DC prebreakdown light in silicone-oil/polymer-film composite with sphere-sphere electrodes

This paper describes an experimental study on dc prebreakdown light in a silicone-oil/polymer-film composite with sphere-sphere electrodes using an optical system consisted of a 20 m-long image guide scope and a gated image intensifier. When the film was located on the positive-sphere, a film breakdown was caused by deposited charges on the film and then it induced a complete breakdown. When the film was located on the negative-sphere, a discharge channel in the oil often appeared at the initial stage and it extended over the gap within several nanoseconds. The breakdown processes for both the polarities are discussed on the basis of the photographs.