The various causes of demagnetization in permanent magnet motors and how to prevent and maintain them are the topics of this article. Through this article, readers will learn how to ensure the stable and efficient operation of permanent magnet motors, providing long-lasting and reliable power support.
Causes of Demagnetization in Permanent Magnet Motors
High-Load Operation
The permanent magnets in permanent magnet motors are highly sensitive to temperature. During operation, if the internal temperature continues to rise due to excessive load, cooling system failure, or other reasons, exceeding the limit that the permanent magnets can withstand, demagnetization is likely to occur.
For example, in industrial scenarios involving prolonged high-load operation, heat accumulates inside the motor, causing the temperature of the permanent magnets to soar. The originally stable magnetic properties gradually degrade, leading to a significant drop in motor efficiency and even equipment failure or shutdown. Moreover, demagnetization in permanent magnet motors caused by high temperatures is often irreversible, resulting in permanent damage to the motor.
Overload Operation
Overload operation acts as an “accelerator” for demagnetization in permanent magnet motors. When a permanent magnet motor operates under overload conditions for an extended period, the stator current increases sharply. This not only exacerbates motor heating (further intensifying the impact of high temperatures on the permanent magnets) but also generates a strong armature reaction magnetic field.
This additional magnetic field severely interferes with the inherent magnetic field of the permanent magnets, akin to constantly “tugging” at the magnetic properties of the permanent magnets in a “tug-of-war.” This gradually reduces the magnetic flux of the permanent magnets, significantly accelerating the demagnetization process. In many cases, what appears to be a sudden demagnetization failure is actually the result of long-term overload operation—a latent “hidden danger” that erupts at a certain moment.
Assembly Errors
During the motor assembly process, if the air gap between the stator and rotor is uneven or the installation position of the permanent magnets deviates, the internal magnetic field distribution of the motor becomes chaotic.
During operation, excessive magnetic stress in localized areas continuously “impacts” the permanent magnets, gradually leading to demagnetization in permanent magnet motors. Like a precision gear set, misalignment during installation causes additional wear during operation, affecting overall performance. Assembly errors similarly harm the permanent magnets in motors.
External Magnetic Fields
When permanent magnet motors are exposed to strong external magnetic fields in their environment (such as nearby high-power electromagnets or high-frequency electromagnetic equipment), the external magnetic field interacts with the internal magnetic field of the permanent magnets.
Particularly, strong reverse magnetic fields directly interfere with the magnetic domain arrangement of the permanent magnets, disrupting their originally stable magnetic structure and causing demagnetization. This issue requires special attention in environments with complex electromagnetic conditions, such as factory workshops or laboratories, where magnetic shielding for the motors should be implemented.
Strategies to Solve Demagnetization in Permanent Magnet Motors
Proper Selection of Motor Power
Demagnetization in permanent magnet motors is related to the power selection of permanent magnet motors. Correctly selecting the motor power can prevent or delay demagnetization. The main cause of demagnetization in permanent magnet synchronous motors is excessive temperature, with overload being the primary reason for overheating. Therefore, it is advisable to leave a certain margin when selecting the motor power. Based on the actual load conditions, a margin of around 20% is generally appropriate.
Improved Design
Appropriately increasing the thickness of the permanent magnets is an effective measure. From the perspective of permanent magnet synchronous motor design and manufacturing, the relationship between armature reaction, electromagnetic torque, and permanent magnet demagnetization must be considered.
Under the combined influence of the magnetic flux generated by the torque winding current and the radial force winding, the permanent magnets on the rotor surface are prone to demagnetization. When the motor air gap remains unchanged, the most effective way to prevent demagnetization is to increase the thickness of the permanent magnets appropriately. Additionally, in structural design, an internal ventilation circuit can be incorporated into the rotor to cool the magnets.
Strict Control of Assembly Quality
Conduct rigorous magnetic performance testing on purchased permanent magnets. Introduce high-precision inspection equipment during motor manufacturing and assembly to ensure air gap uniformity and the installation accuracy of the permanent magnets. This helps reduce the risk of demagnetization in permanent magnet motors from the production source.
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