Molecular Dynamic Simulation and Experimental Study on Gases’ Diffusion Characteristics and Coefficients in Transformer Oil

In power transformers, the degradation of the insulating oil due to aging, overheating, and electric discharge leads to the production of characteristic gases including H2, CH4, <inline-formula> <tex-math notation="LaTeX">$\text{C}_{{2}}\text{H}_{{2}}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\text{C}_{{2}}\text{H}_{{4}}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\text{C}_{{2}}\text{H}_{{6}}$ </tex-math></inline-formula>, CO, and CO2. The composition and concentration of these gases provide valuable insights into the operational condition of the transformer. Dissolved gas analysis (DGA) is a vital diagnostic and predictive technique for transformer faults, which is closely associated with the transportation of gases in the oil through convection and diffusion. This study employs a combination of molecular dynamics simulation and experimental measurement to determine the diffusion coefficients <inline-formula> <tex-math notation="LaTeX">${D}$ </tex-math></inline-formula> of the seven characteristic gases in a naphthenic mineral oil across a range of temperature (<inline-formula> <tex-math notation="LaTeX">${T}$ </tex-math></inline-formula> = 20 °–90 °C) and dc electric field strength (<inline-formula> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> = 0–3 kV/mm). The calculated and measured results of the diffusion coefficients exhibit a strong agreement, demonstrating a positive correlation with temperature following <inline-formula> <tex-math notation="LaTeX">${D}\propto \text{e}^{-\text {a}/\text {T}}$ </tex-math></inline-formula>, in which the influence from a weak dc electric field ranging from 0 to 3 kV/mm could be negligible.