Magnetizing method of permanent magnet

Magnetizing method of permanent magnet

The magnetic stability of the permanent magnet's magnetic performance is one of the most important magnetic performance indicators to measure the quality of the permanent magnet. It is expressed by its demagnetization rate, that is, the magnetic induction decay rate of the permanent magnet. Because the magnetic performance will never be eternal, it will naturally produce magnetic induction attenuation with internal and external causes. Its internal causes include magnetic changes caused by changes in the structure of magnetic materials and magnetic effects after magnetization; its external causes include magnetic changes caused by the influence of temperature, interfering magnetic fields, mechanical stress, contact with strong magnetic bodies, and radioactive effects. is the main factor.

Once the permanent magnet auxiliary exciter is demagnetized, it must be re-magnetized. There are two kinds of magnetization methods: DC pulse magnetization method and DC power generation magnetization method.

1. DC pulse magnetization method

For maintenance due to loss of magnetization, on each magnetic pole of the disassembled rotor, use a plastic magnet wire with a cross-sectional area of not less than 2mm2 to wind the magnetizing coil. The two winding heads are drawn out, and after the whole machine is assembled, it can be magnetized by DC pulse method. After magnetization, disassemble the permanent magnet auxiliary exciter again to pull out the rotor (the rotor must be pulled out or inserted into the rotor with special equipment for electricians to prevent damage to the motor and human injury accidents), remove the magnetization coil, and then re-insert the rotor into the stator. Sub-core for overall assembly.

2. DC power generation magnetization method

After the whole machine is assembled, the DC generator or AC controllable rectification device is used for magnetization. The magnetizing voltage is 60V, the magnetizing current is about 500A, and the magnetizing time is about 2 to 3 seconds. Magnetization must be stabilized after magnetization. The rare earth permanent magnet material sintered NdFeB permanent magnet can be stabilized by more than five sudden short circuits; the permanent magnet material Alnico 5 permanent magnet can be stabilized by air twice.

The DC magnetizing method is a relatively simple magnetizing method, which can be used under the operating conditions of the factory and the installation site, as long as the magnetizing DC power supply is connected to the stator winding of the permanent magnet auxiliary exciter to magnetize.