All film power capacitors-degradation under alternating electrical stress of impregnated polypropylene films; effect of the epoxide additive

The aging of impregnated PP (polypropylene) film was carried out on model capacitors at 80 degrees C under 50 Hz AC electrical stress (135 Vrms/ mu m). The aging is estimated from the local measurement of breakdown voltage of the PP film. The effects on the aging of impurities (electrolyte, water, oxygen) and of epoxide additive, added to the impregnating liquid, were observed. It is shown that the aging of impregnated PP film is greatly amplified by the impurities (electrolyte, water, oxygen) added to the impregnating liquid. Oxygen has the strongest effect. During aging, points in the film having low breakdown voltage expand, which leads to capacitor breakdown and limits in this way its lifetime.<
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