Three-phase asynchronous motor continuous control circuit

The three-phase asynchronous motor continuous operation control circuit is shown in Figure 4-2.
  Compared , three additional links are added: First, the auxiliary   moving contact KM of the contactor KM is connected
in parallel with the start button SB2. The function is to press the start button SB2, the contactor KM is energized, the motor M
  starts and runs, and the KM auxiliary moving contact   in parallel
with SB2 is also closed. When the start button SB2 is released, KM still causes the contactor KM coil to continue When energized, the motor M continues to run continuously.
  This effect is called "self-locking". The KM contact is called "self-locking". The second contact is to control
  the motor to stop. A stop button SB1 is added. Press the stop button SB1. Cut off the control circuit, the main contact
  of the contactor KM shoe L is disconnected, and the motor stops; thirdly, a thermal relay FR is added. When
  the motor is overloaded and heats up, after a period of time, its moving contact is disconnected, the control circuit is cut off , and the contact The main contact of the device
  KM is disconnected and the motor stops.