Life tests of a conventional enamel varying the environmental conditions

This paper concerns the outcome of a life test campaign performed on twisted pairs specimens insulated by non corona resistant polyamide-imide enamel. Twisted pairs have been subjected to AC voltage having 50 Hz frequency: different voltage amplitude levels higher than the partial discharge inception voltage (PDIV) have been considered. The tests have been performed into an environmental chamber in order to control the temperature and the relative humidity (RH%) values. The partial discharge (PD) activity is strongly influenced by the environmental conditions and the change of the PD intensity considerably affects the time to breakdown of the enamel insulation. During the tests acquisition of digital partial discharges were realized and the obtained patterns are here presented. The gathered data allow to put in relation the collected life time values for each different voltage amplitude and relative humidity levels. The enamel total breakdown have been considered as end point criterion.