Surface potential decay measurements on fluorinated polymeric insulation for high voltage DC applications

Space charge accumulation in polymeric insulation is an increasingly important area in high voltage DC transmission as its presence distorts the local electric field, leading to premature failure. By using fluorination process, the surface of polymeric insulation is chemically treated and consequently modifies charge transport characteristics of the material. In doing so, excellent surface properties similar to fluoropolymers can be obtained without compromising the bulk characteristics of the polymeric insulation. The modifications in chemical components at the surface of polymeric insulation should lead to corresponding modifications in electrical properties as well. Different surface fluorinating conditions were investigated and the fluorinated samples were electrically characterised and tested, so an optimal processing condition can be achieved to meet practical requirements for high voltage DC insulating material. This paper will focus on the surface potential decay from negative corona discharge and PEA measurements on fluorinated epoxy samples of different fluorination times in a controlled environment. It has been found that there is a significant change in surface potential decay characteristics with the introduction of surface fluorinated layer. The effects of fluorination process on surface potential decay mechanisms responsible for the observed phenomena were thoroughly discussed.