Research On The Insulation Characteristics Of SF₆/N₂ Mixture In Low Temperature Environment

Due to the excellent insulation performance, SF6(Sulfur- hexafluoride gas) has widely application in gas- insulated switchgear(GIS), gas- insulated transmission line(GIL) and other electrical equipments, as the only gas insulating medium used in the industry. However, with the increasing importance of environment protection, in <K yoto Protocol>, SF6 is one of the six gases restricted to use. In addition, because of the large molecular mass, SF6 is easy to liquefy, which makes its insulation performance greatly reduce after liquefying under the environment of high gas pressure and low temperature. Thus, research on the substitution of SF6 has been concerned by many scholars. Among many alternative gases, the mixture of SF6 and N2 has a great application prospect. Moreover, the study on the insulation performance of SF6/N2 at low temperature is of great significance to its application of the transmission system in the cold area.Based on the analysis of Steady State Townsend(SST) discharge principle of SF6/N2 mixture, a SST experiment device at low temperatures is built up, which is able to achieve low-temperature environment, the electrode replacing and spacing adjustment and many more. Afterwards, the ionization coefficient s and attachment coefficients of SF6 /N2 in several mixing proportions under 0~-15℃ are calculated. According to the results, estimate dielectric limits and analyze the effect of temperature on them.Electrodes are replaced with rod-plane and hemisphere-plane to achieve non- uniform electric fie lds of different field non- uniformity factors. Breakdown voltages of SF6/N2 mixture in non- uniform field are performed at temperature within 0~-15 ℃ and gas pressure within 15kPa~60kPa. Moreover, the influence of temperature on breakdown voltage is analyzed.According to the synergis m of SF6/N2 mixt ure, synergy coefficients at each temperature and gas pressure are calculated based on the breakdown volta ges obtained from the experiment. Addition, the effect of temperature and pressure on synergy is analysed.