Oxidation in insulating oil

IT is generally agreed that of the component parts of impregnated paper, the impregnating oil is most susceptible to deterioration. There is, however little definite knowledge of the processes leading to instability. Instability manifests itself in changes in electrical properties. An increase in dielectric loss, if allowed to continue, ultimately leads to failure. Marked chemical changes often accompany these changes in electric properties, but whether or not the changes are caused by electrical stress, as related to the inherent chemical structure of the oil, or by residual impurities, as related to stress and structure, or by both jointly is as yet unknown. Obviously oxidation, with its generation of acids and consequent increase in chemical dissociation and electrical conductivity is a powerful cause of instability. Although careful provision is made for the elimination of oxygen in the manufacture of insulation, it is recognized that traces of oxygen must remain under all circumstances, and the determination of the degree of its activity as a cause of insulation instability becomes a matter of great importance.