Study on the dielectric spectrum characteristics of oil-paper casing in the high-voltage frequency domain under uneven moisture conditions

This paper investigates the high-frequency dielectric spectrum characteristics of oil-paper bushings under non-uniform moisture conditions. By conducting frequency-domain dielectric spectroscopy tests on oil-paper insulation samples with different moisture contents, the effects of non-uniform water distribution on the dielectric properties of insulation materials are analyzed. The experimental results show that non-uniform water distribution increases the interface polarization intensity, resulting in a higher $\mathrm{C}^{\prime}$ for non-uniformly moistened media compared to uniformly moistened media, with a significant increase in the low-frequency range as the non-uniformity index increases, and a maximum change rate of 41.05%. Since conduction loss dominates the low-frequency range and polarization loss dominates the high-frequency range, $C^{\prime \prime}$ increases with the non-uniformity index in the high-frequency range, with a maximum change rate of 100.18%, and decreases in the low-frequency range, with a maximum change rate of 68.74%. Additionally, a “loss peak” appears in the frequency range of $10^{-1}$ to $10^{1} \mathrm{~Hz}$. This study provides a theoretical basis for condition monitoring and fault diagnosis of oil-paper insulation systems.