Comparison of the Dissipation Factor of Insulating Resins With and Without Anhydride Curing Agents

The most main wall insulations of rotating electrical high voltage machines consists of several layers of wound mica tape impregnated with epoxy resins. Methylhexahydrophthalic anhydride and Hexahydrophthalic anhydride are the state-of-the-art curing agents in epoxy insulations and are therefore essential components of the insulation system. Both anhydrides were proposed to the candidate list of Substances of Very High Concern and are therefore part of the European REACH authorization process. The prohibition or restricted use of both anhydrides in Europe in the future is possible and puts high pressure on the European manufacturers of electrical devices. Possible substitutes are available, but have to be qualified e.g. with respect to their dielectric properties. Hence, this paper compares several insulating resin systems with and without anhydride curing agents regarding their dielectric loss behavior. The results reveal that the curing agent has a measurable effect on the dielectric losses. Furthermore, the investigated anhydride-free insulation systems are a viable substitute at least with regard to their dielectric losses.