Characterization of Electrothermal Aged Insulation Structures of Vehicle Cable Terminal Under Vibration Load in Terahertz Frequency Domain

The vehicle cable terminals play a vital role in the safe and stable operation of high-speed trains. To accurately obtain the aging status of vehicle cable terminals under vibration loads, it is proposed herein that the terahertz frequency domain (TFD) characteristics are utilized to identify the aging state, meanwhile, nondestructive testing is achieved in noncontact conditions. Initially, based on the concept of equivalent modeling, a three-layer composite cable terminal model is launched, as the vibro-electrothermal combined aging experiments are conducted under different time gradients. Then, TFD characteristic tests were conducted on the aged samples, obtaining the spectra of transmittance, extinction coefficient, dielectric loss, and refractive index. The results showed that along with the aging time increasing, the extinction coefficient showed a downward trend, while the transmittance, dielectric loss, as refractive index increased to varying degrees. Moreover, with the assistance of Fourier transform infrared spectrometer (FTIR), partial discharge (PD), and scanning electron microscope detection, and via analyzing the interaction characteristics between light and dielectric, further research is conducted to obtain the variation law in physicochemical properties of composite insulation materials under long-term effects of vibration load with electrical/thermal stress. Finally, the aging status of cable terminals was evaluated using the entropy weight method and improved radar spectrogram. The above results indicate that the TFD parameters are able to reflect the aging status of vehicle cable terminals effectively, providing a novel approach to evaluating the aging status of composite insulation structures using nondestructive terahertz testing.