Lightning Impulse Breakdown Characteristics in Compressed N2 and CO2 and Feasibility of their Gases' Application to Gas-Insulated Buses

SF6 has been identified as a greenhouse gas with a long atmospheric lifetime. In the long term, it is preferable to reduce the amount of SF6 used. Therefore, it is important to discuss the possibility of using environmentally friendly gases as alternative insulation gases for practical gas-insulated apparatuses. In the selection of an alternative gas, it is thought that high-pressure natural gases, such as air, nitrogen (N2), and carbon dioxide (CO2), are promising environmentally friendly candidates. In this paper, we describe the basic insulation characteristics of N2 and CO2 in the high-pressure range of up to 2.0MPa under a quasi-uniform electric-field gap and under a non-uniform one in the presence of a metallic particle, and the characteristics are compared with those of SF6. Moreover, we discuss the estimation of the cross-sectional size of a gas-insulated apparatus using high-pressure N2 or CO2, based on insulation and thermal designs.