A Far-Field Evaluation Method for Interfacial Defects Existed in Composite Insulators Based on Transient Thermal Wave

The interfacial defect of composite insulators is common, which is majorly responsible for the fracture of insulators after the acid resistant core rod is used. Based on the active infrared detection method, the far-field evaluation method can effectively keep the operation safety of transmission lines by detecting subtle internal defects which are difficult to find by the traditional non-destructive detection methods. Above all, the propagation law of heat has been studied. The difference of the surface temperature between defective and reference area has been calculated when the thermal excitation meet the Dirac function. Second, the plate and short insulator samples with interfacial defects have been produced. The defects in plate samples could be easily distinguished by radiation quantity but not in insulators. In order to increase the resolution of experimental result, the derivate of the data has been further processed in the Logarithmic coordinate system. The difference between defective area and reference area has approximately enlarged 7 times and 1 mm defect in insulators, which is the smallest, could be distinguished. The detecting distance has been expanded from several millimeters to 50 centimeters which offers a possibility to the online application. Finally, according to the test results, a preliminary standard for thermal wave evaluation focused on the interfacial defects has been proposed.