IV. Заполните пропуски, выбрав нужный вариант.
1. A compound generator is a ... series and shunt generator (designed, combined). 2. This voltage ... is undesirable where constant voltage loads are used (drop, increase). 3. If the series windings are so proportioned that the terminal voltage is practically ... at all loads it is "flat-compounded" (different, constant). 4. An "overcompounded" generator has its series fields so selected that the full-load voltage is ... than no-load voltage (greater, less). 5. The "undercompounded" machines are ... used (often, seldom).
V. Задайте вопросы, употребив вопросительное слово where (обстоятельство места).
1. One shunt coil and one series coil are always mounted on a common pole piece. 2. Compound generators were designed to overcome the drop of terminal voltage which occurs in a shunt generator when the load is increased. 3. Usually in flat compounded generators the full-load voltage is the same as the no-load voltage. 4. In a differentially compounded generator the shunt and field coils are in opposition.
VI. Выразите согласие или несогласие с данными утверждениями, употребив выражения : I cannot agree with you ; I am afraid you are not right; You are quite right; I agree with you (парная работа).
1. There are two sets of field coils in a compound generator – one in series with the armature, and one in parallel with the armature. 2. If the series field is connected so that its field aids the shunt field the generator is called "differentially" compound. 3. The voltage characteristic of the cumulative compound generator depends on the ratio of the turns in the shunt and field windings. 4. Flat-compounded generators are used to provide a constant voltage to loads far away from the generator. 5. The increase in terminal voltage does not compensate for the drop in the long feeder lines. 6. Most cumulative compound generators are flat-compounded. 7. The terminal voltage can always be controlled by varying a field rheostat in series with the shunt field.
VII. Расскажите о назначении генераторов смешанного возбуждения, употребив данные слова и словосочетания:
сompound generator, the drop in terminal voltage, shunt generator, load, voltage drop, undesirable, constant voltage loads, lighting systems, by adding the series field, the strength of the total magnetic field, load current, due the added current, through the armature resistance, constant voltage output, overcomes, occurs, is increased, is, are used, increases, is, are used, increases, is overcome, is attained.
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U N I T 2
ALTERNATORS AND A.C. MOTORS
Text 1
Alternators
The a.c. generator is the most important for the production of electrical power.
A.C. generators, or "alternators", vary greatly in size depending on the power they are required to supply. For example, the alternators used in atomic energy power stations are very large, generating hundreds of kilowatts at very high voltages.
Regardles of size, however, all electrical generators, whether d.c. or a.c., depend for their operation on the action of a coil cutting through a magnetic field, or of a magnetic field cutting through a coil. As long as there is relative motion between a conductor and a magnetic field, a voltage will be generated.
In order that relative motion may take place between a conductor and a magnetic field, all generators are made up of two mechanical parts – a rotor and a stator.
You know that in a d.c. generator the revolving part is always the armature. In an a.c. generator, however, this is not usually true.
There are two types of alternators – the revolving-armature type and the revolving-field type. The revolving-armature type alternator is similar in construction to the d.c. generator in that the armature rotates through a stationary magnetic field. But in the d.c. generator, the e.m.f. generated in the armature windings is converted into d.c. by means of the commutator; whereas in the alternator, the generated a.c. is brought to the load unchanged, by means of slip rings.
The revolving-armature alternator, however, is only found in alternators of small power rating, and is not generally used.
The revolving-field type of alternator has a stationary armature winding and a rotating field winding. The advantage of having a stationary armature winding is that the generated voltage can be connected directly to the load. Fixed connections are much more easily insulated than would be slip rings at very high voltages; so high-voltage alternators are usually of the rotating field type.
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The maximum current which can be supplied by an alternator depends on the maximum heating loss which can be sustained in the armature. This heating loss heats the conductors, and if excessive, destroys the insulation. Alternators are rated in terms of this current as well as in terms of voltage output. That is to say, every alternator rating is expressed in volt-ampers (or, in the case of large machines, in kilovolt-amperes) of the apparent power which the alternator can supply.
Words and Word Combinations
| alternator n | генератор переменного тока |
| means n | средство, способ |
| by means of | посредством |
| generate v | производить, генерировать |
| regardless a | невзирая на, не считаясь с |
| depend on v | зависеть от |
| cut through v | включать через |
| relative a | относительный |
| conductor n | проводник |
| as long as adv | пока |
| revolving a | вращающийся |
| similar a | сходный, похожий |
| rotate v | вращаться |
| stationary a | неподвижный, постоянный |
| e.m.f. – electromotive force | электродвижущая сила |
| winding n | обмотка |
| convert v | превращать |
| commutator n | преобразователь тока |
| load n | нагрузка |
| slip a | контактный |
| ring n | кольцо |
| power rating | номинальная мощность |
| however cj | однако, тем не менее |
| advantage n | преимущество |
| connect v | соединять |
| сonnection n | связь, соединение |
| directly adv | прямо, непосредственно |
| fixed a | неподвижный |
| insulate v | изолировать |
| insulation n | изоляция |
| since cj | так как |
| encounter v | встретиться |
| supply v | подавать, подводить |
| heating loss | тепловые потери |
| heat v | нагревать |
| sustain v | поддерживать |
| excessive a | чрезмерный |
| destroy v | разрушать, нарушить |
| rate v | рассматривать, расценивать |
| rating n | (номинальная) мощность |
| in terms of | с точки зрения |
| output n | мощность, выработка |
| apparent power | кажущаяся мощность |
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E x e r c i s e s
I. Прочитайте следующие слова и назовите глаголы, от которых они образованы. Переведите их на русский язык :
generator, production, alternator, operation, conductor, construction, connection, insulation.
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