Terahertz Nondestructive Testing Method of Oil-paper Insulation Debonding and Foreign Matter Defects

Defects, such as debonding and foreign matters in transformer insulation paperboard, lead to local field strength concentration, thereby seriously affecting the safe operation of equipment. At present, industrial X-ray computed tomography scanning technology is mostly used to detect such defects. However, the equipment is expensive, the operation is complicated, and radiation hazard exists. In this study, terahertz time domain spectroscopy is introduced to explore the nondestructive testing method of oil-paper insulation defects. Three typical insulation paperboard defects of interface debonding, metal foreign matter mixing, and local carbonization traces were taken as the research objects. An artificial defect model is prepared. The time and frequency domain waveform characteristics of terahertz pulse wave propagating in the defect model are tested and analyzed. The results show that when the thickness of insulation paperboard covering is less than 5 mm, based on the amplitude and delay characteristics of terahertz time-domain signal, the location and size of typical internal defects can be accurately obtained, and time spectrum imaging can be realized. This study proves theoretically and experimentally the feasibility of noncontact and nondestructive testing for the internal defects of insulation paperboard by using terahertz technology.