Three-phase asynchronous motor energy consumption braking circuit diagram and working principle explanation

Today we will illustrate a three-phase asynchronous motor energy-consuming braking circuit.

First, let's understand the principle of dynamic braking: when the motor is disconnected from the three-phase AC power supply, the DC power supply is immediately connected to the two-phase winding of the motor stator. The DC current flows through the winding, generating a static DC magnetic field. At this time, the rotor of the motor rotates due to inertia, cutting the DC magnetic flux and generating an induced current. Under the interaction of the static magnetic field and the induced current, a braking torque is generated to hinder the rotation of the rotor, so the motor speed drops rapidly, thereby achieving the purpose of braking.

Figure 1

Figure 1 is a three-phase motor forward and reverse circuit with dynamic braking. The red part in the figure represents the live part.

Let's analyze how it works below.

Figure 2

Figure 2, close the circuit breaker QF.

Figure 3

Figure 3, first, press the forward start button SB2. The forward contactor KM1 coil is energized and attracted, and the auxiliary contact KM1-1 is closed and self-locked. KM1-2 disconnects the reverse interlock point. KM1-3 disconnects the interlock point with the brake circuit contactor KM3. At this time, the motor runs forward.

Figure 4

Figure 4 analyzes the energy consumption braking process when stopping. Press the stop button SB1, KM1 is released, and the three-phase AC power supply of the motor terminal is disconnected. At the same time, as shown in the figure, the normally open contact of SB1 is closed, so that the coil of contactor KM3 is energized, KM3-2 is closed and self-locked, and the normally closed contact of KM3-1 is disconnected. The main contact of KM3 is closed, connecting the primary circuit of the transformer and the DC circuit that passes through the two phases of the motor, and DC power is passed to the two phases of the motor.

When the KM3 coil is energized, the time relay KT coil is also energized and the delay starts, for example, set it to 3 seconds. (The length of the set time depends on the actual situation.)

Figure 5

Figure 5, after a delay of 3 seconds, the motor stops. The normally closed contact of KT is disconnected, KM3 is released, the main contact is disconnected, and the DC circuit is disconnected. At this time, KM3-1 is closed, and the forward and reverse rotation can be operated for the second time.

The principle of motor reversal is the same.