Reasons for the demagnetization of permanent magnet motor and preventive measures
Once the permanent magnet motor loses its magnetism, it can basically only choose to replace the motor. The cost of repair is a big stroke. How to judge the loss of magnetism of the permanent magnet motor? Let's look down.
1. When the machine starts running, the current is normal. After a period of time, the current becomes larger. After a long time, the inverter will be overloaded.
If there is no problem with both, it is necessary to judge by the back electromotive force, disconnect the machine head from the motor, perform no-load identification, and run at no-load to the rated frequency. At this time, the output voltage is the back electromotive force, if it is lower than the motor nameplate. The motor can be demagnetized by the back electromotive force of 50V or more.
2. After the demagnetization of the permanent magnet motor, the running current will generally exceed the rated value.
Those that report overload only when running at low speed or high speed or occasionally report overload are generally not caused by demagnetization.
3, permanent magnet motor demagnetization is a certain time, some months or even a year or two
If the manufacturer selects the wrong type and causes the current to be overloaded, it is not the motor demagnetization.
Motor demagnetization reason
The cooling fan of the motor is abnormal, causing the motor to heat up.
The motor is not equipped with a temperature protection device
Ambient temperature is too high
Motor design is not reasonable
How to prevent demagnetization of permanent magnet motor? ? ?
Correct selection of permanent magnet motor power
Demagnetization is related to the power selection of permanent magnet motors.
Correct selection of the power of the permanent magnet motor can prevent or delay demagnetization.
The main reason for the demagnetization of permanent magnet synchronous motors is that the temperature is too high and the overload is the main cause of excessive temperature.
Therefore, when selecting the power of the permanent magnet motor, there must be a certain margin. According to the actual situation of the load, generally about 20% is suitable.
Avoid heavy load starting and frequent starting
The cage type asynchronous start synchronous permanent magnet motor tries to avoid direct start or frequent start of heavy load.
During the asynchronous starting process, the starting torque is oscillating. In the starting torque valley, the stator magnetic field is demagnetizing to the rotor pole.
Therefore, it is best to avoid overloading and frequent starting of asynchronous permanent magnet synchronous motors.
1: Appropriate increase in the thickness of the permanent magnet
From the perspective of design and manufacture of permanent magnet synchronous motors, the relationship between armature response, electromagnetic torque and permanent magnet demagnetization should be considered.
Under the action of the magnetic flux generated by the torque winding current and the magnetic flux generated by the radial force winding, the rotor surface permanent magnet is liable to cause demagnetization.
In the case that the air gap of the motor is constant, the most effective way to ensure that the permanent magnet does not demagnetize is to appropriately increase the thickness of the permanent magnet.
2: There is a ventilation slot circuit inside the rotor to reduce the temperature rise of the rotor
An important factor affecting the reliability of permanent magnet motors is permanent magnet demagnetization.
If the temperature rise of the rotor is too high, the permanent magnet will produce irreversible loss of magnetism.
In the structural design, the internal ventilation circuit of the rotor can be designed to directly cool the magnetic steel. Not only reduces the temperature of the magnetic steel, but also improves the efficiency.