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The academic study of electric machines is the universal study of electric motors and electric generators. By the classic definition, ''electric machine'' is synonymous with ''electric motor'' or ''electric generator'', all of which are electromechanical energy converters: converting electricity to mechanical power (i.e., electric motor) or mechanical power to electricity (i.e., electric generator). The movement involved in the mechanical power can be rotating or linear. Although transformers do not contain any moving parts they are also included in the family of electric machines because they utilise electromagnetic phenomena.〔Flanagan. Handbook of Transformer Design and Applications, Chap. 1 p1.〕 Electric machines (i.e., electric motors) consume approximately 60% of all electricity produced. Electric machines (i.e., electric generators) produce virtually all electricity consumed. Electric machines have become so ubiquitous that they are virtually overlooked as an integral component of the entire electricity infrastructure. Developing ever more efficient electric machine technology and influencing their use are crucial to any global conservation, green energy, or alternative energy strategy. ==Classifications== When classifying electric machines (motors and generators) it is reasonable to start with physical principle for converting electric energy to mechanical energy. If the controller is included as a part of the machine all machines can be powered by either alternating or direct current, although some machines will need a more advanced controller than others. Classification is complicated by the possibilities of combining physical principles when constructing an electrical machine. It can, for example, be possible to run a brushed machine as a reluctance machine (without using the rotor coils) if the rotor iron has the correct shape. Generally all electric machines can be turned inside out, so rotor and stator exchange places. All rotating electric machines have an equivalent linear electric machine where stator moves along a straight line instead of rotating. The opposite—linear to rotary dual—is not always the case. Motors and generators can be designed with or without iron to improve the path of the magnetic field (teeth to reduce the air gap is a common example) and with and without permanent magnets (PM), with different pole number etc., but still belong to different classes of machines. Electric machines can be synchronous meaning that the magnetic field set up by the stator coils rotates with the same speed as the rotor; or asynchronous, meaning that there is a speed difference. PM machines and reluctance machines are always synchronous. Brushed machines with rotor windings can be synchronous when the rotor is supplied with DC or AC with same frequency as stator or asynchronous when stator and rotor are supplied with AC with different frequencies. Induction machines are usually asynchronous, but can be synchronous, if there are superconductors in the rotor windings. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「electric machine」の詳細全文を読む スポンサード リンク
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