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the circuit of phase failure protector for electric motor(3)

2016-09-02 22:48  
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the circuit of phase failure protector for electric motor(3)
After the starting button is pressed,AC contactor KM is conducted to pull in.The normally open contacts KM1-KM4 do not get through.The electric motor M goes to work.If the three-phase AC power supply is normal,the LEDs inside VLC1-VLC3 are all lighted.The optical transistors are all conducted.V is saturated to conduct.K pulls in.The normally open contacts get through.When S2 is disconnected,KM could stay pull-in.If one of the phase in three-phase alternating-current supply is missing,the optical coupler in voltage detecting circuit is stopped.V couldn't conduct.K doesn't pull in.When S2 is disconnected,KM is no longer pull-in.The phase failure reaches the goal of automatic protection.