Study of the Dielectric Frequency Response of Mineral Oil on addition of Carboxylic Acids

Mineral oil is one of the insulation bridges used in transformer alongside the solid insulation. The degradation of the cellulose solid insulation leads to the formation of low molecular weight carboxylic acids, whereas the degradation of oil insulation leads to the formation of high molecular weight acids. These acids in the presence of moisture, oxygen and heat, further degrades the solid liquid insulation system leading to the unanticipated failure of the high voltage equipment. This paper studies the effect of each acid individually on the liquid insulation using frequency domain spectroscopy. The frequency response of the fresh and acid contaminated mineral oil is studied from 10kHz to 1mHz. The results show dielectric frequency response depend on the type of acid. The frequency response of individual acid supplemented oil insulation gives information on the effective change of the electric characteristics of oil such as dielectric permittivity, impedance, capacitance, and dissipation factor with respect to acid type.