Squirrel-cage motor auto-coupling step-down start manual control circuit - News - Global IC Trade Starts Here.

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Single chip microcomputer STM32L151CCU6

Photocoupler

Squirrel cage motor auto-coupling step-start manual control circuit

The auto-coupling step-down startup is a starting method for reducing the voltage of the motor terminal by using an autotransformer. The autotransformer generally has two sets of taps to obtain different output voltages (generally 80% and 65% of the power supply voltage), and auto-coupling at startup. A set of taps (for example: 65%) in the transformer is connected to the circuit of the motor. When the speed of the motor is close to the rated speed, the autotransformer is cut off, and the motor is directly connected to the three-phase power supply to enter the running state.

1. Close the air switch QF to turn on the power.

2. Press the start button SB2, the AC contactor KM3 coil circuit is energized, the main contact is closed, and the autotransformer is connected to a star shape. The KM1 coil is energized with its main contacts closed, the power is connected to the motor by the 65% tap end of the autotransformer, and the motor is started at low voltage.

3, KM1 normally open auxiliary contact closure to open the coil circuit of the intermediate relay KA, KA energized and self-locking KA's normally open contact closure to prepare for the KM2 coil loop energization.

4. When the motor speed is close to the rated speed, release the button SB2, press the button SB3, the KM1, KM3 coils will be cut off, the autotransformer will be cut off, the KM2 coil will be powered and self-locked, and the power supply will be directly connected to the motor. Press to run.

5. The overload protection during motor operation is completed by the thermal relay FR.

6. Interlocking links;

Contactor interlock: KM2 normally closed contact is connected to KM3, KM1 coil circuit

KM1 normally closed contact is connected to KM2 coil circuit

Button interlock: Press button SB2 normally open contact to connect KM3, KM1 coil circuit

Button SB2 normally closed contact to connect KM2 coil circuit

Press button SB3 normally open contact to connect KM2 coil circuit

Press button SB3 normally closed contact to connect KM3, KM1 coil circuit

Squirrel-cage motor auto-coupling step-down start manual control circuit wiring diagram

Installation and commissioning

1. Motor self-coupling step-down circuit, suitable for any three-phase squirrel cage asynchronous motor.

2. The power of the autotransformer should be the same as the power of the motor. If it is less than the power of the motor, the autotransformer will damage the insulation and burn the winding due to the large starting heat.

6, with motor test; after the no-load test is correct, restore the wiring with the motor. In the test with the motor, attention should be paid to the exchange process between start-up and operation. Pay attention to the change of the sound and current of the motor. It is difficult or not to start the motor. If there is any abnormality, stop it immediately.

7. Start again; the auto-coupling step-down starting circuit can't operate frequently. If the start-up is unsuccessful, the second start should be more than 4 minutes. After 60 seconds of continuous start, it should be powered off for 4 hours to start running again. It is to prevent the starting current in the autotransformer winding from being too large and the heat to damage the insulation of the autotransformer.

Common malfunctions

1. When starting with load, the motor sound is abnormal, the speed is low and can't be close to the rated speed, and there is a big inrush current when it is connected to the running. Why?

Analyze the phenomenon; the motor sound is abnormal, the speed is low and cannot approach the rated speed, which indicates that the motor is difficult to start. It is suspected that the tap selection of the autotransformer is unreasonable, the motor winding voltage is low, and the load of the starting torque is small and the load is large.

Disposal; after the tap of the autotransformer is changed to the 80% position, the test failure is eliminated.

2. When the motor is switched from start to run, there is still a large inrush current or even a trip.

Analyze the phenomenon; this is caused by the short switching time of the motor starting and running. The time is too short. The starting current of the motor has not decreased. The speed is close to the rated speed and it is switched to the full-pressure running state.

Treatment; prolong the start-up time phenomenon.