Molecular Dynamic Simulation and Experimental Study on Gases’ Diffusion Characteristics and Coefficients in Transformer Oil
Huantong Shi, Wei Sun, Ran Zhuo, Zhiming Huang, Qiulin Chen, Lianhong Zhong, Yuan La, Xingwen Li, Mingli Fu
Abstract
In power transformers, the degradation of insulating oil due to aging, overheating, and electric discharge leads to the production of characteristic gases including H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , CO and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . 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 within the oil through convection and diffusion. This study employs a combination of molecular dynamics simulation and experimental measurement to determine the diffusion coefficients <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> of the seven characteristic gases in a naphthenic mineral oil across a range of temperature (T = 20~90 °C) and DC electric field strength ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> = 0~3 kV/mm). The calculated and measured results of the diffusion coefficients exhibit a strong agreement, demonstrating a positive correlation with temperature following D∝e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-a/T</sup> , in which the influence from a weak DC electric field ranging from 0 to 3 kV/mm could be negligible.