TRANSFORMER CORE WITH MAGNETIC SCREENING

NOYAU DE TRANSFORMATEUR A BLINDAGE MAGNETIQUE

English Abstract

The present invention relates to novel pharmaceutical compositions based on
anticholinergics and etiprednol, processes for preparing them and their use in
the
treatment of respiratory diseases.

French Abstract

L'invention concerne un noyau de transformateur comportant un intérieur de noyau réalisé en matériau magnétisable. Des flux de dispersion magnétiques produisent des courants parasites dans les parties extérieures du noyau, provoquant des pertes de puissance et des échauffements locaux élevés. Un blindage entourant partiellement l'intérieur du noyau, réalisé dans au moins un matériau magnétisable en couches, permet de canaliser les flux de dispersion et de les évacuer de la partie extérieure de l'intérieur du noyau. Ceci permet de réduire considérablement la formation de courants parasites à l'intérieur du noyau et d'empêcher des échauffements locaux élevés et des pertes de puissance.

Claims

8
CLAIMS:
1. A transformer core having a core interior made from
magnetizable material, wherein a screen is arranged at least
partially around the core interior, the screen having a
laminated structure comprising at least one magnetizable
material, and a device for producing an axial pressure on the
core interior is arranged between the core interior and the
screen and the laminated structure of the screen is aligned
parallel with a stray flux direction of a magnetic field, which
acts on the outside of the core interior, wherein the screen is
subdivided into segments.
2. The transformer core as claimed in claim 1, wherein
the length of the screen in the axial direction is equal to or
greater than the axial length of the coil body around the
transformer core.
3. The transformer core as claimed in claim 1 or
claim 2, wherein the core interior is made up of laminated core
segments and the screen is arranged along the outside of the
outermost core segment.
4. The transformer core as claimed in any one of
claims 1 to 3, wherein the screen is fixed by means of a tape
binding around the screen.
5. The transformer core as claimed in any one of
claims 1 to 4, wherein an insulating material between the
screen and the tape binding fixes the screen.

9
6. The transformer core as claimed in any one of
claims 1 to 5, wherein the magnetizable material of the screen
is an electrical steel sheet.

Description

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Description
Transformer core with magnetic screening
The invention relates to a transformer core having a core
interior made from magnetizable material.
In the operation of transformers, as well as the magnetic main
flux, which is channeled in the core, magnetic stray fluxes
also occur, which in part enter the limbs of the transformer
core at right angles. Very often, a clamping device, which
holds the laminated core and which holds the coil body arranged
around the core under axial pressure, is arranged around the
outside of the core interior.
Transformer core as defined by the invention is any
magnetizable core, which is intended for use in an
electromagnetic machine, such as for example a transformer or a
choke. Core interior as defined by the present invention is the
magnetizable part of the transformer core for guiding the
magnetic flux.
Magnetic stray fluxes produce eddy currents in the outer core
segments and/or in the clamping device, which can lead to a
considerable local heating of the core and of the clamping
device. Previously, this problem has been countered by
subdividing the outer core areas into segments of small width
and reducing the power losses and the local heating by the use
of narrow or slotted clamping devices. The disadvantage of
this, however, is that although the power losses can be
reduced, on the other hand a local

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heating, particularly in the case of transformers with high
power, cannot be prevented.
Screening around the whole coil body is also known from the
prior art. For example, DE 36 27 890 Al describes a transformer
having a magnetic screen and a method for producing such a
screen. According to that invention, the transformer has a
three-limbed laminate stack with transformer windings wound
around the center limb, the magnetic screen being made from a
copper short-circuiting strip, which is guided around the
laminate stack and windings transversely with respect to the
limb longitudinal direction. DE 39 40 025 Al discloses a screen
for transformers made from magnetizable material. The screen
winding according to the invention is wound between two winding
sections of a transformer, a magnetizable material with a low
permeability being used for the screen winding. The
disadvantage of these windings known from the prior art is that
although external disturbing influences on the whole coil body
can be prevented, magnetic stray fluxes within the coil body,
in particular on the outside of the core, cannot be eliminated.
The object of some embodiments of the present invention is
therefore to reduce or prevent magnetic stray fluxes, which act
on the outside of the core interior - and, if present, within
the clamping device on the outside of the core interior.
Advantageously, a screen is arranged at least partially around
the core interior, the

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screen having a laminated structure comprising at least one
magnetizable material. By using laminated magnetizable
materials, such as electrical steel sheets for example, the
stray flux is guided into the sheets and produces only low
power losses in the laminated screen. Because the magnetic
stray fluxes are guided, no eddy currents are produced in the
outside of the core interior so that the power losses and local
heating within these areas are greatly reduced or completely
eliminated. The power losses within the screen and a local
heating are greatly reduced compared with a transformer core
without screening according to the invention.
Advantageously, a device for producing an axial pressure on the
core interior is arranged between the core interior and the
screen. The use of a laminated core interior requires an axial
pressure to be permanently maintained on the laminated core
interior. These devices, usually also referred to as clamping
devices, are arranged immediately against the core interior.
Because of the need for a high strength, these devices for
producing an axial pressure frequently consist of electrically
and magnetically conducting materials, such as steel or other
metallic sheets for example. In the event of magnetic
disturbing influences, high heating and power losses are
produced locally within these clamping devices for producing an
axial pressure due to induced eddy currents. Conventionally,
the clamping device is made up of laminated metals, which -
like the outer areas of the core interior - are additionally
subdivided into segments. According to the prior art, this
minimizes the maximum

