Air Gap Detection and Analysis of XLPE Cable Insulation Based on Terahertz Time Domain Spectroscopy

Abstract

The implied air gap defects will seriously affect the insulation cross-linked polyethylene (XLPE) and cause potential safety issues. In this paper, a novel nondestructive detection method of XLPE based on terahertz time-domain spectroscopy (THz-TDS) was proposed. The multi-layer dispersion model of XLPE with air gap defects was established and the defect feature of air gap had been investigated carefully. Based on theoretical model, actual XLPE sample was used to simulate the air gap defects artificially. Then the transmission THz-TDS system was employed to carry out the spectral imaging experiments. There sultsshow that obvious difference in both amplitude and phase can be observed by comparing the normal signal with the defect signal. Further analysis of the signal spectrum can obtain the geometric size information of the air gap defect hidden in XLPE, and the calculation error is less than 2.9%. In addition, the characteristics of air gap can be represented more intuitively by THz imaging technique. The terahertz imaging algorithm proposed in this paper can extract the position and shape information of air gap defect conveniently. Through theoretical analysis and experimental verification, this paper proves the feasibility of a new non-destructive testing method based on THz-TDS system for concealed air gap defects in XLPE, which provides a new idea for non-destructive detection of cable insulation defects and can be applied to other electrical equipment detection.