KR101003933B1 - Transformer core with magnetic shield - Google Patents

Abstract

The present invention relates to a transformer core comprising an interior of a core formed of magnetic material. Leakage fluxes generate eddy currents in the outer core regions, which cause power losses and local overheating. The leaking magnetic fluxes are channeled and guided away from the outer region inside the core by the shielding, which shielding partially surrounds the core interior and is formed of at least one layered magnetic material. This allows the formation of eddy currents inside the core to be significantly reduced and also prevents local overheating and power loss of the transformer core.

Description

Transformer core with magnetic shielding {TRANSFORMER CORE COMPRISING MAGNETIC SHIELDING}

The present invention relates to a transformer core having a core interior formed of a magnetic material.

In operation of the transformers, not only the main magnetic flux channeled in the core, but also magnetic stray fluxes, partly perpendicular to the rim of the transformer core, occur. Very often, clamping devices are provided around the outer surface inside the core that secure the laminated core and also secure the coil body which is arranged around the core under axial pressure.

Transformer cores as defined by the present invention are any magnetic cores intended for use in electromagnetic machines such as, for example, transformers or chokes. The core interior as defined by the present invention is the magnetic part of the transformer core for guiding the magnetic flux.

The stray fluxes generate eddy currents in the outer core segments and / or in the clamping device, which can lead to significant local heating of the clamping device and the core. Previously, this problem was prevented by subdividing the outer core areas into smaller width segments and by reducing power loss and local heating using narrow or slotted clamping devices. However, a disadvantage of such a method is that, on the other hand, even though the power loss can be reduced, local heating cannot be prevented, especially in the case of transformers with high power.

Screening around the entire coil body is also known in the art. For example, DE 36 27 890 A1 discloses a transformer with a magnetic screen and a method for producing such a screen. According to such an invention, the transformer has a three-limbed laminate stack with transformer windings wound around the central rim, wherein the magnetic screen is made of a copper shorted strip, the strip being rim lengthwise. It is laterally guided around the stack and windings. D 39 40 025 A1 discloses a screen for transformers made of magnetic material. The screen winding according to such an invention is wound between two winding sections of a transformer, and a magnetic material having a low permeability is used for the screen winding. A disadvantage of such windings known in the art is that stray fluxes in the coil body, in particular on the outer surface of the core, cannot be eliminated, although external disturbing effects on the entire coil body can be avoided.

It is therefore an object of the present invention to reduce or prevent stray fluxes acting on the outer surface inside the core and, if present, within the clamping device on the outer surface inside the core.

This object is achieved by the subject matter of claim 1. Preferably, the screen is at least partially disposed around the core interior, and the screen has a laminated structure comprising at least one magnetic material. By using laminated magnetic materials such as, for example, electrical steel sheets, stray magnetic flux is guided to the electrical steel sheets, resulting in only low power losses in the laminated screen. Since stray fluxes are guided, no eddy currents are generated on the outer surface inside the core, thereby significantly reducing or completely eliminating power loss and local heating in these areas. According to the invention, power loss and local heating in the screen are significantly reduced compared to transformer cores without screening.

Preferably, a device for generating axial pressure on the inside of the core is disposed between the inside of the core and the screen. Use of the stacked core interior requires that the accumulators be permanently maintained on the stacked core interior. Such devices, also commonly referred to as clamping devices, are arranged directly within the core. Due to the need for high forces, these devices for generating accumulators are frequently made of electrically and magnetically conductive materials such as steel or other metal plates. In the case of magnetic disturbance effects, high heating and power losses are locally generated due to eddy currents induced in such a clamping device to generate a pressure accumulation. Typically, the clamping device is formed of stacked metals, which are further subdivided into segments as well as the outer area inside the core. According to the prior art, this minimizes the maximum 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 formed in modular form around the core interior and around the device for quickly applying pressure. The segmented structure of the screen also allows a screen to be created that directly matches the transformer. This avoids the risk of significant local overheating of the device and / or the outer core region for generating the accumulator. Thus, transformers with larger stray fluxes can be formed more reliably than before. Likewise, power loss is significantly reduced when using the transformer core according to the invention.

Also, larger powers can be realized per transformer rim. With the transformer core according to the invention, the clamping device and the segmented structure of the outer region inside the core can be completely eliminated, resulting in a significantly easier and cost effective structure of the transformer.

