Determination of the remaining lifetime of power transformers liquid insulations based on the absorption/resorption currents

In this paper, the electrical resistivity (determined with absorption/resorption currents) is used as a diagnostic factor in order to assess the mineral oil condition and to evaluate its elapsed and remaining lifetimes. Based on experimental results of thermal accelerated ageing, the lifetime values at constant temperature are calculated by the IEC and activation energy methods. The chosen end-of-life criterion was the oil resistivity value of 0.15 TΩm. Finally, the lifetime at constant temperature and elapsed and remaining lifetimes for two variations of oil temperature are calculated.