Техническое чтение для энергетиков. Бухарова Г.П. - 26 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

28
have been forming theories on this subject. For some time they could see no real
difference between the newly-discovered phenomenon and the former understanding
of static charges. Then the famous French scientist Ampere (after whom the unit of
current was named) determined the difference between the current and the static
charges. In addition to it, Ampere gave the current direction: he supposed the current
to flow from the positive pole of the source round the circuit and back again to the
negative pole.
We consider Ampere to be right in his first statement but he was certainly
wrong in the second, as to the direction of the current. The student is certain to
remember that the flow of current is in a direction opposite to what he thought.
Let us turn our attention now to the electric current itself. The current which
flows along wires consists of moving electrons. What can we say about the electron?
We know the electron to be a minute particle having an electric charge. We also
know that that charge is negative. As these minute charges travel along a wire, that
wire is said to carry an electric current.
In addition to travelling through solids, however, the electric current can flow
through liquids as well and even through gases. In both cases it produces some most
important effects to meet industrial requirements.
Some liquids, such as melted metals for example, conduct current without any
change to themselves. Others, called electrolytes, are found to change greatly when
the current passes through them.
When the electrons flow in one direction only, the current is known to be d. c.,
that is, direct current. The simplest source of power for the direct current is a battery,
for a battery pushes the electrons in the same direction all the time (i.e., from the
negatively charged terminal to the positively charged terminal).
The letters a.c. stand for alternating current. The current under consideration
flows first in one direction and then in the opposite one, The a.c. used for power and
lighting purposes is assumed to go through 50 cycles in one second. One of the great
advantages of a.c. is the ease with which power at low voltage can be changed into an
almost similar amount of power at high voltage and vice versa. Hence, on the one
hand alternating voltage is increased when it is necessary for long-distance
transmission and, on the other hand, one can decrease it to meet industrial re-
quirements as well as to operate various devices at home.
Although there are numerous cases when d.c. is required, at least 90 per cent of
electrical energy to be generated at present is a.c. In fact, it finds wide application for
lighting, heating, industrial, and some other purposes.
One cannot help mentioning here that Yablochkov, Russian scientist and
inventor, was the first to apply a.c. in practice.
TYPES OF ELECTRIC CURRENT
An electric current may be produced in a variety of ways, and from a number of
different types of apparatus, e.g. an accumulator, a d.c. or an a.c. generator, or a

Страницы