Why can't the three-phase motor stop running after pressing the stop button after normal operation?
After the three-phase motor is running normally, you can't stop the operation by pressing the stop button. Where is the problem?
The motor load operation consists of two parts: the main circuit and the control circuit.
The main circuit consists of the main breaker, the contactor main contact, the motor load and so on. The control circuit is composed of a sub-breaker, a stop button, a start button, a contact-assisted normally open contact, an electromagnetic coil, and the like.
Generally, when the motor needs to run, first close the main breaker and the sub-breaker. When the start button is pressed, the control circuit loop path, the contactor solenoid is electrically connected, the contactor main contact is sucked, and the motor is connected. The power supply starts running. At the same time, the contactor assists the normally open contact to close, and after the start button is released, the motor continues to run.
When the motor needs to stop running, press the stop button, the control circuit is open, the contactor solenoid is de-energized, the main contact of the contactor is disengaged, the main circuit is open and the power input is cut off, and the motor stops running.
It can be seen from the running and stopping of the motor that the contactor plays a key role in this process, that is, when the motor is running, the main contact of the contactor is closed. When the motor is stopped, the contactor main contact is open.
Then, can you judge this, the motor does not stop after pressing the stop button, is the contactor malfunctioning? No.
To determine if the contactor is faulty, you must continue to check. The inspection method is as follows:
First, check whether the contactor electromagnetic coil is charged and sucked
Method: Use a multimeter to check whether the voltage at both ends of the contactor coil is normal and whether it is normally sucked. If it is, then the stop button is faulty and the button cannot be disconnected normally. If not, the contactor is faulty and the contactor contact sticking does not break the main power supply normally.
Second, check whether the main contact of the contactor is stuck
Method: Disconnect the main breaker and cut off the main power. Use a multimeter to detect the continuity of the contactor's main contacts. If the contactor main contact is open, the stop button is faulty and the button contact cannot be broken normally. If the contactor main contact is closed, the contactor is faulty and the main contact is stuck.
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