Study of the compatibility of self-healing polypropylene capacitors with impulsive conditions met in power electronics applications

One of the most frequent reasons for failure of self-healing polypropylene capacitors is the detachment of the `sprayed ends´ from the electrode edges. This is typical in power-electronic applications due to the action of voltage and current pulses which may result in electrical, thermal, and mechanical stresses. A study is carried out starting from the hypothesis that, according to previous results obtained, one of these stresses is dominant and a combined effect is not to be considered. Assuming that the thermal stress is the most significant one, several tests have been carried out in order to verify such hypothesis. The purpose of these tests was to check whether current pulses with different wave-shapes but with the same value of Joule´s integral lead to the same degradation level of the end-edge contact. The degradation level is ascertained by measuring the tan δ variation, since the degradation of the contact results in an increase in the equivalent series-resistance of the capacitor. Contrary to the starting assumption, the results obtained show only a partial dependence of the degradation level on the thermal stress, revealing also a contribution of the electrical and mechanical stresses