Assessment of Degradation of Oil-Paper Insulation Caused by Thermal Aging in the Presence of Acids

The a ging of oil-impregnated paper insulation under high thermal stresses leads to cellulose chain scissions. These chain scission reactions produce organic acids, accelerating the aging process and shortening the insulation life. Therefore, the detection of organic acids in oil-paper insulation can provide vital information regarding overall insulation health. However, it is very difficult to evaluate the presence of acids in oil-paper insulation from dielectric measurements because it is often masked by moisture. In the present work, a methodology has been developed that is capable of acid detection in oil-paper insulation even in the presence of high moisture content. This has been achieved through the analysis of dielectric measurements, i.e., dc conductivity and impedance spectroscopy performed on carefully prepared oil-paper insulation samples in the laboratory. The impact of low molecular organic acids on dielectric relaxation processes in the presence and absence of high moisture content and the resulting insulation degradation has also been studied.