III. Заполните пропуски, выбрав нужный вариант.
1. When a.c. is applied to a ... ..., the current through the armature and field change simultaneously. 2. Cutting down the size of the field reduces the ... ... . 3. The a.c. series motor is a varying-speed machine with ... speeds for ... loads. 4. Fractional horsepower series motors are used for driving small ... . 5. The ... ... motor is called a "universal motor".
(low, large, appliances, series motor, a.c., d.c., motor torque)
IV. Найдите многокомпонентные определительные словосочетания в приведенных ниже предложениях. Переведите их на русский язык.
1. The number of field turns in the a.c. series motor is less than in the a.c. series motor. 2.The a.c. series motor is never built above fractional horsepower sizes for 50-cycle operation. 3. It is a varying-speed machine. 4. Fractional horsepower series motors are used for driving fans, electric drills, etc. 5. The a.c./d.c. motor finds wide application in small electric appliances.
V. Задайте вопросы, ответами на которые могут быть следующие предложения.
1. The direction of rotation remains unchanged. 2. In order to decrease the reactance of the field. 3. The characteristics of it are similar to those of the d.c. series motor. 4. It is varying-speed machine, with low speeds for large loads and high speeds for light loads. 5. It can operate both on a.c. and d.c. 6. Yes, they are built in small sizes only.
VI. Выразите согласие или несогласие со следующими утверждениями (парная работа).
1. The number of field turns in the a.c. series motor is more than in the d.c. series motor. 2. The a.c. series motor is built above fractional horsepower sizes for 50-cycle operation. 3. The characteristics of the a.c. series motor are similar to those of the d.c. series motor. 4. A universal motor finds wide application in electric appliances. 5. Universal motors operate at a higher efficiency than the a.c. and d.c. series motors.
VII. Переведите в диалоге слова второго собеседника.
1. Will you tell me why is the induction motor the most commonly used a.c. motor?
2. Я думаю, из-за простой и прочной конструкции и довольно низкой стоимости производства.
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1. Does the basic principle of the induction motor operation depend on the type of rotor used?
2. Нет, независимо от типа ротора, основной принцип операции остается тем же.
1. What single-phase motors do you know?
2. Асинхронные двигатели и двигатели с последовательным соединением.
1. It is true that series motors resemble d.c. machines?
2. Да, это так, были даже созданы двигатели с последовательным соединением, которые могут работать и на постоянном и на переменном токе.
1. Thank you kindly for your information.
U N I T 3
D.C. Motors
Text 1
Converting Electrical Power to Mechanical Power
D.C. motors and d.c. generators have essentially the same components, and are very similar in outward appearance. They differ only in the way they are used. In a generator, mechanical power turns the armature, and the moving armature generates electrical power. In a motor, electrical power forces the armature to turn, and the moving armature, through a mechanical system of belts or gears, turns a mechanical load.
A d.c. generator converts mechanical energy to electrical energy. A d.c. motor converts electrical energy into mechanical energy.
The elementary d.c. motor is similar to the elementary d.c. generator. It consists of a loop of wire between the poles of a magnet. The ends of the loop connect to commutator segments, which in turn make contact with brushes. The brushes have connecting wires leading to a source of d.c. voltage.
The commutator plays a very important part in the operation of the d.c. motor. It causes the current through the loop to reverse at the instant unlike poles are facing each other. This causes a reversal in the polarity of the field; repulsion exists instead of attraction; and the loop continues to rotate.
Text 1a
Reversing the Direction of Motor Rotation
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The direction of rotation of a motor depends on the direction of the field and the direction of current flow in the armature. Current flowing through a conductor will set up a magnetic field around this conductor. The direction of this magnetic field is determined by the direction of current flow. If a conductor is placed in a magnetic field, force will be exerted on the conductor by reason the interaction of its magnetic field with the main magnetic field. This force causes the armature to rotate in a certain direction between the field poles.
If either the direction of the field or the direction of the current flow through the armature is reversed, the rotation of the motor will reverse. However, if both of the above two factors are reversed at the time, the motor will continue rotating in the same direction.
Words and Word Combinations
| convert v | превращать |
| essentially adv | по существу |
| outward a | внешний |
| appearance n | наружный (внешний) вид |
| force v | заставлять |
| belt n | ремень |
| gear n | шестерня; привод; зубчатая передача |
| turn v | приводить в движение |
| in turn | в свою очередь |
| play a part | играть роль |
| face v | встречать |
| cause v | заставлять; вызывать |
| repulsion n | отталкивание |
| exist v | существовать; иметь место |
| attraction n | притяжение |
| set up v | создавать; собирать, монтировать |
| determine v | определять |
| exert v | влиять, действовать на |
| by reason of | по причине |
| interaction n | взаимодействие |
| above a | вышеупомянутый |
E x e r c i s e s
I. Прочитайте и переведите слова и словосочетания :
convert – converting, essentially, appearance, gears, similar, cause – causes, reverse – reversal, repulsion, exist, instead of, by reason of, interaction, in a certain direction, at the same time, the same components.
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II. Найдите в тексте эквиваленты данных слов и словосочетаний :
превращение электрической энергии в механическую, очень похожи, соединяющие провода, играет очень важную роль, это вызывает изменение, направление вращения, с главным (основным) магнитным полем, в определенном направлении.
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