Lifetime estimation of vegetable oil for transformers

In this paper the results of an experimental study concerning the vegetable oil´s (subjected to thermal ageing) lifetime estimation based on the activation energy and IEC 60216-1/2001 methods are presented. Three accelerated thermal ageing tests were performed on transformer vegetable oil samples at 135, 155 and 175 °C. The lifetime curves were drawn for three diagnostic factors, namely loss factor, conductivity and total acid number. Using DSC (Differential Scanning Calorimetry) method, the activation energy corresponding to the oxidation reaction has been determined. Subsequently, using the results of thermal ageing at 175 °C, the lifetime curves have been drawn. It is concluded that the activation energy method is quicker and less expensive therefore it could be useful to obtain new information about a new vegetable oil for paper/oil insulations.