Water diffusion into and electrical testing of composite insulator GRP rods

This paper describes water diffusion into and electrical testing of unidirectional glass reinforced polymer (GRP) composite rods used as load bearing components in high voltage composite (non-ceramic) insulators. The tests were performed following ANSI standard C29.11 Section 7.4.2 that can be used to evaluate electrical properties of composites. The unidirectional composite rod materials based on either E-glass or ECR-glass fibers with modified polyester, epoxy and vinyl ester resins were investigated. Two types of ECR-glass fibers were considered, namely high and low seed (voids). The effects of composite surface sandblasting, mechanical pre-loading and nitric acid exposure on the electrical properties of the composites were studied. In addition to the required data of the ANSI standard, the specimen mass gain was also measured after boiling for 100 h. Most importantly, there was no correlation found between the mass gain and the leakage current for different composites. The materials with high seed ECR-glass fibers had much higher leakage currents and they absorbed less moisture than the composites based on either the low seed ECR-glass fibers or E-glass fibers. It was shown in this work that different types of sandblasting, as well as mechanical preloading with and without acid exposure had a negligible effect on the leakage currents and water mass gain of the composite specimens.