Demagnetization Risk of Permanent Magnet Synchronous Motor

Fan EC Motor Permanent Magnet Synchronous Motor Selection Key Part 13---Demagnetization Risk of Permanent Magnet Synchronous Motor

Permanent magnet is an important structural component of permanent magnet synchronous motor. Its magnetic performance directly affects the efficiency, performance and reliability of permanent magnet synchronous motor. Under the influence of temperature, armature reaction, mechanical vibration and other factors, permanent magnets in the motor may produce irreversible demagnetization, resulting in a sharp decline in the efficiency of the motor, and may even cause the motor to stop running.

There are several reasons for demagnetization of permanent magnet synchronous motor:

1. Mechanical and chemical reasons

The mechanical reason for demagnetization of permanent magnets is mainly that violent vibration causes permanent magnets to be damaged and cracked, and the magnetic moment direction of magnetic domains changes, thus causing the magnetic properties of permanent magnets to decline. Chemical demagnetization is mainly caused by improper surface treatment of permanent magnets or corrosion of permanent magnets due to surface coating damage.

2. Temperature

Temperature has a great influence on the magnetic properties of permanent magnets. During the use of permanent magnet synchronous motor, the ambient temperature is changing, its magnetic property changes with the change of temperature, the motor temperature rise control is abnormal, when the temperature rises, permanent magnet may produce irreversible demagnetization.

3. Impact current

The short circuit fault of the motor or the impact current caused by instantaneous overload will cause demagnetization of the synchronous motor.

4. Eddy current

When the motor is under load condition, especially when it is in high-speed weak magnetic field, there are a lot of harmonics in the composite magnetic field of the motor, which will generate eddy current on the surface of the permanent magnet, causing the temperature of the permanent magnet to rise and increasing the demagnetization risk of the permanent magnet.

5. Demagnetization field

If the control system is unstable, excessive demagnetization current will be generated at high speed, which may lead to demagnetization of permanent magnets.

Demagnetization is very harmful to permanent magnet synchronous motors. After demagnetization of the permanent magnet in the permanent magnet synchronous motor, the performance of the motor decreases and the torque is insufficient. If demagnetization is serious, the motor will not be able to drive the load or even burn down. Irreversible demagnetization of permanent magnets will reduce magnetic properties and remanence strength. If the motor load is unchanged, the output electromagnetic power is unchanged, and the torque balanced with the load is generated by increasing the current. With the irreversible demagnetization of permanent magnet synchronous motor, the iron loss and copper loss of the motor will increase and the efficiency of the motor will obviously decrease.