Environmental impact and aging properties of natural and synthetic transformer oils under electrical stress conditions

Against the background of environmental compatibility and unrestricted technical usability, synthetic, and natural transformer oils are critically compared in long-term tests under high voltage using electrical and instrumental analytical methods. Synthetic alkyl esters of pentaerythrol appear to be sustainable and sometimes superior substitutes for mineral oils in terms of chemical stability, viscosity, permittivity, and heat transport. Natural esters of unsaturated fatty acids are found to be unsuitable for equipment exposed to moist air. Adsorbed water appears to be a general problem in transformer oils. The aging mechanisms and molecular changes during long-term operation include radical reactions, and the formation, isomerization and cleavage of CC bonds. Extensive material data are provided