Materials, Methods & Technologies, Volume 12, 2018

Abstract: Power transformers are one of the most important elements of electricity transport and distribution systems. Their failure and accidental shutdown results in significant economic losses and pollution of the air, soil or water. Therefore, monitoring the state of transformers and especially their insulation systems is a permanent concern for users of these equipments. This paper presents a study on the evaluation of oil-paper insulation of power transformers, using a new diagnostic factor, i.e. insulation resistance. The laboratory model used for the experiments, the methods and procedures for the accelerated ageing of samples (“motorette”), the absorption and resorption current measuring system, the equations to calculate the insulation resistance and the estimated, consumed and remaining lifetime corresponding to the constant and variable temperature operation of the insulation are presented. Finally, the results of a numerical calculation of the lifetime for a power transformer that has been operating for 4 years and for which the temperature variation curve is known, are also presented.