In this paper, the effect of the surface roughness of the conductor on the breakdown voltage under the conditions of CO2, O2 mixed gas among eco-friendly gases and SF6 gas was analyzed and tested.