Note: Descriptions are shown in the official language in which they were submitted.
2164481
Se 23.12.1994 94/183
TITLE OF THE INVENTION
High-voltage installation
BACKGROUND OF THE lNV~N'l'lON
Field of the Invention
The invention proceeds from a high-voltage
installation according to the preamble of claim-1.
Discussion of Backqround
High-voltage installations which have a
grounded, metallic enclosure which is filled with
insulating gas, for example SF6, and whose internal
surface situated opposite the high-voltage-carrying
active parts is provided with a protective coating are
known. Said protective coating is intended to render
said surface smooth, inter alia so that it can be
cleaned without fibers or other residues of cleaning
aids being retained by surface roughness of the
internal surface, as a result of which the dielectric
strength of the gas-insulating gap would be reduced.
For the same reasons, the surface of the active parts
is also frequently provided with a similar protective
coating in such installations.
The publication DE 41 20 309 A1 discloses a
high-voltage installation having a metallic enclosure
which is filled with insulating gas and surrounds the
voltage-carrying active parts. Provided on the
internal surface of the enclosure, and also on the
external surface of the active parts, is a partly
multilayered protective coating. In this high-voltage
installation, a reduction in the dielectric strength of
the insulating-gas gaps as a result of freely mobile or
fixed particles can occur only to a limited extent.
However, these protective coatings are, as a rule,
unsuitable for converting chemically active switching
residues or aggressive decomposition products into
nonhygroscopic substances.
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In modern high-voltage installations of the
type described above, insulating parts composed of
quartz-powder-filled or glass-fiber-reinforced casting
resin are used only to a limited extent since the
decomposition products of the insulating gas filling
the high-voltage installation attack the silicates of
the filling or reinforcement. If sulfur hexafluoride
(SF6) is used as the insulating gas, as is now mostly
the case, in particular the hydrofluoric acid (HF)
which is then produced acts in a particularly
aggressive manner on the silicates. If such an
insulating part is coated with one of the conventional
protective lacquers, said protective coating can only
somewhat delay the penetration of the aggressive
decomposition products. As experiments showed,
conventional protective layers 100 ~m to 200 ~m thick
had an inadequate protective action of only one to
three hours' duration at room temperature. If a
longer-lasting protection of the insulating part is to
be achieved, the protective-lacquer layer has to be
applied more thickly, which necessitates an expensive
application of a plurality of lacquer layers each
having intervening drying processes. A lasting
protection against said aggressive decomposition
products cannot, however, be achieved in this way.
SUMMARY OF THE INVENTION
Accordingly, as it is defined in the
independent claims, one object of the invention is to
provide a novel high-voltage installation having a
protective layer which is impermeable to liberated,
chemically aggressive decomposition products, in
particular hydrofluoric acid, during the service life
of the installation.
The advantages achieved by the invention are
essentially to be seen in the fact that solid-state
insulators having silicate-cont~;ning fillers can now
be provided with a protective layer which prevents,
with great reliability, the aggressive decomposition
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products, in particular the hydrofluoric acid, from
being able to attack the silicate-containing fillers
and thus being able to weaken the insulator
mechanically and dielectrically. It is a substantial
economic advantage if said solid-state insulators,
which can be produced comparatively inexpensively, can
now also be used in an aggressive environment with the
aid of a protective layer which is simple to apply.
It is furthermore advantageous that, on the
one hand, the aggressive decomposition products are
rendered harmless and that, consequently, the number of
freely mobile particles in the insulation gaps is
reduced at the same time.
The aggressive decomposition products
penetrating into the protective layer are reliably
converted into nonhygroscopic, electrically insulating
substances which are bound in the protective layer.
The high-voltage installation is provided
with a metallic housing which is filled with insulating
gas and surrounds voltage-carrying active parts. In
addition, it is provided with insulators for the
electrically insulating support of the active parts in
the housing and with drive means formed in an
electrically insulating manner for the actuation of the
mobile sections of the active parts. The insulators
and the drive means formed in an electrically
insulating manner are coated with a protective coating.
The protective coating is formed in such a way that
decomposition products formed in the insulating gas
during the operation of the installation penetrate into
the protective coating, and it has at least one
component which reacts with the decomposition products
to form at least one solid, nonhygroscopic and
electrically insulating reaction product.
