Investigation of dielectric properties of cold C₃F₈ mixtures and hot C₃F₈ gas as Substitutes for SF₆

In order to reduce the global warming potential resulting from SF₆ widely used as an insulating and arc quenching medium, the substitutes need to be found. This paper focuses on different cold C₃F₈ mixtures (at room temperature) as an insulating gas and hot C₃F₈ gas (at temperatures of 300-3500 K) as an arc quenching medium, which seem to be a good replacement of SF₆. Firstly, the dielectric properties, including the reduced ionization coefficient α / N, reduced electron attachment coefficient η / N and reduced critical electric field strength (E / N)_cr, of the cold C₃F₈-CF₄, C₃F₈-CO₂, C₃F₈-N₂, C₃F₈-O₂ and C₃F₈-Ar mixtures are calculated numerically using the two-term approximation of the Boltzmann equation. The dependence of such dielectric properties on the buffer gas proportion is investigated. Among the various C₃F₈ mixtures, the C₃F₈-N₂ mixture has the lowest α / N and the C₃F₈-CF₄ mixture has the largest η / N, and moreover, the C₃F₈-N₂ mixture is the best insulator in terms of breakdown strength because it has the largest (E / N)_cr. Secondly, the (E / N)_cr of hot C₃F₈ at temperatures up to 3500 K and various pressures is determined and compared with that of hot SF₆ gas. It is found that the hot C₃F₈ gas has much poorer dielectric performance than hot SF₆ because the (E / N)_cr of C₃F₈ decreases significantly above room temperature. Graphical abstract: [Figure not available: see fulltext.]