Determination of gases and gas pressure in GIS spacer voids

The gas contents of voids found in commercial epoxy spacers and laboratory samples are investigated as part of a broader investigation into the aging characteristics of GIS (gas-insulated switchgear) spacers. Gas chromatography techniques were successful in identifying permanent gases and organic vapors in epoxy spacers. Simple crushing and, where practical, drilling were used to release the gaseous effluents. Analyses performed on production epoxy spacers yielded predominantly nitrogen and oxygen with, in much smaller concentrations, uncured residues and curing by-products similar to those dissolved in the epoxy mass. Given the high temperatures at the time of formation of the cavities, diffusion processes in the liquid-like mass will establish rapid equilibrium between the voids and the surrounding epoxy mass. Control of the gas and pressure content in epoxy cavities is similarly difficult to achieve where desired because of diffusion effects in the curing mass. While oxygen depletion can be readily ascribed to reaction with the uncured epoxy, the presence of excess nitrogen cannot yet be explained satisfactorily.<>