Influence of Oxidation on the Electrical Properties of Inhibited Naphthenic and Paraffinic Transformer Oils

The dc electrical conductivity and dielectric losses of inhibited naphthenic and paraffinic transformer oils were measured as a function of the oxidation time. It is shown that both properties vary with the dissolved-copper, peroxide and soluble-acidity contents of the oils and that these Variations in the electrical properties with oxidation time are directly related to the generation of the aging by-products. Empirical equations relying on these three parameters and describing the conductivity and tan6 of oxidized oil are presented. The role of the chemical structure of the two oils is briefly discussed as well as the effects of filtering the oils after sludge formation.