Direct Voltage Breakdown of Silicone Oil/Polymer Film Composite with Needle/Plane Electrode System

The direct breakdown voltage was measured for a needle-plane electrode system in silicone oil, with polymer films of polypropylene, polyethylene terephthalate, fluorinated ethylene propylene, and polyamide on the plane. In the silicone oil alone, the breakdown voltage increased with increasing gap distance for both polarities, the values being highest with the needle negative. In the silicone oil/polymer film composite, with the needle positive, the breakdown voltage was higher than for the oil alone. Although breakdown initiated at the needle tip, the polymer film acted as a barrier to increase the system breakdown voltage. However, with the needle negative the breakdown voltages of all the composite systems, with exception of the polyamide film, were lower than for the oil alone. This is attributed to negative ions deposited on the film which create a high field and initiate breakdown in the film.