Note: Descriptions are shown in the official language in which they were submitted.
CA 02263881 2004-12-16
Description
A Hermetically Sealed Vacuum Load Interrupter
Switch with Flashover Protection Features
The invention relates to a load interrupter
switch in accordance with the preamble of Claim 1.
Such load interrupter switches are known, for
example, as switch-disconnectors in railway operations.
In this case, in the closed position the vacuum
interrupter chamber is connected electrically in
parallel, together with the switching mechanism
accommodated in an insulating housing, to the traction
circuit designed for the full nominal equipment
current. During disconnection, the main contacts
firstly open when de-energized and in the process
commutate the current onto the series circuit,
connected in parallel, of the vacuum interrupter
chamber and auxiliary switching point, which has an
actuating fork. As soon as the main contacts have moved
apart far enough from one another, the vacuum
interrupter chamber is quickly actuated via a tilting
mechanism, a d the breaking arc occurring in the
interior of the interrupter chamber is reliably
extinguished at the first current zero without
appearing externally.
However, it has proved in practice that the vacuum
interrupters or interrupter chambers used have
CA 02263881 2006-03-17
la
relatively large dimensions and are attended by high
production costs. Consequently, for some time use has
been made of vacuum interrupter chambers of a lower
voltage series than that for which the switche is
designed. It is therby possible to reduce both the
CA 02263881 2006-03-17
2
dimensions and he production costs, the active part in
the vacuum interrupter chamber generally permitting such
use.
However, the reduction in overall size is also
attended by reduction in the spacing of the metallic end
plates of the housing of the vacuum interrupter chamber.
The external insulation, which is stressed during and
after the disconnection, is, however, therefore
insufficient in the case of free air in the surroundings.
In order to solve this problem, the vacuum
interrupter chambers are arranged in a medium of higher
dielectric strength. It is possible in this case to
apply, inter alia, insulating oil, for example mineral
oil or silicone oil, various esters or an insulating gas
such as, for example, sulphurhexafluoride (SF6). These
media displace the air in the surroundings of the vacuum
interrupter chambers and, since they have a high
dielectric strength, an external flashover is prevented.
However, these media have the disadvantage of
not being unobjectionable with regard to their
environmental compatibility. Since such load interrupter
switches have been in use over many years, leaks due to
ageing of components an don the basis of external
influences cannot be completely ruled out. It is
therefore possible in some circumstances for medium to
escape into the surroundings.
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2a
A further disadvantage of such media is that
they require continuous monitoring. In the case of the
use of insulating oil it is necessary, for example, to
check the oil level, and since such load interrupter
switches are installed on high masts in most cases of
use, a corresponding outlay is required here. The
situation is similar in the case of insulating gas, in
the case of which the pressure must be checked.
Furthermore, it is also known to improve the
external insulation of the vacuum interrupter chambers by
encapsulation using epoxy resin, for example.
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However, ageing processes can lead in this case to an
air gap and thus to an external flashover of the vacuum
interrupter chamber in the region between the epoxy
resin casing and the outer housing. Such ageing
processes give rise, for example, to stress cracks due
to after-shrinkage of the cast resin jacket,
embrittlement due to loss of effectiveness by
flexibilizers which were used during encapsulation, or
the formation of gaps by detachment of the resin jacket
from the outer housing of the vacuum interrupter
chamber as a consequence of differential material
expansion during frequent alternating stress between
hot and cold. This risk cannot therefore be entirely
removed. A further disadvantage resides in the fact
that such an encapsulated vacuum interrupter chamber
can be accessed in the case of dismounting only by
destroying the enclosure.
The embodiments known so far are therefore
complicated and can be employed only conditionally for
universal use, for example on overhead line towers, or
are frequently rejected because of possible
endangerment of the environment.
Document FR-2 698 481 A1 discloses a load
interrupter switch having a vacuum interrupter chamber,
an electrically insulating body made from silicone
being arranged between the housing of the vacuum
interrupter chamber and an outer housing. Said silicone
body is tubular and has elastically deformable ribs
either on the outside or on the inside. It is made so
that it simultaneously makes intimate contact with the
outer surface of the interrupter chamber housing and
the inner surface of the outer housing. The aim here is
to achieve an absence of a gap in order to avoid an
electric flashover. In addition, it is possible during
mounting to introduce an insulating grease in the
region between the interrupter chamber housing and the
inside of the silicone body, while the ribs on the
AMENDED SHEET
CA 02263881 2001-09-14
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outside are compressed at least slightly in order to
produce a seal.
