Prebreakdown phenomena in an impregnated insulating system

During accelerated life-testing of impregnated polypropylene capacitors, breakdown may occur due to discharges in liquid voids. The authors have determined the experimental conditions for detection of discharges and studied various parameters such as the nature of the liquid, the additives, and temperature. The deterioration of the polypropylene films in capacitor models impregnated with MBT at 150 V _rms/μm 80°C was not due to discharges, but to electrochemical phenomena enhanced by a high liquid conductivity and the presence of impurities such as electrolyte and water. The influence of epoxide additives on the lifetime of capacitor models for 300 V_rms /μm is explained. Without additive, discharges and breakdown occur in a few hours or less