Frequency domain spectroscopy characteristics of oil-impregnated paper bushings with radial and axial nonuniform moisture distribution

Abstract Oil-impregnated paper (OIP) bushings are essential equipment for connecting transformer windings and external busbars, and the damp state of their insulating paper is a critical factor in determining safe and stable operation. In recent years, frequency domain spectroscopy (FDS) technology has continually been utilized to evaluate the damp state of bushings. However, existing FDS studies mainly focus on uniformly damped OIP bushings, with limited research on the nonuniform moisture states of bushings. Therefore, this article predicts FDS dates of bushings with various nonuniform moisture distributions to analyze the impact of moisture levels and the wettest region’s position on the FDS curves. The research results indicate that with the increase in average moisture and the wettest point’s outward movement, complex relative permittivity’s real and imaginary components increase, with the average moisture content playing a dominant role. This study provides guidance for the nonuniform moisture condition assessment and wettest area localization of the OIP bushings.