Annealing Effect with High DC Stress in Epoxy Resin on Insulating Degradation

This paper evaluates the insulation performance change of acid anhydride epoxy resins when subjected to annealing and annealing with DC stress. In this increasingly electrified society, the evolution of power conversion technology is essential. Power modules are critical devices used for power conversion, and they are known to generate heat due to Joule heat during operation. Therefore, insulating materials used in power modules are also required to exhibit high insulation performance at high temperatures under electric fields. However, epoxy resins, which are expected to be used for the insulating material, are known to accumulate space charge in such conditions, being worried about decreasing insulation performance. However, this degradation has not yet been fully studied. Therefore, this paper evaluates the leakage current measurement of epoxy resin using a current integrated charge method, the so-called Q(t) method. At first, since a relatively high voltage is applied to the epoxy sample at a high temperature in the Q(t) measurement, it is found that such a voltage application induces an improvement in the insulating performance of the sample. However, when the high voltage was applied to the sample at a higher temperature after the Q(t) measurement, it was found that there was an apparent insulating degradation in the sample. In contrast, such degradation was not observed after annealing without the voltage application. Therefore, we concluded that insulating degradation was induced in the electric field at high temperatures.