Dielectric and mechanical assessment of cellulosic insulation during transformer manufacturing

Due to the impact of cellulose of paper insulation on transformer life, it is imperatire to remove moisture from the oil and the solid insulation. Several techniques have been implemented during manufacturing of power transformers to reduce water content in transformers. These drying processes can involve different costs and time, and they can damage the insulation paper. In this work, a drying process has been implemented in the laboratory trying to simulate the most aggressive conditions that can be suffered by the paper in transformer manufacturing in a real industry. Once the moisture content of papers was lower than 0.5%, the effect of the drying process on paper degradation was evaluated using the analysis of mechanical and dielectric properties and the degree of polymerization. Different commercial papers were studied to quantify the possible degradation induced by the drying process. The results of the mechanical strength study showed a reduction on the degree of polymerization from 1100 to 850 after 4 days of drying. The dielectric analysis of the samples showed different behavior in one of the solids evaluated and it was also found a decreased hygroscopic capacity of degraded samples in comparison with new samples.