The at least one component is given the form of
a nanostructured material. Al203 or MgO are provided
as the nanostructured material. An epoxy lacquer or a
lacquer based on polyester, on acrylic resin or on
polyurethane is provided as the base for the protective
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coating. However, it is also possible to use a resin
which is provided with a polyester (PETP) fiber
reinforcement as the base for the protective coating.
This type of protective coating is particularly
advantageous, since it then can be used, for example,
as the base for the filament winding of an insulating
tube.
The component to be added in the form of a
pigment makes the surface of the protective coating
matt, thus advantageously improving at the same time
the adherence of further layers of the protective
coating which may additionally be applied.
Further refinements of the invention are the
subject of the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention,
its development and many of the attendant advantages
thereof will be readily obtained as the same becomes
better understood by reference to the following
detailed description when considered in connection with
the accompanying drawings, which represent merely one
embodiment and wherein:
Fig. 1 shows a first partial section through a high-
voltage installation according to the invention,
Fig. 2 shows a second partial section through a high-
voltage installation according to the invention, and
Fig. 3 shows a partial section through an insulating
tube, for example an explosion chamber insulating tube.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like
reference numerals designate identical or corresponding
parts throughout the several views and all elements not
necessary for a direct understanding of the invention
are omitted, in Fig. 1 a first, greatly simplified
partial section through a high-voltage installation
according to the invention is shown. A substantially
cylindrically constructed metallic housing 1 of a
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pressure-tight design encloses an interior space 2
which is filled with pressurized insulating gas, for
example SF6. Arranged in the center of the housing 1
are voltage-carrying active parts 3, shown in a very
simplified form. The housing 1 is connected in a
pressure-tight manner by means of a flange connection 4
to a further, substantially cylindrically constructed
metallic housing 5 of a pressure-tight design. This
housing 5 also encloses a further interior space 6
which is filled with pressurized insulating gas, for
example SF6. Arranged in the center of the housing 5
are voltage-carrying active parts 7, shown in a very
simplified form. The two interior spaces 2 and 6 are
separated from each other here by a partitioning
insulator 8 which is of a disk-shaped design and is let
into the flange connection 4 in a pressure-tight
manner. The partitioning insulator 8 has a disk-shaped
insulator body 9, into which a cast-in fitting 10 is
cast in a pressure-tight manner. The cast-in fitting
10 is connected electrically conductively to the active
parts 3 and 7. The partitioning insulator 8 supports
the active parts 3 and 7 against the housings l and 5.
The interior spaces 2 and 6 are subjected to
decomposition products which are formed, for example,
by arcs generated in power switches or other switchgear
(not shown).
The insulator body 9 has been produced here
from quartz-powder-filled and/or glass-fiber-reinforced
casting resin. The surfaces of the insulator body 9
are provided with in each case a protective coating 9,
which may be of a single-layered or multilayered
composition. In the figure, the protective coating 11
is shown comparatively thick, for the sake of better
viewing clarity; as a rule, the individual layers of
these protective coatings 11 have thicknesses of a
few ~m to about 100 ~m. Greater thicknesses of the
protective coatings 11 are achieved by repeated
application of the corresponding layer, if appropriate
with intervening drying processes. The surfaces of the
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active parts 3 and 7 are coated entirely or partially
with one of the conventional protective layers 12. The
internal surfaces of the housings 1 and 5 are coated
entirely or partially with one of the conventional
protective layers 13. However, it is also possible,
instead of these protective layers 12 or 13, to apply
entirely or partially protective coatings having a
material composition corresponding to that of the
protective coating 11. Furthermore, it is conceivable
to coat the protective coatings 12 or 13 entirely or
partially with a further protective coating whose
material composition corresponds to that of the
protective coating 11.
