Diffusion Mechanisms of Dissolved Gases in Transformer Oil Influenced with Moisture Based on Molecular Dynamics Simulation

Dissolved Gas Analysis (DGA) of insulating oil is widely used for diagnosing transformer incipient faults. Moisture is a major contaminant and degradation byproduct of transformer insulating oil. In this paper, molecular dynamics simulation was used to study the influence of moisture on the diffusion movement of dissolved gases in the insulating oil. Cycloalkanes (C₂₀H₄₂), alkanes (C₂₀H₃₈), and aromatic hydrocarbons (C₂₀H₂₆) are selected as the basic structural units in the constructed transformer oil simulation system. 0%, 1%, 3%, and 5% moisture molecules are added to insulating oil, respectively, and the insulating oil generates seven kinds of gas molecules through cracking. With an anhydrous model used as a benchmark, we researched the diffusion trajectory, the diffusion coefficient (D), free volume (V_F), and the moisture-gas interaction energy of each gas molecule as a function of moisture content. Through this study, we found that the increase of moisture content enlarges the V_Fvalue of dissolved gas in insulating oil, which makes the gas in oil easier to diffuse. Besides, the moisture can also alter the mean square displacement (MSD) of dissolved gases; the mutual energy of molecules is mainly affected by the electrostatic interaction energy. This study can contribute to a better understanding of the influence of different moisture contents on the diffusion movement of dissolved gas in transformer oil from the micro level.