During the use of permanent magnet variable frequency air compressors, the biggest risk is demagnetization caused by high temperature. As we all know, the key component of permanent magnet motors is magnetic steel, and magnetic steel is afraid of high temperature. It will gradually demagnetize under long-term high temperature conditions. The higher the temperature, the greater the risk of demagnetization. Once demagnetization occurs, the speed is very fast, and after partial demagnetization, the current of the motor will continue to increase, energy consumption will increase, and the user's electricity cost will increase. At the same time, there is the possibility that the motor will "strike" at any time.
Once the permanent magnet motor loses magnetism, basically only the motor can be replaced, and the cost of maintenance is a large sum. So how to judge whether the permanent magnet motor has lost magnetism?
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 reported as overloaded.
First, it is necessary to confirm that the air compressor manufacturer's inverter selection is correct, and then confirm whether the parameters in the inverter have been changed.
If there is no problem with either, it is necessary to judge by back electromotive force, disconnect the 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 back electromotive force on the motor nameplate by more than 50V, it can generally be said that the motor is demagnetized.
2. The running current of the permanent magnet motor after demagnetization generally exceeds the rated value by a large margin
Those situations where overload is reported only at low or high speed or occasionally reported are generally not caused by demagnetization.
3. It takes a certain amount of time for the permanent magnet motor to demagnetize, some for several months or even one or two years
If the manufacturer selects the wrong model and causes the current overload to be reported, it does not belong to motor demagnetization.
Reasons for motor demagnetization
An important indicator of the performance of permanent magnet motors is the high temperature resistance level. If it exceeds its temperature resistance level, its magnetic flux density will decrease. It can be judged that the motor may be demagnetized. The high temperature resistance level can be divided into: N series, resistant to more than 80 degrees; H series, resistant to 120 degrees; SH series, resistant to more than 150 degrees.
Therefore, the following points can also be used to judge whether the temperature is high
1. The motor cooling fan is abnormal, causing the motor to be overheated
2. The motor is not equipped with a temperature protection device
3. The ambient temperature is too high
4. The motor design is not suitable