Nondestructive Detection of Submillimeter Air Cavities in Alumina-Doped Epoxy Resin Composites Using the Infrared Thermography

The alumina doped epoxy resin composites have been widely used to prepare the basin-type insulators in gas-insulated switchgear (GIS). In recent years, the air cavity defects in the basin-type insulators became one of the most common factors to induce GIS faults. Therefore, the development of novel detection techniques for air cavities in epoxy resin composites is of great importance. In this study, multiple epoxy resin samples containing various submillimeter air cavities were prepared. Long pulse thermography (LPT) was employed to detect defects in the epoxy resin composite, and multiple data processing methods were applied to extract the characteristics of the air cavity defects. Quantitative analysis was also used to characterize the detection effectiveness in different thermograms. Experimental results show that derivative thermograms are capable of detecting air cavity defects with a diameter of 0.2 mm at a depth of 1.2 mm. The derivative thermograms can reduce noise and sharpen the defect recognition, exhibiting a high signal-to-noise ratio (SNR). This study also analyzes the impact of the aspect ratio on the detection result, which indicates that the defect with a small aspect ratio is difficult to detect. Based on the infrared thermography technology, this work provides a promising route for defects detection in basin-type insulators.