Influence of oxygen on solid carbon formation during arcing of eco-friendly SF₆-alternative gases

During the arc breaking process of high-voltage circuit breakers, the eco-friendly SF₆-alternative gases will inevitably decompose and generate various decomposition products. In some cases, this will contain solid by-products such as solid carbon, which will have a deterioration effect on the electrical insulation performance of the equipment. It has been found that adding a proper amount of O₂ can effectively inhibit the formation of solid carbon. In this paper, based on the improved Gibbs free energy minimization method, a calculation model considering the solid decomposition products was established, and the arc plasma composition of CO₂/O₂ mixtures with the new eco-friendly gases, such as C₄F₇N, C₅F₁₀O, HFO-1234ze(E) and HFO-1336mzz(E), in local thermodynamic equilibrium state was calculated. The change of decomposition products with the initial O₂ ratio is studied, and the criterion expression of inhibiting solid carbon formation is obtained. We also applied the method to the calculation of other SF₆-alternative gases containing sulfur atoms such as NSF₃ and CF₃SO₂F. Finally, we showed that solid carbon can be inhibited when a proper molecule formula is satisfied. This work may provide new ideas for further exploring the potential of SF_6-alternative gases.