EP2206126B1 - Transformer core having a stray field shield - Google Patents

Abstract

The invention relates to a transformer core having a stray field shield, comprising at least one core leg (2', 2'', 2''') carrying a winding arrangement (13) and formed from a laminate stack (3), said laminate stack (3) being sealed by end plates (7', 7''), each end plate (7', 7'') being associated with a stray field shield (4', 4'') that comprises coated laminate plates (40', 40''), the layer planes (15) of which are disposed perpendicular to the layer planes (14) of the laminate stack (3), characterized in that the laminate plates (40', 40'') are disposed with laminate plate faces (9', 9'') pointing toward the laminate stack (3) to abut an exterior width surface (8', 8'') of an associated end plate (7', 7'').

Description

Technical area

The invention relates to a transformer core with a stray shield having at least one winding assembly bearing core core formed from a laminated core, wherein the laminated core is closed by Endlamellen, each Endlamelle is associated with a stray field screen having laminated laminations whose layer planes perpendicular to the layer planes of Laminations of the core leg are arranged, and wherein the laminations are arranged adjacent to the laminated core sheet metal lamination end faces on an outer wide surface of an associated end plate.

State of the art

In electrical machines, machine parts, such as the rotor of an electric motor, the core leg of a transformer or a throttle, performed laminated. As a result, eddy current losses induced by the temporal change of a magnetic flux can be kept low. In an electric machine but also occurs a so-called stray flux, which also causes eddy current losses in the core, although this is always much smaller than the main flow, which is performed in the machine parts.

It is also known that in particular those field lines of the leakage flux which penetrate into a broad surface of an end lamella of a core-core laminated core, there induce magnetic losses by induction, the unwanted local heating (also referred to in the literature as "hot spots") of the core material can cause. In the case of an oil transformer, this can heat the oil to an excessively high temperature, which can impair the technical reliability of the transformer.

Out AT 413 158 B and US-A-3,614,695 In each case transformers are known in which a pull rod is made of layered sheets. This tie rod is a separate component and not an integral part of the core.

Also from GB 218,918 a transformer is known with a laminated magnetic shield, which is also not integrated in the magnetic core of the transformer.

To reduce the magnetic power loss of a transformer or a throttle, is further from the DE 1 237 677 a magnetic shield known, which shields the leakage flux from the core of a transformer or a throttle. This magnetic shield consists of laminations, which are layered into a laminated core. The sizing levels of the magnetic shield laminations are perpendicular to the finishing planes of the core leg laminations. The magnetic shield is firmly clamped by means of clamping wedges or clamping strips between the core leg and the surrounding winding with the interposition of one, the magnetic shield plate laminations supporting solid support plate. The magnetic shield and the mounting take up a load in the winding window Installation space, so that the electrical winding that surrounds the core leg, must be sized larger.

From the DE 10 2005 008 302 A1 For example, a transformer core with a shielded magnetic shield is known. Again, a tensioning device is arranged between the shield and the transformer core, which requires a larger winding. The tensioning device is designed segmented or slotted because of the formation of eddy currents. All these statements have in common that magnetic shielding is a separate element and is expensive to manufacture.

Illustrations of the invention

The invention is based on the object to provide a transformer core, in which the formation of eddy currents, which are caused by leakage flux, is kept as low as possible in the simplest possible way.

This object is achieved by a transformer core having the features of patent claim 1. Advantageous embodiments of the invention are defined in the dependent claims.

The invention is based on the basic idea of designing the outer core stage as a stray field shield in the case of a transformer core formed from a laminated core, so that the stray flux is prevented from entering into a laminar lamination of the core arm. The stray field patch screen is arranged such that the layer planes are perpendicular to the layer planes of the core leg Belchpakets and that the lamination end faces of the stray field shield directly on an outer broad surface of an associated Endlamelle. In this installation position, the stray field shield can be fixed in different ways, for example by friction or by material bond.

