Reasons for demagnetization of Nanyang explosion-proof motor | permanentmagnet synchronous motor

2023-11-22 09:53:00

The manufacturer of explosion-proof motors in Nanyang stated that the major risk during the use of permanent magnet synchronous motors is demagnetization caused by high temperatures. Once a permanent magnet motor loses excitation, it can basically only be replaced with a replacement motor, and the cost of repair is a large amount. How to determine if a permanent magnet motor loses excitation?

1. When the machine starts working, the current is normal. After a period of time, the current increases, and over time, it will report that the frequency converter is overloaded. The primary requirement is to acknowledge that the frequency converter selection of the air compressor manufacturer is correct, and then to acknowledge whether the parameters in the frequency converter have been modified. Assuming that there are no issues with both, it is necessary to use the back electromotive force to distinguish between the machine head and the motor, perform no-load identification, and operate at the rated frequency with no load. At this time, the output voltage is the back electromotive force. Assuming that it is more than 50V lower than the back electromotive force on the motor nameplate, the motor demagnetization can be recognized.

2. After demagnetization, the operating current of permanent magnet motors generally exceeds the rated value by a large amount. The situations where overload is only reported during low or high speed operation or occasional overload is generally not caused by demagnetization.

3. Demagnetization of permanent magnet synchronous motors requires a certain amount of time, and some months or even one to two years may assume that the manufacturer's selection error caused current overload, which does not belong to motor demagnetization. One important goal of permanent magnet motors for demagnetization is their high temperature resistance level. Beyond this level, their magnetic flux density will sharply decrease. The high-temperature resistance level can be divided into N series, with a resistance of over 80 degrees Celsius; H series, resistant to 120 degrees; SH series, resistant to over 150 degrees. The cooling fan of the motor is malfunctioning, resulting in high temperature of the motor. The motor is not equipped with a temperature protection device, and the ambient temperature is too high.

How to prevent demagnetization of permanent magnet motors?

The Nanyang explosion-proof motor manufacturer stated that the correct selection of permanent magnet motor power demagnetization is related to the power selection of permanent magnet motors. Properly selecting the power of a permanent magnet motor can prevent or delay demagnetization. The primary cause of demagnetization in permanent magnet synchronous motors is excessive temperature, and overload is the primary cause of excessive temperature. Therefore, when selecting the power of a permanent magnet motor, a certain margin should be left. According to the practical situation of the load, generally around 20% is more suitable.

Avoid heavy load starting and repeated starting of cage type asynchronous starting synchronous permanent magnet motors. Try to avoid direct or repeated heavy load starting. During asynchronous starting, the starting torque oscillates, and in the valley of the starting torque, the stator magnetic field demagnetizes the rotor magnetic poles. Therefore, try to avoid overloading and repeated starting of asynchronous permanent magnet synchronous motors.

(1) The appropriate thickness of the permanent magnet should be added from the perspective of planning and manufacturing of permanent magnet synchronous motors, considering the connection between armature reaction, electromagnetic torque, and permanent magnet demagnetization. Under the combined action of the magnetic flux generated by the torque winding current and the magnetic flux generated by the radial force winding, the permanent magnet on the rotor surface briefly causes demagnetization. A useful way to ensure that the permanent magnet does not demagnetize while the air gap of the motor remains unchanged is to appropriately add the thickness of the permanent magnet.

(2) There is a ventilation slot circuit inside the rotor, and if the temperature rise of the rotor is too high, the permanent magnet will experience irreversible demagnetization. When planning the structure, it is possible to plan the internal ventilation circuit of the rotor and directly cool the magnetic steel. Not only did it lower the temperature of the magnetic steel, but it also increased the power.

The above information was compiled and released by the Nanyang explosion-proof motor manufacturer. Thank you for watching.