III. Выберите из правого столбика слова или словосочетания, чтобы закончить предложения.
| 1. The windings are spaced so that the voltage induced in any one is ... ... | star connection delta connected |
| 2. Three leads coming out of the three-phase alternator are connected together to form ... ... | alternators phase voltage |
| 3. If the phases are connected end-to-end in a three-phase stator, it is called ... ... | three-phase alternators |
| 4. In the delta connection the line voltages are equal to the ... ... | phase-displaced |
| 5. The "star" and the "delta" connections are used for ... | |
| 6. The most efficient alternators are ... ... ... |
IV. Найдите многокомпонентные определительные словосочетания в приведенных ниже предложениях и переведите их на русский язык.
1. The three-phase alternators have three single-phase windings. 2. Most of the alternators used now are three-phase-winding machines. 3. It is common to use three-phase transformers with three-phase alternators. 4. The transformer is called a "delta-delta" transformer if the primary and secondary are connected in delta. The total voltage across any two line leads is the vector sum of the individual phase voltages.
V. Заполните пропуски предлогами up, in, between, of, for, to, with. Переведите предложения на русский язык.
1. The point ... connection is called a neutral. 2. The windings form only one path ... current flow ... phases. 3. In the delta connection the line voltages are equal ... the phase voltage. 4. The "star" and the "delta" connections are used ... alternators. 5. Three-phase transformers are used ... connection ... three-phase alternators. 6. A device is made ... ... three single-phase transformers.
VI. Выразите согласие или несогласие с данными утверждениями, используя следующие фразы: You are quite right; I agree with you; I am afraid you are not right; On the contrary (парная работа).
1. The voltage induced in any of three single-phase windings is phase-displaced by 180 degrees from the other two. 2. Three leads, one from each phase, are connected together to form a "star" connection. 3. The line voltage is 2.73 times the phase voltage. 4. When the windings form only one path for current flow between phases, the line and phase currents are not equal. 5. The line currents are equal to the vector sum of the phase currents. 6. Two-phase and single-phase alternators are more efficient than three-phase alternators.
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VII. Расскажите о трехфазном генераторе переменного тока, пользуясь набором слов и словосочетаний:
to be spaced, to be phase-displaced, lead, "star" connection, line voltage, vector sum, to be equal, "delta" connection, to be out of phase, primary, secondary, transformer.
VIII. Переведите ответы собеседника с русского языка на английский, употребив выражения: You are quite right, As far as I know, As a rule.
– What is the a.c. generator?
– Это самое важное средство для производства электроэнергии.
– A voltage is generated when there is relative motion between a conductor and a magnetic field, isn’t it?
– Да, вы абсолютно правы.
– And what types of alternators do you know?
– Насколько я знаю, существуют два типа генераторов переменного тока: с вращающимся якорем и вращающимся полем.
– What can you say about the prime mover for alternators of high ratings?
– Как правило, это высокоскоростная паровая турбина, приводимая в движение паром под высоким давлением.
Text 4
Types of A.C. Motors
Since a major part of all electrical power generated is a.c. many motors are designed for a.c. operation. A.C. motors can, in most cases, duplicate the operation of d.c. motors and are less troublesome to operate.
A.C. motors are particularly well suited for constant-speed applications, since the speed is determined by the frequency of the a.c. applied to the motor terminals. A.C. motors are also made, however, which have variable speed characteristics within certain limits.
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A.C. motors can be designed to operate from a single-phase a.c. supply or from a multi-phase a.c. supply. Whether the motor is single-phase or multi-phase, it operates on the same principle. This principle is that the a.c. applied to the motor generates a rotating magnetic field, and this rotating magnetic field causes the rotor of the motor to turn.
A.C. motors are generally classified into two types: (1) the synchronous motor and (2) the induction motor. The synchronous motor is an alternator operated as a motor, in which a.c. is applied to the stator and d.c. is applied to the rotor. The induction motor differs from the synchronous motor in that it does not have its rotor connected to any source of power.
Of the two types of a.c. motors mentioned, the induction motor is by far the most commonly used.
Text 4a
The Synchronous Motor
The synchronous motor is so called because its rotor is synchronized with the rotating field set up by the stator. Its construction is essentially the same as that of the salient-pole alternator. You know that the application of three-phase a.c. to the stator causes a rotating magnetic field to be set up around the rotor. But since the rotor is energized with d.c., it will act like a bar magnet. If a bar magnet is suspended in a magnetic field, it will turn until it lines up with a magnetic field. In the same way, the energized rotor of a synchronous motor, acting like a magnet, will line up with the magnetic field caused by the application of three-phase a.c. to the stator. If the magnetic field turns, the rotor will turn with the field. If the rotating magnetic field is strong, it will exert a strong turning force on the rotor, which will therefore be able to turn a load as it rotates.
The speed of rotation of the magnetic field depends on the frequency of the three-phase a.c. supply.
The synchronous motors are used for loads which require constant speed from no-load right through to the full-load condition.
Words and Word Combinations
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| major a | больший |
| design v | предназначать |
| case n | случай |
| duplicate v | дублировать |
| troublesome a | трудный |
| particularly adv | очень, особенно |
| suit v | годиться, подходить |
| application n | применение |
| determine v | определять |
| frequency n | частота |
| terminal n | зажим, ввод |
| supply n | подвод, подача, питание |
| synchronous motor | синхронный двигатель |
| induction motor | асинхронный двигатель |
| differ v | отличаться |
| source n | источник |
| by far | намного |
| commonly adv | обычно; зд. широко |
| synchronize v | синхронизировать, совпадать по времени |
| set up v | воздвигать, обеспечивать |
| cause v | вызывать |
| energize v | пропускать ток |
| har magnet | стержневой магнит |
| line up v | выравниваться, располагаться на одной оси |
| exert v | вызывать |
| turning force | вращательное усилие; вращающая сила |
| full load | полная нагрузка |
E x e r c i s e s
I. Прочитайте слова и определите, какие из них сходны с русскими по звучанию. Переведите их на русский язык :
major, to be designed, to duplicate, troublesome, particularly, to be determined, frequency, variable, characteristics, to supply, to cause, generally, to be classified, to be synchronized, application, magnet, through, condition.
II. Найдите в тексте эквиваленты следующих слов и словосочетаний :
синхронный двигатель, асинхронный двигатель, менее трудный, определить скорость, подача переменного тока, действовать по принципу, отличаться от, источник энергии, широко использоваться, совпадать по времени, вызывать, стержневой магнит, располагаться на одной оси, полная нагрузка, постоянная скорость, вращающая сила.
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