Simulation effect of SiO2 nanoparticles on the water molecules diffusion inside insulating oil at different temperatures

The performance of transformer insulating oil will gradually decrease with the long-term operation of transformer. Previous researches have shown that temperature is one of the important factors affecting the insulation performance of transformer insulation oil, and the addition of nanoparticles can effectively improve the insulation properties of oil. In order to further reveal the influence of temperature and nanoparticles on the diffusion ability of water molecules in insulating oil, the diffusion behavior of water molecules in pure oil model (AW-1) and model (AW-2) containing nano-SiO2 particles at 303K, 323K, 343K, 363K and 383K temperatures are studied in this paper. The simulation results showed that nano-SiO2 particles can effectively reduce the influence of temperature on the diffusion behavior of water molecules in oil. In two models, the free volume fraction of moisture in oil will be improved with the increase of temperature, which provides more space for the movement of water molecules. However, in the AW-1 model, the growth rate of the free volume fraction is around 2.2 %, while that in the AW-2 model is around 1.5 %. Moreover, according to the analysis of the radial distribution function (RDF) between different atoms in the two models, the covalent bond and the hydrogen bond between the atoms weakens due to the increase of temperature. In addition, with the increase of temperature, the interaction energy between water molecules and oil gradually decreases in two models. In the AW-1 model, with the increase of temperature, the reduction rate of interaction energy is about 4.5 %, in the AW-2 model, the reduction rate of interaction energy is about 2.5 %, which indicates that the influence of temperature on the AW-2 model is smaller. Therefore, adding nanoparticles to the oil can effectively restrain the movement of water molecules in the oil, so as to improve the insulation performance of transformer insulation system.