Wind power generation is one of the important applications of Ndfeb magnets. At present, the global wind power installed capacity has more than 200 million KWH.At present, the increasing gear box used in traditional AC excited doubly-fed asynchronous wind turbine has been gradually eliminated by the progress of direct drive engine of permanent magnet wind turbine fan blades.However, due to factors such as over-expansion and a sharp increase in rare earth feedstock, the overcapacity of wind power equipment is 260%.
Wind turbines operate in very harsh conditions. They must be able to withstand heat, cold, sand, humidity and even salt spray. Wind turbines are usually designed to last 20 years. At present, sintered NdFeb permanent magnets are used in small wind turbines and megawatt permanent magnet wind turbines. Therefore, it is very important to select the magnetic parameters of neodymium permanent magnets and to require the corrosion resistance of the magnets.
1. Typical magnetic properties of sintered NdFeb (high remanence and coercivity)
Neodymium permanent magnet material is based on intermetallic compound Re2Fe14B. The main components of the rare earth elements neodymium (Nd), iron (Fe), boron (B). Among them, the rare earth element is mainly neodymium (Nd). In order to obtain different properties, it can be replaced by other rare earth metals such as dysprosium (Dy) and prasedymium (Pr). Iron can also be partially replaced by other metals such as cobalt (Co) and aluminum (Al). The content of boron is small, but it plays an important role in the formation of intermetallic compounds with tetragonal crystal structure, which makes the compounds have high saturation magnetization. High uniaxial anisotropy and high Curie temperature.
The third generation of rare earth permanent magnet Ndfeb is the strongest permanent magnet in contemporary magnets. Its main raw materials are rare earth metal neodymium 29%-32.5% metal element Iron 63.95-68.65% non-metal element boron 1.1-1.2% added dysprosium 0.6-8% niobium 0.3-0.5% aluminum 0.3-0.5% copper 0.05-0.15% and other elements.
Neodymium magnets are available in several grades.In the design of permanent magnet motors, advanced NdFeB is usually selected to obtain high air-gap magnetic density.Neodymium magnets with high coercivity are required due to the presence of alternating demagnetizing fields and the demagnetizing effect of instantaneous high current when the load changes abruptly when the motor is running.
2. Good temperature stability
Wind turbines can work in the wilderness and can withstand heat and cold. At the same time, the motor loss also causes the motor temperature to rise. Sintered neodymium magnets can operate at a maximum temperature of 230°C.
The Curie temperature of neodymium magnets is about 310°C. When a magnet passes the Curie point during operation, it changes from ferromagnetic to paramagnetic. At Curie temperature, the remanence of neodymium decreases with the increase of temperature, and its remanence temperature coefficient (Br) is -0.095-0.105%/. The coercivity of Nd-Fe-B decreases with the increase of temperature, and the coercivity temperature coefficient βjHc is -0.54 ~ 0.64%. If the appropriate coercive force is selected, the magnet will still have a high coercive force at the maximum operating temperature of the motor design.Otherwise you lose motivation.
3. The magnetic properties of the wind Ndfeb magnet are consistent
Large permanent magnet wind turbines typically use thousands of neodymium magnets. Each pole of the rotor contains a number of magnets. The consistency of the rotor pole requires the consistency of the magnet, including the consistency of dimensional tolerance and magnetic properties. The so-called magnetic consistency includes: the magnetic deviation between different individuals should be small, and the magnetic properties of a coarse single magnet should be uniform.
4. Neodymium magnet corrosion resistance
Neodymium Fe-B combination contains active dilute: earth elements, which are prone to oxidation and rust. In applications, unless Ndfeb is encapsulated and isolated from air and water, Ndfeb should be considered as a surface corrosion protectant. Common anti-corrosion coatings are nickel, galvanized and electrophoretic epoxy resins. Surface phosphating can prevent NdFeb from rusting for a short time in a relatively dry environment. Rare earth intermetallic compounds can react with hydrogen at a certain pressure and temperature. When Ndfeb absorbs hydrogen, it heats up and breaks down. Hydrogen crushing in NdFeb production takes advantage of this property.
5. The reliability of neodymium magnet
The design life of the wind turbine is 20 years, that is, the electromagnetic steel needs to be used for 20 years. Its magnetic properties are not significantly attenuated, and the electromagnetic steel is not significantly corroded.
6. Impact resistance
The fan operating environment is not as good as other engines, because it is generally set up in an open area, so there is almost no barrier to help it reduce the impact force when it encounters strong winds and storms. The impact force will bring very strong vibration of the fuselage, which also requires that the production of the fan needs to be particularly rigorous, and the magnet needs to ensure the integrity and stable magnetic properties under long-term vibration. This also eliminates the possibility of using other natural corrosion-resistant magnets.
7. Thermal conductivity
Wind turbines will continue to rotate during operation, and the high-speed friction between metals, magnets and other materials and closed Spaces are not easy to heat, and the magnets will rapidly heat up. In order to reduce the temperature of the magnet in a controllable time range, the thermal conductivity of the magnet is required to be higher. Eddy currents are reduced by reducing the surface resistance.
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Introduction to the uses of neodymium magnets;