A review of moisture diffusion coefficients in transformer solid insulation - Part 2: Experimental validation of the coefficients

The objective of this article is to experimentally verify the diffusion coefficients proposed by the various researchers. To validate these coefficients, drying experiments were carried out on impregnated and nonimpregnated paper and on pressboard samples. Taking into account the characteristics of the tested samples, two different experiments were performed: For nonimpregnated insulation, thermo-gravimetric experiments were performed determining the weight of a sample while being dried. . For impregnated paper, drying experiments were carried out in hot oil in which samples were periodically extracted and analyzed by the Karl Fischer method. The drying experiments were simulated using a diffusion model [2], solved by finite element analysis. The simulations were carried out using the diffusion coefficients proposed by the various researchers. Finally, the experimental results were compared with the simulated ones, and the accuracy and the range of application of the various coefficients were determined.