Creeping discharge characteristics under non-uniform field on single pulse voltage application in CO2/N2 mixtures
N2, CO2 and their mixtures as well as SF6/N2 mixtures have been interested in the practical application as an insulating medium in place of SF6. However, the insulation characteristics of those gases under the non-uniform field have not been clarified. Especially, creeping flashover characteristics have not been elucidated. In this work, creeping discharge characteristics in CO2/N2 mixtures under steep-front pulse voltage on non-uniform field have been investigated. It is well-known that CO2 gas is also electronegative gas, but its electronegativity is very weak. In the case of CO2/N2 mixed gas, the dependency of gas content on flashover voltage is quite different from that in the case of SF6/N2 seen in our previous work, a maximum value of flashover voltage has been observed for 10 to 30% CO2 admixture into N2. This behaviour is seen not only in the negative polarity, but also in the positive polarity. This type of dependency is reported only limited gas mixture under uniform field. Moreover, this behaviour strongly depends on the thickness of solid dielectrics on which surface creeping discharges develop. From creeping corona observations, the corona growth at early stage is suppressed for CO2 mixtures of 10 and 30% compared with that for pure N2. In 30% CO2, broad corona emission is appeared widely on the solid dielectrics just like observed in pure N2. On the contrary, in pure CO2, creeping corona extension is relatively suppressed due to the electron attachment. Namely, both the effects, field relaxation by accumulated charges and electron attachment by negativity, are active.