V. Найдите многокомпонентные определительные словосочетания в приведенных ниже предложениях. Переведите их на русский язык.

1. The rotor is a self-contained unit. 2. A "squirrel-cage winding" is made up of heavy copper bars. 3. The rotor gets as close to the moving stator field as its weight and its load will allow. 4. The rotating magnetic field generated in the stator induces an e.m.f. in the rotor. 5. The induction motor is commonly used because of its robust construction and low manufacturing cost.

VI. Заполните пропуски предлогами in, between, to, by, up, from.

1. The induction motor derives its name... the fact that a.c. currents are induced... the rotor circuit. 2. A "squirrel-cage winding" is made... of a heavy metal ring. 3. No insulation is required... the core and the bars. 4. The current in the rotor circuit is caused... this induced e.m.f. 5. If a.c. is applied... the stator windings, a rotating magnetic field is generated. 6. The rotor moves... the same direction as the stator field.

VII. Определите функцию выделенных слов. Переведите предложения на русский язык.

Образец: сonnecting – причастие I, определение; used – причастие II, определение; is connected – причастие II, часть простого глагольного сказуемого.

1. The induction motor is a laminated cylinder with slots in its surface. 2. No insulation is required between the core and the bars because of the very low voltage generated in the rotor bars. 3. The rotating field cuts the bars of the rotor. 4. An induced current tries to oppose the changing field. 5. The force excerted on the rotor by the reaction between the rotor and the stator fields will set about trying to cancel out the continuous motion of the stator field.

VIII. Выразите свое согласие или несогласие с данными утверждениями, используя следующие фразы: You are quite right; I agree with you; I’m afraid you are not right; You are wrong (парная работа).

1. The induction motor is not commonly used. 2. The stator construction of the induction motion and of the synchronous motor is different. 3. The air gap between the rotor and the stator is kept very small to obtain maximum field strength. 4. Since the stator field is rotating continuously, the rotor cannot line up with it, but must always follow along behind it. 5. The rotor and the stator move in different directions and never line up with each other.

IX. Дайте характеристику aсинхронного двигателя, пользуясь набором слов и словосочетаний:

simplicity, robust construction, source of voltage, laminated cylinder, winding, slots, core, bars, "wound rotor", to induce, current, rotor circuit, to set up, to induce a current, conductors of the rotor, to line up.

Induction motors are designed for three-phase, two-phase, or single-phase operation. But in every case the a.c. applied to the stator must generate a rotating field which will pull the rotor with it.

You have already seen how three-phase a.c. applied to a three-phase symmetrically distributed winding will generate a rotating magnetic field. A two-phase induction motor has its stator made up of two windings placed at right angles to each other around the stator.

If the voltages applied to phase A-AI and B-BI are 90 degrees out of phase, the currents which will flow in the phases will be displaced by 90 degrees. Since the magnetic fields generated in the coils will be in phase with their respective currents, the magnetic fields will also be 90 degrees out of phase with each other. These two out-phase magnetic fields, whose coil axes are at right angles to each other, will add together at every instant during their cycle to produce a resultant field which will rotate one revolution for each cycle of a.c.

From 180 degrees to 360 degrees the resultant magnetic field rotates through another half-cycle and completes a revolution.

Thus, by placing two windings at right angles to each other, and by exciting three windings with voltages 90 degrees out of phase, a rotating magnetic field can be created.

I. Прочитайте слова и назовите те, которые сходны с русскими по звучанию:

to design, to pull, symmetrically, to distribute, angle, axe, cycle, resultant, revolution, to complete, to excite, to create, already, phase.

II. Найдите в тексте эквиваленты следующих слов и словосочетаний:

генерировать поле, двухфазный асинхронный двигатель, прямой угол, расположиться под прямым углом, не совпадающий по фазе, перемещаться на 90 градусов, складывать(ся), результирующее поле, круговое вращение, завершить оборот, создать поле.

