Техническое чтение для энергетиков. Бухарова Г.П. - 56 стр.

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58
"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 and the alternator. The
former 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.
Fig. 7 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. Alternators may be divided into two types: 1. alternators that
have a stationary armature and a rotating electromagnet; 2. alternators whose ar-
mature serves as a rotor but this is seldom done. In order to get a strong e.m.f., the ro-
tors 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 Bratskaya hydroelectric station is equipped
with 225,000 kilowatt (kW) generators. Soviet scientists constructed more powerful
generators which are installed at the Krasnoyarskaya station. The Konakovskaya, the
Zaporozhskaya and the Uglegorskaya steam power-stations have large rated capacity.
Our industry produces even greater power installations of 1,200 MW for the steam
power plants which play such an important par, in the electrification plan of the
USSR.
POWER TRANSMISSION
They say that about a hundred years ago, power was never carried far away from
its source. Later on, the range of transmission was expanded to a few miles. And

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