German Utility Model G 93 14 754 U1 has
disclosed a vacuum interrupter having an encapsulation
resistant to internal pressure. The encapsulation of
this vacuum interrupter comprises an inner coating made
from a hard foam plastic, and an outer burst-proof
jacket. The inner coating, preferably consisting of a
polyurethane foam, is uniformly porous, in order, in
accordance with the teaching of this document, to permit
the best possible thermal insulation, so that in the case
of failure a temperature sufficient to ignite the
surrounding gas cannot be reached. The burst-proof
jacket is constructed as a wound body, and comprises
threads or strips which are impregnated with a cured
plastic. It is constructed bearing tightly against the
foam coating and dimensioned such that it can absorb the
bursting force which occurs in the event of a fault
inside the vacuum interrupter.
In the case of this prior art, as well,
sheathing of the interrupter includes a permanently
foamed plastic material whose properties can be impaired
by ageing. In particular, embrittlement or detachment of
the foam coating from the outer housing of the
interrupter can occur. In addition, this encapsulated
vacuum interrupter can be dismounted only given
destruction of the enclosure.
It is therefore an object of an aspect of the
invention to create a load interrupter switch which is
reliably capable of use over a long time without
monitoring and can, in addition, be dismounted.
According to one aspect of the invention, there
is provided a load interrupter switch for voltages above
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1 kV, having a vacuum interrupter chamber whose contacts
are closed or opened by means of a switching mechanism,
the vacuum interrupter chamber having a housing with
metallic end plates which encloses the switching contacts
situated in the vacuum, and a cylindrical housing middle
part made from an electrically insulating material, which
housing is surrounded by a coating which is made from a
dielectric material and grips the edges of the two end
plates behind, it being the case that provided on the
outside of the dielectric coating is a jacket of
complementary construction, which is made from insulating
material and pressurizes the outer circumference of the
dielectric coating, characterized in that the dielectric
coating is formed by a prefabricated sleeve which
consists of an elastomeric material of high dielectric
strength which is pressed against the housing without a
__ ,___ _ _______.___ ,_,.....__.,... ....~..r,~.... ,~ ~~..,o ~~,.vor.
CA 02263881 2006-03-17
Furthermore, impairment of the environment by
escaping media is thereby avoided, as a result of which
the load interrupter switch according to the invention
can be used, for example, without objection in protected
5 water gathering grounds as well. A continuously useable
load interrupter switch which can be universally employed
is thereby provided.
A further advantage resides in that mounting
the load interrupter switch according to the invention is
substantially simplified. Thus, the construction with a
prefabricated sleeve
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5a
permits preassembly of the arrangement, which means there
is no need for outlay on final mounting or filling, for
example high up on the mast. Since no liquid or gaseous
medium is handled, there is a substantial simplification
in the complexity of transporting and installing the load
interrupter switch according to the invention.
The load interrupter switch according to the
invention is at the same time simple to produce and can
be dismounted if required. In addition, the space
requirement and the costs for the vacuum interrupter
chamber can be kept low.
It is also advantageous when, on the outside of
the sleeve, a pressure housing of complementary
construction is provided, which is made from insulating
material and pretensions the outer circumference of the
sleeve in the elastic region. The result of this, on the
one hand, is that the sleeve presses firmly against the
vacuum interrupter chamber, and further that no air gap
which could permit an external flashover is produced on
the outer circumference of the sleeve. The possible path
length for an external flashover is virtually no longer
possible. Safe working conditions and the reliability of
the load interrupter switch are thereby further
increased. Furthermore, the vacuum interrupter chamber
is thereby centred and fixed in the pressure housing.
Advantageous developments of the invention
follow from the feature s of the subclaims.
