Contribution to the Study of the Aging of Mineral Insulating Oils.

New and taken from service mineral oils were subjected to photochemical, electrical and thermal stresses. corrosive sulfur content was determined before and after the aging. The sludges produced during these different degradation processes were characterized by infrared spectroscopy. Some new results were obtained, namely: an increase of the corrosive sulfur content following an exposition to the light; the sludges produced in the aging of mineral oils are rich in organic sulfur compounds; some recent new oils could change slowly under the action of an electrical stress; the combined effect of light and electric field lead to the formation of sludges which fasten to conductive and insulating parts. These sludges may be the source of a failure; aged or regenerated oils seem very sensitive to the action of an electric field; abundant sludges may quickly be produced by electrolysis and electrophoresis.