Influence of creeping distance and gas pressure on negative creeping discharge for composite insulation consisting of N-2/SF6 and solid dielectric under pulse voltage

Creeping discharge characteristics on negative polarity of a composite gas/ solid insulating system with N-2/SF6 mixed gas have been studied by inserti ng a solid insulator between a needle electrode and a plane electrode. In t he case of the shorter creeping distance, the flashover voltage on the nega tive needle increased with increasing SF6 gas content, which was a positive effect of the SF6 gas mixture. When creeping distance was increased, a con siderable decrease in the flashover voltage on the negative needle under th e gas pressures P of 0.2 MPa and 0.3 MPa was observed by the addition of a small amount of SF6 into N-2. The effect of SF6 gas mixture for the flashov er voltage on the negative needle changed from positive to negative at a th reshold creeping distance. Furthermore, the threshold creeping distance dep ended on the gas pressure.