Forward and reverse control circuit of three-phase asynchronous motor

In production, it is often necessary to change the direction of rotation of the motor. According to the principle of the three-phase asynchronous motor , to change the direction of the motor, you only
need to swap any two of the three power cords connected to the three-phase power supply
, and change the three wires of the motor. The phase current sequence is sufficient. Commonly used
control circuits can be implemented using reverse switches, buttons, contactors and other electrical components
.
    Figure 4-4 shows a control circuit in which two start buttons control two contactors respectively to change
the three-phase current phase sequence of the motor and realize forward and reverse rotation of the motor
. Among them, contactor KM1 is used to control the forward rotation of the motor, and contactor
KM2 is used to control the reverse rotation of the motor. It can be seen from the main circuit that if
the two contactors KM1 and KM2 work at the same time due to misoperation, the six
main contacts will Closing will cause a three-phase power short circuit, which is never allowed
. Therefore, the design of the control circuit must ensure that only one of the two contactors
KM1 and KM2 can work under any circumstances. To this end, the auxiliary breaking contact
of a reversing contactor KM2 is connected in the forward control circuit. KM2 is connected in series with the auxiliary breaking contact KM1
of a forward contactor in the reverse control circuit .
In this way, when the forward contactor KM1 is working,
its movable contact KM1 is disconnected and the reverse control circuit is cut off; on the contrary,
when the reverse contactor KM2 is working, its movable contact KM2 is disconnected and the reverse control circuit is cut off. The forward control circuit is cut off. This ensures that the two contactors KM1
and KM2 will not work at the same time. This mutually restricted control is called "interlock" control, and the auxiliary contacts KM1 and KM2 are called "unlock"
contacts.