Influence of Electrical Accelerated Aging on the Conductivity and Activation Energy of Free Ions in Mineral Oil

Most power transformers operating in electric grids have an insulation system made of cellulose paper and mineral oil. Generally, the service life of a power transformer is often assimilated with the lifetime of its insulation system. Therefore, the failure of the insulation system causes the most severe consequences, starting from the long interruption of the power energy to hazardous explosions that endanger human lives and have a devastating effect on the environment. This paper presents an experimental study of the influence of accelerated aging of mineral oil under the action of the electric field and partial discharges on the electric conductivity of unaged and accelerated-aged oil. To assess the main dielectric properties of mineral oil, the dielectric spectroscopy method was employed, and the real and imaginary parts of the relative permittivity with complex conductivity were determined. The obtained results prove the aging process’s important effect on the conductivity values and the nature of free charge carriers generated under the action of electric field and partial discharges.