EP1849169B1 - Transformer core comprising magnetic shielding - Google Patents

Description

The invention relates to a transformer core with a core interior of magnetizable material.

In the operation of transformers, in addition to the core channeled magnetic main flux, magnetic leakage fluxes also occur, some of them perpendicularly entering the legs of the transformer core. Very often, a tensioning device is arranged around the outside of the core, which holds the layered core and the coil body arranged around the core under axial pressure.

Transformer core according to the invention is any magnetizable core for the intended use in an electromagnetic machine, such. a transformer or a choke. The core inside in the sense of the present invention is the magnetizable part of the transformer core for guiding the magnetic flux.

Magnetic leakage fluxes generate eddy currents in the outer core segments and / or in the clamping device, which can lead to considerable local heating of the core or the clamping device. Heretofore, this problem has been addressed by dividing the outer core regions into small-width segments and reducing power losses and localized heating by using narrow or slotted clamping devices. The disadvantage here, however, that while the power losses can be reduced, on the other hand, a local warming, especially with high power transformers, is not prevented.

Also known from the prior art shields around the entire bobbin. That's how it describes DE 36 27 890 A1 a transformer with a magnetic shield and a method for producing such a shield. According to the local invention, the transformer has a three-legged laminated core with wound around the middle leg transformer windings, wherein the magnetic shield consists of a copper shorting strip, which is guided transversely to the leg longitudinal direction around the laminated core and the windings. The DE 39 40 025 A1 discloses a shield winding for magnetizable material transformers. The shielding coil according to the invention is wound between two winding sections of a transformer, wherein a magnetizable material with a low permeability is used for the shielding winding. A disadvantage of these windings known from the prior art is that, although external disturbing influences on the entire bobbin are prevented, however, non-magnetic stray fluxes within the bobbin, in particular on the core outside, are prevented.

CH 484 499 A discloses a transformer core according to the preamble of claim 1.

The object of the present invention is therefore to reduce or prevent the magnetic stray fluxes acting on the outside of the core interior and, if present, inside the tensioning device on the outside of the core interior.

The problem is solved by the subject matter of patent claim 1. According to the invention, a shield is at least partially disposed around the core interior, wherein the shield has a layered structure with at least one magnetizable material. The use of layered magnetizable materials, such as electrical sheets, conducts the leakage flux into the sheets and causes little power loss in the laminated shield. Due to the guidance of the magnetic leakage fluxes, no eddy currents are generated in the outer side of the core, so that the power losses and local heating within these ranges are greatly reduced or completely avoided. The power losses within the shield and local heating are greatly reduced compared to a transformer core without shielding according to the invention.

According to the invention, a device for generating an axial pressure on the interior of the core is arranged between the core interior and the shield. The use of a layered core interior requires the permanent maintenance of axial pressure on the layered core interior. These devices, which are usually also referred to as tensioning devices, are arranged directly on the core of the core. Because of the need for high strength, these devices for generating axial pressure often consist of electrically and magnetically conductive materials, such as steel or other metallic sheets. Within these clamping devices for generating an axial pressure locally high heating and power losses are caused by induced eddy currents in magnetic interference. Conventionally, the tensioning device is constructed of layered metals which, like the outer regions of the core interior, are additionally subdivided into segments. This minimizes the maximum according to the prior art possible power of the transformer using the described transformer core.

According to the invention, the shield is divided into segments. The subdivision of the shield into segments allows, on the one hand, a rapid and modular construction of the shield around the interior of the core or around the device for exerting the axial pressure. The segmental structure of the shield also allows to create a shield adapted directly to the transformer. As a result, the risk of large local overheating of the device for generating the axial pressure and / or the outer core regions is prevented. In this way, transformers with larger stray fluxes can be built more reliably than before. Also, the power losses when using a transformer core according to the invention are substantially reduced.

Furthermore, larger power per transformer leg can be realized. The segmented structure of the outer regions of the inner core or the clamping device can be completely eliminated in a transformer core according to the invention, whereby a much simpler and less expensive construction of the transformer can be realized.

It is preferably provided that the length of the shield in the axial direction is equal to or greater than the length of a coil former provided around the transformer core. In the limiting case, the shield can be arranged along the entire transformer leg and thus also reduce the negative magnetic stray influences on the final yoke and other optionally existing structural elements. According to the invention, it is provided that the orientation of the layered structure of the shield parallel to a possible Stray flux direction of a magnetic field is aligned. The orientation may be aligned parallel with respect to the generated within the transformer or with respect to an external possible leakage flux direction. The magnetic flux is ideally guided along the stratification and thus led away at the tensioning device or from the outer regions of the inner core.

