A refined mathematical model for prediction of bubble evolution in transformers

Measurements of physical characteristics have been made for the materials in a transformer oil-cellulose insulation system. Algorithms were generated for the temperature dependence of the Henry´s law constant for water in mineral oil and the partial pressure of water vapor in oil-impregnated cellulose having varying moisture contents. More precise information was also obtained for the rate of water generation from thermal decomposition of cellulose. These data were used to refine a mathematical model for identification of conditions suitable for free gas bubble evolution in transformers under changing temperature conditions. The modified model was applied in several parametric analyses of conditions in an operating transformer to illustrate the role of the principle variables