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Although gas-insulated system (GIS) and substations belong to the most reliable components of electric power networks, failures still occur in their long-term operation. In order to estimate the probability of malfunctions in advance, a system for monitoring the quality of the insulating gas [SF.sub.6] was established, which is based on the use of ion mobility spectrometry (IMS). In a set of experiments, partial discharge (PD) was generated inside a test GIS. The [SF.sub.6] was periodically analyzed using IMS. The results of this analysis is presented and the influence of impurities remaining inside the compartment is discussed. The analysis of gas contained in a circuit breaker in a hydroelectric power plant before and after operation is described as well as the structure of a system for automatic on-site sensing of [SF.sub.6] decomposition.

A simulation of different electrical discharges under [SF.sub.6] 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 [SF.sub.6] discharge cell under various conditions at the Institut fur Spektrochemie und Angewandte Spektroskopie (ISAS) in Dortmund. The same materials were exposed to [SF.sub.6] 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 [SF.sub.6] atmosphere show surface reaction only in the topmost nm, whereas with sparks, sulfur (S) and especially fluorine (F) compounds are detected to ~40 [micro]m depths. A first comparison between surface analysis and Fourier transform infrared (FTIR) measurements of the reactive gaseous products indicates a correlation of [SF.sub.6] decomposition and the extent of electrode degradation.