In Fig. 2, a second, greatly simplified partial
section through a high-voltage installation according
to the invention is shown. The substantially
cylindrically constructed metallic housing 1 of a
pressure-tight design encloses the interior space 2
which is filled with pressurized insulating gas, for
example SF6. Here too, voltage-carrying active parts,
shown in a very simplified form, are arranged in the
center of the housing 1. Shown here as an active part,
for example, is a disconnector 14. The disconnector 14
has a movable contact 15, which slides in a guiding
part 16, and a fixed mating contact 17, which is set up
for receiving the movable contact 15. Both the guiding
part 16 and the fixed mating contact 17 are positioned
in the housing 1 by insulators (not shown), which are
designed as partitioning insulators or as supporting
insulators provided with openings. The movable contact
15 is moved out of an insulating material in the axial
direction by a drive rod 18 connected displaceably to
it. The drive rod 18 is actuated by means of a drive
shaft 19 mounted in a rotatable and pressure-tight
manner in the housing 1. The drive driving the drive
shaft 19 is not shown. The drive rod 18 may also have
other forms.
The electrically insulating drive rod 18 has
been produced here from quartz-powder-filled or glass-
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fiber-reinforced casting resin. The surfaces of the
drive rod 18 are provided completely with a protective
coating 11, which may be of a single-layered or
multilayered composition. In the figure, the
protective coating 11 is shown comparatively thick, for
the sake of better viewing clarity; as a rule, the
individual layers of these protective coatings 11 have
thicknesses of about 50 ~m to a few 100 ~m. Greater
thicknesses of the protective coatings 11 are achieved
by repeated application of the corresponding layer, if
appropriate with intervening drying processes.
Various types of power switches which are used
in gas-insulated switching installations have explosion
chambers with pressure-resistant, electrically
insulating explosion chamber tubes. These explosion
chamber tubes may also be produced from quartz-powder-
filled and/or glass-fiber-reinforced casting resin if
they are coated with the protective coating 11. In
Fig. 3, a partial section through such a cylindrically
designed explosion chamber tube 20 is shown, which tube
has a center axis 23. The explosion chamber tube 20
has in addition a wall 21, the outside of which is
coated with a protective coating 11 if this tube is
used in a metal-enclosed gas-insulated switching
installation. If the tube is used in an SF6 switch
which is intended for outdoor installation, this outer
protective coating 11 is not necessary. In the case of
the explosion chamber tube 20, the internal surface is
provided with a further protective coating 22, which
either has the same composition as the mentioned
protective coating 11 or which, for example in the case
of explosion chamber tubes 20 wound on a winding
mandrel, is formed as a polyester-fiber-reinforced
resin layer, a chemically reactive component comprising
at least one very finely dispersed pigment being
admixed with the resin before processing. These
pigment particles are distributed homogeneously in the
resin. However, a PETP-fiber nonwoven together with an
epoxy resin with which corresponding pigment particles
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have been admixed may also be used. In the production
of such explosion chamber tubes 20, as a rule first of
all the fiber reinforcement is applied in the form of a
nonwoven to the winding mandrel, this nonwoven is then
impregnated with the polyester resin. The pigment
particles distributed homogeneously in the polyester
resin have such small dimensions that they cannot be
arrested by the nonwoven, i.e. the pigment particles
are also distributed homogeneously in the finished
protective coating 22. Thereafter, the wall 21 is
wound onto this protective coating 22 in a known way,
and after the curing of this wound composite part the
protective coating 11 is applied on the outside.
The base for the protective coating 11 is
formed in each case by a lacquer which has a
comparatively high surface resistance and consequently
a good creep resistance; furthermore, it must be
chemically resistant to aggressive decomposition
products and be thermally resistant. In addition, the
lacquer must not be hygroscopic. An acrylic lacquer or
a lacquer based on polyester or based on polyurethane
or based on epoxy resin is frequently used, but other
types of lacquer are also conceivable, depending on the
intended application. The chemically reactive
component in the form of very finely dispersed pigments
is admixed with the lacquer before processing. As a
rule, 3 to 30 percent by weight of this component are
admixed.
Depending on the area of use of the protective
coating 11, various, correspondingly prepared
substances may be used as the very finely dispersed
pigments, such as for example carbides, nitrides and
metal oxides such as ZnO, Fe203, Bi2o3, PdO, AgO, TeO,
CuO~ Sb23~ Ti2~ ZrO2, Al203, In2O3, SnO, V20s and
MgO. For use in metal-enclosed gas-insulated switching
installations which are filled with SF6 gas, A1203
and/or MgO can be used particularly advantageously.
