Discharge characteristics of CF3I/N2 mixtures under lightning impulse and alternating voltage

As the greenhouse effect of SF
₆
gas, the research on seeking alternative insulating gas to SF
₆
has become an imperative case. CF
₃
I and its mixtures have been considered as the most promising insulating gas to replace SF
₆
gas. In this paper, the discharge characteristics of gas gap and insulator in CF
₃
I/N
₂
gas mixtures under lightning impulse and alternating voltage were investigated. The effect of voltage, pressure as well as decomposition product after flashover were studied. Experimental results showed that in inhomogeneous electric field the breakdown voltages of CF
₃
I/N
₂
with 30% CF
₃
I gas is lower than SF
₆
/N
₂
mixtures with 20% SF
₆
. However, the flashover voltage of insulator in CF
₃
I/N
₂
is higher than that in SF
₆
/N
₂
mixtures. When compared to CF
₃
I/N
₂
itself, the 50% breakdown voltage under positive lightning impulse were lower than that under negative lightning impulse. The CF
₃
I/N
₂
gas mixtures with insulator also had polarity effect and appear polar reversal phenomenon. Under lightning impulse, there is no decomposition product on the surface of insulator after flashover but under alternating voltage, obvious iodine was produced on the surface of insulator.