The invention is characterized in that the transition between the sheet metal slats and the yoke is formed flush. The stray field screen is thus not a separate element, but participates in the leadership of the main river part. In other words, according to the invention, the outer stage of the core fulfills a dual function: on the one hand it absorbs the leakage flux entering from the air space, on the other hand it also carries a part of the main flow. Since the leakage flux enters the front side of the screen device, the formation of eddy currents is severely limited by the correspondingly thin sheets. The magnetic losses decrease. The training so-called "hot spots" is lower. In an oil transformer, the oil heats less, which improves the technical reliability. The arrangement of the stray field shield according to the invention enables a compact construction, since the laminations end faces of the stray field shield abut directly on an end plate of the core leg. In the winding window, little additional space is required for the screen, so that the copper volume of the electrical winding, which encloses the core leg, and thus the production costs can be kept low.

With regard to the production, it may be particularly advantageous if the individual laminations of the stray field shield are held together by an adhesive. For this purpose, an adhesive is introduced during manufacture between adjacent slats of the stray field screen. The application of the adhesive can be done automatically with known metering devices, which is advantageous in manufacturing.

The determination of the stray field-laminated core can also be done by a metal adhesive bond with advantage. For this purpose, an adhesive is applied to the lamination end faces of the litter field shield lamination or on the outer wide surface of an associated end lamella of the core limb during manufacture. The metal adhesive connection eliminates the usual, usually solid-trained fastening devices, such as clamping wedges or clamping strips.

It is recommended that the lamella thickness of the core leg laminated core and the lamella thickness of the stray field shield to choose the same size. This makes storage easier during production.

A very special advantage can be achieved by the laminated core of the stray field screen is made of the same soft magnetic material as the laminated core of the core leg. As a result, residual material that accumulates in the production of a transformer type can be profitably used for the production of the stray field screen. This further reduces the production costs. In addition, less production waste is generated.

It can be favorable if the laminated core of the core limb is composed of partial laminated cores in such a way that the circumferential contour, viewed in cross-section, has steps in a first region of the laminated core ( Fig. 3 while in another region it is a circular arc concentric about the core thigh axis. As a result, the volume of the cylinder portion is used efficiently for the shielding of the leakage flux. The stray field does not require any additional construction volume and consequently there is no additional requirement for conductor material for the production of the electrical winding.

A further amount for cost reduction can be achieved by the adhesive is applied only part of the area on the wide surfaces of the laminations of the litter field.

With regard to the strength of the adhesive bond, it may be advantageous if the laminations facing the leg axis lamination end face are arranged flush in a plane.

It has proven useful if the joining surfaces of the metal adhesive bond have been pretreated by mechanical or chemical surface treatment methods.

A particularly high strength of the metal adhesive bond can be achieved if the lamination end faces have a low mechanical roughness, e.g. are ground.

An adhesive based on Cyanoacrylate acid esters has proven to be particularly favorable in terms of mechanical strength and manufacturing aspects.

Brief description of the drawings

To further explain the invention, reference is made in the following part of the description to the drawings in which further advantageous embodiments, details and further developments of the invention can be found.

Figur 1

einen erfindungsgemäßen Transformator in einer räumlichen Skizze mit einem Schirmblechpaket längs des Kernschenkels;

Figur 2

eine Querschnittsdarstellung einer ersten Ausführung des Kernschenkels der Figur 1;

Figur 3

eine Querschnittsdarstellung einer zweiten Ausführung mit einem aus Teilblechpaketen stufenweise zusammengesetzten Kernschenkel.

It shows:

FIG. 1

a transformer according to the invention in a three-dimensional sketch with a shroud package along the core leg;

FIG. 2

a cross-sectional view of a first embodiment of the core leg of FIG. 1 ;

FIG. 3

a cross-sectional view of a second embodiment with a step-wise composite of partial laminated cores core legs.

Embodiment of the invention

The perspective view of FIG. 1 shows a simplified representation of a known Drekelkeltransformator whose core 1 is laminated. The core 1 consists essentially of the three core legs 2 ', 2 ", 2"', the lower yoke 5 and the upper yoke 6. Each of the legs 2 ', 2 ", 2"' carries a winding assembly 13, which in FIG. 1 is indicated by a broken line drawing.

