Aging of impregnated PP films under high ac electric fields

Polypropylene films impregnated with benzyltoluene were aged at different electrical fields (100 V_rms/μm<E_a<300 V/μm). After aging, the film breakdown voltage was measured and its degradation was analyzed by FTIR spectroscopy. At low applied fields, the film was oxidized in the regions where small discharges occurred and its breakdown voltage had decreased. At higher applied fields (>180 V/μm), bright points and intense discharges were observed, the film very quickly broke down. At about 130 V/μm, an epoxy additive was an effective stabilizer of the dielectric. At higher fields, bright discharges were observed and the life-time of the model capacitor decreased quickly with the applied voltage, reaching values shorter than those without epoxydes