A user raised a question regarding whether holding the shaft of a permanent magnet motor could cause the winding to burn up. In order to address this question, let’s discuss the issue briefly.
Firstly, let’s consider a three-phase motor.
The plugging test is a necessary inspection item for three-phase asynchronous cage motors to verify compliance with certain performance indicators.
When a motor is started at rated voltage, the current of the motor can reach 5-7 times the rated current.
If the motor cannot be started normally for some reason, or the rotor is at rest, or the motor rotor is in a low-speed state, then the motor makes a very low sound, and the motor winding will be in danger of burning in a short time.
To ensure the safe operation of this motor, soft start and over-current protection can be used to avoid excessive current during motor starting and the winding burning problem that occurs when the motor runs under voltage and happens to hold the shaft unexpectedly.
In the case of a permanent magnet synchronous motor, the motor starts and runs through the inverter, and the parameters of the inverter are set to protect the motor from special operating conditions.
However, when the rotor stalling condition occurs in a motor powered directly by the inverter power supply, it can lead to a surge of current and a demagnetization problem at the same time.
The correct selection of the power of a permanent magnet motor can prevent or delay demagnetization.
The main cause of demagnetization in permanent magnet synchronous motors is high temperature, which is primarily caused by overload.
Holding the shaft of the motor can result in severe overload, and thus, the motor should be operated with a certain amount of margin in power selection.
Additionally, heavy load starting and frequent starting should be avoided in order to prevent demagnetization.
During the asynchronous starting process, the starting torque is oscillating, and in the starting torque valley section, the stator magnetic field can demagnetize the rotor pole.
Therefore, it is recommended to avoid heavy load and frequent starting of asynchronous permanent magnet synchronous motors.
