Squirrel cage asynchronous motor reverse braking control circuit

Reverse braking is a braking method that applies a power supply with a changed phase sequence to the motor after the normal power supply of the motor is cut off, so as to stop the motor quickly. When reverse braking starts, the normal power supply of the motor is cut off, and the motor continues to run in the original direction under the action of mechanical inertia. When the power supply with a changed phase sequence is added, the relative speed between the rotor and the stator rotating magnetic field is close to twice the synchronous speed, so at this moment the stator current is equivalent to twice the full voltage direct starting current, and the reverse braking torque is also large, and the braking is rapid.

The reverse braking control circuit is shown in the figure below. After pressing the start button SB2, the contactor KM1 is energized and self-locked, and the motor runs normally. After the speed increases, the speed relay KS installed coaxially with the motor operates, and the normally open contact of KS closes, preparing for KM2 to be energized. When the stop button SB1 is pressed, KM1 is powered off and reset, while KM2 is powered on and self-locked, and the motor enters reverse braking operation, and the speed drops rapidly. When the speed drops to a certain value (less than 100r/min), the KS contact opens, KM2 is powered off, and the braking process ends.

The disadvantage of reverse braking is that the braking current is very large, causing great circuit impact and mechanical impact. Therefore, in order to limit the braking current, a braking resistor R is generally connected in series in the braking circuit.