The complicated interaction between motion of non-return valve

return gas valve and pressure relief valve and gas flow field of self-blast SF

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circuit breaker is existed.The mathematic model of continuous motion of valve is set up on the basis of the actual motion rule of the three valves and with the use of Newton’s Second Law

at the same time

the gas flow field of the self-blast SF

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circuit breaker during the high current arcing stage and continuous motion of valve are simulated and analyzed on the basis of 2D axial symmetric magnetic hydro-dynam

ics（MHD）model of arc with combination of real physical property parameters of gas.It is shown by the study that the hot gas reflux generated by arcing is the main reason of high pressure in the thermal expansion chamber and of enclosure of non-return valve.The variation of gas pressure on the different monitoring points is closely related to arcing current

position of stationary arc contact and state of valves.The motion of non-return valve is influenced by the magnitude of the arcing current and the pressure of the thermal expansion chamber.The fluctuation on its both sides is occurred due to stress at the moment of motion completion.The return gas valve is always at closed condition at the arcing stage.The operating action of pressure relief valve is greatly associated with the state of non-return valve

the pressure of puffer chamber and force of spring.The operation of the pressure relief valve can influence the distribution of gas flow field around the valve

causing both sides of the valve to be stressed and fluctuation of motion.