An Enhanced X Model of Oil-Impregnated Paper Bushings Including Axial and Radial Nonuniform Thermal Aging

The X model is a conventional tool of frequency-domain spectroscopy (FDS) technology for assessing the insulation state of oil-impregnated paper (OIP) bushings. However, the accuracy and applicability of the X model are questionable because it overlooked the effect of nonuniform thermal aging, and there are no models and mathematical formulas that can be applied to nonuniform thermal-aged OIP bushings. To solve this issue, an enhanced X model is proposed by considering the radial and axial nonuniform thermal aging of OIP bushings. The enhanced X model’s mathematical formula was deduced initially. Then, the complex relative permittivity (CRP) of three types of nonuniform thermally aged OIP bushings was tested. Comparing the calculated CRP based on the enhanced X model to the laboratory-measured CRP reveals that the average relative errors of the real and imaginary parts of the CRP are 7.24% and 10.94%, respectively, which indicates that the accuracy and practicability of the enhanced X model are good. It is anticipated that the contributions will provide a theoretical foundation for the state assessment of the OIP bushings under nonuniform thermal aging.