Evaluation of mass transfer rate of dissolved gases in transformer oils

Dissolved Gas Analysis (DGA) method is one of the most effective techniques to monitor the condition of transformers. In this method, free gas leakage condition is required as any leakage of dissolved gases might distort the DGA results and mislead the diagnosis of transformer fault. In this paper, a mass transfer model based on two-film theory is built to simulate the gas leakage process from transformer oil when it is in contact with air. The mass transfer coefficients of dissolved fault gases in mineral oil have been calculated at different temperatures based on an experiment. The mass transfer coefficient at certain temperature can be predicted by the Arrhenius equation. According to the ascertained mass transfer coefficient, oil surface and volume, gas leakage from a sampling rate can be estimated. For practical application, the gas leakage from oil sampled by bottle is quantified.