Influence of chemo-rheological properties of silica-filled liquid epoxy resins on partial discharge behavior of coils

This paper describes the investigation of chemo-rheological properties of silica-filled liquid epoxy resins and its correlation to electrical properties of solid insulation, such as the partial discharge behavior of epoxy resin coils. Results of this investigation show that low viscosity is absolutely essential for a good impregnation of insulation layers. High maximum viscosity values, high surface energy of the resin part as well as filler morphology cause poor impregnation behavior. Optimum partial discharge properties may only be obtained if full impregnation within the insulation layer is achieved. As soon as one single void is left in the insulation, the partial discharge inception voltage drops by a factor of 10. Partial discharge data from the epoxy-resin impregnated coil show a significant improvement upon applying epoxy systems with excellent impregnation characteristics.