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Owing to the fact that the dimensions of the
sleeve are selected such that the sleeve applies
pretensioning to the vacuum interrupter chamber, the
creation of an air gap between the sleeve and the
housing of the vacuum interrupter chamber is reliably
prevented. Consequently, the relatively large
dimensional tolerances of the vacuum interrupter
chamber can also be compensated. The reliability of the
load interrupter switch is thereby further increased.
Furthermore, sealing of the pressure housing
with respect to external influences is achieved when
the sleeve has at least one sealing bead which runs in
the axial direction of the pressure housing and comes
to lie in the mounting joint of the pressure housing.
The consequence of this is reliably to avoid the
possibility of dirt and in particular water, for
example, penetrating into the pressure housing. Failure
of the load interrupter switch can thus be effectively
avoided. Furthermore, the unipartite construction of
the sleeve with the sealing bead facilitates the
mounting of the arrangement.
If, in addition, the sealing bead has a
thickened part which can be pinched in the mounting
joint of the pressure housing, the reliability of this
seal on the pressure housing is further increased.
The risk of an external flashover is still further
reduced by virtue of the fact that circumferential shields are
provided which project on the outer circumference of the sleeve in
a fashion essentially parallel to the end plates.
AMENDED SHEET
F
CA 02263881 2006-03-17
6a
It is further advantageous when the sleeve has
at least one cut-out for holding sleeve material
displaced during the pressure loading. The result of
this is that the sleeve bears cleanly against the
circumferential surface of the vacuum interrupter chamber
without the sleeve being damaged by the pressure forces
applied. The reliability of the load interrupter switch
i c thoroh~r fmrt-hAr i nrraacar~
CA 02263881 1999-02-18
_ ) _
The at least one cut-out is advantageously
constructed as a circumferential annular groove in the
inner periphery of the sleeve. A uniform pressure
distribution over the entire circumference of the
vacuum interrupter chamber is thereby achieved.
If the sleeve is provided with at least one
pocket on at least one end face in the region of at
least one end plate, it is possible for the length of
the vacuum interrupter chamber to be set in the mounted
state without damage to the material of the sleeve,
since said material can escape into the at least one
pocket. The reliability of the sleeve, and thus the
operational reliability of the load interrupter switch
is thereby increased.
If the at least one pocket is, moreover,
constructed annularly, the result is a uniform
distribution of the pressure load on the end face of
the sleeve.
The sleeve according to the invention is
preferably made from EPDM (ethylene-propylene
terpolymer) or silicone rubber, which have good elastic
properties and are also incompressible. Such materials
permit reliable sealing of the interface between the
vacuum interrupter chamber and the sleeve and/or
between the sleeve and the pressure housing of the load
interrupter switch. An external flashover can thereby
be reliably avoided.
By virtue of the fact that the load interrupter
switch is constructed as a switch-disconnector in the
case of which a visible isolating distance is arranged
in series with the vacuum interrupter chamber, it is
also possible to carry out visual monitoring from a
relatively large distance in order to determine whether
the load interrupter switch is closed.
If in the closed state of the load interrupter
switch a circuit for high continuous current-carrying
capacity is connected in parallel with the vacuum
interrupter chamber or in parallel with the series
circuit of the vacuum interrupter chamber/visible
CA 02263881 1999-02-18
isolating distance, the vacuum interrupter is relieved
when the load interrupter switch (switch-disconnector)
is in the closed state. This has the advantage that the
existing high voltages are applied to the vacuum
interrupter chamber only during the switching
operations. In this case, a continuous current can be
conducted which is higher than the rated current of the
interrupter chamber or the series circuit of the vacuum
interrupter chamber and visible isolating distance. The
service life of the load interrupter switch is thereby
substantially increased.
The invention is explained below in more detail
in an exemplary embodiment with the aid of the figures
of the drawing, in which:
Fig. 1 shows a sectional representation of a load
interrupter switch according to the invention,
it being the case that a section in the parting
plane of the pressure housing is represented on
the left-hand side of the main axis, and a
section in another plane through a half housing
of the pressure housing is represented to the
right of the main axis; and
Fig. 2 shows a simplified sectional representation in
accordance with the line A-A in Fig. 1.
