An experimental study to investigate the effects of partial discharges (PD), of electric field and of relative humidity during surface PD tests on thin polymer films

It is possible to conceive that the degradation of thin polymer films subjected to surface partial discharges (PD) is due both to the direct PD action and to an electrical aging process due to the electric field acting in the film below the target micro-areas of PD during the instants of discharges. Therefore an innovative testing procedure has been implemented to check such an assertion. Three different polyimide 25 μm thick films have been selected for the surface PD tests. Such tests have been carried out at different humidities till breakdown of the films. The results (lifetimes) obtained in the present case showed no evidence of a contribution of the above electrical aging factor to the films degradation. However this outcome cannot be generalised, as the electrical aging phenomena depends both on the thickness and on the dielectric strength of the films under consideration. When necessary, the testing procedure presented here can be applied to check the situation