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possible power of the transformer when the described
transformer core is used.
Preferably, the screen is subdivided into segments. On the one
hand, subdividing the screen into segments allows the screen to
be built up around the core interior and around the device for
exerting the axial pressure quickly and in a modular fashion.
The segmented structure of the screen also allows a screen to
be produced, which is directly matched to the transformer. This
avoids the risk of considerable local overheating of the device
for producing the axial pressure and/or of the outer core
areas. Transformers with larger stray fluxes can therefore be
built more reliably than before. Likewise, the power losses are
significantly reduced when using a transformer core according
to the invention.
Furthermore, greater powers can be realized per transformer
limb. With a transformer core according to the invention, the
segmented structure of the outer areas of the core interior and
of the clamping device can be dispensed with completely, as a
result of which a considerably easier and more cost-effective
structure of the transformer can be realized.
According to sane embodiments of the invention, the length of the scraminde
axial direction is designed to be equal to or greater than the
length of a coil body, which is provided around the transformer
core. In the limiting case, the screen can be arranged along
the whole transformer limb and therefore also reduce the
negative magnetic stray influences on the terminating yoke and
other structural elements that may be present. Preferably, the
orientation of the laminated structure of the screen is
designed to be aligned parallel with a

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possible stray flux direction of a magnetic field. In doing so,
the orientation can be aligned parallel with respect to the
stray flux direction produced within the transformer or with
respect to an external possible stray flux direction. Ideally,
the magnetic flux is guided along the lamination and therefore
to the clamping device and guided away from the outer areas of
the core interior.
A preferred characteristic of the invention is that the core
interior is made up of laminated core segments and the screen
is arranged along the outside of the outermost core segment or
along the device for producing an axial pressure.
Furthermore, the screen is fixed together with the core
interior by means of a - normally insulating - tape binding.
The screen is additionally fixed and electrically insulated
within the tape binding by means of an insulating material -
for example pressboard or cast resin. Ideally, the magnetizable
material of the screen is an electrical steel sheet, such as is
used in electromagnetic devices.

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5a
In accordance with the invention, there is provided a
transformer core having a core interior made from magnetizable
material, wherein a screen is arranged at least partially
around the core interior, the screen having a laminated
structure comprising at least one magnetizable material, and a
device for producing an axial pressure on the core interior is
arranged between the core interior and the screen and the
laminated structure of the screen is aligned parallel with a
stray flux direction of a magnetic field, which acts on the
outside of the core interior, wherein the screen is subdivided
into segments.
Further advantageous embodiments can be seen from the claims.
The subject matter of the invention is explained in detail with
reference to the following figures. In the figures:
Fig. 1 shows a schematic section drawing of the transformer
core according to the invention with two encompassing coil
bodies;
Fig. 2a shows a schematic cross-section sectional drawing of
the transformer core according to the invention with two
single-part screens;

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Fig. 2b shows a schematic cross-section drawing of the
transformer core according to the invention with
two segmented screens.
Fig. 1 shows a schematic section drawing of the transformer
core 1 according to the invention along the axial orientation
of the transformer core 1. A clamping device 3 for producing an
axial pressure on the core interior 2 and the coil body 5 can
be seen along the outside of the laminated core interior 2.
Around the clamping device 3 is arranged a screen 4, which
prevents the penetration of the stray flux - caused by the
electrical currents in the encompassing coil cores 5 - into the
core interior 2 and into the clamping device 3. Core interior
2, clamping device 3 and the screen 4 are fixed by means of a
tape binding 6. With an appropriate choice of material, the
tape binding 6 fulfills a further function as an insulating
sleeve around the core interior 2. The longitudinal axis along
the transformer core 1 is shown as a dotted line.
The figures Fig. 2a and Fig. 2b each show a cross section of
the transformer core 1 according to the invention. As well as
the laminated structure of the core segments forming the core
interior 2, a clamping device 3 encompassing the core interior
2 can be clearly seen. The clamping device 3 can be structured
either continuously or in segmented form in the radial
direction. The screen 4 is connected to the clamping device 3
according to the figures Fig. 2a and 2b. As shown in the figure
Fig. 2a, the screen 4 can have a laminated structure along the
whole surface to be screened. Alternatively, according to the
figure Fig. 2b, a segmented structure of laminated elements of
the screen 4 can be advantageous with regard to a modular
structure of the transformer

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core 1 and its screen. The screen 4, which either completely
encompasses the transformer core 1 but at least along the
orientation of the yoke, is fixed by an external tape binding
6. The screen 4 around the core interior 2 can alternatively be
fixed to the core interior 2 by means of connecting elements,
by means of the clamping device 3 or by means of further fixing
elements (not shown). The screen 4 can also be fixed around the
core interior 2 or the clamping device 3 under tension or
pressure by means of the material fixing of the screen.

Representative Drawing