Terahertz identification method for core rods fracture of composite insulators

Composite insulator mandrels in high-voltage transmission systems are subjected to coupled electro-thermal-mechanical stresses, making them susceptible to internal fracture damage that threatens grid safety. Traditional detection techniques exhibit significant limitations in early fracture identification, deep defect localization, and quantitative damage assessment. This paper proposes a terahertz identification method for composite insulator mandrel fractures based on terahertz time-domain spectroscopy (THz-TDS), systematically elucidating the electromagnetic response mechanisms and multi-dimensional feature extraction strategies for fracture defects. Transmission-mode non-destructive testing was performed on glass fiber reinforced epoxy resin (GFRP) mandrel specimens in the 0.1–2.5 THz frequency range using a CCT-1800 THz-TDS system. The research reveals: 1) The dielectric discontinuity interface induced by mandrel fractures alters terahertz wave propagation paths, generating distinctive frequency-domain energy spectrum characteristics in the 0.1–0.75 THz band, with significant transmitted energy attenuation in fractured regions; 2) Through multi-frequency comparative analysis, 0.458 THz was determined as the optimal characteristic frequency for fracture boundary identification, demonstrating superior imaging contrast and spatial resolution compared to 0.568 THz; 3) Time-domain pulse wave-form analysis indicates that multiple reflection effects at fracture interfaces enhance negative peak amplitudes and peak delays, with peak-to-peak imaging enabling precise fracture localization. The established two-dimensional integrated diagnostic system of "frequency-domain energy spectrum differential qualitative identification and time-domain waveform characteristic quantitative assessment" provides a novel technical approach for condition monitoring and preventive maintenance of composite insulators in power systems, offering significant engineering application value for ensuring safe and reliable operation of high-voltage transmission lines.