The operating environment of wind turbines is very harsh, it must be able to withstand high temperature, cold, wind sand, humidity and even salt spray test. Wind turbines are designed to last 20 years. At present, both small wind turbines and megawatt permanent magnet wind turbines are selected sintered NdFeB magnet. Therefore, the selection of NdFeB permanent magnetic parameters and the requirements of corrosion resistance of magnets are very important.
Typical magnetic properties of sintered NdFeB magnet in wind turbines
Ndfeb permanent magnet, known as the third generation of rare earth permanent magnet, is the highest magnetic material so far. The main phase of sintered NdFeB magnet is intermetallic compound Nd2Fe14B, which has a saturation magnetic polarization strength (Js) of 1.6T. The maximum magnetic energy product of magnet can be increased by increasing the proportion of main phase, the orientation of grain and the density of magnet.
The demagnetization curve of NdFeB at room temperature is approximately straight. Therefore, when designing permanent magnet motors, NdFeB materials with high BH is often chosen to obtain high air gap magnetic density. When the motor is running, due to the existence of alternating demagnetizing field and the sudden change of load, the demagnetizing field generated by instantaneous large current requires the selection of sintered NdFeB magnet with high coercivity.
The corrosion resistance of NdFeB
NdFeB material contains active rare earth elements, easy oxidation, easy corrosion. In application, unless NdFeB is encapsulated and isolated from air and water, it is necessary to do surface anti-corrosion treatment of NdFeB. Common anti-corrosion coatings include nickel electroplating, electrogalvanizing and electrophoretic epoxy resin. Surface phosphating treatment can play a role in the relatively dry environment of NdFeB corrosion prevention for a short time。