Study On Arcing And Breaking Characteristics Of SF₆/N₂ Gas Ring Main Unit

SF₆ gas has excellent insulating,arc extinguishing and medium recovery capabilities,so it is widely used in electrical equipment.However,due to the greenhouse effect of SF₆,the study of SF₆ alternative gases has received wide attention.In this paper,SF₆/N₂ gas mixture is taken as the research object,gas mixing ratio and opening speed is taken as the influencing factors.By the method of simulation and test,the effects of different influencing factors on arc combustion characteristic and breaking performance of gas ring main unit are determined under micro-positive pressure.According to the peak value of recovery voltage that the ring main unit can withstand,the synergistic effect of SF₆ and N₂ mixture on breaking capacity of ring main unit is discussed.Firstly,based on the three-dimensional magneto hydro dynamic model of gas arc,the arc combustion process of SF₆/N₂ gas inside the arc extinguishing chamber of ring main unit with different mixing ratio and opening speeds is simulated and analyzed.Due to the influence of gas physical parameters,pure N₂ arc combustion is the most intense,and the back breakdown phenomenon is very serious,while pure SF₆ arc combustion is relatively flat.The increase of SF₆ content will make the mixed gas arc combustion more stable and the width of the arc column thinner.When SF₆ is more than 40%,the change of arc shape caused by the increase of SF₆ is no longer obvious.Then,the arcing test circuit is set up,and the arc combustion characteristic inside the arc extinguishing chamber of the ring main unit is tested.The experimental results are in agreement with the simulation results.The arcing characteristic of 40%SF₆/60%N₂ is close to that of pure SF₆.Its arc combustion is stable,the arc column is narrow,the arc voltage is high,and there is no phenomenon of the drop of arc extinguishing peak.The increase of SF₆content can increase the arc voltage of mixed gas,and the faster the opening speed is,the higher the arc voltage is,which is conducive to arc extinction.Finally,the synthesis test circuit is set up.The breaking performance of 20%SF₆/80%N₂and 40%SF₆/60%N₂ in the ring main unit was tested.The results show that the higher the SF₆content and the faster the opening speed,the higher the peak recovery voltage that the ring main unit can withstand,the better the breaking performance of the ring main unit.The breaking capacity of the ring main unit when it is charged with 40%SF₆/60%N₂ is equivalent to that of pure SF₆.By using the transient peak of recovery voltage that a ring main unit can withstand when it is successfully disconnected,the synergistic effect factor of the two mixed gases under the same conditions is calculated.The results show that both gas mixtures exhibit synergistic effect and the synergistic effect of 40%SF₆/60%N₂ is stronger than20%SF₆/80%N₂.