Determining of Gas Solubility in Various Insulation Liquids in New and Aged Conditions

Knowledge of the gas solubility of the various gases in the different insulation liquids currently on the market and in power transformers, whether hermetically sealed or free-breathing, can provide indication on the gas behavior of the insulation liquids during load changes and thus large temperature or pressure changes. This may facilitate the differentiation between the presence of a fault in the transformer when a protective system, such as a Buchholz relay, is triggered or whether ambient gases are just bubbling out of the liquid and entering the gas phase or the expansion tank as undissolved gases. The occurrence of gas bubbles represents an increased risk of initiating partial discharges. Moreover, the gas solubilities are also required in the dissolved gas analysis (DGA), especially by using the headspace extraction method. This contribution shows that there are not only large differences in the gas solubilities of the various insulation liquids, but also in the measurement of the gas solubilities, the so-called Ostwald coefficient, themselves. In addition, various influencing parameters on the specific gas solubility were investigated, such as the type and chemical composition of insulation liquid, their density and their aging condition.