Effect of Formic Acid on Furfural Diffusion in Transformer Oil–Paper Insulation Based on Molecular Dynamics Simulation

Furfural content dissolved in transformer oil is affected by the furfural diffusion in oil–paper insulation. Previous studies focused on the effects of temperature and moisture on furfural diffusion, while the effect of formic acid on furfural is ignored. Given this, the effect of formic acid on the diffusion properties of furfural is studied in this work through molecular dynamics simulations and macroscopic experiments. First, oil-cellulose-furfural molecular models with different formic acid mass fractions are built, and molecular dynamics simulations are performed separately. Also, the furfural diffusion coefficients for different molecular models are determined. Then, insulating paper with different formic acid mass fractions is prepared, and the furfural diffusion coefficients are calculated by combining the measured data and Fick’s second law. Finally, the effect of intermolecular interaction energy on the furfural diffusion in the oil–paper insulation is analyzed. The results revealed that formic acid increased the van der Waals force between furfural and insulating oil, which enhanced the adsorption of furfural and promoted furfural diffusion into the oil. This work explains the effect of formic acid on furfural diffusion and provides a theoretical basis for furfural analysis.