Decomposition characteristics of C₄F₇N/CO₂ mixture under AC discharge breakdown

Recently, the C₄F₇N/CO₂ mixture has been highly considered as a promising SF₆ alternative due to its low greenhouse effect and excellent electrical performance. Apart from its dielectric strength and arc-quenching capability, the decomposition characteristics of C₄F₇N/CO₂ also play an important role in its future applications in gas-insulated electrical equipment. Therefore, decomposition experiments of the C₄F₇N/CO₂ mixture were carried out under multiple AC discharge breakdowns by using a needle-to-plate electrode configuration. The compositions of the gas mixture before and after breakdowns were detected by using a gas chromatography-mass spectrometer. The results show that a trace amount of C₃HF₇ exists in the C₄F₇N product; the decomposition of the C₄F₇N/CO₂ mixture mainly produces CO, CF₄, CO₂, C₂F₄, C₂F₆, C₃F₈, CF₃CN, C₃F₆, C₄F₆, C₄F₁₀, C₂F₅CN, C₂N₂, HCN, C₂F₃CN, and HF. As the number of breakdowns increases, the content of most decomposition products increases significantly, while the content of C₃HF₇ decreases. The possible formation pathways of the decomposition products were determined, and the corresponding reaction enthalpies were calculated by quantum chemistry calculation. Relevant results not only reveal the decomposition characteristics of C₄F₇N/CO₂ under AC breakdowns but also help us to better understand the corresponding physicochemical mechanisms, which will provide a good reference for stable operation and safe maintenance in applications.