The advantages of permanent magnets are their compactness and energy efficiency-no power supplies or cooling systems are required. Permanent magnet structures are well suited to generate uniform fields, which are static or variable, as well as multipole field patterns and field gradients with rapid spatial variation. Ní Mhíocháin, in Encyclopedia of Materials: Science and Technology, 2001 4 Concluding Remarks 19 The same topology was also chosen as the one with the highest potential for taking advantage of novel power factor and structural optimization techniques. The C-core TF PMDD generator with an inner rotor and flux concentration was defined as the topology that combines successfully all the beneficial attributes of a TF machine – high force density, high current loadings and reduced copper losses – with the highest torque/mass ratio compared to RF and AF machines or other TF PMDD designs. The C-cored AF PMDD machine suggested in References 8, 82 and 83 provides a structural topology with all the positive attributes of an air cored AF machine – such as structural simplicity, zero cogging torque and increased efficiency – and can effectively maintain the airgap clearance against electromagnetic and structural bending forces, reducing at the same time the structural and active mass requirements compared to other AF or RF PMDD designs. Slotted RF PMDD machines with an inner rotor and surface-mounted PMs are the lightest and most reliable RF machines. Therefore, PMDD machines can be more attractive for offshore wind turbine applications. Additionally, the performance of power electronics has been improving and a further reduction in the cost of PM materials is expected in the near future. PMDD machines have several advantages, such as increased reliability and higher energy yield, which make them superior to both EEDD and SRG machines. Zavvos, in Electrical Drives for Direct Drive Renewable Energy Systems, 2013 1.4 Conclusion Įlectrical generators for direct drive systems: a technology overview 19 shows the magnetization characteristics for common PM materials. They have less residual flux density compared to alnico and therefore they are less subject to demagnetization than alnico. Ferrite PMs are ceramic materials and are made from iron oxide and barium or strontium carbonate powders. Some of the major drawbacks of the NdFeB magnets are the limited temperature range and the need to protect from corrosion. NdFeB PM has a high energy product with the most cost-effective material used in PM applications in electrical machines. The development of the rare earth magnet, called neodymium iron boron (NdFeB), came about in the 1980s. During the 1960s a new class of magnetic materials known as rare-earth PMs was developed. In the 1950s, the ferrite PMs were placed in the market. They are good in high temperature applications. A family of alloys of aluminum nickel and cobalt (called alnico) that has a high residual flux density B r (remnant field) was discovered in the 1930s. Development of PMs started in Japan at the beginning of the 19th century. PMs are widely used in electromechanical devices, such as loudspeakers and PM motors. They are characterized by high remnant field ( B r) and high coercive field ( H c) and called hard materials. They are normally alloys of iron, nickel, and cobalt. PMs are capable of establishing a magnetic field without a current flow. Some disadvantages of permanent magnet EMS are the large initial cost of the permanent magnet, maintenance requirements for the rotating components, and the need to achieve rotation. Another advantage of this technique is its small space requirements compared with the bulkiness of the EMS systems. This significantly reduces the cost of electrical facilities. Permanent magnet EMS has the advantage of low electrical power consumption at approximately 2 kW h − 1 per ton ( 52). The rotation of the permanent magnets at speeds of 500 rpm can be used to produce a required stir-cast microstructure in a 150-mm-diameter billet. Rotation of the permanent magnet is achieved by rotation with an electric motor either inside a hollow crucible or circumferentially outside of EMS stir caster. Permanent magnet EMS produces an intense stirring in semisolid alloy slurries. Brabazon, in Comprehensive Materials Processing, 2014 5.07.2.2.2 Permanent Magnet EMS Casting, Semi-Solid Forming and Hot Metal FormingĪ.H.
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