THE ALTERNATOR

(ГЕНЕРАТОР ЗМІННОГО СТРУМУ)

      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.

II. Form nouns, denoting devices with the help of the suffix – or. Translate them

      To alternate, to commute, to conduct, to generate

III. Read the text and write out the key words, characterizing the alternator

IV. Translate the following word combinations paying attention to the Participle 2

     The leads from the armature can be continuously insulated from….., the vertical type of alternator applied for large water-wheel generator; alternators with a revoking armature and a stationary field used in small sizes mostly for special purposes; a machine driven by a source of mechanical power; the direction of an induced e. m. f. …      

V. State 5 questions to the text

VI. Points for discussion:

1. The structure of the alternator;

2. The application of the alternator.