Mathematical and experimental analysis of the field drying of power transformer insulation

A mathematical model was developed to predict the adsorption and diffusion of moisture by oil-impregnated transformer insulation during field installation and the diffusion, desorption and evaporation of moisture during vacuum drying practices. A field drying experiment was performed on a new 93 MVA power transformer to verify the accuracy of the drying model. Four paper models were inserted in the transformer during manufacture to monitor, the course of moisture diffusion during the study. Insulation temperatures were also monitored to evaluate a hot oil spray process in uniformly heating the transformer insulation. Good agreement was achieved between mathematical predictions and field moisture measurements. High temperature processes are essential to the rapid removal of moisture during field vacuum drying operations