III. Заполните пропуски, выбрав нужный вариант.

1. The a.c. applied to the stator must... a rotating field which will... the rotor with it. 2. A two-phase induction motor has its stator...... of two windings... at right angles to each other around the stator. 3. The voltages... to phases A-AI and B-BI are 90 degrees out of phase. 4. The magnetic fields... in the coils will be in phase with their respective currents. 5. From 180 to 360 degrees the magnetic field... through a half-cycle and... a revolution.

IV. Найдите многокомпонентные определительные словосочетания в приведенных ниже предложениях. Переведите их на русский язык.

1. Three-phase a.c. applied to a three-phase symmetrically distributed winding generates a rotating magnetic field. 2. Two out-of-phase magnetic fields add together at every instant during their cycle. 3. A two-phase induction motor has its stator made up of two windings. 4. The resultant magnetic field rotates through another half-cycle, completes a revolution from 180 to 360 degrees.

V. Соедините парные простые предложения в одно сложноподчиненное, употребив союзы: since, how, which, if, whose.

1. The a.c.... is applied to the stator must generate a rotating field. 2. You know... three-phase a.c. applied to a three-phase winding will generate a rotating magnetic field. 3.... the voltages are 90 degrees out of phase, the currents will be displaced by 90 degrees. 4.... the magnetic fields generated in the coils will be in phase with their respective currents, the magnetic fields will also be 90 degrees out of phase with each other. 5. Two out-of-phase magnetic fields,... coil axes are at right angles to each other, will add together.

VI. Расскажите об устройстве двухфазного асинхронного двигателя, пользуясь набором следующих слов и словосочетаний:

to be designed, to generate a rotating field, to be placed at right angles, to be out of phase, respective currents, to produce a resultant field, to complete a revolution, to excite a winding.

A single-phase induction motor has only one phase, and runs on single-phase a.c. This motor is extensively used in applications which require small low-output motors. The advantage gained by using single-phase motors is that in small sizes they are less expensive to manufacture than other types. Also they eliminate the need for three-phase a.c. mains. Single-phase motors are used in communication equipment, fans, refrigerators, portable drills, grinders, etc.

Single-phase motors are divided into two kinds: (1) induction motors and (2) series motors. Induction motors use the squirrel-cage rotor and a suitable starting device. Series motors resemble d.c. machines in that they have commutators and brushes.

A single-phase induction motor has only a stator winding. This winding generates a field which can be said to alternate along the axis of the single winding, rather than to rotate.

When the rotor is stationary, the expanding and collapsing stator field induces currents in the rotor which generate a rotor field. The opposition of these exerts a force on the rotor, which tries to turn it 180 degrees from its position. But since this force is exerted through the centre of the rotor, the rotor does not turn.

But if something starts the rotor turning, the turning force in that direction is aided by the momentum of the rotor. The rotor will increase speed until it turns nearly 180 degrees for each alternation of the stator field. For remember that, since slip is necessary to cause an induced rotor current, at maximum speed the rotor must turn slightly less than 180 degrees every time the stator field reverses polarity.

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. They are therefore less efficient than three-phase or two-phase motors whose torque is more uniformly acting.

I. Прочитайте слова и назовите их русские эквиваленты:

single-phase, extensively, application, to gain, expensive, to manufacture, to eliminate, equipment, refrigerator, to be divided, machine, to exert, necessary, slightly, to reverse, pulsating, therefore, efficient, uniformly, grinder.

II. Найдите в тексте эквиваленты следующих слов и словосочетаний:

работать на однофазном переменном токе, маломощный двигатель, получать преимущество, менее дорогостоящий, исключать необходимость, вентилятор, двигатель с последовательным соединением, пусковое устройство, переключатель, пытаться, сжимающийся, расширяющийся, увеличить скорость, немного повернуться, благодаря (чему-либо), действовать равномерно.

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