Effects of Buffer Gases on Plasma Properties and Arc Decaying Characteristics of C₄F₇N–N₂ and C₄F₇N–CO₂ Arc Plasmas

C₄F₇N is one of the most promising candidate to replace SF₆ as arc quenching medium. Some buffer gases (N₂ and CO₂) are usually mixed with C₄F₇N to reduce the operating temperature. In order to provide priori knowledge of the arc quenching performance for C₄F₇N mixtures, the plasma properties including equilibrium compositions, thermodynamic properties, transport coefficients, and net emission coefficients of C₄F₇N–N₂ and C₄F₇N–CO₂ arc plasmas are calculated and the effects of buffer gases are discussed. Taking these properties as input, a 1D arc decaying model is constructed to describe arc decaying characteristics. According to the evolution of axial temperature and arc conductance over time, the arc decaying process is divided into three stages, i.e. the thermal recovery stage, the pre-dielectric recovery stage, and the post-dielectric recovery stage. We focus on the first two stages and describe them by the thermal recovery time (or rate) and the pre-dielectric recovery time (or rate) respectively. According to the results of 1D arc decaying modelling, the descending order of the thermal recovery ability for the gases studied in this work is: SF₆ ' C₄F₇N ' 75%C₄F₇N–25%N₂ ' 75%C₄F₇N–25%CO₂ ' 50%C₄F₇N–50%N₂ ' 25%C₄F₇N–75%N₂ ' 50%C₄F₇N–50%CO₂ ' CO₂ ' 25%C₄F₇N–75%CO₂ ' N₂; and the pre-dielectric recovery ability is: N₂ ' SF₆ ' CO₂ ' 25%C₄F₇N–75%CO₂ ' 25%C₄F₇N–75%N₂ ' 50%C₄F₇N–50%CO₂ ' 75%C₄F₇N–25%CO₂ ' 50%C₄F₇N–50%N₂ ' 75%C₄F₇N–25%N₂ ' C₄F₇N.