Effect of Temperature on Methanol Equilibrium in Oil-paper Insulation System of Power Transformers

Methanol in oil can be used to evaluate the aging status of oil-paper insulation system of power transformers. Many scholars have shown that the production of methanol in oil is closely related to the degradation of paper. However, the methanol distributed in oil is affected by the oil-paper adsorption equilibrium. In this paper, the equilibrium distribution of methanol between oil and paper at different temperatures were investigated. The equilibrium experiments were conducted by soaking methanol-oil standard solution with ordinary Kraft paper at 20°C, 45°C and 60°C respectively. The results showed that temperature obviously affects the adsorption capacity of oil and paper for methanol: with the increase of temperature, the equilibrium time of methanol between oil and paper is accelerated. Within a certain temperature range, the adsorption capacity of paper for methanol will decrease with the increase of temperature. However, when the temperature was near the boiling point of methanol, the content of methanol in oil declined, which might be related to the existence of gaseous methanol at high temperature. At this time, the equilibrium distribution model of methanol changed from the two-phase model of oil-paper system to the three-phase model of oil-paper-gas system.