Development of Oil-Impregnated, All-Polypropylene-Film Power Capacitor

Newly developed all-polypropylene-film power capacitors are described. The size of the capacitors is about half and their dielectric loss is less than one-seventh that of conventional paper-film capacitors. It is vitally important that thin gaps between the films themselves and between the film and the electrode foil are filled with an insulating fluid leaving no voids. Another important item is the diffusion of the insulating fluid into the film. This influences swelling and dissolution of the film. It should also be noted that diffusion and swelling depend upon temperature. All of these factors could, at times, cause the occurrence of voids even if the fluid is completely impregnated into the gaps during the first stage. These voids, of course, decrease corona inception voltage. We have succeeded in the development of oil impregnated, all film, power capacitors by studying insulating fluids, films, and several factors in the production of capacitors to yield good electrical insulation free from voids.