Degradation behaviors of silicone gel encapsulation material with moisture intrusion

In the applications of offshore wind turbines and high-speed trains, the power electronic devices suffer in harsh working conditions of high humidity. The moisture invades devices and induces failure of power modules. Therefore, it is necessary to investigate the degradation behaviors of encapsulation material with moisture intrusion. In this paper, the moisture absorption, chemical, and electrical properties of silicone gel under 85 °C&85%RH with long aging time is characterized. And the aging at 85 °C is chosen as a control. The influence of moisture absorption on the performance of silicone gel is discussed. The results showed that the wettest position locates at the mid-depth in silicone gels after desorption, which can be called as "depth effect" and is first discovered. Besides that, the mass loss during the aging is also observed and a comprehensive explanation considering the competition of absorption and dissolution is given here. Furthermore, a new phenomenon defined as "delayed degradation effect" is discovered. It is that the effect of moisture intrusion on electrical performance degradation in thin samples is delayed. In conclusion, moisture intrusion will degrade the electrical properties of silicone gel, so attention should be paid to power electronic devices working in high humidity conditions.