Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to Q compressed-gas-insulated ~igh-voltage
switch installation having a casing enclosing the conductor carrying the
high voltage, and a compressed-gas insulated outdoor bushing, for connection
to an overhead line, in the wall of the housing enclosing the said switch
installation.
Known high-voltage switch installations, insulated with pressur-
ized SF6 gas, operate according to predetermined requirements in an ambient-
temperature range of between -25 and ~40 C. In high-voltage switch install-
ations of this kind, at -25C the pressure at which liquefaction of the
insulating agent is to be expected is 6 bars. If the pressure is 3.3 bars,
for example, then liquefaction of the insulating agent is to be expected at
about -40 C. In high-voltage switch installations of this kind, there is a
considerable increase, below this liquefaction pressure, in the cost of
achieving the required dielectric strength, and there is also a dimensional
increase.
If high-voltage switch installations of this kind are to be sub-
jected to ambient temperatures of -55 C, for example, it is usually necess-
ary to adopt special measures. A certain amount of protection against very
low temperatures may be obtained by accommodating compressed-gas-insulated
high-voltage switch installations in buildings, but problems arise when an
installation of this kind comprises a compressed-gas-insulated outdoor bush-
ing for connection to an overhead line, which is to be exposed to a minimal
temperature of the order-of -55C.
It is the purpose of the invention to provide a high-voltage
switch installation of the type mentioned at the beginning hereof which will
have economically acceptable dimensions and operating pressures and will
maintain its insulating properties even at temperatures in the -55C range.
According to the invention there is provided an indoor high-voltage
switch instal~lation having a tubular casing enclosing the conductor carrying
the high voltage and containing an insulating compressed gas and a compressed-
gas-insulated outdoor bushing for low outdoor temperatures for connection to
an overhead line, said outdoor bushing being disposed at the outer end of the
casing which penetrates the wall of a building enclosing the switch install-
ation, characterized in that a hollow conductor is provided in the outdoor
bushing, in a portion oE the casing penet:rating the wall, and at least in
an adjacent section of the casing enclosed by the building for carrying a
flow of gas, and that the said conductor comprises, in the vicinity of the
free end of the outdoor bushing on the one hand, and in the adjacent section
of the casing separated by a gas-tight supporting insulator on the other hand,
openings connecting the enclosed bushing interior and a gas chamber contained
in said adjacent casing section for the flow of gas, said Elow of gas being
set in motion by a circulating device connected to the gas chamber and to
said portion of the casing penetrating the wall which is partitioned off from
the gas chamber by the supporting insulator.
The invention makes it possible to keep the gas density within the
bushing, i.e. the dielectric strength of the compressed~gas-insulated out-
door bushing, at a specific value independent of the ambient temperature,
since the flow of gas makes it possible to heat up the outdoor bushing from
the interior of the compressed-gas-insulated high-voltage switch installation.
It i9 highly advantageous if the gas-carrying connecting lines of
; the grounded circulating device open into the partitioned-off gas chamber
casings, since this makes it possible to pass the heat loss, which occurs
~- when the conductor carrying the high voltage is under load, by means of a
flow of gas, directly to the outdoor bushing, and to return the said gas
through the insulated area between the conductor carrying the high voltage,
the casing, and the porcelain insulator of the outdoor bushing. There is
thus no need to take special precautions to insulate the grounded circulating
devices.
The circu:Lating device may be equipped with a heater in order to
ensure that the compressed-gas-insulated high-voltage switch installation,
and the outdoor bushing, remain serviceable even when the installation is
under a light load or no load at all.
An example of an embodiment of a compressed-gas-insula~ed high-
voltage installation is described hereinafter, and its method of operation
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is explained, in conjunction with the drawing attached hereto, wherein:
Figure 1 is a diagrammatic representation, in cross section, oE a
compressed-gas-insulated high-voltage switch installation;
Figure 2 shows a detail of the installation, with a compressed-
gas-insulated outdoor bushing.
In Figure 1, a compressed-gas-insulated high-voltage switch
installation is shown diagrammatically inside a housing l. As shown more
particularly in Figure 2, conductor 3, carrying the high voltage, is
enclosed in a casing 4 and has an outdoor bushing 6 which passes through wall
5 of the said housing and is intended to provide a connection to an overhead
line. It is assumed that temperatures as low as about -55 C obtain outside
housing 1. Such temperatures are capable of impairing the dielectric
strength of the parts of the installation exposed thereto, especially the
interior of the outdoor bushing, as a result of liquefaction caused by
decreasing gas density.
As shown in Figure 2, conductor 3, which carries the high voltage,
is made hollow in outdoor bushing 6, the outer casing of which may, as usual,
be made of porcelain. Conductor 3 is also hollow in a part of casi:ng 4 in
housing 1, for the purpose of carrying a flow of gas.
In the vicinîty of free end 7 of outdoor bushing 6 on the one
hand, and in an adjacent section 4a of the casing, separated by a gas-
tight supporting insulator 8 from gas chamber 9, on the other hand, the said
conductor is equipped with passages 10 through which gas Elows in the direc-
tion of the arrows shown in Figure 2, the said flow of gas being set in motion
by means of a circu:Lating device 12 which is connected to gas chambers 9 and
ll in casing section 4a. Gas-carrying connecting lines 13, 14 of the said
circulating device open, to this end, into gas chambers 9, 11. Circulating
device 12 is located within housing 1 and is-not affected by the low outside
temperature. Desirable heating of the flow of gas indicated by the arrows
may be provided by the heat released by conductor 3 when the installation is
operating at its rated load.
Circulating device 12 may, however, be equipped with a heater which
will heat up the cold insulating agent drawn from connecting line 13, thus
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ensuring effective heating of outdoor bushing 6 whenever the installation
is switched off.
The arrangement outlined above has the advantage that the ground-
ing of the circulating device presents no problems. This makes it possible
to control the heating of the gas chambers, and the circulation, without
expensive equipment. It is possible to use the temperature of the conductor
or of the gas to switch off the circulation.
The solution according to the invention has advantages in all
cases where, with existing dimensions and because of the difficulty of
increasing the pressure, industrially pure SF6 gas, or mixtures o-f gas which
liquefy at low temperatures, e.g. SF6 and nitrogen, cannot be used success-
fully, and where an effective pressure drop would require a special, large-
dimension design for low-temperature use.
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