The insulation characteristics and decomposition components of C4F7N/N2 gas mixture, a potential substitute for SF6, were first explored by breakdown experiments/gas chromatography–mass spectrometer. The structural properties of C4F7N molecule and the decomposition mechanism of C4F7N/N2 gas mixture were analyzed based on the density functional theory calculation and ReaxFF molecular dynamics simulation. We found that C4F7N/N2 mixture has great self-recovery performance. The decomposition of C4F7N in a discharge mainly produces CF4, C2F6, C3F8, CF3CN, C2F4, C3F6, and C2F5CN, among which the relative content of C2F6, CF4, and CF3CN is higher. ReaxFF-MD simulations show that CF3, CN, F, and C3F7 are the four main free radicals produced by C4F7N. The decomposition characteristics of N2 are better than that of C4F7N. The addition of N2 has a certain buffering effect to avoid the massive decomposition of C4F7N. The global warming potential value of a gas mixture containing 20% C4F7N decreased by 94.32% compared with SF6. Relevant results not only reveal the decomposition characteristics of C4F7N/N2 mixture in a discharge comprehensively, but also provide a reference for engineering application and emission of a C4F7N/N2 gas mixture.

This paper investigates the dielectric breakdown properties of humid air, taking into account ion kinetics. Initially, an overall kinetic scheme that includes all the main reactions likely to happen in humid air is established for the first time. Then, the calculation method of dielectric properties is improved, based on more comprehensive avalanche model considering both spatial growth and temporal processes. Better consistency between present results and experimental values confirms the validity of the improved method and kinetic schemes. Finally, the effective ionization Townsend coefficients αeff in humid air at different humidity and gas pressures are calculated and analyzed considering ion kinetics. Reduced critical electric field strength (E/N)cr can be determined when αeff  =  0. The results show that (E/N)cr in humid air increases sharply in the beginning and then tends to be constant with the humidity rises. Besides, the mechanism of humidity’s effect on dielectric breakdown properties is well explained: at relatively low E/N, αeff decreases with the increase of humidity mainly due to more frequent three-body conversions, while at higher E/N, the main reason is the increased number of attachment reactions.

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