The braking torque is generated by changing the phase sequence of the power supply in the stator windings of the motor to force the motor to stop quickly. The one-way starting reverse braking control circuit is introduced here.
One-way starting reverse braking control line is shown on the right. The main circuit of this line is the same as that of the forward and reverse control line, except that three current limiting resistors R are added in reverse braking. In the line, KM1 is the positive running contactor, KM2 is the reverse braking contactor, and SR is the speed relay, whose shaft is connected to the motor shaft (represented by dotted lines in the figure). The working principle of the circuit is as follows: First turn on the power switch QS:
B
Unidirectional start: press SB1→ contactor KM1
rU2
Coil power →KM1 interlocking contact break pair
rU
KM2 interlock, KM1 self-locking contact closed

PPC907BE 3BHE024577R0101

PPC907BE 3BHE024577R0101

PPC907BE 3BHE024577R0101

Lock and KM1 main contacts close → motor M starts running → when the motor speed rises to a certain value (about 100 RPM) →SR dynamic contact closes to prepare for braking;
Reverse braking: Press the compound button
SB2→SB2 breaking contact breaks first :KM1 coil power off, SB2 moving contact closed after →KM1 self-locking contact breaks off, KM1 main contact breaks off, M temporary power off, KM1 interlocking contact closure →KM2 coil power on →KM2 interlocking contact break off, KM2 self-locking contact closure, KM2 main contact closure → motor M series connection R reverse contact braking → when the motor speed drops to a certain value (about 100 RPM) →SR normally open contact break →KM2 coil power off →KM2 interlocking contact closure release interlocking, KM2 self-locking contact breaks off, KM2 main contact breaks off → motor M stops rotating from the power supply, and the braking ends.
In reverse braking, because the rotating magnetic field and the relative speed of the rotor (n1+ n) is very high, the induced current in the rotor winding is very large, resulting in a large current in the stator winding, which is generally about 10 times the rated current of the motor. Therefore, reverse braking is suitable for the braking of small capacity motor below 10kW, and for the motor above 4.5kW reverse braking, it is necessary to string the current limiting resistance R in the stator loop to limit the reverse braking current.