ESTIMATING LIFETIME OF PP, PI AND PVDF UNDER ARTIFICIAL VOID CONDITIONS USING STEP-STRESS TESTS

Lifetimes of three different capacitor dielectrics, polypropylene (PP), polyimide (PI) and polyvinylidene fluoride (PVDF), were evaluated under high electric field, using a step-stress method. Three layers of the insulating film were used for each dielectric material. To determine the influence of a void in the middle layer, two different configurations were used: with and without an artificial void in the middle layer. Various time intervals for the step-stress test, ranging from 20 s to 120 s, were selected. The inverse power law equation was used in the analysis of the experimental data, with the value of power exponent determined from the step-stress for each material and configuration. The equivalent constant stress lifetime of PP, PI and PVDF were then estimated for both configurations from the step-stress data. The results show that lifetime becomes significantly shorter in the presence of a void in the middle layer. The constant k for the power model was also found to be influenced by permittivity and dielectric loss of the dielectric films.