Environmental aspects of high voltage gas insulated switchgear that uses alternatives to SF_6 and monitoring and long-term performance of a pilot installation

摘要

Gas mixtures containing C5 perfluoroketone (C5 FK) and a background gas consisting of CO_2 (or N_2) and O_2 have been proposed as alternatives to SF_6 in gas insulated switchgear (GIS). These alternatives completely avoid the potential drawbacks and restrictions related to the high global warming potential of SF_6 - including the possibility of high taxes, stringent rules for handling SF_6 and documenting its use, or even an outright ban. We first discuss the decomposition and resulting by-products of C5 FK. A simple approach adopted from existing standards is used to estimate the overall toxicity of the gas mixture based on the toxicity of the individual by-products and their respective concentrations. In this way, it can be ensured that, even in the event of unexpected leakage, the by-products do not pose a health hazard. We describe two experiments carried out to determine the concentration of decomposition by-products generated by partial discharge and arcing as a function of the charge and the energy deposited, respectively. The results of these experiments allow us to conclude that C5 FK based gas mixtures can be used safely and effectively in GIS. In the second part of this paper we describe how C5 FK mixtures (or other gas mixtures used as alternatives to SF_6) have been monitored in an effective way using a combination of pressure, temperature, and density sensors in an existing pilot GIS installation (ewz substation Oerlikon new). Generally, monitoring the density of the insulating or switching gas or gas mixture in GIS is sufficient to ensure that the equipment can operate reliably. In some cases, however, it may be important to measure also the concentration of the component of the gas that provides high dielectric strength in those compartments where significant decomposition can be expected (e.g. circuit breakers). To verify the accuracy of the pressure-temperature-density measurement approach for this purpose, gas samples were acquired from several compartments in the pilot GIS installation and analyzed in the laboratory using gas chromatography mass spectrometry and Fourier transform infrared spectroscopy. The different measurements showed that, while some C5 FK decomposes over time, especially in compartments where arcing occurs, the decomposition rate is so low (even in compartments where switching arcs are present) that the performance of the installation is not affected over its rated lifetime.