Electrical Failure Properties of Cast Epoxy Resins

Impulse and ac breakdown properties of transparent cast epoxy resins are reported having either a castin needle electrode or a needle-shaped recessed gold film electrode deposited by vacuum evaporation or sputtering, given a divergent electric field. Dielectric breakdown always initiates from the needle tip where the electric field strength is the highest. The dielectric breakdown process, which consists of tree initiation, tree propagation, and the complete puncture of the cast epoxy resin is investigated. This process varies considerably with the wave form of the applied voltage. Chemical analysis by Fourier transform infrared spectroscopy (FTIR) indicates that chemical reactions caused by voltage application take place in the epoxy during the induction period until the initiation of the tree. The dielectric breakdown strength is considerably influenced by the electrode configuration, and also by resin formulation.