Three-phase asynchronous motor forward and reverse circuit diagram and working principle explanation

Figure 1

Figure 1 is a conventional three-phase asynchronous motor forward and reverse circuit diagram. Some friends pointed out that if the motor is running and suddenly reverses, it will have a great impact on the motor and even cause a phase short circuit. In order to prevent this phenomenon, the circuit has been improved. As shown below:

Figure 2

Figure 2 shows a button interlock and a power-on delay time relay. Let's analyze its working principle. The red part in the figure is the live part.

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Figure 3

Figure 3, close the circuit breakers QF1 and QF2. The coil of the time relay KT is energized and the delay starts, with a set time of 3 seconds.

Figure 4

Figure 4, after a delay of 3 seconds, the KT normally open point is closed. As shown in the figure, the forward and reverse buttons are effective.

Figure 5

Figure 5, press the forward start button SB2, the KM1 coil is energized and attracted, KM1-2 is closed for self-protection, and the KM1-3 interlocking point is disconnected. KM1-4 is disconnected, and the time relay KT coil is de-energized. The KT normally open point is restored to open, but KM1-1 is closed, so the KM1 coil is still kept attracted. The motor runs forward.

Figure 6

Figure 6, press the stop button SB1, KM1 contactor releases, the motor stops. At this time, KM1-4 resumes closing, KT coil is energized again, and begins to extend. After 3 seconds, KT normally open point closes, changing to the state of Figure 4.

Figure 7

Figure 7, press the reverse start button SB3, the motor reverses, the same principle as the forward rotation.

In short, each operation step is extended by 3 seconds, avoiding malfunctions caused by reverse steering too quickly.