Study On SF₆ Partial Overthermal Decomposition Products With Organic Solid Insulating Materials

SF6 gas-insulated equipment have been considered as rare maintenance, or even none maintenance high voltage electrical equipment. But several reasons would lead the abnormal local temperature rease of the equipment, seriously could lead to partial overheating fault(POF), such as the poor connection of their bus connectors and knife contactors, the high medium conductivity caused by the surface dirty of insulators, the magnetic short circuit and magnetic saturation of iron core, and so on. Our previous studies have shown that: when POF occurs in SF6 gas-insulated equipment with organic solid insulation materials, it not only make SF6 decompose, but also lead to the pyrolysis and carbonization of the organic solid insulation materials, and the overall insulating properties deterioration of SF6 gas-insulated equipment, finally make a great threat to the security and reliability of the entire SF6 gas-insulated equipment and the power grid. At present, in addition to the method of using SF6 thermal decomposition characteristics to monitor POF proposed by our research group, there is no effective methods of POF monitoring, a lot of basic research work need to be carried out as soon as possible. Therefore this paper construct a physical defect model for experimental simulation study, according to the typical defect which is POF involving organic solid insulating materials. A series SF6 thermal decomposition experiment with organic solid insulating materials at partial overheating temperature range of 200~500℃ were launched, on the basis of the SF6 thermal decomposition platform and the formation laws of SF6 thermal decomposition components were achieved. Combined thermal gravimetric analysis with x-ray photoelectron spectroscopy analysis, elements and their presence form of metals and organic solid insulating material after the experiment were obtained, the cracking and corrosion mechanism of solid insulating materials were acquired at the same time. The results show that: the main components of SF6 thermal decomposition with solid insulating materials are CS2, CF4, CO2, SO2F2, SOF2, H2 S and SO2. Due to the different formation mechanism of SF6 decomposition components, the concentration and effective gas formation rate of these components show different increase trends while the partial overheating temperature elevates, and the physical significance of each component is not the same. Stainless steel heating component after the experiment containing Fe, F, O, C, S and other elements, the exist form of Fe and O is Fe2O3, the possible exist form of Fe and F is FeF2, solid insulation materials after the experiment added F, S and other elements due to the corrosive effects of HF and H2 S. it is the discrepancy of the pyrolysis degree of insulation materials under different partial overheating temperatures and the erosion effect of HF and H2 S lead to the different change rules of main elements, e.g., C, O, F and S element. Last, the different fracture sequences of the chemical bonds of solid insulating materials lead to the different weight loss rules under different temperatures.