Terahertz spectroscopic study of optical and dielectric properties of typical electrical insulation materials

Abstract

Researchers and engineers are constantly developing novel techniques to accurately measure the electromagnetic properties of electrical insulators. These properties provide useful information about the insulators' performance and aging degree, which may help users to take necessary actions to prevent potential risks to the safety and stability of electric power systems. In this study, terahertz (THz) time-domain spectroscopy (THz-TDS) is used to analyze the spectral absorption and dielectric dispersion of five electrical insulation materials viz. epoxy resin (PER), E-glass fiber-reinforced polymer-matrix composite (GFRP), cross-linked polyethylene (XLPE), electrical porcelain (E-PRL), and high temperature vulcanized silicone rubber (HTVSR), in the THz frequency range (0.1 THz-1.8 THz). The refractive index, absorption coefficient, and complex relative permittivity of each sample are experimentally measured using the THz-TDS system and theoretically calculated using the original Debye model (i.e., based on the relaxation process of the individual samples’ dipoles). Experimental and theoretical results of the refractive indices and dielectric constants of the individual samples are highly correlated with 0.22% and 0.17% aggregate maximum errors, respectively. The values of dielectric constants and imaginary permittivities are found to be the highest and the lowest for E-PRL and XLPE, respectively. In terms of dielectric performance, XLPE exhibits the highest and most stable dielectric performance, followed by the E-PRL, whereas PER, HTVSR, and GFRP exhibit fluctuating and slightly less stable dielectric performance. This study shows the great potential of THz nondestructive testing (NDT) and structural health monitoring (SHM) for the defect detection and service life prediction of electrical insulators.