In accordance with the representation in the
figures, a load interrupter switch 1 has a pressure
housing with two half housings 11 and 12 which are
constructed from insulating material and in an
essentially mirror-symmetrical fashion. Arranged in the
half housings 11 and 12 are, inter alia, a vacuum
interrupter chamber 2 and a switching mechanism 3. The
mode of arrangement and the functioning of the vacuum
interrupter chamber 2 and the switching mechanism
correspond to the known embodiments, for which reason a
detailed explanation is dispensed with in this
connection. What is essential is that in the interior
the vacuum interrupter chamber 2 has switching contacts
which are closed or opened by the switching mechanism
3. For this purpose, the switching mechanism 3 is
CA 02263881 1999-02-18
_g_
constructed with an eccentric actuating element 31
which acts on a moveable contact 21 of the vacuum
interrupter chamber 2.
In addition to the moveable contact 21, the
vacuum interrupter chamber 2 has a stationary contact
22 which is arranged opposite the moveable contact 21.
The vacuum interrupter chamber 2 further has a housing
23 which is provided with metallic end plates 24 and 25
which seal a cylindrical housing middle part 26. The
housing middle part 26 is produced from electrically
insulating material. Prevailing inside the vacuum
interrupter chamber 2 is a high vacuum which ensures
reliable are interruption in the case of disconnection,
and reliable voltage stability in the disconnected
state.
In order to ensure that no external flashover
of the voltage occurs between the end plates 24 and 25
of the vacuum interrupter chamber 2, a sleeve 4 made
from EPDM (ethylene-propylene terpolymer) is arranged
around the vacuum interrupter chamber 2. This sleeve 4
is constructed in this case in such a way that it
embraces the edges of the two end plates 24 and 25 of
the vacuum interrupter chamber 2. Furthermore, the
dimensions of the sleeve 4 are selected such that
tolerance deviations in the vacuum interrupter chamber
2 can be compensated, and the sleeve 4 nevertheless
bears under pretensioning against the circumferential
surface of the vacuum interrupter chamber 2.
Consequently, there is no continuous air gap between
the end plates 24 and 25.
The sleeve 4 is, in turn, embraced and
pretensioned by the half housings 11 and 12 of the load
interrupter switch 1. Because of the pretensioning, no
air gap which would permit an external flashover of the
voltage between the end plates 24 and 25 of the vacuum
interrupter chamber 2 exists between the sleeve 4 and
the mounted half housings 11 and 12.
In accordance with the representation in
Fig. 1, the sleeve 4 has annularly constructed shields
CA 02263881 1999-02-18
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41 which are held in corresponding cut-outs in the half
housings 11 and 12. The shields 41 serve in a known way
to lengthen the path (leakage path) along the surface.
The sleeve 4 also has four cut-outs 42, which
are arranged on the inner circumferential surface and
have an annular configuration. When the half housings
11 and 12 are closed, pressure is exerted on the sleeve
4 and, since the latter is produced from an elastomeric
material which is elastic but essentially
incompressible, the cut-outs 42 permit the material of
the sleeve 4 to escape into the free spaces thereby
formed. This prevents damage to the sleeve 4 and
results in good sealing of the interface between the
sleeve 4 and the vacuum interrupter chamber 2.
Furthermore, an annular pocke t 43 is
constructed at the end of the sleeve 4 which grips over
the end plate 25 in the region of the stationary
contact 22. Since vacuum interrupter chambers 2 have
relatively large length tolerances, it is necessary in
some circumstances to set the length and/or position of
the vacuum interrupter chamber 2 in the load
interrupter switch 1. In order to permit the
deformation of the sleeve 4 necessary for the purpose
in this end face region, the annular pocket 43 serves
as a chamber for equalizing the volume of the displaced
material.
In accordance with the representation in
Fig. 2, the sleeve 4 further has a sealing bead 44 with
a thickened part 45. These are arranged in each case on
the two mounting joints of the half housings 11 and 12
of the load interrupter switch 1 for the purpose of
sealing with respect to external influences. The
thickened part 45 is held in this case in
correspondingly constructed depressions or grooves on
the joint surfaces of the half housings 11 and 12, and
pinched when the half housings 11 and 12 are closed.
The sealing bead 44 with the thickened part 45 in this
case has a length which corresponds essentially to the
total length of the sleeve 4. However, it can also be
CA 02263881 1999-02-18
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constructed in the entire mounting j oint region of the
half housings 11 and 12 in one piece with the sleeve 4
as a cord for sealing the pressure housing.
