Drying of already impregnated oil-paper insulation

It is well known that the paper-oil insulation is so prepared. that the paper installed in the high voltage apparatus is first dried up with the influence of high vacuum and elevated temperature. Then, under vacuum the paper is impregnated with oil. Sometimes, the high voltage apparatus with oil-paper insulation. after a short period under working conditions loses his good dielectric properties because of high content of moisture. This is mostly because of penetration of atmospheric water in the apparatus. Now, it is interesting to know if there is possible to dry such an apparatus and how. In this paper we describe the experiments carried out on a model of the oil paper insulation with high water content in the paper. The insulation is dried up with influence of high vacuum and elevated temperature during some time. The results show that such drying on a model is possible. The needed vacuum, temperature and time for drying the model are presented and discussed. The experiments an real apparatus are planned, but not presented in this paper.