I. Read the text using a dictionary when you cannot understand any part of the text.

II. Speak on an electric motor using the text and Fig. 15.

 

 

Lesson 5.

 Text.

Transformers.

One of the great advantages in the use of the alternating currents is the ease with which the voltage may be changed by means of a relatively simple device known as a transformer. Although there are many different types of transformers, and a great variety of different applications, the principles of action are the same in each case.

The basic arrangement consists of a laminated iron core forming a closed magnetic circuit on which two separate win­dings are mounted. One winding, called the primary, is con­nected to the a. c. supply, and the other winding, the secon­dary, produces a voltage which can have any desired value if the respective windings are suitably designed.

The transformer relies for its action upon the fact that when a magnetic field passing through a coil is changed or varied a voltage is produced in the coil. The amount of this voltage is proportional to the number of turns in the coil and to the rate at which the magnetic field varies.

In general, it is approximately true that the ratio of the primary to the secondary voltage is equal to the ratio of the number of primary turns to the number of secondary turns. This ratio is not exact because of leakage effects in the mag­netic circuit.

 

Words and word combinations:

 

by means of — посредством, при помощи
in each case — в каждом случае
a.c. supply — источник переменного тока

primary winding — первичная обмотка

the transformer relies for its action upon the fact — работа трансформатора основана на

Is proportional to the number of turns — пропорционален числу витков 

It is approximately true — приблизительно верно

is equal to the ratio — равен отношению

because of leakage effects — из-за утечки

 

II. Find the following words and word combinations in the text:

 

 

Lesson 6.

Text.

Care of electrical equipment.

As a rule electrical equipment operates reliably. Still it does not mean that it deserves no attention. It is necessary to give the equipment frequent inspections, keep it well cleaned, lubri­cated and repaired. Undue heating, vibration, sparking should be immediately removed.

Heating may be due to overload or to a short circuit be­tween turns, lack of oil in bearings. Vibration may be due to unproper foundation, unbalance in the moving parts of the machine.

Conductors may get heated because of overload or by reason of damage of the insulation of the conductor.

An electrical machine of any kind requires certain condi­tions under which it may operate reliably: temperature and freedom of access of surrounding air, need for protection against dirt, dust, type and duration of load, etc.

Rotating machines should be placed on solid foundations.

Conductors should be protected against mechanical damage.

All measures of safety precaution must be undertaken.

 

Words and word combinations:

It does not mean that it deserves no attention — это не значит, однако, что он не требует никакого внимания   

keep it well cleaned — держать в чистоте      

undue heating — чрезмерное нагревание      

may be due to — может быть из-за

a short circuit between turns—короткое замыкание между витками

or by reason of damage — из-за повреждения

on solid foundation — на прочном основанииmeasures

of safety precaution —меры по технике безопасности

 

 

Lesson 7.

The Care of Motors

The only care, which is needed for home electrical motors, is to see that the bearings are properly oiled. The bearings are the supports for the two ends of the armature shaft which permit the shaft to turn.

Many recently built motors have sealed bearings. It means bearings are so constructed that they never need oiling. But look for an oil hole on each bearing of the motor in your home. Many new appliances are provided with instructions, which tell how often to lubricate the bearings and how many drops of oil to apply.

Too much oil may cause as much trouble as no oil. Oil may penetrate into the commutator and brushes. Too much oil may soften the insulation on the wires and also collect dust to prevent air circulation, thus causing the motor to heat.

Don't forget about brushes. Carbon blocks held by springs against the commutator are typical brushes, when the carbon wears out, new ones must be installed. Installing brushes on many motors is not a difficult job.

Words and word combinations:

bearings – подшибник

 armature - якорь

 shaft -вал

to apply- применять

penetrate - проникать

air circulation – циркуляция, круговорот

сarbon block – углеродистый блок

Assignment:

I. Find the following words and word combinations in the text:

Не забывайте о щетках, устанавливая щетки, приборы снабжены инструкциями, должны быть установлены, позволяет валу поворачиваться (вращаться), масло может проникать, углеродистый блок.