Influence of the filler on the breakdown and partial discharge behavior of heat-resistant cast resins

This paper reports on experimental investigations dealing with the influence of the filler on the breakdown and the partial discharge behavior of different cast resin systems. The tests were carried out with a heat-resistant epoxy and a polyurethane resin system in combination with different mineral fillers. The breakdown strength of the insulating materials was measured as a function of the temperature in a uniform as well as in a highly non-uniform electrical field. Additionally the partial discharge inception voltage (PDIV) was determined by using a highly non-uniform electrode arrangement. The contribution reveals that the wollastonite filled epoxy resin shows a worse electrical strength than the corresponding silica filled material. Furthermore it will be displayed that mechanical stresses can have a significant impact on the electrical behavior of cast resins. The experiments with a silica filled epoxy isocyanurate system show that this material has lower breakdown and partial discharge inception voltages but a better temperature stability compared to the corresponding epoxy system.