Look at Fig. 12 and speak on power generation in Russia.

Retell the text.

LESSON TEN

TRANSFORMERS

The transformer is a device for changing the electric current from one voltage to another. As a matter of fact, it is used for increasing or decreasing voltage. A simple trans­former is a kind of induction coil. It is well known that in its usual form it has no moving parts. On the whole, it re­quires very little maintenance, provided it is not misused and is not damaged by lightning.

We may say that the principal parts of a transformer are two windings, that is coils, and an iron core. They call the coil which is supplied with current "the primary winding," or just "primary" for short. The winding from which they take the current is spoken about as the "secondary winding" or "secondary", for short. It is not new to you that the former is connected to the source of supply, the latter being connected to the load.

The primary alternating current produces an alternating magnetic flux in the iron core, and this alternating magnetic flux passes through the turns of the secondary winding. Accord­ing to well-known electro-magnetic laws, this flux produces an alternating e. m. f., or voltage, in the secondary winding. In spite of the fact that there is no electrical connection be­tween the two circuits - the primary and the secondary - the application of a voltage to one is known to produce a voltage at the terminal of the other.

When the number of turns of wire on the secondary is the same as the number on the primary, the secondary voltage is the same as the primary, and we get what is called a "one-to-one" transformer. In case, however, the number of turns on the secondary winding is greater than those on the primary, the output voltage is larger than the input voltage and the transformer is called a step-up transformer. On the other hand, the secondary turns being fewer in number than the primary, the transformer is known as a step-down transformer. One should add in this connection that to "step up" means to in­crease the voltage. On the contrary, to "step down" means "to reduce".

A transformer operates equally well to increase the volt­age and to reduce it. By the way, the above process needs a negligible quantity of power. It is important to point out that the device-under consideration will not work on d. c, but it is rather often employed in direct-current circuits.

Inefficiency in a transformer is caused mainly by heat losses due not only to current flowing in the coils, but also to unwanted current induced in the core of the transformer.

 

Currents induced in the core are generally called "eddy cur­rents." The flow of eddy currents is stopped in its progress and the efficiency of the transformer is increased by constructing the transformer core of flat sheets of soft iron,

In Fig. 13 it is seen how transformers are used in stepping up the voltages for distribution or transmission over long distances and then in stepping these voltages down, where they are to be used. In this figure, one may see three large step-up transformers which are used to increase the potential to 275,000 volts for transmission over long-distance transmis­sion lines. At the consumer's end of the line, in some distant locality, three step-down transformers are made use of to reduce that value (i. е., 275,000 volts) to 2,300 volts. Local transformers, in their turn, are expected to decrease the 2,300 volts to lower voltages,

 

suitable for use with small mo­tors arid lamps. One could have some other transformers in the system, such as those to be employed for operating door bells or powering radio sets and television sets, for example. They lower the voltage even further. On the whole all radio sets and all television sets are known to use two or more kinds of transformers. These familiar examples of electronic equip­ment could not work without transformers. The facts you have been given above illustrate the wide use of transformers and their great importance.

Another alternating-current system of transmission and distribution is shown in Fig. 14. You are asked to follow the whole process,, that is, to describe it from beginning to end.

 

Exercises

1. Learn the following active words:

Damage                         повреждение

eddy current                  вихревой ток

flux                               течение, поток

induce                           вызывать, стимулировать

input                             подводимый ток

maintenance                  тех. обслуживание

output                           выход, выработка

primary                         первичный

secondary                     вторичный

2. Translate the following sentences:

(a) 1. The new discovery was much spoken about. 2. This house is lived in. 3. This apparatus is often made use of.

(b)1. The students were asked to carry on the experiment. 2. You will be given two new magazines. 3. I was told to translate the instructions.

(c) 1. This substance was supposed to have some important features. 2. This device is assumed to be the best for converting heat into work. 3. The new power plant is known to have been put into operation. 4. This invention was considered to be of great practical importance. 5. A magnetic flux is assumed to consist of magnetic lines of force taken as a whole.

3. Translate the following sentences:

1. Говорят, что этот прибор описан в предыдущей статье. 2. Считали, что ток течет от положительного потен­циала к отрицательному. 3. Говорят, что мой друг хороший математик. 4. Известно, что Ломоносов основал Москов­ский университет. 5. Кажется, что это вещество имеет некоторые другие свойства. 6. Известно, что переменный ток меняет свое направление.

4.      Form as many words as possible using suffixes and prefixes. De­fine what parts of speech the new words are and translate them:

engine, apply, differ, electrify, value, opposite, trans­former, magnet, conductance

5. Form nouns from the following verbs using either suffix –ment or -tion:

construct, develop, consider, distribute, deflect, equip, connect, require, produce, state                                                       

6. What is the English equivalent for the following:

на основе (чего-либо), теплотехника, по этой причине само собой разумеется, повышать напряжение, повышать ток, понижать ток, оказывать сопротивление

7. Arrange the following words and expressions in pairs of syno­nyms:

(a) amount, among, matter, application, at present, engine, tube

(b) now, pipe, quantity, substance, between, use, machine

8. Arrange the following words and expressions in pairs of antonyms:

(a) left, increase, beginning, d.c., above, step-up, at rest, high, short, more

(b) end, low, long, step-down, in motion, less, decrease, below, a.c., reght

9. Form statements that are not true to the fact. Ask other students
to correct them.

10. Translate the following sentences paying special attention to
the words in bold type:

1. The Fahrenheit scale is mainly used in English-speaking countries but it is not used in our country. 2. His scien­tific activity lasted but twenty years but in these twenty years he did very much.3. Motors are widely employed not only in industry but also in our daily life. 4. There is but one measuring scale in the instrument. 5. Everyone took an exam­ination in physics but that student. 6. A simple trans­former is but a kind of an induction coil.

