Effect of moisture on breakdown voltage of polyesterimide used in electrical machines

This paper deals with the influence of humidity on breakdown voltage of polyesterimide. The specimens were submitted to an hydrolytic aging, under 90% humidity and 30°C temperature, until 3000 h. The breakdown tests were executed under AC and DC voltage. A statistical analysis of the breakdown voltage data was carried out using Weibull model. The 90% confidence bounds were calculated and plotted. The study shows that breakdown voltage varies versus the aging time. Its increase is allotted to the crosslinking of the material structure. Whereas its decrease is ascribed to the plastificization of the polymer. The breakdown voltage under DC ramp is higher than that obtained under AC ramp. The DC breakdown voltage depends on the polarity.