Oxidation stability enhancement of a blend of mineral and synthetic ester oils

Mineral oils have been used in transformers for cooling and insulation for many years. Despite their long-time success, mineral oils are facing critiques by the electrical power industry in terms of thermal performance-mineral oils have relatively low flashpoint and fire point and will burn in the event of a fault [1], [2], [3]; environmental performance-mineral oils are less biodegradable, toxic in nature, and hazardous in the soil and water [4]; and risk assessment-mineral oils are imperilling near hospitals, near high rise buildings, and in residential areas. In this search, it has been reported that ester-based dielectric oils are a good replacement for mineral insulating oils, exceeding all of the technical demerits of mineral oils, and can operate at higher temperatures [5]-[8]. Nevertheless, the cost of these ester-based oils is comparatively higher than mineral oils [9], resulting in diminished interest in the use of these oils as a replacement. With an augmented fire margin, the industry can avoid fire mitigation equipment, deluge systems, and fire walls, and with application of safer technology, the industry can save on burden stashes and high insurance premiums. These benefits far overweight the additional cost invested on ester dielectrics. Moreover, the major drawback of the ester dielectrics is their poor oxidation stability compared with mineral oils [10].