Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a capacitive voltage
transformer, comprising a capacitive voltage divider, a resonance
reaction coil and an intermediate transformer connected to the
divider point of said voltage divider at least the secondary
winding of the intermediate transformer being sealed in casting
resin.
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This type of voltage transformer is disclosed in DE-AS
12 41 908; the windings of the intermediate transformer and
particular by its secondary windings are embedded in casting
resin. On its upper end this cast resin block has a flange with
l.U which it abuts against the earthed casing and on which the
capacitive voltage divider is secured by means of a porcelain
insulator encompassing-the capacitive voltage divider.
Insulating oil is used as impregnating and insulating agent for
the capacitive voltage divider.
1~
A capacitive voltage transformer of a different type is
described in DE-PS 15 41 800, wherein the resonance reaction coil
is inserted between the divider point of high and low voltage -
2U side divider capacitor of the voltage divider and theintermediate transformer and thus lies on high voltage potential
of the order of 20 kV. As usual, the intermediate transformer is
connected in series with the resonance reaction coil.
The present invention provides a capacitive voltage
2~ transformer of the type initlally described with which a rational
production of all the transformer components is achieved and in
particular a type of construction of all the individual
components that is safe to operate and at the same time
externally compact, i.e., of the voltage divider, of the
3~ resonance reaction coil and of the intermediate transformer, is
to be attained.
According to the present invention there is provided a
capacitive voltage transformer, comprising a capacitive voltage
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divider, a resonance reaction coil and an intermediate
transformer connected to the divider point of said voltage
divider at least the secondary winding of the lntermediate
transformer being sealed in casting resin in which the secondary
winding of the intermediate transformer is connected first to the
divider point of the capacitive voltage transformer, in series
!i with at least one component of the secondary winding of the
intermediate transformer, the secondary winding of the resonance
reaction coil is then added as a higher stage, the intermediate
transformer with all the winding and core components is sealed in
an open air-resistant casting resin block and the casting resin
u block carries the voltage divider and is flanged thereto.
The present invention is distinguished particularly by
the fact that the intermediate transformer constitutes an open
air-resistant structural element that completely integrates its
1~ active components (windings and iron core) and that this element
be connected directly with the capacitive voltage divider. Not
only is the intermediate transformer electrically connected
directly to the divider point of the capacitive voltage divider,
but, contrary to the prior art particularly DE-AS 12 41 908, it
~U is virtually taken out of the earthed metallic casing. The
intermediate transformer thus forms an electrically and
mechanically independent unit, which can be produced separately,
pretested and connected in a simple manner to the other units of
the capacitive voltage transformer according to the present
2~ invention, namely to the capacitive voltage divider and to the
metal casing for the resonance reaction coil.
In one embodiment of the present invention below said
casting resin block there is a free space which is defined by a
3U metal casing for housing the resonance reaction coil. Desirably
said surface of the casting resin block is provided with
metallization which is connected to the metal casing on the earth
potential so as to be electrically conducting.
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In another embodiment of the present invention the gas-
or liquid-impregnated divider capacitors of the capacitive
voltage divider are completely encompassed by a casting resin
casing, said casting resin casing being applied in uphill casting
while displacing the gaseous or liquid insulating agent in the
casting mould. Suitably ribs are provided on the casting resin
!.i sheathing of the voltage divider, said ribs forming a single
homogeneous body with the casting resin sheathing or being
separately connected to the casting resin sheathing. Desirably
the electric connection between the capacitive voltage divider
and the secondary winding of the intermediate transformer is
obtained via a plug contact pin.
The present invention will be further illustrated with
reference to the accompanying drawings in which:
Figure 1 is a lateral view of a capacitive voltage
transformer according to one embodiment of the present invention
in transverse section;
2U Figure 2 is a top plan view of the voltage divider of
Figure l; and
Figure 3 illustrates the corresponding circuit for the
capacitive voltage transformer of Figures 1 and 2.
The capacitive voltage transformer 1 comprises two
divider capacitors 3 and 4 forming a capacit~ve voltage divider
2, which divider capacitors 3 and 4 are superposed and flanged
with one another in a conventional manner. The divider
capacitors 3 and 4 are secured to a casting resin block 5 so as
3U to be impervious to gas and liquid, particularly they are
sealingly screwed thereto. The casting resin block 5 of open
air-resistant casting resin, particularly of cycloaliphatic
casting resin, completely envelops the active components, i.e.,
the secondary windings 7 (not separately shown) including the
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corresponding iron core 8 of the intermediate transformer 6.
A metal casing 9 at earth potential is provided under
the casting resin block 5. The metal casing 9 includes a free
space 10 for housing the resonance reaction coil 11 required for
!i the capacitive voltage transformer. With its one winding end
said resonance reaction coil 11 is connected to ground or earth
potential as is evident from the electric circuit diagram in
Figure 3. Therefore, the entire resonance reaction coil 11 lies
on low voltage or earth potential.
