AC breakdown performance analysis of SF6/N2 and SF6/CO2 gas mixtures for ring main unit (RMU) switchgear application

In high voltage applications, sulphur hexafluoride (SF6) gas has been utilized as the electrical insulation and/or current interrupter due to its strong electronegative properties. However, SF6 owns unfavorable impact to the environment since it was listed in Kyoto Protocol 1997 as a potent greenhouse gas. As one of the alternatives to minimize the usage of pure SF6, the breakdown behavior of SF6/N2 and SF6/CO2 gas mixtures at 10 % SF6 content are investigated under non-uniform field at pressure level between 0.11 MPa to 0.15 MPa, which focusing for ring main unit (RMU) switchgear application. In this study, the AC breakdown voltage test on both SF6 gas mixtures were conducted inside a pressure vessel using R6-plane electrode configuration, where the gap distances between the electrode were varied between 5 mm to 30 mm. The results show that the AC breakdown voltage of SF6/N2 and SF6/CO2 at 10 % amount of SF6 is above 40 % as relatives to pure SF6, throughout all gap distances and pressure levels. Moreover, it is also found that the AC breakdown voltage of SF6/CO2 is higher than SF6/N2 when the electrode gap is increased above 15 mm, suggesting the significant role of electrode gap distances in suppressing the breakdown streamer in SF6/CO2