Applications of ultrasonic NDE techniques for location and characterization of defects in epoxy composite GIS spacers

Ultrasonic inspection of gas-insulated high-voltage substation (GIS) spacers has been conducted and, based on the limited evaluation to date, it appears to provide a viable means of detecting defects. Using commercially available ultrasonic equipment coupled to a motor drive and software data collection system, this method has been successful in locating voids, agglomerates of contaminating particles, and epoxy-metal interface debonding in GIS spacers that failed to pass factory qualification tests. Manual probe application has also proven capable of locating defects. A series of defects including voids, metal contaminants, and paper fragments could be detected in a set of test specimens. A spatial resolution of approximately 1 mm has been attained. The correlation between ultrasonic results and forensic examination has been very good. The spacers used in this evaluation had previously been subjected to nondestructive X-ray tomographic inspection, which failed to disclose any internal defects. Scattering of the ultrasonic signal by the inorganic fillers has resulted in enlargement of the apparent dimensions of features. The fillers have not hindered detection of features within epoxy sections approximately 180 mm thick