Arc degradation of SF6 in the presence of polymeric insulating materials

An investigation has been made of the degradation reactions due to the application of an electric are at the polymeric insulating material/SF₆ interface. Polyethylene, Teflon, epoxy and phenolic resins were used as the solid insulating materials in the study. The degradation process was observed to occur in two separate steps. In the first step, the polymeric materials are pyrolyzed by the are (are degradation). The second step involves a gas-phase reaction between the SF₆ and the volatile products generated by the are degradation. Analysis of the arc-degradation products by gas chromatography, mass spectrometry and infrared spectrophotometry indicates a significant difference between the composition of the various reaction products and the corresponding products of a degradation reaction carried out thermally. The principal reaction products of the gas-phase reactions between SF₆ and the volatile degradation products were identified as CF₄, SOF₂, SF₄, SiF₄, HF and also CO in the cases of epoxy and phenolic resins. General reaction mechanisms for the formation of these products are proposed. The implications of these results regarding the use of such insulating systems in electrical apparatus are discussed.