APPLICATION OF OXIDATION INDUCTION TIME AND COMPENSATION EFFECT TO THE DIAGNOSIS OF HV POLYMERIC CABLE INSULATION

Oxidative stability tests were performed on field and laboratory-aged crosslinked polyethylene (XLPE), ethylene-propylene rubber (EPR) and p olypropylene (PP) insulations using differential scanning calorimetry. Flat films and miniature cables aged in the laboratory were subjected to a wide range of aging conditions that included thermal, electrical and a combination of thermal-electrical aging, in dry and wet environ ments. The results were analyzed using the Eyring rate theory. It is s hown that for a given material the oxidative stability data can be des cribed by a single linear relationship between the activation entropy Delta S and the activation enthalpy Delta H of the oxidative process, and thus are governed by the so called compensation effect. It is argu ed that the position of a data point representing a certain operating condition of an insulation on the Delta S vs. Delta H compensation plo t is a measure of the degree of degradation and can be used as a diagn ostic indicator of the operating conditions of the insulation.