In recent years, permanent magnet variable frequency screw air compressors have been trusted by more and more customers due to their high efficiency, energy saving, and stable pressure. However, the manufacturers of permanent magnet motors on the market are uneven. If the selection is improper, it may lead to the risk of loss of magnetism of the permanent magnet motor. Once the permanent magnet motor loses its magnetism, it is basically the only option to replace the motor, resulting in high maintenance costs. How to judge whether the permanent magnet motor is out of magnetism?
1 When the machine starts to run, the current is normal. After a period of time, the current becomes larger. After a long time, it will report that the inverter is overloaded. First, it is necessary to confirm that the selection of the inverter of the air compressor manufacturer is correct, and then confirm whether the parameters in the inverter have been modified. Load identification, the no-load operation to the rated frequency, the output voltage at this time is the back EMF, if it is lower than the back EMF on the motor nameplate by more than 50V, the motor can be demagnetized.
2 After the permanent magnet motor is demagnetized, the running current will generally exceed the rated value by a lot. Those situations that only report overload at low speed or high speed or occasionally report overload are generally not caused by demagnetization.
3 It takes a certain amount of time to demagnetize a permanent magnet motor, some months or even a year or two. If the manufacturer selects the wrong type and causes the current overload, it does not belong to the demagnetization of the motor.
4 Reasons for motor demagnetization
a. The cooling fan of the motor is abnormal, resulting in the high temperature of the motor
b. The motor is not provided with a temperature protection device
c. The ambient temperature is too high
d. The motor design is unreasonable
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