Analysis of wiring diagram and control principle of two-speed motor

Analysis of wiring diagram and control principle of two-speed motor

First, the principle of two-speed motor control principle

According to the formula of the speed of three-phase asynchronous motor: n1=60f/p

There are many ways to realize the speed regulation of the three-phase asynchronous motor. For example, the frequency conversion speed regulation (YVP variable frequency speed control motor is used together with the frequency converter) to change the excitation current speed regulation (using the YCT electromagnetic speed regulating motor with the controller to achieve the poleless Speed regulation), can also change the motor variable pole speed regulation, that is, by changing the connection method of the stator windings to change the magnetic pole pairs of the rotating magnetic field of the stator, thereby changing the rotational speed of the motor.

According to the formula; n1=60f/p, the synchronous speed of the asynchronous motor is inversely proportional to the number of pole pairs, the number of pole pairs is doubled, the synchronous speed n1 is reduced to half of the original speed, and the rated speed n of the motor is also reduced by approximately half, so change The number of pole pairs can be used to change the motor speed (this is also the common 2-pole motor synchronous speed is 3000 rpm, 4-pole motor synchronous speed 1500 rpm, 6-pole motor synchronous speed 1000 rpm, etc.). This kind of speed regulation method is graded, can not smooth speed regulation, and only applies to squirrel cage motor, which is the principle of speed regulation of two-speed motor

Second, the control circuit analysis (two-speed motor wiring diagram as shown below)

1. Close the air switch QF and introduce the three-phase power supply.

2. Press the start button SB2, the AC contactor KM1 coil circuit is energized and self-locking, KM1 main contact is closed, three-phase power supply is introduced for the motor, L1 is connected to U1, L2 is connected to V1, L3 is connected to W1; U2, V2, W2 are suspended . The motor is operated under the Δ connection method, at which time the motor p=2, n1 = 1500 rpm.

3. FR1 and FR2 are overload protection components for motor △ operation and YY operation, respectively.

4. If you want to switch to high speed operation, press SB3 button, the normally closed contact of SB3 is disconnected, the contactor KM1 coil is de-energized, KM1 main contact is disconnected, U1, V1, W1 and three-phase power supply L1, L2 L3 is detached. Its auxiliary normally closed contact is restored to close, ready for energizing the KM2 coil loop. At the same time, the KM2 coil circuit of the contactor is energized and self-locking, and its normally open contact is closed. The three leading ends U1, V1 and W1 of the stator winding are connected together, and the three-phase power sources L1, L2 and L3 are connected to U2 and V2. W2, at this time the motor is running under YY connection, at this time the motor p=1, n1=3000 rpm. KM2's auxiliary normally open contact is disconnected to prevent KM1 from malfunctioning.

5. The normally open contact of SB2 in this control loop is connected in series with the KM1 coil. The normally closed contact of SB2 is connected in series with the KM2 coil. Similarly, the normally closed contact of the SB3 button is connected in series with the KM1 coil, and the SB3 is normally open in series with the KM2 coil. This kind of control is the interlock control of the button, which ensures that the two connection methods of △ and YY cannot occur at the same time. At the same time, the KM2 auxiliary normally closed contact is connected to the KM1 coil circuit, and the KM1 auxiliary normally closed contact is connected to the KM2 coil circuit. Interlock control.