Migration of Water at Silicone Oil/Silicone Rubber Interface Considering the Swelling Behavior

To understand the swelling-influenced water migration behavior at the silicone oil (SO)/silicone rubber (SiR) interface in oil-filled terminations, the swelling characteristics and molecular dynamic principles of SO were first studied at different temperatures and initial water contents, followed by the indepth analysis on the time-varying law of the diffusion of water at the interface. The results showed that the swelling process of SO obeyed the Langmuir diffusion model. With the increase of temperature, the equilibrium swelling mass remained unchanged, where the swelling rate increased. When the initial water content of SO is lower than 40 ppm, water migrates from SiR to SO, the direction of which is reversed as the water content exceeding 40 ppm. The water migration rate increases with temperature, but the equilibrium water content in the two dielectrics remains constant. Further analysis shows that the water migration process in the SO-SiR system is not only affected by the potential difference caused by the concentration gradient, but also by the synergistic effects of the swelling behavior of SO and the hydrogen bond adsorption of ATH/silica. Specifically, the process can be divided into three stages, namely the rapid water migration stage with the swelling behavior synergized, the slow water migration stage after swelling equilibrium, and the water balance stage. Increasing temperature can accelerate the swelling of SO and the migration of water, while weakening the hydrogen bond adsorption effect of fillers, resulting in an increase in the time difference between SO swelling equilibrium and water migration equilibrium.