Electrical tree propagation along mica barriers in dependence on the resin components

For various types of epoxy resin and various kinds of ion-exchange on the mica surface the electrical tree propagation in the mica epoxy interface has been investigated. Apart from statistical scattering a significant spread by more than one order of magnitude in tree propagation time was found. Furthermore, the optical appearance of the corresponding trees was observed. Branch- and bush-type trees were found yielding shorter or longer tree propagation times, respectively. The observed spread is ascribed to the combination of resin and mica. However, the composition of the resin has the strongest influence. Thus, for further improvements of mica epoxy insulation it is more promising to study the components of the resin compared to an ion-exchange on the mica surface.