The magnetic properties of permanent magnets are calculated according to the design of the electromagnetic calculation. The selected permanent magnet material grades, main magnetic performance parameters and dimensions are processed and manufactured by the permanent magnet material manufacturing unit according to the design requirements, and the permanent magnets are magnetized and thermally aged in advance. , AC demagnetization or low temperature demagnetization.
First, the magnetization method of permanent magnets
The magnetic stability of the magnetic properties of a permanent magnet is one of the most important magnetic performance indicators for measuring the quality of a permanent magnet. It is expressed by its demagnetization rate, that is, the permanent magnet magnetic induction attenuation rate. Because the magnetic properties will never be permanent, it will naturally cause magnetic induction attenuation with internal and external causes. Its internal causes include changes in the structure of magnetic materials and magnetic changes resulting from magnetic effects after magnetization; its external causes include changes in magnetic properties due to temperature, interference magnetic fields, mechanical stress, contact with ferromagnetic substances, and radioactive effects, and its external causes Is the main factor.
Once the permanent magnet secondary exciter loses magnetism, 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
Maintenance due to demagnetization On each magnetic pole of the disassembled rotor, the magnetizing coil should be wound with a plastic cross section of not less than 2mm2. Each magnetic pole is continuously wound. Each adjacent magnetic pole has a different winding direction and will be continuously wound. After the two winding heads are led out, after the whole machine is assembled, the DC pulse method can be used for magnetization. After magnetization, remove the permanent magnet auxiliary exciter again to withdraw the rotor (extracting the rotor or inserting the rotor must use special electrical equipment to prevent damage to the motor and accidents). After removing the magnetizing coil, reinsert the rotor into the stator. The sub-cores are assembled as a whole.
2.DC generation magnetization method
After the whole machine is assembled, a DC generator or an AC controllable rectifier is used for magnetization. The magnetizing electric voltage is 60V, the magnetizing current is about 500A, and the magnetizing time is about 2 to 3 seconds. After magnetization, magnetic stabilization must be performed. Sintered neodymium-iron-boron permanent magnets with rare-earth permanent magnet materials can be used for more than five sudden short-circuit magnetic stabilization treatments; while aluminum-nickel-cobalt 5 permanent magnets for permanent magnet materials can be used for air stabilization treatment twice.
The DC power generation magnetization method is a relatively simple magnetization 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, the magnetization can be performed.
2. Demagnetization and magnetization stabilization methods of permanent magnets
The permanent magnet auxiliary exciter is different from the general AC exciter, so without comprehensive understanding of the magnetic circuit structure of the permanent magnet auxiliary exciter and the magnetic materials, grades, magnetic properties and permanent magnetization methods, it is Do not disassemble and arbitrarily, otherwise it will cause the risk of demagnetization due to disassembly and assembly. Especially if the structure is not well understood, and the necessary technical precautions, safety protection measures and necessary process equipment are not taken, hastily disassembling or assembling will not only damage the motor, but also cause errors and careless operation. And cause a personal accident.
Aiming at the factors of permanent magnet demagnetization, the corresponding magnetic performance technical requirements are proposed to the permanent magnetic material manufacturing unit. However, mistakes and carelessness in the process of storing and assembling permanent magnets by motor manufacturing units can also cause artificial demagnetization. Because the permanent magnet is used as the permanent magnetic energy source for the permanent magnet type secondary exciter, it is required to absolutely ensure that the magnetic circuit of the two poles of the N pole and the S pole of the permanent magnet cannot be shorted to form a magnetic short circuit under the structure design and under any conditions. Will cause artificial demagnetization of permanent magnets.
However, how to stabilize the magnetization and what method is used to stabilize the magnetization, as well as the method and frequency of magnetization stabilization, must be determined according to the permanent magnet material selected for the design.
Permanent magnet magnetic stabilization methods: there are two methods: sudden short-circuit magnetic stabilization and air magnetic stabilization. It is worth emphasizing to the designer that no matter what kind of magnetic stabilization method is adopted in the design, the type test of the permanent magnet auxiliary exciter product must be carried out in accordance with the industry standard JB / T9578 “Technical Conditions of Rare Earth Permanent Magnet Synchronous Generators”. After the short-circuit test, the performance of the product must meet national and industry standards and design requirements.
3. Magnetic performance test of permanent magnet inspection samples
For the magnetic performance test of the permanent magnet test sample, a pulsed magnetic field with an intensity of 400 kA / m or more is used for saturation and magnetization. The device for generating the pulsed magnetic field has two types: thyristor control mode and capacitor discharge mode.
Post time: Mar-12-2020