A new magnetic hydro-dynamics model for nozzle arc emphasizing the interaction ofarc with PTFE(polytetrafluorethylene)vapour is established based on the conservation equations.The interruption of auto-expansion circuit breaker is simulated numerically by finite elementmethod and the influence of PTFE vapour on the arc is analysed with this model.The resultsreveal that the flow field inside the arc chamber is determined by the arc current,the arcingtime,the nozzle arc and the clogging of its thermal boundary.The establishment of quenchingpressure relies on both SF6 gas and PTFE vapour that absorbed arc energy in the nozzle.ThePTFE vapour leads to an increase in the pressure of nozzle arc obviously,and a decrease in thetemperature of arc.But it enhances the temperature of arc at zero current and slows down thedecreasing rate of arc temperature as the current decreases.
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