Graded Surface Roughness of Epoxy: A Novel Approach of Surface Modification to Enhance Surface Flashover Voltage

The optimized surface condition of the polymer dielectrics in HVDC applications can dramatically alter their flashover characteristics. The proposed work in this paper aims to elevate the DC flashover voltages of epoxy after being physically polished with sandpaper of different gradings. The non-polished and homogenously polished specimens with roughness
$\mathrm{R}_{\mathrm{a}}=0.54,3.16,5.24$
and 8.35
$\mu\mathrm{m}$
are obtained. Moreover, the epoxy with graded surface roughness is fabricated and the flashover test of all the samples is conducted in vacuum. The DC flashover voltages of the homogenously polished samples for either positive or negative polarity are obviously improved compared to the pristine epoxy and increase by increasing the surface roughness. The specimen with graded surface roughness in the perpendicular direction to the electrodes shows the highest improvement in the flashover characteristics. Surface conductivity, surface potential and surface trap characteristics are further studied to investigate the mechanism of the proposed concept. It can be inferred from the results and theoretical explanation that the proposed surface conditioning method can help to improve the insulation strength of the future dielectrics for HVDC applications.