III. Заполните пропуски, выбрав нужный вариант.
1. The speed is determined by the ... of the a.c. applied to the motor terminals. 2. The synchronous motor is an ... operated as a motor, in which a.c. is applied to the ... and d.c. is applied to the ... . 3. In the synchronous motor the rotor is synchronized with the ... ... set up by the stator. 4. The application of ... ... to the stator causes a rotating magnetic field around the rotor. 5. The strong rotating magnetic field exerts a strong ... ... on the rotor.
(three-phase a.c., rotor, stator, frequency, rotating field, turning force, alternator)
IV. Выберите из правого столбика слова и словосочетания, чтобы закончить предложения.
| 1. A major part of all electrical power generated is ... | synchronous motor |
| 2. A.C. motors can duplicate the operation of ... ... | induction motor |
| 3. A.C. motors can be designed to operate from a ... ... ... | bar magnet |
| 4. A.C. motors are classified into two types: ... ... and ... | three-phase a.c. supply |
| 5. The construction of the synchronous motor is the same as that of the ... ... | a.c., single-phase a.c. supply |
| 6. The rotor energized with d.c. acts like a ... | d.c. motors |
| 7. The speed of rotation of the magnetic field depends on the frequency of the ... ... | salient-pole alternator |
V. Найдите многокомпонентные определительные словосочетания в приведенных ниже предложениях и переведите их.
1. A.C. motors are well suited for constant-speed applications. 2. A.C. motors can be designed to operate from a multiphase a.c. supply. 3. The a.c. applied to the motor generates a rotating magnetic field. 4. The speed of rotating of the magnetic field depends on the frequency of the three-phase a.c. supply. 5. The synchronous motors are used for loads which require constant speed from no-load right through to the full-load condition.
VI. Преобразуйте данные ниже простые предложения в сложноподчиненные. Соедините главное и придаточное предложения союзами since или if. Переведите составленные вами предложения на русский язык.
Образец. The primary and secondary are connected in star. The transformer is called a "star-star". – If the primary and secondary are connected in star, the transformer is called a "star-star".
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1. The rotor is energized with d.c. It will act like a bar magnet. 2. A major part of all electrical power generated is a.c. Many motors are designed for a.c. operation. 3. A bar magnet is suspended in a magnetic field. It will turn until it lines up with a magnetic field. 4. The magnetic field turns. The rotor will turn with the field. 5. The rotating magnetic field will exert a strong turning force on the rotor. It is strong.
VII. Заполните пропуски предлогами into, with, by, for, up, from, on. Переведите предложения на русский язык.
1. Whether the motor is single-phase, it operates ... the same principle. 2. A.C. motors are generally classified ... two types. 3. The induction motor differs ... the synchronous motor. 4. We call synchronous motor so because its rotor is synchronized ... the rotating field set ... ... the stator. 5. The synchronous motors are used ... loads requiring constant speed.
VIII. Выразите согласие или несогласие с данными утверждениями, используя следующие фразы: You are quite right; I agree with you; I cannot agree with you; On the contrary (парная работа).
1. A.C. motors can hardly duplicate the operation of d.c. motors and are troublesome to operate. 2. A.C. motors are well suited for constant speed applications. 3. It is possible to design a.c. motors to operate from a multi-phase a.c. supply. 4. The induction motor differs from the synchronous motor in that it has its rotor connected to a source of power. 5. The induction motor is the most commonly used. 6. The construction of the synchronous motor differs from that of the salient-pole alternator.
IX. Расскажите о: a) типах двигателей переменного тока, b) синхронном двигателе, пользуясь набором слов и словосочетаний:
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a) to be designed, to be suited, constant-speed applications, to operate, single/multi-phase a.c. supply, to operate on the principle, to cause, synchronous motor, induction motor;
b) to be synchronized with, rotating field, to set up, bar magnet, to line up with a magnetic field, to exert a strong turning force, to be used, full-load condition.
Text 4b
The Synchronous Motor
(continued)
One of the disadvantages of a synchronous motor is that it cannot be started from a standstill by applying three-phase a.c. to the stator.
The instant a.c. is applied to the stator, a high-speed rotating field appears. This rotating field rushes past the rotor poles so quickly that the rotor does not have a chance to get started; it is repelled first in one direction and then in the other.
In other words, a synchronous motor in its pure form has no starting torque. It is usually started, therefore, with the help of a small induction motor, or with windings equivalent to this incorporated in the synchronous motor. When the rotor has been brought near to synchronous speed by the starting device, it is energized by connecting it to a d.c. voltage source. The rotor then falls into step with the rotating field.
Now you will see how single-phase a.c. applied to a stator winding will produce a pulsating magnetic field which can also be used to drive a motor.
Every time a rotor approaches a stator winding, the direction of the stator field must be such as to attract the pole, and to give it a torque in the direction of its motion. So the field current in a stator winding must pass through half a cycle in the interval between rotor poles of opposite polarity approaching the winding.
Note that small single-phase synchronous motors may use permanent-magnet rotors which do not have field windings nor require d.c. to be applied to them.
Words and Word Combinations
| disadvantage n | недостаток |
| standstill n | остановка, бездействие |
| instant 1. n 2. a | мгновение, момент; немедленный, текущий |
| rush v | устремляться, двигаться |
| past prep | мимо; за |
| repel v | отталкивать(ся), отбрасывать |
| pure a | чистый |
| starting device | пусковое устройство |
| incorporated p.p. | встроенный |
| fall into step | впадать в синхронизм, синхронизировать |
| drive v | приводить в движение |
| approach v | приближаться |
| attract v | притягивать |
| field current | ток возбуждения (ток намагничивания) |
| require v | нуждаться; требовать |
| field winding | обмотка возбуждения |
E x e r c i s e s
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I. Прочитайте слова и определите, какие из них сходны с русскими по звучанию. Переведите их на русский язык :
synchronous, disadvantage, to apply, quickly, direction, torque, induction, equivalent, to be energized, pulsating, through, half, interval, opposite, polarity, permanent, to require.
II. Найдите в тексте эквиваленты следующих слов и словосочетаний :
трехфазный переменный ток, устремляться мимо, полюса ротора, иметь возможность, заводить (запускать), пусковое устройство, приводить в движение двигатель, синхронизировать, ток возбуждения, притягивать полюс, обмотка возбуждения, нуждаться.
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