The Effect of Oxidation on the Dielectric Properties of an Insulating Oil

The dielectric constant and loss, as well as the resistivity of a cable insulating oil, have been measured as a function of temperature and frequency before and after successive oxidations. The dielectric loss, and its distribution of relaxation times changes slightly with the degree of oxidation, but the resistivity decreases by more than an order of magnitude. However, the activation energy for conduction remains unchanged. A previously unreported result is that the frequency of the maximum of the dielectric loss decreases with the degree of oxidation. A tentative semiquantitative molecular model to account for the activation energy for conduction is presented.