Research of nondestructive methods to test defects hidden within composite insulators based on THz time-domain spectroscopy technology

In this manuscript, we introduced a novel far-field nondestructive testing (NDT) for defects within composite insulators based on the terahertz time-domain spectroscopy (THz-TDS) technology. Impulse waves ranging from 0.02-2 THz were used to test onsite overheated 500 kV composite insulators and samples with artificial void defects. By analyzing the amplitude of time-domain waveform, as well as delay and Euclidean distance from the reference curve, defects as deep as 0.4 mm can be accurately positioned and the dimension of voids defects as small as 1.5 mm can be measured with the error less than 3%. Meanwhile, unlike the existing near-field nondestructive testing, the stand-off distance of system could be as far as 15 cm. It does not require much of the accuracy and the repeatability is amazingly high. Therefore it can carry out long distance detection towards composite insulators on the premise of enough power. In the end, this system was also utilized to measure the thickness of silicone rubber.