The A1203, or the MgO, is prepared with the aid of one
of the known processes such that particles in the
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nanosize range are produced; these particles have a
size of about 5 nm to 50 nm. A particle size of 25 nm
has been found to be particularly favorable with regard
to the behavior of the particles in the chemical
S reaction. With this particle size, the pigment
fraction in the lacquer achieves an effective surface
area of an optimum size without however over-thickening
the lacquer, which would hinder its processing.
1st exemplary embodiment:
Nano-Al2O3 type C of the Degussa company,
Frankfurt, FRG, is used as the very finely dispersed
pigment. An acrylic resin, to be mixed from two
components A and B, of the Dold company, CH-8304
Wallisellen, Switzerland, is provided as the lacquer.
parts by weight of the lacquer component A,
designated by IB-16/A, product number F 5190, are used.
The lacquer component A is mixed with 3 to 30 percent
by weight, based on the finished lacquer, of nano-Al2O3
type C to form a mixture. The mixture is
advantageously storable in a closed container, since
the pigment is of such a fine form that it cannot
settle in this mixture. 1 part by weight of the
lacquer component B of the acrylic lacquer, designated
by IB-16/B, product number F 5191, is admixed with the
mixture. The resulting lacquer ready for processing
may be diluted, if need be, with xylene, with ethyl
acetate or with general purpose thinner.
The admixture of 30 percent by weight of nano-
Al2O3 results in a protective coating 11 with a matt
surface. This matt surface is to be regarded as having
good grip and particularly well suited for permiting a
further layer of the protective coating 11 to adhere
particularly well. The thickness of the individual
layers is dependent on the consistency of the lacquer;
in the dry state, a thickness in the range from 40 ~m
to about 80 ~m is aimed for. As the top layer, as a
rule the protective coating 11 receives a pigment-free
varnish, permiting particularly good cleaning of the
coating.
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In the case of this exemplary embodiment, the
particle size of the admixed nano-Al2O3 type C was
20 nm. Protective coatings 11 produced with this
lacquer and of a total thickness of about 200 ym have
kept decomposition products of the SF6 gas away from
the insulator body 9 protected therewith for more than
ten hours. Fatigue tests accordingly show clearly
better results than the tests with customary lacquers.
These fatigue tests have not yet been concluded at
present.
The effectiveness of the chemically reactive
component contained in the lacquer and in the form of a
very finely dispersed pigment is evident from the
following reaction equation:
Al2O3 + 6HF ~ 2AlF3 + 3H2O
The hydrofluoric acid HF is converted into the solid,
nonhygroscopic compound AlF3, rem~; n; ng in the
protective coating, and into water. The water leaves
the lacquer coating and is rendered harmless by the
active filter in connection with the respective
interior space of the metal-enclosed gas-insulated
high-voltage switching installation. The compound AlF3
is electrically insulating; the insulation strength of
the partitioning insulator 8 is not adversely affected
by this compound remaining in the protective coating
11 .
2nd exemplary embodiment:
An approximately 60 mm wide strip of polyester
(PETP) nonwoven is wound with half overlap around a
winding mandrel. After completion of the winding, this
arrangement is impregnated with a mixture of
cycloaliphatic epoxy resin with nanostructured MgO. Of
the nanostructured MgO, 3 to 30 percent by weight were
admixed. The curing of the resin to form the
protective coating 22 took place under reduced
pressure. Then, a glass-fiber-reinforced plastics tube
tGRP) was wound onto this protective coating 22 in the
conventional filament-winding process. After curing of
this blank, a plastics tube which has on the inside a
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protective coating 22 with a reinforcement of a
polyester (PETP) nonwoven is obtained. If this
plastics tube is intended for installation in a
metal-enclosed gas-insulated switching installation,
its outside is also provided with a protective coating
11 .
The effectiveness of this very finely dispersed
pigment contained in the lacquer is evident from the
following reaction equation:
MgO + 2HF ~ MgF2 + H2O
The hydrofluoric acid HF is converted into the solid,
nonhygroscopic compound MgF2, remaining in the
protective coating 22 or 11, and into water. The water
leaves the lacquer coating and is rendered harmless by
the active filter in connection with the respective
interior space of the metal-enclosed gas-insulated
high-voltage switching installation. The compound MgF2
is electrically insulating; the insulation strength of
the explosion chamber tube 20 is not adversely affected
by this compound rP~; n; ng in the protective coating 22
or 11.
