Electrical properties of 12 μm biaxially oriented poly(ethylene naphthalate 2,6 dicarboxylate) films related to ageing

PEN films have been irradiated by corona discharges in a global action cell in a plane to plane electrode configuration disposed in an oven, allowing different temperatures of irradiation, and thereby reproducing the working conditions of insulating systems, e.g. combined high temperature and a possible irradiation by partial discharges. Ageing under these conditions has been carried on for two hours. In a first part, a morphological determination of the surface of the films is presented. Since this morphology is shown to be the high temperature (β) one, it has been used to explain dielectric relaxation measurements of samples aged at temperature near the high temperature crystallisation of 245°C, assuming a phase transition process