The circuit-breaker insulating pull rods are critical insulating and load-bearing components in high-voltage switchgear. Internal metallic inclusions and air gaps in glass fiber fabric-reinforced epoxy materials may compromise insulation reliability. In this paper, artificial defects with different geometries and burial depths are introduced into composite specimens and investigated with terahertz time-domain reflection detection. The results show distinct responses for the two defect types. Metallic inclusions produce strong and localized reflections and pronounced shielding of back-surface and multiple-reflection signals, whereas air gaps exhibit more dispersed responses while allowing substantial THz transmission to deeper interfaces. And the reconstructed depth positions agree well with the designed locations. These results demonstrated that THz-TDS technology enables non-contact detection and visualization of typical internal defects in composite insulating pull rods of high-voltage switchgear.

insulating pull rod,glass-fabric-reinforced epoxy composite,metallic inclusion,air gap,THz detection