In contrast to the use of very finely dispersed
Al2O3, the use of very finely dispersed MgO offers the
additional advantage that the penetration time of the
gaseous hydrofluoric acid (HF) is extended by more than
double. Further fatigue tests are also envisaged with
protective coatings 22 of such a form.
It may, however, also be advisable not only to
provide the insulators with the protective coating 11,
but additionally to provide the protective coating 11
in a region or in several regions of the high-voltage
installation, to be precise in particular wherever
switching gases or other switching residues can occur
in a particularly concentrated form.
The electrically insulating parts produced from
quartz-powder-filled and/or glass-fiber-reinforced
casting resin have a particularly high mechanical
strength; now, thanks to the protective coating 11, 22,
this advantageous material can also be used in gas-
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insulated switching installations, in particular also
in SF6-filled high-voltage installations, which brings
with it considerable commercial advantages.
Furthermore, it is conceivable also to coat
with a protective coating 11 outdoor insulators
produced from quartz-powder-filled and/or glass-fiber-
reinforced casting resin, in order to protect these
insulators better against environmental effects in this
way. It is also possible, with the aid of chemically
suitable components, to adapt the protective coating 11
to particularly critical environmental effects, in
order to extend their service life advantageously in
this way.
In the metal-enclosed gas-insulated switching
installations, the aggressive decomposition products
occur as a rule only during a limited time after the
respective switching operations, since in these
installations there are provided active filters which
continuously clean and dehumidify the insulating gas.
The protective coatings 11 and 22 are therefore
subjected to the aggressive decomposition products in
each case only during this limited time. In addition
to this is the fact that the decomposition products,
which although diffused into the protective coating 11,
22 have not yet been chemically converted, diffuse out
of the protective coatings 11, 22 again when the
concentration of the aggressive decomposition products
in the insulating gas of the high-voltage installation
has reduced. The chemical effectiveness of the nano-
pigments incorporated in the protective coatings 11, 22is accordingly preserved over a comparatively long
period of time. If the application thickness of the
protective coatings 11, 22 is increased, and possibly
also the number of successively applied coatings, the
duration of effect of the coatings can be further
extended. In the metal-enclosed gas-insulated
switching installations, it is always ensured that the
contamination time, during which the aggressive
decomposition products act on the protective coatings
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11, 22, accumulated during the entire service life of
the installation is significantly less than the
effective time of these coatings. The protective
coatings 11, 12 accordingly need not be renewed before
the end of the normal service life of the installation.
The metal-enclosed gas-insulated switching
installations, which are designed for above-averagely
frequent switching actions, are provided with
correspondingly adapted protective coatings 11, 22, so
that insulating parts of silicate-cont~;n;ng materials
can be used without any problems in these high-voltage
installations as well.
In contrast to the use of very finely dispersed
Al2O3, the use of very finely dispersed MgO offers the
additional advantage that the penetration time of the
gaseous hydrofluoric acid tHF) is extended by more than
double.
If pigments with a coarser structure than the
described nanostructure are used, the chemical
effectiveness is somewhat impaired; however,
applications where such a coarser structure can be used
advantageously are quite conceivable. Furthermore, it
is also possible to use pigments which have a coarser
structure, mixed with nanostructured material, in order
to achieve in this way a specific adaptation to
particular given operational requirements.
Obviously, numerous modifications and
variations of the present invention are possible in
light of the above teachings. It is therefore to be
understood that, within the scope of the appended
claims, the invention may be practiced otherwise than
as specifically described herein.
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LIST OF DESIGNATIONS
1 Housing
2 Interior space
5 3 Active parts
4 Flange connection
Housing
6 Interior space
7 Active parts
10 8 Partitioning insulator
9 Insulator body
Cast-in fitting
11 Protective coating
12, 13 Protective layer
15 14 Disconnector
Movable contact
16 Guiding part
17 Mating contact
18 Drive rod
20 19 Drive shaft
Explosion chamber tube
21 Wall
22 Protective coating
23 Center axis
