Mechanism Influence of Low Molecular Acid on Alcohol Diffusion in Oil–Paper Insulation Based on Molecular Dynamics Simulation

Alcohol indicators in oil are utilized to evaluate the aging status of transformer paper insulation. The fluctuation of alcohol concentration in insulating oil affects the accuracy of aging assessment. Low molecular acid (LMA) is a significant factor influencing the concentration of alcohol in insulating oil. However, the mechanism of LMA on alcohol diffusion in oil–paper insulation has not been intensively studied. Therefore, the microscopic mechanism of alcohol diffusion under the influence of LMA is investigated based on molecular dynamics simulation and experimental verification. The results show that LMA can promote alcohol diffusing from insulating paper to insulating oil, and the promoting effect of acetic acid is more evident than formic acid. Subsequently, analysis based on interaction energy finds that LMA can enhance the van der Waals forces between alcohol and insulating oil and destroy the hydrogen bond network formed by alcohol and cellulose. Consequently, the free volume in cellulose increases with LMA mass fraction, which results in the promotion of alcohol diffusion. This work expects to provide a theoretical reference for aging assessment of paper insulation based on alcohol indicators.