Permanent Magnet Motors: Common Faults And Issues in Operation

Compared with conventional motors, permanent magnet motors are relatively new in many fields. Thanks to their inherent energy-saving advantages and excellent operating performance at both high and low speeds, they have become the preferred choice for customers and been vigorously promoted once introduced to various application areas in recent years.

However, it also has a critical defect: the risk of demagnetization. In addition, some unprofessional manufacturers deliberately use low-grade permanent magnets to pursue high profits, resulting in a huge gap in the reliability of permanent magnet motors on the market. Some experience gradual performance degradation over time, while others suffer from widespread demagnetization. Here, we focuse on the demagnetization issue for reference and analysis when users encounter related problems.

DemagnetizationThis issue may occur if the design calculation is inaccurate and low-grade magnetic materials are selected. Overheating demagnetization is a sensitive topic; degraded magnetic properties of the magnets can also lead to overcurrent and overheating. When the load current during operation exceeds the demagnetization resistance of the magnets, irreversible demagnetization of the magnetic steel will take place.

Interactive Deterioration Between Magnetic Properties and Current DemagnetizationThis is a key concern in the application of those motors. Once the magnetic properties deteriorate during operation, the motor current will surge instantaneously, causing severe overheating. This further degrades the magnetic properties of the magnets, which in turn drives the current to rise again. This interactive vicious cycle can lead to motor failure in a very short time.

Magnet DetachmentIn actual assembly, magnetic steel is fixed to the core with adhesive, and potting adhesive is filled between permanent magnets to enhance bonding strength and prevent the magnets from flying off due to centrifugal force during high-speed rotation. Magnet detachment may occur under the combined effects of poor adhesive performance, insecure insertion, excessive temperature, water ingress or high humidity inside the motor cavity, resulting in direct mechanical friction and loss of motor driving function.

The demagnetization caused by the above internal and external factors is limited to the motor itself. In practice, permanent magnet motors must be equipped with special-purpose frequency converters during operation. The performance of the frequency converter also exerts a significant impact on permanent magnet motors, and demagnetization prevention mainly relies on software control, whose mechanism is based on the above discussion and will not be elaborated further. Relevant practical topics are welcome for future special discussions.