NUMERICAL AND EXPERIMENTAL INVESTIGATION ON HOT VACUUM DRYING FOR INSULATING MATERIALS OF 154 kV SF6 GAS INSULATED TRANSFORMER
The life span of the power transformer that is composed with the electric units sensitive to moisture is greatly dependent on the drying level finally reached through the multi-step drying process. In generally the dielectric strength of insulating materials drops rapidly when the moisture content exceeds 3 percents. In this study, we assumed that the moisture flow is governed by the modified Darcy' law which is expressed with the function of the moisture content. The effective diffusivities of the insulating materials were caught through the actual specimen test. In addition, by separately modelling each part concerned instead of the entire domain with the complex geometry, we could drastically save the computational cost. In this paper the exact drying time to reach to the required drying level for a 154 kV gas transformer is numerically presented as well as proved by comparing with the experimental results. The two results showed a good agreement. And it is confirmed that the drying time (180 hrs) presently carried out in fields can be shortened to one third (60 hrs).