IV. Напишите (прочитайте) следующие предложения, поставив сказуемое в пассивной форме в прошедшем и будущем времени.
Образец. 1) These machines are called "prime movers".
These machines were called ...
These machines will be called ...
2) The parallel connection is often called "shunt".
The parallel connection was often called "shunt".
The parallel connection will be called "shunt".
1. In assembling the generator, the fields are mounted in the stator and one end housing is bolted to the stator frame.
2. The armature is then inserted between the field poles and the housing end with the brush assemblies mounted last.
V. Выразите согласие или несогласие с данными утверждениями, используя следующие фразы: Yes, it is right; No, it is wrong (парная работа).
1. If you know the components essential to the generator operation you will do fault-finding and maintenance work much easier.
2. In most d.c. generators the armature coil is mounted on the rotating part, which is then referred to as the "armature".
3. The generator itself does not convert mechanical power into electrical power.
4. The generators must have machines which will supply the mechanical energy necessary to turn the rotors.
5. The magnetic fields are not necessary for generator action.
6. Series field windings are composed of many turns of fine wire.
VI. Переведите слова одного из собеседников на английский язык.
1. Do you know what parts do all generators consist of?
2. Все генераторы состоят из вращающейся части и неподвижной части.
1. How are these parts called in d.c. generators?
2. Вращающаяся часть называется якорем, а неподвижная часть называется индуктором.
1. Can you tell what the generator itself does?
2. Я знаю, что сам генератор превращает механическую энергию в электрическую энергию.
1. And what machines supply the generators with mechanical energy?
2. Эти машины – "первичные двигатели".
VII. Расскажите об устройстве генератора постоянного тока, употребив следующие слова и словосочетания:
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d.c. generator(s), rotating part, stationary part, armature, field, mechanical energy, electrical energy, "prime mover(s)", there are, are called, converts ... into ..., is supplied by.
1. Do all generators consist of a rotating and stationary part?
2. Is the armature coil in most d.c. generators mounted on the rotating part?
3. Does the generator itself generate electricity?
4. Do shunt windings consist of turns of heavy wire?
5. Are series field windings composed of many turns of fine wire?
6. Are the magnetic fields necessary for generator action?
7. Do "prime movers" supply the electrical energy?
Text 5
D.C. Generator Construction and Operation
(continued)
Armature Assembly: In practically all d.c. generators, the armature rotates between the poles of the field. The armature assembly is made up of a shaft, armature core, armature windings and commutator. The armature core is laminated, and is slotted to take the armature windings. The armature windings are usually wound in forms and then placed in the slots of the core.
The commutator is made up of copper segments insulated from one another, and from the shaft by mica. Small slots are provided in the ends of the segments to which the armature windings are soldered. The shaft supports the entire armature assembly and rotates in the end bearings.
There is a small air gap between the armature and pole pieces to prevent rubbing between the armature and pole pieces during rotation. This gap is kept to a minimum in order to keep the field strength at a maximum.
Brushes: The brushes ride on the commutator, and carry the generated voltage to the load. They are usually made of a high grade of carbon, and are held in place by brush holders. A flexible braided conductor called a "pigtail" connects each brush to the external circuit.
You have learnt that a current flow can be induced in a conductor when it cuts through a magnetic field.
Wire conductors used in generators are always wound around metal cores, and eddy currents would be induced in these metal cores just as useful current is induced in the wires of the generator. But eddy currents are waste currents since they have no useful purpose and only heat the metal cores. Consequently, the machine operates at low efficiency. It is therefore important that eddy currents in core material must be kept to a minimum.
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This is done* by having the cores made up of laminations, or thin plates of metal, rather than out of one solid piece**. These laminations are insulated from each other, and this limits the eddy current to that which can flow in the individual lamination.
*this is done – зд. этого достигают.
** rather than out of one solid piece – a не из одного сплошного куска.
Words and Word Combinations
| armature n | якорное устройство |
| be made up of | состоять из |
| shaft n | вал |
| core n | сердечник |
| laminate v | расщеплять на тонкие слои, делать из пластин |
| slot v | прорезать пазы |
| slot n | паз, канавка, желобок |
| wind v | наматывать |
| to wind in form | наматывать по шаблону |
| segment n | пластинка |
| mica n | слюда |
| provide v | предусматривать |
| solder v | паять |
| end bearing | концевой подшипник |
| air gap | воздушный зазор |
| prevent v | предохранить, предотвратить |
| rubbing n | трение |
| keep v | поддерживать, сохранять |
| strength n | сила |
| ride on v | скользить по |
| high grade | высокая марка |
| carbon n | углерод |
| to hold in place | удерживать (на месте) |
| brush holder | щеткодержатель |
| flexible a | гибкий, эластичный, мягкий |
| braided | оплетенный |
| pigtail n | гибкий проводник |
| external a | наружный, внешний |
| eddy currents | вихревые токи |
| useful a | полезный |
| waste a | ненужный |
| purpose n | цель, назначение |
| heat v | нагревать |
| at low efficiency | с низкой производительностью |
| lamination n | пластинка |
| plate n | лист |
E x e r c i s e s
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I. Прочитайте следующие слова и переведите их на русский язык:
practically, entire, rubbing, shaft, rotation, rotates, strength, high grade, brush holder, flexible, external, eddy current, waste, efficiency, laminations, insulated, purpose.
II. Найдите в тексте эквиваленты следующих слов и словосочетаний:
якорное устройство, обмотка якоря, пазы сердечника, воздушный зазор, высокая марка углерода, можно индуцировать, полезный ток, с низкой производительностью, это делают (достигают), один сплошной кусок, отдельная пластинка, соединять с.
III. Выберите нужный предлог: between, of, from, to, by.
1. The armature rotates ... the poles ... field. 2. The armature windings are usually wound in forms and then placed in the slots ... the core. 3. The copper segments are insulated ... one another and ... the shaft ... mica. 4. There is a small air gap... the armature and pole pieces. 5. The brushes carry the generated voltage ... to the load. 6. A flexible conductor connects each brush ... the external circuit.
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