Why does the permanent magnet motor lose magnetism? These 3 problems must be solved!

Permanent magnet materials are the key raw materials of permanent magnet motors. During demagnetization problems always occur. From the analysis of actual failure cases, it can be attributed to the following aspects:

If the calculation is not accurate enough during the motor design, and a lower grade is selected by mistake, such as the permanent magnet of 155℃ grade should be selected instead of 180℃ grade, the following situation may occur: the initial test record index of the test process is very good, and as the motor gradually tends to thermal stability, the relevant indexes of the motor begin to deteriorate, and deviate more and more from the design expectations. At a certain moment, the current increases sharply, the inverter stops quickly, and the overcurrent code is displayed. Test the no-load characteristics of the motor again, indicating that the motor has lost magnetism and the magnet must be replaced.

Overheating and demagnetization is a sensitive topic. The decline in magnetic properties of magnetic steel can also lead to overcurrent and overheating. If the influence of magnetic properties of magnetic steel is excluded and only thermal factors are considered, it can be determined that there are two situations in which overheating and demagnetization will occur: first, the internal circulation ventilation path of the motor is unreasonable, which violates the natural law of heat conduction and causes local heat accumulation; second, the thermal load of the winding is too high, and the heat generation exceeds the heat exchange level of the motor heat exchange system.

When the motor is running, when the load current exceeds the anti-demagnetization ability of the magnetic steel, it will cause irreversible demagnetization of the magnetic steel, further increasing the load current and aggravating the irreversible demagnetization of the magnetic steel. This cycle will add fuel to the fire, accelerating the irreversible demagnetization like an avalanche until it loses magnetism.

In recent years, the application areas of permanent magnet motors have been gradually expanding, especially in variable load occasions such as fans, water pumps, and air compressors. The application and energy-saving effects of permanent magnet motors are more obvious, but how to ensure the safety of motor and equipment operation is an issue that motor manufacturers, users, and permanent magnet suppliers should consider.