When the load interrupter switch 1 is opened in
operation, the contacts 21 and 22, which are under
pretensioning by springs, are released by the switching
mechanism 3, with the result that they open the
switching contacts in the vacuum interrupter chamber 2.
Because of the high voltage applied, which can be
45 kV, for example, depending on the application, the
arrangement tends to seek a path for a possible
discharge of voltage through an arc. This is not
possible inside the vacuum interrupter chamber 3
because of the vacuum.
Since the sleeve 4 bears under pretensioning
against the housing 23 of the vacuum interrupter
chamber 2 and is connected, likewise under
pretensioning, to the pressure housing of the load
interrupter switch 1, there is no air gap present which
would permit a voltage flashover. A flashover through
the material of the sleeve 4 is likewise not possible
because of the high dielectric strength of the material
used for the sleeve 4. Such an external flashover is
therefore prevented.
In an example of use, the load interrupter
switch is used as a switch-disconnector and arranged in
series with a visible isolating distance. In this
arrangement, a traction circuit designed for continuous
load current is connected in parallel with the vacuum
interrupter chamber and an auxiliary switching point
connected in series with the latter, as a result of
which the vacuum interrupter is relieved with the
switch-disconnector switched through. To disconnect the
switch-disconnector, the first step is to open the main
contact in the known way, resulting in the voltage
being conducted completely across the vacuum
interrupter chamber 2. Subsequently, the contacts 21
and 22 of the vacuum interrupter chamber 2 are
separated and the connection is completely interrupted
CA 02263881 1999-02-18
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without an arc flashover being able to form in the load
interrupter switch 1.
The invention permits further approaches to
configuration in addition to the exemplary embodiment
set forth here.
The dimensions and configuration of the sleeve
4 can vary, depending on the design and type of
construction of the vacuum interrupter chamber 2. It is
essential in each case in this regard that the sleeve 4
bears against the vacuum interrupter chamber 2 in such
a way that no air gap is possible therebetween.
The sleeve 4 need not be constructed with
shields 41, but can also have an outer circumferential
surface which is of a different configuration or smooth
if it allows the safety of the load interrupter switch
1, for example on the basis of low prevailing voltages.
In the example shown, the cut-outs 42 in the
sleeve 4 have semicircular cross sections and are
constructed at four points around the vacuum
interrupter chamber 2. Both the configuration and
number of the annular cut-outs 42 can deviate from
this. Furthermore, it is also possible to provide the
cut-outs 42 with an annular configuration, instead of
the embodiment shown, at points on the inner
circumferential surface of the sleeve 4.
The pocket 43 in the sleeve 4 can also be
provided on both end faces. Moreover, the configuration
and the number of pockets 43 can vary in a way similar
to that in the case of the cut-outs 42.
The sleeve 4 can be used in an arbitrary way in
conjunction with vacuum interrupter chambers 2,
something which also includes switching elements other
than switch-disconnectors. Thus, use i~ circuit-
breakers and the like is also conceivable.
The pressure housing can also comprise more
than two part housings, the number of the sealing beads
44 being matched to the number of the mounting joints.
Furthermore, it is also possible to provide in
parallel with the vacuum interrupter chamber 2 a
CA 02263881 1999-02-18
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continuous current or primary current contact system
which permits the load interrupter switch 1 to be
designed for various nominal or continuous currents in
conjunction with the use of a specific vacuum
interrupter chamber 2.
The invention thus creates a load interrupter
switch 1 for voltages in the kV range and having a
vacuum interrupter chamber 2 which is embraced without
a gap by a sleeve 4 constructed from elastomeric
material of high dielectric strength. The sleeve 4 is,
for its part, clamped by the half housings 11 and 12 of
the load interrupter switch 1. In this way, an external
flashover of the high voltage between the end plates 24
and 25 of the vacuum interrupter chamber 2 is
effectively suppressed during the switching operation
without the need for liquid or gaseous media for this
purpose. As a result, by contrast with conventional
load interrupter switches there is no need for a high
outlay on monitoring, and the load interrupter switch
is unobjectionable with regard to the environment.
