III. Выберите из правого столбика слова или словосочетания, чтобы закончить предложения.
| 1. A single-phase induction motor has only one ... | stator winding |
| 2. Single-phase motors eliminate the need for three-phase a.c. … | rotor |
| 3. Induction motors use squirrel-cage ... | phase |
| 4. Series motors resemble ... ... | mains |
| 5. A single-phase induction motor has only one ... ... | d.c. machines |
| 6. A single-phase induction motor developes a pulsating ... | torque |
IV. Найдите многокомпонентные определительные словосочетания в приведенных ниже предложениях. Переведите их на русский язык.
1. A single-phase induction motor runs on single-phase a.c. 2. Communication equipment, refrigerators, potable drills etc. require small low-output motors. 3. If the rotor is stationary, the expanding and collapsing stator field induces currents in the rotor which generate a rotor field. 4. Since the field due to the single-phase a.c. voltage applied to the stator winding is pulsating, single-phase a.c. induction motors develop a pulsating torque.
V. Измените приведенные ниже предложения так, чтобы указанные в новых предложениях действия относились к будущему и прошедшему времени.
Образец. The resultant magnetic field completes a revolution.
1. The resultant magnetic field will soon complete a revolution (Future Indefinite).
2. The resultant magnetic field completed a revolution (Past Indefinite).
1. A single-phase induction motor has only one stator winding. 2. The opposition of the fields exerts a force on the rotor. 3. The rotor increases speed until it turns nearly 180 degrees for each alternation of the stator field. 4. At maximum speed the rotor turns slightly less than 180 degrees every time the stator field reverses polarity.
VI. Задайте вопросы, ответами на которые могут быть следующие предложения.
1. This motor is mainly used in applications which require small low-output motors. 2. Single-phase motors are divided into induction motors and series motors. 3. Of course, they resemble d.c. machines in that they have commutators and brushes. 4. Yes, a single-phase induction motor has only stator winding. 5. The opposition of the fields exerts a force on the rotor which tries to turn it 180 degrees from its position. 6. Because the field due to the single-phase a.c. voltage applied to the stator winding is pulsating.
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VII. Выразите согласие или несогласие со следующими утверждениями (парная работа).
1. A single-phase induction motor is used in applications which require high-output motors. 2. Induction motors use a suitable starting device and the squirrel-cage rotor. 3. Series motors have nothing in common with d.c. machines. 4. If we have a stationary rotor, the expanding and collapsing stator field induces currents in the rotor which generate a rotor field. 5. Single-phase a.c. induction motors are more efficient than two- or three-phase motors because their torque acts less uniformly.
VIII. Расскажите об однофазном двигателе, его достоинствах и недостатках, пользуясь набором следующих слов и словосочетаний:
to run, low-output motors, advantage, to eliminate the need, induction motor, series motor, stator winding, to alternate, stationary rotor, to exert a force, turning force, to be aided, to cause a current, to develop a pulsating torque, less efficient, to act uniformly.
Text 8
A.C. Series Motors
You learnt that if the d.c. current through a series motor field and armature is reversed, the direction of rotation remains unchanged. When a.c. is applied to a series motor, the current through the armature and field change simultaneously and, therefore, the motor will rotate in one direction.
The number of field turns in the a.c. series motor is less than in the d.c. series motor, in order to decrease the reactance of the field so that the required amount of current will flow. Cutting down the size of the field reduces the motor torque. Therefore the a.c. series motor is never built above fractional horsepower sizes for 50-cycle operation.
The characteristics of the a.c. series motor are similar to those of the d.c. series motor. It is a varying-speed machine, with low speeds for light loads. The starting torque is also very high. Fractional horsepower series motors are used for driving fans, electric drills and other small appliances.
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Since the a.c. series motor has the same general characteristics as the d.c. series motor, a series motor has been designed which can operate both on a.c. and d.c. This a.c./d.c. motor is called a "universal motor", and finds wide application in small electric appliances. Universal motors operate at a lower efficiency than either the a.c. or d.c. series motors and are built in small sizes only.
Words and Word Combinations
| remain v | оставаться |
| simultaneously adv | одновременно |
| in order | для того, чтобы |
| reactance n | реактивное сопротивление, реактивность |
| amount n | количество |
| fractional a | менее одной л.с. |
| similar a | подобный, сходный |
| vary v | изменять(ся) |
| appliance n | прибор |
| application n | применение |
E x e r c i s e s
I. Прочитайте слова и назовите те, которые сходны с русскими по звучанию. Переведите их :
armature, rotation, to be applied, simultaneously, direction, to decrease, reactance, fractional, operation, characteristics, load, light, machine, appliance, general, to design, universal, either, size, horsepower, to remain.
II. Найдите в тексте эквиваленты следующих слов и словосочетаний :
направление вращения, одновременно, уменьшить реактивное сопротивление поля, требуемое количество, двигатель с последовательным соединением менее одной л.с., универсальный двигатель, электрический прибор, широкое применение.
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