Evolution of dielectric properties of cross-linked polyethylene under thermal-oxidative aging

An investigation of thermal-oxidative degradation of cross-linked polyethylene (XLPE) has been carried out in this paper. As the key characteristics, dielectric properties are important for assessing the insulation state of cables. XLPE specimens were thermally aged at 165 °C and removed at regular intervals for analysis. The dielectric properties were investigated through the Frequency Domain Spectroscopy (FDS) and the structural changes were analyzed with the Fourier transform infrared (FT-IR) spectroscopy. And the Haviliak-Negami dielectric model is applied to extract the characteristic parameters. The experiment and fitting results show that the dipolar polarization strength Δε
α
, the DC conductivity σ
dc
, the relative permittivity at high frequency ε
∞
, and the thermal expansion coefficient β increase gradually with the aging time. It is found that the quantitative analysis of the frequency domain spectroscopy can be well applied to the state assessment of XLPE cables.