A preferred feature of the invention is that the core interior is constructed of layered core segments and the shield is disposed along the outside of the outermost core segment or along the axial pressure generating device.

Furthermore, the shield is fixed together with the core inside with a - usually insulating bandage. Within the bandage, the shielding with an insulating material - for example, pressboard or cast resin - additionally fixed and electrically insulated. Ideally, the magnetizable material of the shield is an electrical sheet as used in electromagnetic devices.

Fig. 1

Schematische Schnittzeichnung des erfindungsgemäßen Transformatorkerns mit zwie umliegendem Spulenkörper;

Fig. 2a

Schematische Querschnittsschnittzeichnung des erfindungsgemäßen Transformatorkerns mit zwei einstückigen Abschirmungen;

Fig. 2b

Schematische Querschnittszeichnung des erfindungsgemäßen Transformatorkerns mit zwei jeweils segmentweisen aufgebauten Abschirmungen.

Further advantageous embodiments are given in the claims. The subject invention will be explained in detail with reference to the following figures. It shows:

Fig. 1

Schematic sectional view of the transformer core according to the invention with zwie surrounding bobbin;

Fig. 2a

Schematic cross-sectional sectional view of the transformer core according to the invention with two integral shields;

Fig. 2b

Schematic cross-sectional drawing of the transformer core according to the invention with two each segmentally constructed shields.

The figure Fig. 1 shows a schematic sectional view of the transformer core 1 according to the invention along the axial orientation of the transformer core 1. Along the outside of the layered core 2 inside a clamping device 3 for generating an axial pressure on the inner core 2 and

the bobbin 5 visible. To the clamping device 3, a shield 4 is arranged, which is an intrusion of the leakage flux - caused by the electrical currents in the surrounding bobbins 5 - in the core 2 and in the clamping device 3. Kerninneres 2, jig 3 and the shield 4 with a bandage 6 fixed. The bandage 6 meets - with appropriate choice of material - as an insulating sheathing around the inner core 2 another function. The longitudinal axis along the transformer core 1 is shown as a dashed line.

The figures Fig. 2a and Fig. 2b each show a cross section of the transformer core according to the invention 1. In addition to the layered structure of the inner core 2 forming core segments, a core inner 2 enclosing clamping device 3 is clearly visible. The tensioning device 3 can be constructed in the radial direction either continuously or segmented. To the clamping device 3 according to the figures Fig. 2a and 2b closes the shield 4. As in the figure Fig. 2a shown, the shield 4 may have a layered structure along the entire surface to be shielded. Alternatively, according to FIG Fig. 2b a segmented structure of layered elements of the shield 4 in view of a modular structure of the transformer core 1 and its shielding be advantageous. Via an outer bandage 6, the shield 4, which encloses either the transformer core 1 completely but at least along the orientation of the yoke, the shield 4 is fixed. The fixation of the shield 4 to the inner core 2 may alternatively via fasteners to the inner core 2, with the clamping device 3 or with other fasteners (not shown). Also a fixation of the shield 4 by means of the material consolidation of the shield under tension or pressure around the inner core 2 and the clamping device 3 is possible.

Claims (6)

1. Transformer core (1) having a core interior (2) made from magnetizable material, wherein a screen (4) is arranged at least partially around the core interior (2), wherein the screen (4) has a laminated structure comprising at least one magnetizable material, and wherein a device (3) for producing an axial pressure on the core interior is arranged between the core interior (2) and the screen (4), characterized in that the screen (4) is subdivided into segments and the laminated structure of the screen (4) is aligned parallel with a possible stray flux direction of an external magnetic field.
2. Transformer core (1) according to Claim 1, characterized in that the length of the screen (4) in the axial direction is equal to or greater than the axial length of the coil body (5) provided around the transformer core (1).
3. Transformer core (1) according to one of Claims 1 to 2, characterized in that the core interior (2) is made up of laminated core segments and the screen (4) is arranged along the outside of the outermost core segment.
4. Transformer core (1) according to one of Claims 1 to 3, characterized in that the screen (4) is fixed by means of a tape binding (6) around the screen (4).
5. Transformer core (1) according to one of Claims 1 to 4, characterized in that an insulating material between the screen (4) and the tape binding (6) fixes the screen (4).
6. Transformer core (1) according to one of Claims 1 to 5, characterized in that the magnetizable material of the screen (4) is an electrical steel sheet.

Images