In-situ measurements of the electrical stresses induced by corona streamers on polymer foils under AC conditions

This work deals with air corona gaps submitted to AC voltages with an insulating coating on the low field electrode. Such gaps with a point-to-plane geometry are suitable for inducing accelerated streamer ageing phenomena on the surface and in the bulk of insulating materials. They are thus as useful for dielectric testing of materials, as they are for studies on partial discharges effects or on other failure phenomena which can cause malfunctions in high voltage equipment. The aim of the present paper is to report on in-situ oscillographic measurements which can give a direct access to the electrical properties of dielectric samples submitted to severe electrical stresses (in this case, polypropylene films 15 μm thick). An AC point-to-plane corona deposits charges of alternating sign on the sample surface. The resulting potential across the polymer foil and the current through it are recorded. As it has been shown that this current determines the lifetime of the polymer foil, it follows that the present method will be of interest for the testing and the qualification of similar insulating materials