The Perfluorocarbon Liquid/Plastic Film Capacitor Technology and High Voltage Dielectric System

Sandia National Laboratories has developed a capacitor technology based upon impregnation of plastic film capacitor rolls with perfluorocarbon insulating liquids. Perfluorocarbon liquids are made from various hydrocarbon liquids through a complete exchange of the hydrogen atoms with fluorine atoms. The plastic films evaluated to date include polyester, polysulfone, polypropylene, polycarbonate, and polyimide. After in-depth evaluation of the perfluorocarbon impregnants in capacitor research, development, and recently in production, we conclude that they are highly effective materials for this application. No other single liquid displays their range of required properties. Perhaps their most valuable properties as impregnants are their low surface tensions (12 dyne/cm) coupled with low kinematic viscosities (0.4 cS). These result in void-free impregnation and wetting of the interior surfaces of plastic film rolls without need for such auxiliary measures as interleaved paper wicks. In research directed toward developing a long life, repetitive ive pulse, high reliability, and high energy density capacitor technology, another capability of these liquids has been demonstrated. If a low temperature perfluorocarbon arbon liquid is chosen, an evaporative coolant function will stabilize the system temperature below that which would cause thermal degradation of the critical electrical properteis of the plastic film dielectrics.