Comparison analysis to thermal aging properties of vegetable and mineral insulating oils

The paper presents a comparison investigation to thermal aging behaviors between vegetable and mineral oil-paper insulation. Insulation pressboard samples were aged at 130 °C for 80 days in presence of either vegetable or mineral insulating oils, with copper wires together in well-sealed stainless vessels. The vessels contain some air in their vacant space at the beginning of the thermal aging experiments. The aged oil properties, including moisture content, acid number, viscosity, furfural concentration, dielectric loss, and AC breakdown voltage of oil samples, were measured at each interval of thermal aging experiment. The vegetable has a higher moisture content than mineral oil. Dielectric loss increases marginally with aging time in mineral oil while the increase is drastic for vegetable oil.