A METAL-ENCLOSED HIGH-VOLTAGE SWITCHING SYSTEM WITH A CURRENT TRANSFORMER

SYSTEME DE COMMUTATION HAUTE TENSION DANS UN BOITIER METALLIQUE, AVEC TRANSFORMATEUR DE COURANT

English Abstract

In a current transformer (1) within a capsule housing (6) of a
high-voltage switching metal-enclosed high-voltage switching
system, between the secondary winding and the high-voltage
line (10) there is a first tube, in particular a supporting
tube (2) that is conductively connected at its first end with
the capsule housing (6) and which at its second end is
electrically connected to a second tube (8). The second tube
lies against the inside wall of the capsule housing (6), with
an insulating layer (9) between them. A closed conductive loop
is avoided because of the insulating layer (9) and because of
the fact that the second tube lies on the inside wall of the
capsule housing the current transformer is effectively sealed
against travelling waves within the capsule housing (6).

Claims

Claims
1. A metal-enclosed high-voltage switching device with a
cylindrical capsule-type housing (6) and a current
transformer (1) that is arranged within this, the
secondary winding of which coaxially surrounds a
high-voltage line (10), a first tube (2) and a second
tube (8) being provided between the secondary winding of
the current transformer (1) and the high voltage line
(10), this first tube (2) being conductively connected at
its first end with the capsule housing (6) and being
electrically insulated from this at the remaining points,
characterized in that the first tube (2) is conductively
connected at its second end with the second tube (8)
which lies on the inner wall of the capsule housing (6)
with an interposed insulating layer (9), such that the
area of contact of the capsule housing (6) is of a length
in the axial direction that is great compared to the
thickness of the insulating layer (9).
2. A metal-enclosed high-voltage switching system as
described in Claim 1, characterized in that the second
tube (8) overlaps the first tube (2) in the axial
direction, at least in part.
3. A metal-enclosed high-voltage switching system as
described in Claim 1 or Claim 2, characterized in that
the insulating layer (9) is of a material that greatly
attenuates electromagnetic waves.
4. A metal-enclosed high-voltage switching system as
described in one of the preceding claims, characterized
in that the insulating layer (9) is of plastic.

5. A metal-enclosed high-voltage switching system as
described in one of the preceding claims, characterized
in that the second tube (8) is cemented to the inside
wall of the capsule housing (6) by means of the
insulating layer (9).
6. A metal-enclosed high-voltage switching system as
described in one of the Claims 1 to 5 , characterized in
that the first tube (2) forms one piece with the second
tube (8) and in particular in that the first tube (2) and
the second tube (8) are formed as a single casting.
7. A metal-enclosed high-voltage switching system as
described in one of the Claims 1 to 5, characterized in
that the second tube (8) is conductively connected to the
first tube (2)) by a shielding electrode (7) of the
current transformer (1).
8. A metal-enclosed high-voltage switching system as
described in one of the Claims 1 to 5 , characterized in
that the second tube (8) is formed as a flange of the
first shoe (2) that is curved outward.

Description

o~ 3 ~ FILE, PtN*J THlS ~ME~ c~
TE~ TRANSLATI 216
A Metal-Enclosed High-Voltage Switching System
with a Current Transformer
The present invention relates to a metal-enclosed high voltage
switch gear with a capsule-type housing and a current
transformer that is arranged within this, the secondary
winding of said transformer surrounding coaxially a
high-voltage line, a first tube being arranged between the
secondary winding of the current transformer and the high
voltage line, the first end of said tube being connected
electrically with the capsule-type housing and being
electrically insulated from this at the remaining points.
A high-voltage switch gear of this kind is known, for example,
from E 0 060 636 B1. In the high-voltage switching system
gear described therein, a ring core current transformer is to
be so shielded that no excess voltage occurs at the test
terminals as a result of traveling waves within the
capsule-type housing. An electrically-conductive shielding
body that partially overlaps the tube so as to electrically
insulate it in part, and which is connected to the capsule so
as to be electrically conductive, is provided for this
purpose.
It is the task of the present invention to simplify the
construction of a metal-enclosed high-voltage switching
system, to achieve good shielding for the current transformer,
and reduce costs for installing the current transformer in the
capsule housing.
According to the present invention, this task has been solved
in that the first tube is conductively connected at its second
end with a second tube that is adjacent to the inside wall of
the capsule housing, with an insulating layer interposed
between them.

