A comparative study of impact of electrical stress and thermal aging on transformer oil

There is a general agreement that in service conditions the quality of insulating fluids gradually deteriorates under the impact of electrical, thermal and chemical stresses. The object of this contribution is to compare the variation of transformer oil parameters in different aging tests: thermal aging, electrical aging and the combination of both. The effects of the three different types of aging on the physicochemical and electrical properties of transformer oil have been examined, with the aim of investigating the stress which strongly affects the gassing tendency and physicochemical properties of oil under the service conditions. In this regard, various scenarios were considered. The study was carried on mineral oil under: electrical stress, thermal aging and a combination of both stresses. The ASTM methods are used to monitor the deterioration of liquid insulation step by step. The results obtained using laboratory-grade equipments indicate that the rate of increase or decrease in parameters is different from aging type for other and the electrical field accelerate strongly the degradation of new and aged oil. The study is made on a naphthenic commercial-based mineral oil.