In order to increase the breakdown field strength of polypropylene film

alumina layer is evaporated on the surface of the polypropylene film to form composite dielectric film.The film of the evaporated alumina is subject to metallized evaporation

made into capacitors and their performances are tested.It is shown by the result that although the dielectric constant of the composite film does not have significant variation

yet the breakdown field strength of the capacitor increases.The composite film capacitor has good self-healing performance

which can achieve isolation self-healing and effectively prevent short circuit breakdown of capacitor due to over-limit self-healing.