Lifetime estimation of vegetable and mineral oil impregnated paper for power transformers

In this paper the results of an experimental study concerning the vegetable and mineral oil impregnated paper subjected to thermal ageing is presented. Using activation energy method, the paper lifetime is calculated. Samples of vegetable and mineral oil impregnated paper were aged at 155 °C. Dielectric properties, water content and degree of polymerization of aged samples were measured. Using the activation energy for paper degradation calculated from DSC (Differential Scanning Calorimetry) data, the lifetime curves were drawn and hence the lifetime values at different operating temperatures were calculated. It was observed that the lifetime values are higher for vegetable oil impregnated samples as compared to mineral oil ones.