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The surface of the casting resin block 5, namely, the
lateral faces 5a and 5b and the upper front surface 5c, are
provided with a conductive coating 12 at earth potential,
preferably of an electrically conducting metallization, which is
1~ so connected to the metal casing 9 at earth potential that it is
electrically conducting.
Each of the divider capacitors 3 and 4 of the
2U capacitive voltage divider 2 consists of windings or of a stack
of winding bodies, which are impregnated or saturated with an
insulating medium. A casting resin sheathing 13 is provided as a
sheathing for said divider capacitors 3 and 4. The sheathing 13
is produced, when required in a broken mould, in that the divider
capacitors 3 and 4 are lmpregnated with the insulating medium
(liquid or gaseous) in the mould and that casting resin is
introduced into the casting mould from below. The casting resin
thus introduced rises in the casting form and displaces the
saturating or insulating medium to the extent required for the
necessary impregnation. By means of this conventional
3U displacement or uphill casting a substantial amount of
impregnating or saturating medium is saved in the finished
voltage divider 2 and in the divider capacitors 3 and 4.
On the outside of the casting resin sheathing 13 ribs
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14 are provided in a conventional manner. They can be moulded on
simultaneously with the production of the casting resin sheathing
13 so that said sheathing and the ribs 14 form a single body of
homogeneous material.
However the ribs 14 can also be subsequently installed
!; on the casting resin sheathing 13 of the two divider capacitors 3
and 4 particularly with the use of silicone resin.
The special advantage of using the so-called
dlsplacement and uphlll casting method lles ln that the amount of
u impregnating agent required for the impregnation of the divider
capacitors 3 and 4 is reduced to a minlmum so that the capacitive
voltage divider 2 either requires no conservator tank at all or
it requires one having only a minimal volume. An electrically
conducting hollow screening ring, which usually is flanged
1~ between the two divider capacitors 3 and 4, is particularly
suitable for this purpose.
Figure 2 shows the above-described capacitive voltage
2U transformer 1 in top view. In this representation the
arrangement of fixed feet lS, of the clamp box 16 and of the
power line carrier 17 can be clearly seen. Furthermore, the
individual components of Figure 2 have the same reference numbers
as those in Figure 1.
2~ A circuit of the capacitive voltage transformer
according to the present invention is diagrammatically shown in
Figure 3. In this Figure the capacitive voltage divider again
has the reference number 2 and comprises the divider capacitors 3
and 4. TP denotes the voltage tap for the direct connection of
3U the intermediate transformer 6 to the capacitive voltage divider ~ `
2. In this case the intermediate transformer, which is directly
electrically connected to the voltage tap TP, has two secondary
windings 7 and two measuring windings 18, 19 while the resonance
reaction coil 11 connected in series with the intermediate
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transformer 6 has one measuring or control winding 20.
The electric connection between the capacitive voltage
divider 2 and the intermediate transformed 6 is obtained via a
plug contact pin 21, when required via a multicontact of
conventional design. In Figure 1 an electric feed line 22 has
!.i been additionally plotted. Said feed line 22 impresse~ the
potential of customarily 20 kV on the intermediate transformer 6
at the divider point TP between the divider capacitors 3 and 4.
A further electric line 22 shown in Figure 1 connects the
conductive coating 12 of the casting resin block 5 to the end of
the divider capacitor 4 that lies on earth potential.
The casting resin sheathing 13 of the divider
capacitors 3 and 4 preferably consists of elastic casting resin,
particularly of polyurethane, which can absorb the thermal
expansions of the quantitatively extremely small impregnating
agent without requiring an additional conservator tank. However,
as briefly mentioned hereinbefore, a conservator tank of mall
volume can be provided, particularly as annular screening
electrode at the junction between the divider capacitors 3 and 4.
2U
A particularly distinguishing feature of the capacitive
voltage transformer according to the present invention is that
all the components, namely the capacitive voltage divider 2, the
intermediate transformer 6 and the resonance reaction coil 11 can
2~ be produced and pretested separately and on having passed the
preliminary test they can be mounted ~ointly in the simplest
manner. The casting resin technology used for both the voltage
divider 2 and the intermediate transformer 6 is on a very high
technological level so that the breakdown quota is very low from
3U the outset and can even be reduced further by prefabricating
these components. With the casting resin technology applied the
sizes of the capacitive voltage divider 2 and of the intermediate
transformer 6 can be reduced to optimal values. Furthermore
because the resonance reaction coil 11 is series-connected and is
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housed in the metal casing 9, the dimensions of the resonance
reaction coil 11 can also be reduced to a minimum.
Thus not only is the capacitive voltage transformer
according to the present invention distinguished by a high degree
of operating reliability but it is also distinguished by an
extremely compact construction.
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