A correlation of bushing shed geometry with epoxy resin formulation in an electrically tracking environment

It has been shown that there is a very pronounced correlation between shed design and resin formulation for epoxy cast bushings. Consistent with the standard NEMA requirements for a given voltage class, the following should be observed: 1. Design of an epoxy cast bushing should be considered on its own merit and not unduly prejudiced by standard porcelain design practices. 2. Shed designs such as those shown in Figures 3 and 4 with uniform taper and without deep undercuts have given good performance in long time dust and fog tests. Such sheds exhibited surface arcing and had the least deleterious effect on the resin substrate. 3. Assuming (1) and (2) above, alumina trihydrate filled mixtures even with benzene rings in the chemical structures can perform satisfactorily.