Simulation of positive surface discharge in C4F7N gas mixture

C4F7N gas mixture is considered to be a very promising SF6 replacement gas. In order to study the surface discharge characteristics of C4F7N gas mixture under the needle-plane electrodes, a fluid model of surface discharge was established using COMSOL Multiphysics for simulation, and the change patterns of electric field and photon flux during the development of streamer were obtained. By obtaining the change law of photon flux, it can provide the theoretical discharge. The simulation results show that the development process of streamer can be divided into three phases: streamer generation phase, streamer deceleration phase and streamer acceleration phase. During the whole process, the change trend of photon flux is basically consistent with the change trend of electric field. In the acceleration phase, the streamer gradually moves away from the needle electrode, the background electric field gradually decreases, and the frequency generated by the electron collision reaction weakens, leading to the slow development of the streamer, and the electric field and the photon flux at streamer head gradually decrease. In the acceleration phase, the streamer is converted from parallel to the plane electrode to perpendicular to the plane electrode, and the potential gradient becomes larger, leading to a faster development of the streamer and a gradual increase of the electric field and photon flux at streamer head.