DC voltage breakdown in silicone-oil/polymer-film composite

Breakdown phenomena in a silicone-oil/polymer-film composite subjected to DC ramp voltage (0.5 kV/s) and a step voltage were studied with point-plane and plane-plane electrode systems. When the film was placed on the plane anode, the breakdown voltage of the composite with the ramp voltage was less than that for oil alone for both electrode systems as long as the film thickness was thin. Although the breakdown of the film due to charge deposition caused the complete breakdown of the composite for both systems, there was a difference in the transition process from the film breakdown to the complete breakdown. For both electrode systems, when the film was placed on the plane cathode, the increasing rate of the breakdown voltage with the increase in the film thickness was less than that for the film on the anode. In the point-plane system though the film breakdown was brought about by the charge deposition, it could not cause the complete breakdown. The breakdown of the composite was completed by the positive propagation from the point anode. In the plane-plane system, the magnitude of depositing positive charges on the film was too little to cause film breakdown under the ramp voltage. The complete breakdown was induced by the discharge in oil