Molecular dynamics simulation on the distribution and diffusion of different sulfides in oil-paper insulation systems

Abstract

Transformer faults frequently occur because of a deterioration of the insulation performance caused by corrosive sulfides. By studying the distribution and diffusion of different sulfides in oil paper, the mechanism of sulfur corrosion can be further investigated. Here, the diffusion of macromolecular sulfides (represented by DBDS and n-hexadecanethiol) and small molecular sulfides (represented by hydrogen sulfide) in oil-paper insulation systems were studied based on molecular dynamics simulation methods. The simulation results showed that cellulose had a strong interaction with hydrogen sulfide, while oil had a strong interaction with DBDS and n-hexadecathiol. This makes the trajectory and relative concentration of the various sulfides in the oil-Paper system different: DBDS was mainly distributed in oil, n-hexadecathiol was distributed at the oil-paper interface, and hydrogen sulfide was mainly distributed in cellulose. In addition, the diffusibility of DBDS and n-hexadecathiol in oil and cellulose were negatively correlated with the interaction energy: a larger interaction energy resulted in lower diffusion. The diffusion of hydrogen sulfide in oil paper was determined by the free volume fraction. A larger free volume fraction resulted in more intense molecular diffusion. The results of this work can provide a reference for prevention of sulfur corrosion.