Lightning impulse breakdown characteristics of SF6 alternative gases for gas-insulated switchgear

Abstract

Investigations of the lightning impulse breakdown characteristics of a SF6/N2 gas mixture, N2 gas and CO2 gas have been carried out. In the case of the SF6/N2 gas mixture the 50% breakdown (electric) field strength for the positive impulse voltage was slightly lower than that for the negative impulse voltage, and the pressure of the SF6/N2 gas mixture must be increased to approximately twice the pressure of SF6 gas to obtain the same dielectric strength as that of SF6 gas. For CO2 gas, the 50% breakdown field strength for the negative impulse voltage was lower than that for the positive impulse voltage in the case of SF6 gas. However, the dielectric strength of CO2 gas, even at twice the pressure of SF6 gas, was approximately 60% of the strength of SF6 gas, so that the CO2 gas-insulated busbar may be approximately 1.6 times as large as the SF6 gas-insulated busbar. In the case of N2 gas, the 50% breakdown field strength for the positive impulse voltage was lower than that for the negative impulse voltage, and the dielectric strength of N2 gas, even at twice the pressure of SF6 gas, was less than 50% of the strength of SF6 gas, so that the N2 gas-insulated busbar may be approximately 2.1 times as large as the SF6 gas-insulated busbar. A remarkable difference between CO2 and N2 gas was found from the observation of discharge forms and partial discharge properties.