Investigation Of Transformer Health Prediction Through Accelerated Aging Studies of the Natural Ester/Paper Complex

The life duration of cellulosic insulation is an essential aspect in the design of power transformer. Mineral oils have been largely used as liquid dielectrics to extend the service life of transformers. However the environmental and health aspects led to the seeking of alternative liquid dielectrics. Many authors have claimed that the use of bio-based liquids, especially natural esters can slow down the aging process of dielectric paper. The use of natural esters can therefore extend the actual operating life of transformers. Many vegetable oils have been elaborated. In this paper, we focus on palm kernel and castor oils, two non-edible vegetable oils largely present in Central Africa. We show the results of a study of thermal aging of dielectric paper immersed in palm kernel and castor oils. We start by presenting the elaboration and performance analysis processes of methyl esters of palm kernel and castor oils. Next, we develop the aging procedure; the paper was aged at 110°C during 100 hours, samples of oils and insulating paper were taken for analyses. The various tests performed included the determination of the total acid number, the UV-visible spectroscopy and the physical changes of the insulating paper. The results obtained with natural esters are compared to those obtained with mineral oil, which was used as a benchmark. The results obtained with palm kernel and castor oils confirms the excellent dielectric and cooling properties observed with other natural esters.