Abstract
Electric power transformers are important components in power systems. To overcome the problems associated with using mineral oil in power transformers, environmentally friendly oil is proposed. In this paper, it is aimed to evaluate dielectric and thermal properties of environmentally friendly insulating oil under accelerated aging tests. Natural ester oil is considered in this study. The fresh oil is exposed to thermal aging test at 120 degrees C for different aging periods. Three aging periods are considered; 3 days, 6 days and 10 days. The aged samples are then tested for breakdown strength and heat transfer coefficient. To clarify the effect of aging by-products on breakdown strength, the evolution of aging by-products is evaluated using tests of moisture content and acidity in addition to Ultraviolet-Visible Spectroscopy (UV/Vis) spectroscopy. Based on the obtained results, it is found breakdown strength in natural ester oil is less affected by aging by-products. This is clarified considering the moisture saturation limit of natural ester oil and the chemical composition of produced acids in such oil.