Measuring Paper Water Content of Transformers: A New Approach Using Cellulose Isotherms in Nonequilibrium Conditions

In this paper, we discuss a better method to measure the paper water content of transformers using cellulose isotherms. The advantage of the new method is that the transformer oil and cellulosic insulation do not need to be in thermodynamic equilibrium. Instead, the temperature needs to be cycling in order to determine when the direction of water migration, whether out of or into the oil changes. The reversal in water migration can be used to determine the vapor pressure of the water adsorbed by the cellulose. This method was tested using 12 different conditions similar to those within a normally operating transformer. The results showed close agreement when this method is used. The significance is that isotherm equations can now be used even when insulation media are not in equilibrium.