An investigation about the PD degradation of thin polymer films and its correlation with surface charge decay measurements

The adoption, in electrical drives, of power supplies equipped with fast electronic devices lead to new "life" problems (e.g. degradation due to partial discharges) which impact on the design of the relevant electric machines insulation systems. Hereby are reported some results of an investigation about the behaviour of thin PET and PI films (polymers adopted in the above insulation systems) after exposure to the action of surface partial discharges (PD) due to PWM-like voltages. The relevant damage after suitable aging (different humidity (RH%) and different PD exposure times) has been examined through of a procedure based on charge decay measurements on the aged films surface. After corona (both positive and negative) charging the films, the surface charge distribution was obtained at different times, so to get the charge decay profiles. The relevant results, depending on films, ambient PD aging conditions, and corona polarity, showed different degrees of correlation between the films surface degradation, the surface charge distribution and the measured charge decay profiles. The latter profiles analysis suggests that this approach can offer complementary information to investigate the PD degradation phenomena that would impact on the insulation systems performance.