Fundamental Insulation Characteristics and Impulse Ratio of CO2 Gas

Abstract

SF6 gas has been used as an excellent insulating and arc-quenching gas for electric power apparatus such as SF6 gas insulated switchgear (GIS). However, since SF6 gas was specified to be a greenhouse gas because of its high global warming potential (GWP), environmental-friendly gases or gas mixtures alternative to SF6 gas are strongly required to be developed. Especially, the development of insulation gases without SF6 gas is an important task for the future electric power system.We focused our research on CO2 gas and CO2-based gas mixtures such as CO2/O2, CO2/N2 with small GWP as SF6 substitutes, and investigated partial discharge (PD) and breakdown (BD) characteristics under lightning impulse and ac voltage applications. In this paper, PD inception electric field (PDIE), BD electric field (BDE) and the impulse ratio were obtained in CO2, N2, SF6 gases and CO2-based gas mixtures, and discharge mechanisms of CO2 gas were discussed. Experimental results revealed that impulse ratio in CO2 gas was higher than those in SF6 and N2 gases, and dielectric-coating effect in CO2 gas was higher than that in SF6 gas. These results were attributed to the lower generation probability of initial electrons in CO2 gas.