Study on The Effect of Dielectric Film on Gap Breakdown Voltage under DC Voltage in Air, SF6 and SF6/N2 Mixture

The roughness of the electrode surface and the coating of dielectric film on the electrode surface will affect the insulation performance of the gas. In this paper, an experimental platform of spherical-plate electrode is designed. The surface roughness of spherical electrode is $0.05 \mu \mathrm{m}, 0.8 \mu \mathrm{m}, 3.2 \mu \mathrm{m}, 6.3 \mu \mathrm{m}$ and $12.5 \mu \mathrm{m}$. Polyimide dielectric films with thickness of $25 \mu \mathrm{m}$, 50 $\mu \mathrm{~m}, 75 \mu \mathrm{m}$ and $100 \mu \mathrm{m}$ are prepared. Experiments are carried out in air, SF
6
and SF
6
/N
2
mixtures under DC negative polarity respectively by changing the roughness of the spherical electrode and the thickness of the dielectric film. The results show that the rougher the spherical electrode is, the lower the air gap breakdown voltage is. Coating dielectric film can improve the adverse effects of rough electrodes, and the gap breakdown voltage increases with the increase of film thickness.