Condition Assessment of Thermally Aged Polypropylene Cable Insulation Based on Frequency Domain Spectroscopy

This paper aims to investigate the condition assessment of thermally-aged polypropylene/thermoplastic elastomer (PP/TPE) cable insulation based on frequency domain spectroscopy (FDS). PP/TPE samples with different aging times are prepared at an aging temperature of 135 °C, and FDS parameters at the measured temperature from 10 to 110 °C are analyzed by the Havriliak-Negami (H-N) model. The results show that the intensity of α relaxation increases, which is related to the increase of the average dipole moment (μ) and dipole-dipole interactions ( g ). The reason is that the carbonyl index increases during the aging process, which can be found in the Fourier transform infrared spectroscopy (FT-IR). The intensity of δ relaxation first decreases and then increases, which is related to the change of spherulitic structure. In the initial stages of aging, more organized spherulites restrict the hopping of carriers, leading to a decrease in δ relaxation strength. In the later stages of aging, the spherulitic structure is destroyed, reducing the barrier height (Φ) for charge carrier hopping, thereby increasing δ relaxation strength. The relationship between characteristic parameters and insulation parameters is established for a conditional assessment and verified with a sample S ₁ . This paper establishes a feasible approach for a condition assessment of the aging state of cable insulation based on the FDS.