Explanation and analysis of oil-paper insulation based on frequency-domain dielectric spectroscopy

In this paper, to effectively distinguish between the aging and moisture of oil-immersed paper (OIP), and to enhance the accuracy of the nondestructive diagnosis of the insulating state for oil-paper insulation, we perform an in-depth study of the frequencydomain dielectric response theory. First, we present a theoretical explanation for frequency-domain spectroscopy (FDS) based on investigations into the mechanism and characteristics of conductivity loss and polarization loss. Secondly, we explore the classical loss characteristics by performing a systematic analysis of the relationship between the complex dielectric permittivity and the frequency based on the measured FDS curves. Finally, we study the influences of the aging condition and moisture content on FDS. We extract some of the characteristic parameters that are related to the insulation condition. The results obtained indicate that at low frequencies, the FDS characteristic was mainly influenced by the conductivity loss, which may be explained by the Dyre model. At high frequencies, the characteristic was mainly influenced by the polarization loss, which may be explained by the H-N model. In addition, the characteristic at mid-range frequencies was due to both the conductivity and polarization loss. The moisture content significantly affects only the conductance process. Therefore, the characteristic parameter, namely the DC conductivity σ 0, which is closely related to the conductance process, can be used to quantitatively describe the moisture content of OIP. Meanwhile, the characteristic parameters α, β, and τ, which are associated with the polarization process, can be used to quantitatively describe the aging status of OIP.