Sensitivity of dielectric strength of C4F7N binary gas mixture to electric field distribution under lightning impulse

This study explores the breakdown properties of three C
₄
F
₇
N binary gas mixtures under lightning impulse and the reduction of dielectric strength in the presence of insulation defects. The 50% breakdown voltage (U
_50%
) of three C
₄
F
₇
N binary gas mixtures in a quasi-uniform electric field is observed to determine the basic dielectric strength, which has the ranking C
₄
F
₇
N/Air ≈ C
₄
F
₇
N/CO
₂
> C
₄
F
₇
N/N
₂
. A coefficient S
_E
is introduced to quantitatively describe the sensitivity of dielectric strength to electric field inhomogeneity. The S
_E
of different gas medium can be ranked as SF
₆
<; C
₄
F
₇
N/CO
₂
<; C
₄
F
₇
N/Air <; C
₄
F
₇
N/N
₂
, indicating that C
₄
F
₇
N mixed with nitrogen, carbon dioxide, or dry air is less capable of tolerating insulation defects than SF
₆
, which merits consideration in insulation designs..