Detecting damages in outdoor non-ceramic insulators using near field microwave non-destructive testing

This paper presents a novel near-field microwave nondestructive testing technique for defect detection in non-ceramic insulators (NCI). In this work, distribution class 33kV NCI samples with no defects, air voids in silicone rubber and small metallic particles between the fiber core and shank were inspected. The microwave inspection system utilizes an openended rectangular waveguide sensor operating in the near-field at a frequency of 24 GHz. The used inspection system is simple, safe and relatively inexpensive. A data acquisition system was used to record the measured data. The results showed that all defects were repeatedly detected with high sensitivity. Line scans of the samples were obtained revealing the presence of different defects and their location. The technique also demonstrated ability to detect thickness variations in the silicone rubber shank.