Creeping discharge characteristics on negative polarity of a composite gas/solid
insulating system with N2/SF6 mixed gas have been studied by inserting a solid insulator
between a needle electrode and a plane electrode. In the case of the shorter creeping distance,
the flashover voltage on the negative needle increased with increasing SF6 gas content, which
was a positive effect of the SF6 gas mixture. When creeping distance was increased, a
considerable decrease in the flashover voltage on the negative needle under the gas pressures
P of 0.2 MPa and 0.3 MPa was observed by the addition of a small amount of SF6 into N2.
The effect of SF6 gas mixture for the flashover voltage on the negative needle changed from
positive to negative at a threshold creeping distance. Furthermore, the threshold creeping
distance depended on the gas pressure.