Study of characteristic parameter extraction and insulation condition correlation of frequency-domain dielectric spectroscopy for oil-paper insulation systems

In order to evaluate the oil-paper insulation's condition more reliably and effectually by using frequency-domain dielectric spectroscopy (FDS) as a nondestructive test, a dielectric response function model was presented based on dielectric physics in depth study. With this proposed model, the actual FDS curves could be mathematically fitted with high accuracy and some characteristic parameters were extracted. After that, the effect of ageing conditions and the moisture content in paper on FDS characteristics of oil-paper insulation systems were also analyzed by finite element method (FEM) approach. These results indicate that the reconstructed ε^*-f curve is in good agreement with the measured curve. The characteristic parameter, DC conductivity σ₀, can be used to describe the moisture content of oil-immersed paper quantitatively. The relationship between the σ₀ and the moisture content is exponentially correlative. The characteristic parameters α, β and τ can be used to describe the aging status of oil-immersed paper quantitatively. There is a linear correlative relationship between α and aging time t and between τ and t. The relationship between β and t is exponentially correlative. With the increase of moisture in paper, ε″ increases in the whole frequency domain. As the aging proceeds, ε″ increases in frequencies of f<0.01 Hz and 1 Hz<f<100 Hz.