IV. Из правого столбика выберите нужное окончание предложений.
| 1. The armature core is slotted ... | to keep the field strength at a maximum. |
| 2. There is a small air gap between the armature and the pole pieces ... | to take the armature windings. |
| 3. This gap is kept to a minimum in order ... | to prevent rubbing between them. |
V. Данные предложения напишите, заменив пассивную форму активной.
Образец. The commutator is made up of copper segments. – Copper segments make up the commutator.
1. The generated voltage is carried to the load by brushes. 2. Each brush is connected to the external circuit by a flexible conductor. 3. Copper segments of the commutator are separated from one another and from the shaft by mica. 4. The brushes are held in place by brush holders. 5. The armature assembly is made up of the shalf, armature core, armature windings and commutator.
VI. Переведите на английский язык слова второго собеседника.
1. Do you know what the armature assembly is made up of?
2. Да, я знаю это. Якорное устройство состоит из вала, сердечника якоря, обмоток якоря и коллектора.
1. Can you tell why is the armature core laminated?
2. Конечно, могу. Насколько (as far as) я знаю, сердечник делают из пластинок, чтобы вихревые токи в сердечнике сохранялись минимальными.
1. And what is the purpose of the small air gap between the armature and pole pieces?
2. Воздушный зазор между якорем и полюсами магнита предотвращает трение между ними.
1. Why is this air gap kept to a minimum?
2. Его сохраняют минимальным, чтобы сохранять силу поля максимальной.
VII. Употребив данные слова и словосочетания, расскажите о:
– якорном устройстве – armature assembly, shaft, armature core, armature windings, commutator, slots of the core, is made up of, is laminated and slotted, to take, are wound and placed;
– щетках – brushes, commutator, generated voltage, to the load, high grade of carbon, in place, brush holders, a flexible conductor, external circuit, ride, carry, are made of, are held, connects;
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– вихревых токах – eddy currents, metal core, wire conductors, waste currents(s), useful purpose, machine, at low efficiency, it is important, to a minimum, are wound around, are (is) induced, are, have, heat, operates, be kept.
Text 6
Types of Armatures
Armatures used in d.c. generators are divided into two general types. These are the "ring" type armature and the "drum" type armature. The ring type armature was used in early designs of rotating electrical machinery, but today is seldom used.
The drum type armature is the standard armature construction today. The insulated coils are inserted into slots in the cylindrical armature core. The ends of the coils are then connected to each other at the front and back ends.
As a rule, most d.c. armatures use form-made coils. These coils are wound by machines with a proper number of turns and to the proper shape.
The entire coil is then wrapped in tape and inserted into the armature slots as one unit.
The coils are so inserted that the two legs of each coil are under unlike poles. In a two-pole machine, the legs of each coil are situated on opposite sides of the core, and therefore automatically come under opposite poles. In a four-pole machine, the legs of the coils are placed in slots (about one-quarter the distance) around the armature, thus again keeping the coils under unlike poles.
Types of Armature Winding
The windings of drum type armatures may be of two kinds, a "lap" winding or a "wave" winding.
In a lap winding the two ends of each coil are connected to adjacent commutator segments. The way in which the coils in the lap-winding are connected can be seen more easily in the diagram.
You can see that there are two points where the e.m.f.‘s in adjacent conductors are diverting – B and D. If brushes are placed at these points current will flow from the armature winding at A and C into the winding at B and C into the winding at B and D.
Brushes having the same polarity can be connected together, and the armature is thus effectively divided into four parallel paths.
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In general, the number of parallel paths through a lap winding is equal to the number of poles. The terminal e.m.f. is equal to e.m.f. induced in one path; the current delivered to the external circuit is equal to the sum of the currents in each of the parallel paths. For this reason the lap winding is used for high-current applications.
The other type of winding used on drum type armatures is the "wave" winding. In this case the connections are made so that the winding passes under every pole before it comes back to the pole from which it started.
In a simplified drawing of this winding below you will notice that in this case the winding is divided into only two parallel paths.
So, the wave winding has only two parallel current paths, and can use only two brushes regardless of the number of poles. The e.m.f. developed in a wave winding is equal to that induced in one-half of the total number of armature conductors. For this reason the wave winding is used for high-voltage applications.
Words and Word Combinations
| drum armature | барабанный якорь |
| ring armature | кольцевой якорь |
| design 1. v 2. n | проектировать; конструкция |
| machine n | машина, механизм |
| insert v | вставлять |
| as a rule | как правило |
| proper a | надлежащий |
| to the proper shape | нужной формы |
| wrap v | обертывать, завертывать |
| leg n | зд. виток |
| tape n | лента |
| unit n | блок, элемент |
| "lap" winding | петлевая обмотка |
| "wave" winding | волновая обмотка |
| adjacent a | соседний |
| way n | способ |
| divert v | расходиться, отходить |
| number n | количество, число |
| equal a | равный |
| be equal to | равняться, быть равным |
| terminal a | конечный |
| deliver to v | передавать, поставлять |
| sum n | сумма |
| for this reason | по этой причине |
| case n | случай |
| connection n | соединение |
| simplify v | упрощать |
| regardless of | не взирая на |
| develop v | зд. создавать, вырабатывать |
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