Breakdown behavior of oil-impregnated polypropylene as dielectric in film capacitors

The dielectric breakdown behavior of thin metalized PP films for use in Hv capacitors was studied as function of temperature with and without rape-see d oil as impregnation medium. The impregnating oil penetrates into the amor phous regions of the dielectric, With oil impregnation, the dielectric brea kdown strength of the PP film is increased by >25%. A correlation between t he breakdown strength and the degree of impregnation was found. With increa sing temperature the breakdown strength of rr films decreases. Moreover, th e measurements showed abrupt changes of slope in the breakdown strength at defined temperatures. From these results a correlation was established betw een the dielectric breakdown strength of PP films and temperature induced s tructure changes. It was shown that the abrupt changes of slope in the brea kdown strength occurring at defined temperatures are due to the additives c ontained in the PP capacitor films used. Finally, guidelines for further de velopment of impregnated PP films as dielectrics for high power capacitor a pplications are presented.