Polyimide lifetime under partial discharge aging: effects of temperature, pressure and humidity

Recent aircraft designs increasingly use electrical systems with higher voltages. This can lead to the occurrence of partial discharges. Testing for these phenomena is relatively poorly documented in comparison with other standardized tests available for aerospace components. After having investigated the effect of temperature, pressure, and moisture on the partial discharge inception voltage as well as the discharge characteristics, we focused on the effect of these environmental parameters on the behaviour of the energy dissipated by the discharges and on polyimide film endurance during aging under partial discharge. The results show two different behaviours for the variation of energy dissipation along aging time related to environmental conditions. In fact, when a semi-conducting layer is formed in wet conditions due to the interaction between the gaseous by-products and the water molecules, a decrease in the energy measured was revealed. In addition, the relationship between the measured dissipated energy and the polyimide lifetime was investigated and did not present constant trends for the different aging conditions. While it is clear that the material endurance was energy dependent in dry conditions, it was shown that, even when the discharge energies were higher, an increase in the endurance of the dielectric was observed when the superficial semi-conducting layer was formed.