III. Вставьте в предложения нужные слова.
1. D.c. motors and d.c. generators have essentially the ... components (different, same). 2. The moving armature ... electrical power (turns, generates) in a d.c. generator. 3. In a d.c. motor the moving armature ... a mechanical load through a mechanical system of belts or gear (rotates, turns). 4. The ends of the loop connect to ... (brushes, commutator segments). 5. The direction of rotation of a motor depends on the ... of the field and current flow in the armature (direction, strength).
IV. Вставьте в предложения нужные предлоги: with, at, by, through, around, between, to, of, in.
1. The elementary d.c. generator is similar ... the elementary d.c. motor. 2. The commutator segments in turn make contact ... brushes. 3. The commutator causes the current ... the loop to reverse ... the instant unlike poles are facing each other. 4. Current flowing ... a conductor will set up a magnetic field ... this conductor. 5. The direction ... this magnetic field is determined ... the direction of current flow. 6. This force causes the armature to rotate ... a certain direction ... the field poles.
V. Задайте вопросы к дополнениям с вопросительным словом what (с предлогом или без него, обратите внимание на место предлога).
Образец. 1. Current flowing through a conductor sets up a magnetic field around it.– What does current set up?
2. A d.c. generator converts mechanical energy to electical energy. – What does a d.c. generator convert mechanical energy to?
– What does a d.c. generator convert to electrical energy?
1. D.c. motors and d.c. generators are very similar in outward appearance. 2. They differ only in the way they are used. 3. Connecting wires are leading to a source of d.c. voltage. 4. This causes a reversal of the polarity of the field. 5. The direction of this field is determined by the direction of current flow. 6. This force causes the armature to rotate in a certain direction between the field poles.
VI. Выразите согласие или несогласие с данными утверждениями (парная работа).
1. D.C. motors and d.c. generators have different components. 2. They differ in the way they are used. 3. In a motor the moving armature turns a mechanical load. 4. The commutator does not play a very important part in the operation of the d.c. motor. 5. 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.
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VII. Дайте краткие ответы на вопросы собеседника (парная работа).
Образец. 1. Is the elementary d.c. motor similar to the elementary d.c. generator? – Yes, it is.
2. Are the unlike poles facing each other at this instant? – Yes, they are.
3. Does it consist of a loop of wire between the poles of the magnet? – Yes, it does.
4. Do the ends of the loop connect to commutator segments? – Yes, they do.
1. Are d.c. motors and d.c. generators very similar in outward appearance? 2. Do they differ in the way they are used? 3. Does a d.c. generator convert mechanical energy to electrical energy? 4. Does a d.c. motor convert electrical energy into mechanical energy? 5. Do the commutator segments make contact with brushes? 6. Does the commutator play a very important part in the operation of the d.c. motor? 7. Does it cause the current through the loop to reverse at the instant unlike poles are facing each other?
VIII. Расскажите об изменении направления вращения двигателя, употребив данные слова и словосочетания:
direction of rotation (field, current flow), armature, either ... or, through the armature, however, both of the above two factors, at the same time, in the same direction, depends on, is reversed, will reverse, are reversed, will continue rotating.
Text 2
Shunt Motors
The turning moment, or torque, developed by a motor is caused by the force arising from interaction of the magnetic field around the armature coils with main field. The amount of torque developed, therefore, varies with the strength of the main field and of the armature current.
In a shunt-connected motor, the field is connected directly across the voltage source, and is therefore independent of variations in load and armature current. So the torque developed varies directly with the armature current. If the load on the motor increases, the motor, slows down, reducing the back-e.m.f. (which depends on the speed as well as on the constant field strength). The reduced back-e.m.f. allows the armature current to increase, thereby furnishing the heavier torque needed to drive the increased load. If the load is decreased, the motor speeds up, increasing the back-e.m.f. and thereby decreasing the armature current and the torque developed. Thus whenever the load changes, the speed also changes until the motor is again in electrical balance. In a shunt motor the variation of speed from no-load to normal or "full" load is only about 10 per cent of the no-load speed. For this reason, shunt motors are considered constant-speed motors.
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When a shunt motor is started the starting current is small by reason of the added starting resistance; so the starting torque will also be small. Shunt motors are used where constant speed under varying load is desired, and where it is possible for motor to start under light or no-load conditions.
Words and Word Combinations
| shunt (wound) motor | двигатель с параллельным возбуждением |
| turning moment | вращающий момент |
| torque n | крутящий (вращающий) момент |
| develop v | создавать; развивать |
| arise v | возникать, появляться |
| strength n | сила |
| independent of | независимый от |
| variation n | изменение |
| slow down v | замедлять(ся) |
| reduce v | уменьшать, ослаблять |
| back - e.m.f. | сила противодействия, противодействующая сила |
| allow v | позволять |
| thereby adv | посредством этого |
| heavy a | зд. сильный |
| needed p.p. | нужный, необходимый |
| speed up v | ускорять(ся), набирать (увеличивать) скорость |
| whenever cj | всякий раз когда |
| until prp | (до тех пор) пока не |
| add v | добавлять |
| light a | холостой, без нагрузки |
| be desired v | быть желанным (нужным) |
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E x e r c i s e s
I. Прочитайте и переведите следующие слова и словосочетания :
turning moment, torque, interaction, shunt connected motor, independent of, variation, reduce – reducing – reduced, allow.
II. Найдите в тексте эквиваленты следующих слов и словосочетаний:
вращающий момент развиваемый двигателем; сила, возникающая от взаимодействия; основное поле, поэтому не зависит от изменений в нагрузке, уменьшая противодействующую силу, более сильный, увеличившаяся нагрузка, тем самым (посредством этого) уменьшая ток якоря, пусковой ток, добавленное пусковое сопротивление, при изменяющейся нагрузке, при условиях без нагрузки.
III. Вставьте в предложения нужный предлог: of, with, from ... to, under, for, in.
1. The amount ... torque developed, therefore varies ... the strength ... the main field and ... the armature current. 2. ... a shunt motor the variation ... speed ... no-load ... normal or "full" load is only about 10 per sent ... the no-load speed. 3. Shunt motors are used where constant speed ... varying load is desired, and where it is possible ... the motor to start ... no-load conditions.
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