Optical Spectroscopy Analysis of Ester Oils under Thermal Aging Conditions

Ester oils have been proposed recently as alternative insulating liquids to mineral oils inside oil-filled power transformers. They are environmentally friendly, biodegradable and harmless to human body. During the operation of power transformers, the insulating oil is subjected to thermal and electrical stresses. Consequently, it is decomposed, and the aging by-products are generated. As a result, the properties of insulating oil are degraded. This study aims to investigate the impact of thermal degradation on ester oils during the operation of power transformer using UV-Vis optical spectroscopy technique. First, several aged ester oil samples were prepared using an accelerated aging experiment. In addition, aged mineral oil samples were prepared to compare the impact of aging on both. Then, these samples were tested using optical spectroscopy test. The obtained optical spectra have been investigated and the aging by-products could be evaluated. Furthermore, dissipation factor test was carried out on the aged samples to correlate between the thermal degradation and the dielectric properties. The obtained results have assured that ester oils have great potential to substitute mineral oils in the future.