| Summary: | As an important component of the internal insulation system in a transformer, insulating oil will gradually age during the long-term operation of the transformer, which will lead to a degradation of its insulation performance. Previous studies have demonstrated that the addition of nano-SiO2 particles can effectively improve the breakdown voltage of insulating oil. Nano-SiO2 can effectively restrain the movement of water molecules in oil, which is one of the important reasons for nano-SiO2 particles to increase the breakdown voltage. The diffusion behaviors associated with different water contents in insulating oils with different nanoparticle contents are discussed herein, and the mechanisms at work in nano-SiO2 modified insulating oils are described on the molecular level. In this paper, simulations were based on naphthenic mineral oil, according to the mass ratio of the alkanes, which can fully represent the main physical and chemical properties of the insulating oil were employed in building the model, the mass-based percentages of water in the models were 1%, 3% and 5%, within each group, the models included an oil/water mixture containing nano-SiO2 which the mass-based percentages of nano were 1%, 2%, 3%, 4%, 5%. Prior to molecular dynamics simulations, the model was geometrically optimized, after which it was annealed and again geometrically optimized. Those systems that achieved equilibrium and energy convergence after this process could be employed for the molecular dynamics simulation. Through the analysis of the experimental results, the optimal concentration of nano-SiO2 particles for moisture binding in insulating oil was studied from a microscopic point of view. These results should assist in providing a theoretical foundation for further research regarding nano-modified insulating oils. In engineering applications, the content of nanometer SiO2 particles can be changed according to the moisture content at different times in the oil, so as to achieve the optimal binding of water, thus keeping the insulating oil with the best electrical performance.
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