Dielectric properties of paper insulation aged in the presence of vegetable transformer oil

The power transformer´s lifetime is strongly influenced by its insulation system degradation, especially by the paper degradation. As the vegetable oil should replace mineral oil, this paper presents a study concerning the dielectric properties variation of cellulosic paper impregnated with vegetable oil as a function of the ageing duration. In order to characterize the condition of the paper the main dielectric properties have been measured: the relative permittivity and loss factor (in AC) and the electrical conductivity (in AC and DC) for vegetable oil impregnated paper aged (1500 hours) at 135°C and 155°C. A correlation between the variation of the dielectric properties (permittivity and resistivity) with the ageing duration has been found.