ТОР 5 статей:
II. Translate the following phrases, using the given variants of translation.
To consist – состоять: to consist of a stationary part and a rotating part; separated – отдельный, изолированный: the stationary and rotating parts should be separated from each other by an air gap; to serve – служить в качестве чего-либо: the ringshaped portion or yoke serves as a path for the main and commutating pole fluxes.
II. Join the beginnings and the ends
IV. Arrange synonyms in pairs and memorize them:
a) to consist of; to be separated from; to create; to be interposed between; to pass; to rotate;
в) to be divided with; to produce; to introduce into; to permeate; to roll; to revolve; to comprise.
V. Write out the names of the machine parts and describe their operational characteristics.
I. Read the text.
The alternator is an electric machine for generating an alternating current by a relative motion of conductors and a magnetic field. The machine usually has a rotating field and a stationary armature. In a synchronous alternator the magnetic field is excited with a direct current. The direction of an induced e.m.f. is reversed each time when a conductor passes from a pole of one polarity to a pole at another polarity. Most machines of this type are used for lighting and power, but there are alternators with a revoking armature and a stationary field. They are used in small sizes mostly for special purposes.
Any electrical machine is reversible. When a machine is driven by a source of mechanical power, it works as a generator and delivers electrical power. If it is connected to a source of electrical power, it produces mechanical energy, and operates as a motor. The alternator may also be operated as a motor.
The a.c. generator, or alternator, does not differ in principle from the d.c. generator. The alternator consists of a field structure and an armature. The field structure is magnetized by a field winding carrying a direct current. An electromotive force is generated in tine winding of the armature. In alternators the field is usually the rotating element and the armature is stationary. This construction has a number of advantages. Only two rings are needed with a rotating field. These rings carry only a relatively light field current, at a voltage generally of 125, and seldom exceeding 250. The insulation of such rings is not difficult. A stationary armature requires no slip rings. The leads from the armature can be continuously insulated from the armature winding to the switchboard, leaving no bare conductor. The alternator with a rotating field may be further divided into the vertical and the horizontal types.
The vertical type is usually applied for large water-wheel generators where it is desirable to mount the water turbine below the generator. The more common horizontal type is used with diesel and steam engine drive. A low-speed alternator of this type is suitable for a diesel engine drive, a high speed alternator is suitable for a steam turbine drive.
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