ABSTRACT
Very early in the development of transformers, the use of oil was established for its insulating as well as cooling functionality. Since the turn of the twentieth century, the standard insulating media for power transformers have been mineral oil and cellulose. Insulating media in high-voltage transformers consist of paper wrapped around the conductors in the transformer coils plus mineral oil and pressboard to insulate the coils from ground. The primary function of insulating oil is to provide a dielectric medium that acts as insulation surrounding various energized conductors. A secondary function of the insulating fluid is to serve as a dissipater of heat. The third function of the insulating fluid is to serve as an indicator of the operational condition of the liquid-filled equipment. Internal sources of contamination can be controlled only to a limited extent because these sources of contamination are generally chemical reactions (like the oxidation of cellulose and the oxidation of oil) that are constantly ongoing.
