Quantitative Assessment Model of Moisture Equilibrium in Paper-oil Insulation

This paper presents a quantitative method to obtain the rule of water balance between oil and paper efficiently, which can be used in both engineering and laboratory conditions. Firstly, the mechanism of moisture migration in the oil-paper system was clarified, based on which the method of diffusion potential was proposed to quantitatively describe the water diffusion trend of insulating paper and insulating oil. By setting up the experimental platform, the moisture content in the insulating paper under different vapor pressures and temperatures was obtained, and a mathematical formula was established to describe the quantitative relationship. Since the difference in water solubility of mineral insulating oils was small, the mathematical relation between water vapor pressure and temperature and water content of insulating oils in standard IEC-60422 could be referred. The temperature control equation of moisture content in insulating paper and oil was obtained according to the pressure balance rule. Finally, the equation to describe the variation of moisture content in paper with oil moisture, time, and the temperature was established. Besides, a mathematical model is set for the estimation of moisture content in single-layer paper at varying temperatures.