According to the invention, the length of the screen in the axial direction is designed to be equal to or greater than the length of the coil body provided around the transformer core. In the limited case, the screen can be placed along the entire transformer rim, thereby also reducing the negative stray magnetic effects on the terminating yoke and other structural elements that may be present. Preferably, the direction of the laminated structure of the screen is designed to align parallel to the possible stray magnetic flux direction of the magnetic field. In doing so, the directions can be aligned parallel to the stray flux direction generated in the transformer or to the external possible stray flux direction. Ideally, the magnetic flux is guided along the stack to the clamping device and away from the outer region inside the core.

A preferred feature of the present invention is that the core interior is formed of stacked core segments and the screen is arranged along the outer surface of the outermost core segment or along the device for generating the accumulator.

The screen is also secured to the inside of the core through a generally insulative tape bond. The screen is also fixed and electrically insulated within the tape bond, for example through an insulating material such as compressed cardboard or cast resin. Ideally, the magnetic material of the screen is an electrical steel sheet as used in electromagnetic devices.

Other preferred embodiments can be found in the claims. The subject matter of the present invention is described in detail with reference to the drawings.

1 is a schematic cross-sectional view of a transformer core according to the invention with two surrounding coil bodies.

2a is a schematic cross-sectional view of a transformer core according to the invention with two single-part screens.

2b shows a schematic cross sectional view of a transformer core according to the invention with two segmented screens;

1 shows a schematic cross section of a transformer core 1 according to the invention, along the axial direction of the transformer core 1. A clamping device 3 and a coil body 5 for generating an accumulator on the core interior 2 can be seen along the outer surface of the stacked core interior 2. A screen 4 is arranged around the clamping device 3, in which the stray flux caused by electrical currents in the surrounding coil cores 5 is contained within the core 2 and the clamping device 3. To prevent penetration. The core interior 2, the clamping device 3 and the screen 4 are fixed by a tape bond 6. Through proper selection of the material, the tape bond 6 performs an additional function as an insulating sleeve around the core interior 2. The longitudinal axis along the transformer core 1 is shown in dashed lines.

2a and 2b respectively show a cross section of a transformer core 1 according to the invention. The stacking structure of the core segments forming the core interior 2 as well as the clamping device 3 surrounding the core interior 2 can be clearly seen. The clamping device 3 can be configured continuously in the radial direction or in a segmented form. The screen 4 is connected to the clamping device 3 according to FIGS. 2 a and 2b. As shown in FIG. 2A, the screen 4 may have a stacked structure along all surfaces to be screened. Alternatively, according to FIG. 2B, the segmented structure of the stacked elements of the screen 4 may be advantageous for the transformer core 1 and for the modular structure of the screen thereof. The screen 4, which completely surrounds the transformer core 1 but along at least the direction of the yoke, is fixed by an outer tape bond 6. The screen 4 around the core interior 2 may alternatively be fixed by connecting elements, by the clamping device 3 or by another fastening element (not shown). The screen 4 may also be fixed around the core 2 or the clamping device 3 under stress or pressure by means of the adhering material of the screen.

Claims (9)

A transformer core (1) having a core interior (2) formed of a magnetic material, A screen 4 is arranged to surround a portion of the core interior 2 or surround the entire core interior 2 around the core interior 2, The screen 4 has a laminated structure comprising at least one magnetic material, A clamping device 3 for generating axial pressure on the core interior 2 is disposed between the core interior 2 and the screen 4, The laminated structure of the screen 4 is aligned parallel to the possible stray flux direction of the external magnetic field, Transformer core. delete The method according to claim 1, wherein the screen 4 is subdivided into segments. Transformer core. The length of the screen 4 in the axial direction is equal to or greater than the axial length of the coil body 5 around the transformer core 1, according to claim 1. Transformer core. delete 4. A core according to claim 1 or 3, wherein the core interior (2) is formed of stacked core segments and the screen (4) is disposed along the outer surface of the outermost core segment, Transformer core. 4. The screen according to claim 1, wherein the screen (4) is fixed by a tape bond (6) around the screen (4). Transformer core. 4. The insulating material according to claim 1, wherein the insulating material between the screen 4 and the tape bond 6 secures the screen 4. Transformer core. 4. The magnetic material of claim 1, wherein the magnetic material of the screen 4 is an electrical steel sheet. Transformer core.

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