Dielectric Changes of Mineral Oil-Impregnated Paper Insulation under Accelerated Electrical Aging

This paper investigates the degradation of the cellulosic paper-mineral oil insulation system used in power transformers under the influence of high-strength electric fields and partial discharges. The study highlights the changes of the main dielectric properties due to electrical stress that can compromise the insulation performance and power transformer reliability. An experimental setup was designed to simulate accelerated aging by applying high voltage to oil-impregnated cellulose paper samples at different temperatures. Frequency-domain dielectric spectroscopy was used to analyze dielectric property changes such as permittivity, conductivity, and dielectric loss. Results reveal a significant increase in dielectric losses and conductivity with aging duration and temperature, driven by chemical byproducts, moisture, and gas formation under partial discharges. The findings highlight the crucial role of monitoring dielectric parameters and moisture content in detecting insulation degradation early, thereby supporting the development of enhanced maintenance strategies to prolong transformer lifespan in modern electrical grids.