外文翻譯---電動機(jī)的結(jié)構(gòu)特點-其他專業(yè)(已修改)
2025-02-04 09:40 本頁面
【正文】 英文翻譯 第 1 頁 共 8 頁 Construction Features of Electrical Machines The energyconversion process usually involves the presence of two important features in a given electromechanical device. These are the field winding, which produces the flux density, and the armature winding, in which the “working emf is induced. In this section the salient construction features of the principal types of electric machines are described to show the location of these windings, as well as to demonstrate the general position of such machines. Induction Motor This is one of the most rugged and most widely used machines in industry. Its stator is posed of laminations of highgrade sheet steel. The inner surface is slotted to acmodate a threephase winding. In (a) the threephase winding is represented by three coils, the axes of which are 120 electrical degrees apart. Coil aa39。 represents all the coils assigned to phase a for one pair of poles. Similarly coil bb39。 represents phase b coils, and coil cc39。 represents phase c coils. When one end of each phase is tied together, as depicted in (b), the threephase stator winding is said to be Yconnected. Such a winding is called a threephase winding because the voltage induced in each of the three phases by a revolving flux density field are out of phase by 120 electrical degrees—a distinguishing characteristic of a balanced threephase system. The rotor also consists of laminations of slotted ferromagic material, but the rotor winding may be either the squirrelcage type or the woundrotor type. The latter is of a form similar to that of the stator winding. The winding terminals are brought out to three slip rings. This allows an external threephase resistor to be connected to the rotor winding for the purpose of providing speed control. As a matter of fact, it is the need for speed control which in large measure accounts for the use of the woundrotor type induction motor. Otherwise the squirrelcage induction motor would be used. The squirrelcage winding consists merely of a number of copper 英文翻譯 第 2 頁 共 8 頁 bars embedded in the rotor slots and connected at both ends by means of copper end rings. (In some of the smaller sizes aluminum is used.) The squirrelcage construction is not only simpler and more economical than the woundrotor type but more rugged as well. There are no slip rings or carbon brushes to be bothered with. In normal operation a threephase voltage is applied to the stator winding at points abc in currents flow in each phase which together create a revolving m
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