11. Compare:

1. A solenoid and an electromagnet.

2. A direct current and an alternating current.

3. A step-up transformer and a step-down transformer.

4. A stator and a rotor.

LESSON ELEVEN

THE ELECTRIC MOTOR

The electric motor is a device employed for transforming one form of power into another, that is to say, electrical into mechanical. We know it to produce the rotary motion which turns our machinery and various appliances.

We have already seen the generator convert mechanical power into electric power. Now, the process is reversed. It is electricity that is supplied to the machine and it is motion that results. From all that has been said earlier in the previous articles about our getting magnetism from electricity and about the generation of the electric current by using magnet­ism, it is obvious that generators and motors are similar in certain respects. In case we put current into the dynamo instead of our taking current out, it will rotate as a motor. There are certainly some differences in detail but in both of them we find an armature with windings, a commutator and brushes, combined with an electromagnet for producing the magnetic field. However, in an electric motor one shunt winding is not sufficient and a second one called a series winding should be added. "Why is it necessary?" one might ask. The fact is that the motor is required to have a powerful effect at the very moment when the current is switched on, as for instance, in an electric tram or a train. A very strong magnetic field is needed to obtain a so-called powerful starting torque. This is achieved by adding a series winding to the magnet coils (Fig. 15). It is connected not in shunt with the armature but in series with it, so that all the heavy starting current passing through the armature winding, now passes

through the series field coil and provides a strong field neces­sary for starting while the shunt field winding provides the running conditions.

So far nothing was said of what a motor does in our homes. In a modern home there are many different electric motors in machines and devices utilized to meet our daily require­ments: to tell the time, to wash clothes, to cool the refrigera­tor, to clean or brush various things, to shave, to circulate air in a warm room on a hot summer day, and so on. In effect, vacuum-cleaners, washing machines, modern refrigerators,— all work thanks to electric motors. It follows that in the elec­tric motor we have a valuable and powerful appliance capable of fulfilling the required operations exactly and with just the desirable kind of motion, rate of speed, and power. It is readily switched on, at will, and it continues running until we switch it off again. In our present-day wide use of the motor there are often cases when it is simply impossible to replace it by any other suitable engine. Generally speaking, it revolution­ized industry by making use of power that can be transmit­ted from great distances.

No appliance ever created by man has probably such a wide range of size and such a variety of application as a motor. In fact, on the one hand, there are all kinds of mighty giants in the motor world. These giants are known to perform innume­rable operations in coal-mines, in steel mills, chemical facto­ries and so on, in short, in great numbers of factories and works. On the other hand, there exist all kinds of small-sized and even minute motors which are able to power various complex ma­chines. They operate equally well under any conditions: high in the air or immersed in water, lowered into a well or on the table of some famous scientist. Much of our farm equip­ment is also driven by means of electric motors. In short, they find an application wherever and whenever suitable, that is, in industry and science, in agriculture and transport.

Countless highly efficient and powerful motors construct­ed according to the latest achievements of science and engineering are widely employed in our country today.

Exercises

1. Learn the following active words:

brush                            щетка                  

coal-mine                      угольная шахта

commutator                  коммутатор

exist                              существовать

winding                         обмотка

fulfill                             выполнять

mighty                          мощный

perform                         выполнять

rate                               степень

replace                          заменять

rotary                            ротационный, вращательный

shunt                             переключение, ответвление

sufficient                       достаточный

torque                           вращающий момент

2. Translate the following sentences:

1. The flow of current being reduced, the speed of the motor is decreased. 2. It is on the above basis that all our power-plants are constructed at present. 3. We know of this substance having been used at first owing to its high quality. 4. Copper being a good conductor, we were asked to use it when carrying on our research work. 5. By changing the value of the resistance, we can increase the current. 6. Having been used for a long time, the instrument lost its former quality. 7. Were that so­lid substance heated, it would greatly expand. 8. To observe is the primary rule of any experiment. 9. The professor wants us to turn our attention to the problem of semiconductors. 10. The new invention proved to be of great practical impor­tance.

3. Define the function of the words in bold type:

1. The methods applied improved the quality of produc­tion. 2. The machine used showed good results. 3. The ex­periment described attracted everybody's attention. 4. The appliance received required some improvement. 5. The substances utilized neutralized each other. 6. The amount of electricity generated depended on the quality of the coal. 7. The scientists mentioned contributed greatly to the devel­opment of science.

4. Translate the following sentences:

1. Завтра будут получены приборы. 2. Студентам дали новые инструкции. 3. Об этих достижениях много говорят. 4. Меня попросили провести испытание. 5. Пример после­довал за правилом. 6. Нам показали новые материалы.7. Их учат иностранным языкам. 8. Вчера ответили на эти письма.

5. (a) Form verbs applying the suffix - ize:
civil, revolution, equal, neutral

(b) Form verbs applying the prefix over-:

load, throw, grow, come, estimate, power, take, run¹

(c) Form nouns applying suffixes -or, -er:

work, translate, act, speak, steam, boil, conduct, engine, fact, heat

6. Define the function of the words one and bat:

1. One hundred years ago there were neither electric lamps, nor electric motors, nor telephone, nor radio. 2. One might mention many more well-known facts and names. 3. The motor in question is more powerful than the one you spoke about yesterday. 4. There was only one problem to be solved. 5.   Everybody was present at the lecture but Michael Volkov. 6. Motors find their application not only in industry but alsc in agriculture and transport. 7. The first student answer was much better than the last one.