Effect of electric field in the characterization of pultruded GFRP boron-free composite insulator for the extra high voltage by the ionizing radiation

Full text: The pultruded boron-free glass fiber reinforced polymer (GFRP) composite has been widely used material for the electrical insulators in the high, extra and ultra high voltage overhead lines worldwide. In terms of design, the composite insulator has a highly complex geometry and large size. Aging of materials begin as soon as the insulators start their operation due to the strong electric field, mechanical load due to the weight of conductor cables, environment, corona discharge, generation of acids, and as a result, GFRP can fail mechanically by the stress corrosion crack (SCC) and electrical breakdown known as flashover. In order to mitigate the mechanical and electrical failures, the insulators in the field are frequently monitored by visual inspection, infrared thermography, UV detection, variation of measurement of distribution of electric field variation. However, new technologies for characterization and inspection of the composite insulator in the field are required for reliable operation. Imaging characterization using ionizing radiation (X-ray or g-ray) is an interesting technique, however, it can reduce drastically breakdown voltage due to the Townsend discharge, which free electrons are accelerated by an electric field, collide with gas molecules of air, and free additional electrons resulting in an avalanche multiplication that allows an electrical conduction through the air. In this study, in order to evaluate the potential application of ionization radiation for characterization of composite insulator under electric field, testing were conducted in high voltage laboratory by applying voltages up to 640 kV and varying radiation area of the composite insulator. As a result, even though there was an occurrence of flame on Imaging Plate (IP) detector case when it was located near the phase, corona discharge, but no breakdown discharge (flashover) occurred and high quality imaging of radiography could be obtained when X-ray source was employed. (author)