Moisture uptake of mineral oil at different air relative humidities and temperatures

We report here the results of the simulation of a defect in the breathing system of a high voltage transformer. These investigations serve also to evaluate the moisture uptake velocity of mineral oil under selective conditions. The studies were performed at temperatures between 23 and 60/spl deg/C while the surrounding air relative humidity was varied between 20 and 90% to simulate climatic variations. The results were discussed regarding the AC electric strength standard according to VDE or IEC. Finally a correlation between the surrounding air relative humidity, temperature and oil moisture uptake rate is proposed.