A study of factors and mechanisms responsible for the de-metallization of polypropylene films used in dry capacitors

Metalized polypropylene films are used to build power capacitors for ac voltage. The objective of this paper is to study the de-metallization processes that may occur under high electric field. A laboratory model of capacitor is first described. It allows us to visualize the de-metallization and record the corresponding capacitance loss, under various conditions of applied voltage, frequency, mechanical pressure, and gas nature. Four different de-metallization processes can be observed. The residual gas layer existing between films has a primary importance. Replacing air by nitrogen shows that the de-metallization is basically due to the oxidation of the metal.