Extraction of cable dielectric parameters and degradation characterization based on broadband reflection coefficient spectra

Abstract With the increase in the service life of power cables, insulation materials gradually age under long-term thermal stress. The evolution of their dielectric parameters directly reflects insulation performance and operational reliability. For in-service long-distance cables, existing dielectric parameter testing methods are constrained by the measurement structure and signal attenuation, and they cannot easily provide quantitative characterization over a broadband frequency range. This paper realizes broadband cable dielectric parameter extraction and degradation characterization based on coaxial-line resonance theory. The proposed method first obtains the resonance frequencies from the real part of the broadband reflection coefficient. The propagation constant is then inversely calculated, and the real part of the relative permittivity and the dielectric loss tangent (tan δ) at the resonance frequencies are obtained under an open-circuit terminal condition. In the simulation, the calculation errors of the relative permittivity and dielectric loss tangent are controlled within 0.22% and 0.12%, respectively. Frequency-dependent dielectric parameters were extracted from measured reflection-coefficient spectra over 9 kHz–1 GHz. Both the real part of the relative permittivity and dielectric loss tangent increased with thermal-aging time, consistent with resonant-cavity results, while field tests on a three-phase distribution cable identified the degraded phase.