Impregnant-Polypropylene Interactions in the All-Film Capacitor Configuration

Having reviewed the main parameters which control the swelling of polypropylene (PP) film, the authors describe three different approaches for its quantification in the situation of a real capacitor. The first method consists in following the height increase of a stack of flat all-film capacitor windings at different temperatures. The behavior of a large variety of fluids has been studied, allowing an easy ranking of the swelling ability of these different fluids. The influence of the nature of the film in connection with the temperature has also been determined. The second method is even more representative of the capacitor configuration since in this case the geometry of the winding was not permitted to change. In this method the internal pressure within the winding stack was recorded, the variation being the result of the swelling of the film. Large differences of behavior were pointed out. Various PP films showed different abilities to flow under the effect of the pressure induced by the swelling itself. In the third method, the capacitance variations were determined. The mathematical treatment of these variations displayed the different steps of the film swelling, each one having a well defined speed. From these different approaches of the swelling evaluation, some interesting conclusions were drawn indicating the leading role played by the nature of the film in the film-liquid association.