Техническое чтение для энергетиков. Бухарова Г.П. - 67 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

69
cores, all the limbs being of equal cross-sectional area. Each limb carries the primary
and secondary windings for one phase of the supply, and when used for connection to
a meter, the connections are usually arranged star/star.
When a transformer is switched on to a live line, the voltage between the turns of the
high-voltage winding adjacent to the line terminal may be raised momentarily to a
value many times the normal. A similar condition may arise as a result of switching
operations elsewhere on the system and in an extreme case the voltage between suc-
cessive end turns may reach a very high value; such a condition persists only for a
minute fraction of a second but it imposes an additional stress on the inter-turn
insulation which in the absence of precautionary measures may result in failure. The
stress on the insulation is greatest between the first and second turns counting from
the end of the high-voltage winding and diminishes turn by turn*** until, at some
distance from the end, the abnormal stress disappears entirely.
In power transformer practice it is customary to reinforce the insulation between the
end turns of the high-voltage winding and about ten per cent of the winding may be
dealt with in this manner. This reinforcement is graded and is heaviest on the first
few turns, but progressively less and less is added until finally reinforcement ceases,
in a voltage transformer of comparable voltage, the number of turns in the high-
voltage winding is very much greater than in a power transformer and reinforcement
of the insulation on ten per cent of the turns would be impracticable. It is customary,
however, to reinforce the insulation of the whole of the turns in the first section of the
winding. As an additional precaution, a reactance coil consisting of a few turns of
heavily-insulated wire is sometimes connected between the high-voltage terminal and
the end of the high-voltage winding. This reactance acts like a cushion between the
line and the high-voltage winding and reduces the severity of the transient stresses
without adding appreciably to the dimensions of the transformer or impairing its
accuracy.
* fine-gauge wire тонкая проволока (буквально – проволока тонкого калибра); wire gauge
сокращенно обозначается W. G. (см. ниже в тексте)
** the primary – зд. подразумевается the primary winding первичная обмотка
* turn by turn от витка к витку
ELECTRIC CAR
The electric car is not a new idea. It had success with American women in the
early 1900s. Women liked electric cars because they were quiet and, what was more
important, they did not pollute the air. Electric cars were also easier to start than
gasoline-powered ones. But the latter was faster, and in the 1920s they became much
more popular.
The electric car was not used until the 1970s, when there were serious
problems with the availability of oil. The General Motors Co. had plans to develop an
electric car by 1980. However, soon oil became available again, and this car was
never produced.
Today there is a new interest in the electric car. The Toyota Co. recently

Страницы