Influence of Trace SF6 on Surface Corona Characteristics in SF6/N2 Mixtures Under DC Voltages

Abstract

AbstractCorona discharge in gas-insulated power equipment will cause potential harm to the inner insulation of the equipment. Insulation defects near insulator may induce surface corona. Because the insulation performance of insulator is generally lower than that of gas medium, it is easy to cause gap breakdown or surface flashover under relatively low applied voltage, making the equipment outage or damage. SF6/N2 mixtures is a typical electronegative gas with synergistic effect, which is often used for inner insulation of power equipment. A small amount of SF6 can change the insulation performance of gas mixtures and make it retain the useful characteristics of electronegative gas. In this paper, the influence of gas-mixture ratio on surface corona characteristics in SF6/N2 mixtures was studied by setting up the discharge experimental setup of tip-surface compound defect. The variation of light emission patterns under different voltage polarities were analyzed, and the rules of discharge onset and breakdown voltages, current pulse-time parameters were compared. The results have shown that the surface effect mainly affects the streamer corona development. When the SF6 content reaches 1%, both the discharge light emission patterns and the parameters of pulse time under positive and negative polarity are virtually consistent with those in pure SF6. With increasing SF6 content, the onset voltage and breakdown voltage of surface corona discharge increase, and the pulse-time parameters decrease and finally reach saturation.KeywordsSurface coronaSF6/N2 mixturesSurface effectDischarge characteristicsDC voltages