216216~
As an example, the first tube can be formed by the supporting
tube of a ring-core current transformer. This supporting tube
is then secured at one end to the inside wall of the capsule
housing, for example, by means of a screw-type fastening. The
second end of the tube may not be connected conductively to
the capsule housing, for this would then form a conductive
loop that surrounds the annular core, in which current could
be induced by the primary current flowing in the high-voltage
conductor. On the other hand, there should not be too great a
gap between the second end of the tube and the capsule housing
because travelling waves could penetrate into the area of the
secondary winding through such a space, and these would then
cause excess voltage at the test terminals of the current
transformer.
In order to close this intervening space, the present
invention makes provision for a second tube that is connected
conductively to the first tube but separated from the capsule
housing by the insulating layer. It is preferred that the
second tube have its periphery adjacent to the inside wall of
the capsule housing, with an insulating layer interposed
between it and said capsule housing. It is preferred that the
thickness of the insulating layer be slight compared to the
axial extent of the area over which the second tube is in
contact with the insulating layer.
This means that the conductive loop that surrounds the annular
core is broken by the insulating layer. Nevertheless, the
current transformer is largely sealed off against travelling
waves by an intervening space between the second tube and the
inside wall of the capsule housing, this space being
relatively narrow in relation to its length.
One embodiment of the present invention is such that the
second tube overlaps the first tube in the axial direction, at

21~216~
least in part. This design saves space with respect to the
axial length of the current transformer.
One further advantageous embodiment of the present invention
is such that the insulating layer consists of a material that
greatly attenuates electromagnetic waves. The material can,
for example, consist of an epoxy resin that is filled with
attenuating materials.
The choice of such a material that greatly attenuates
electromagnetic waves assures even more effective sealing of
the current transformer against travelling waves and other
electromagnetic interference pulses.
In addition, the present invention can advantageously be such
that the insulating layer is of a plastic.
Such a plastic is easily worked, and in particular can be
poured, so that it can either be applied to the inside wall of
the capsule housing or to the outside wall of the second tube
or, once the current transformer has being installed, it can
be poured into the space between the inside wall of the
capsule housing and the second tube.
A further advantageous embodiment of the present invention is
such that the second tube is cemented to the inside wall of
the capsule housing by means of the insulating layer.
Thus, the current transformer can be fixed even more securely
within the capsule housing by the appropriate selection of a
suitable material for the insulating layer. In addition, the
insulating layer can also dampen mechanical oscillations of
the capsule housing.

21 G21 63
In addition to the foregoing, the present invention can
advantageously be such that the first tube forms one piece
with the second tube, and in particular that the first tube
and the second tube are formed as a single casting.
The supporting tube for the current transformer thus be cast
with the second tube as a single part, which greatly reduces
assembly costs. The shielding electrodes of the current
transformer can also be integrated into this molded part.
The present invention can also be configured advantageously in
that the second tube is connected conductively to the first
tube by means of a shielding electrode of the current
transformer.
The shielding electrodes can be screwed onto the first tube as
separate parts and one of the shielding electrodes can then
support the second tube.
It can also be advantageous that the second tube be formed as
an outwardly curved flange on the first tube. This means that
the first tube and the second tube can be manufactured in a
cost-effective manner and simply installed. A shielding
electrode can also be integrated into this part.
The present invention will be described in greater detail
below on the basis of one embodiment shown in the drawing
appended hereto. This drawing is a longitudinal cross-section
through a tubular capsule housing with built-in ring-core
current transformer.
The current transformer 1 incorporates a first tube 2
(supporting tube) that is a casting, in which a first
shielding electrodes 3 is integrated. The first tube 2
supports the ring cores 4, 5 that are surrounded by the

21~21~ ~
`_
secondary winding (not shown herein) that are encased in
sealing compound (not shown herein) and are connected to the
first tube 2. The shielding electrode 3 is conductively
connected to the capsule housing 6 through a screw-type
connection.
At the end of the supporting tube 2 that is opposite the first
shielding electrode 3, this tube is connected to a second
shielding electrode 7 by means of a screw-type connection. A
second tube 8 is screwed onto the second shielding electrode
7, and this second tube lies against the inside wall of the
capsule housing 6 with an insulating layer 9 interposed
between them.
The first tube 2 and the annular cores coaxially enclose a
high-voltage line 10 through which the current that is to be
measured is flowing.