Influence of reactive SFx gases on electrode surfaces after electrical discharges under SF6 atmosphere

A simulation of different electrical discharges under SF6 atmosphere with subsequent surface and depth profile analysis is employed to investigate the effects that the formed corrosive byproducts have on gas-insulated system (GIS) electrodes. Cu, Al and Ag electrodes were treated with sparks (in the range of 0.15 J/spark) in an SF6 discharge cell under various conditions at the Institut fur Spektrochemie und Angewandte Spektroskopie (ISAS) in Dortmund. The same materials were exposed to SF6 in a GIS test compartment in which partial discharge (PD) occurred (Itaipu, Brazil). The treated materials were analyzed with energy dispersive X-ray (EDX) in a scanning electron microscope, X-ray photoelectron spectroscopy and high frequency (HF) plasma secondary neutral mass spectrometry (SNMS). The SNMS depth profiles were calibrated in order to quantify that part of the corrosive gaseous products having reacted with the solid material. The analysis of the electrodes exposed to the stressed SF6 atmosphere show surface reaction only in the topmost nm,whereas with sparks, sulfur (S) and especially fluorine (F) compounds are detected to similar to 40 mu m depths, A first comparison between surface analysis and Fourier transform infrared (FTIR) measurements of the reactive gaseous products indicates a correlation of SF6 decomposition and the extent of electrode degradation.