XII. Describe fig. 10.

LESSON EIGHTEEN

THE COMPLEX SENTENCE

GENERATORS

The dynamo invented by Faraday in 1831 -is certainly a primitive apparatus compared with the powerful, highly ef­ficient generators and alternators that are in use today. Nev­ertheless, these machines operate on the same principle as the one invented by the great English scientist. When asked what use his new invention had, Faraday asked in his turn: "What is the use of a new-born child?" As a matter of fact, "the new born child" soon became an irreplaceable device we cannot do without.

Although used to operate certain devices requiring small currents for their operation, batteries and cells are unlikely to supply light, heat and power on a large scale. Indeed, we need electricity to light up millions of lamps, to run trains, to lift things, and to drive the machines. Batteries could not supply electricity enough to do all this work.

That dynamo-electric machines are used for this purpose is a well-known fact. These are the machines by means of which mechanical energy is turned directly into electrical energy with a loss of only a few per cent. It is calculated that they produce more than 99.99 per cent of all the world's electric power.

There are two types of dynamos, namely, the generator (Fig. 11) and the alternator. The forraer'supplies d.c. which

is similar to the current from a battery and the latter, as its name implies' provides a.c.

To generate electricity both of them must be con­tinuously provided with energy from some outside source of mechanical energy such as steam engines, steam turbines or water turbines, for example.

Both generators and al­ternators consist of the following principal parts: an armature and an elec­tromagnet. The electromag­net of a d.c. generator is usually called a stator for it is in a static condition while the armature (the rotor) is rotating. Alternators may be divided into two types: 1. alter­nators that have a stationary armature and a rotating electro­magnet; 2. alternators whose armature serves as a rotor but this is seldom done. In order to get a strong e.m.f., the rotors in large machines rotate at a speed of thousands of revolu­tions per minute (r.p.m.). The faster they rotate, the greater the output voltage the machine will produce.

In order to produce electricity under the most economi­cal conditions, the generators must be as large as possible. In addition to it, they should be kept as fully loaded as pos­sible all the time. It is interesting to note here that the big­gest generators ever installed at any hydroelectric station in the world are those installed in the USSR. As you are likely to remember the Bratsk hydroelectric station ts equipped with 225,000 kilowatt (kW) generators. Soviet scientists constructed 500,000 kW generators which are installed at the Krasnoyarsk station. The eight generators of the Ko-nakovo steam power plant which is not far from Moscow have 2,400,000 kW of rated capacity. Our industry is most likely to produce even greater power installations for the steam power plants which play such an important part in the electrification plan of the USSR. Fig. 11 shows the principles the construction of an elementary d.c. genera­tor is based upon. We see the armature, the electromagnet, the shunt winding, the commutator and the load.

If interested in plasma generators, see Supplementary Reading.

Active Words and Expressions

possible, armature, to calculate, compared with, construction, to equip, to be likely, machine, to operate, revolutions per minute (r.p.m.), to rotate, scale, speed, sta-tor, steam power plant, turbine, winding

_Exercises

У. Translate the following sentences:

1. The plants which supply electricity over long distances are equipped with large alternators. 2. When asked about the dynamo the student mentioned its inventor. 3., The exper­iments Oersted made attracted Ampere's attention. 4. The armature and the electromagnet are the principal parts the generator consists of. 5 That the electromagnets are control­lable is a very important thing, since they can attract and repel magnetic materials. 6. The alternator is a machine that generates a.c 7. A bar of iron becomes strongly magne­tized if inserted into the solenoid while the current is flowing.

//. Translate the following sentences:

1. There is a great number of engineering problems the Soviet scientists work at. 2. It is quite impossible to name a scientific problem Lornonosov did not turn his attention to. 3. There are many electric appliances we cannot do with­out. 4. The experiment I told you about will take much time.

5. The direction the needle points in changed several times.

6. The speed a given molecule travels with is greatly increased when a gas is heated.

///. Asnwer the following questions:

1. When did Faraday invent the dynamo? 2. Was Faraday an American scientist? 3. Can batteries supply power on a large scale? 4. What do we need electricity for? 5. What are dynamo electric machines used for? 6. What types of dynamos do you know? 7. What are the principal parts of a generator? 8. In what condition is the stator of an electro­magnet? 9. What generators is the Bratsk hydroelectric sta­tion equipped with? 10. How many generators are installed at the Konakovo steam power plant? 11. What is their rated capacity? 12. Do you know anything about a plasma genera­tor? 13. What does Fig. 11 show?

IV. Form adjectives using the suffixes -able, -ful, -less, -ous:

control, continue, danger, value, replace, need, power, peace, use, life

V. Form adverbs using the suffix Ay:

exact, electrical, general, gradual, negative, natural, opposite, previous, usual, easy