As from the spatial sketch of the FIG. 1 1, each of the legs 2 ', 2 ", 2"' is in each case composed of a (core leg) laminated core 3 and of two additional laminated cores 4 'and 4 ", as explained in more detail below, the laminated cores 4', 4 "as a stray field screen. As seen in the stacking direction, the laminated core 3 is terminated by end blades 7 ', 7 ". This in FIG. 1 front sheet stack 4 'is applied to a front end plate 7' of the laminated core 3; the rearward laminated core 4 '' is applied to a rear end plate 7 '' of the laminated core 3. The laminated core 3 is dimensioned to guide the main flow of the transformer. The two additional laminated cores 4 'and 4''form a stray field shield, ie they serve to shield the magnetic flux leakage: They conduct the leakage flux entering from the air space in the region of the leg 2', 2 ", 2"', so that this not flat in one End lamella 7 'or 7 "(see FIG. 2 ) 'and there can cause eddy currents as a result of induction. In their axial longitudinal extent the laminated cores 4 'and 4 "are each limited by the lower and upper yoke 5 and 6, by blunt on the in FIG. 1 vertically extending laminations of the yoke 5 and 6, respectively. In the region of the impact, the transition between the stray field shield 4 ', 4 "and the yoke 5, 6 is flush.

The FIG. 2 shows a cross-sectional view of the core leg of FIG. 1 , The connection between the laminated core 3 and the stray field shield 4 ', 4 ", which is identified by the reference numeral 16, is effected by a metal adhesive bond, ie by material bond, ie by atomic or molecular forces. ) Welding or solder joint be formed, but it can also be made by frictional engagement by a pressing device, not shown in the drawing.

The laminations 40 ', 40 "of the stray field shield 4' and 4" are also held together by an adhesive. This is at least part of the area between adjacent broad surfaces of the fins 40 ', 40 "applied and not only causes the packaging of the sheets, but also contributes to the electrical insulation between the sheets at the same time Stray field screen 4 ', 4 "possible. Another advantage of the adhesive joints is the fact that thereby operating noise of a transformer can be reduced.

Suitable adhesives are in particular one-component products based on cyanoacrylate acid esters, which Cure humidity. Particularly suitable is an adhesive viscosity of a few hundred mPas, in particular 500-700 mPas, measured at 25 degrees Celsius. These adhesives can be easily applied by automated manufacturing tools in the manufacture of the transformer core. In practice, a pretreatment of the joining surfaces has proven to be particularly advantageous. A mechanical pre-treatment, in particular a grinding of the lamination end faces 9 ', 9 "( FIG. 2 ) of the laminated core 4 ', 4 ", considerably increases the strength of the adhesive bond It is also advantageous if the wide surface 8', 8" (FIG. FIG. 2 For example, this can be done by anodizing this contact surface 8 ', 8 "and / or the lamination end faces 9', 9".

As seen from the cross-sectional representation of FIG. 2 can be easily seen, in each case an end plate 7 'or 7 "closes the laminated core 3 at the top or at the bottom The layer planes 14 of this laminated core body 3 run in FIG. 2 and are substantially perpendicular to the layer planes 15 of the front laminated core 4 and the rear laminated core 4 ".The two laminated cores 4 'and 4" act with respect to the on the entrance surface of the end plate 7' and 7 "directed stray flux as a" magnetic shield " They take up the leakage flux itself and prevent it from entering one of the end plates 7 ', 7 ". Thus, the leakage flux is prevented from causing 3 eddy current losses in a lamination of the laminated core. In FIG. 2 For example, a single field line 11 of the leakage flux is shown. The "magnetic shield" is located directly on the laminated core 3 and forms an integral part of the core leg.

In the production of power transformers usually the core sheets are made from a sheet metal strip of a high-permeability soft magnetic material. A sheet metal web thickness between 0.23 mm and 0.35 mm is customary. The cutting of the individual sheets is done by punching or cutting. Remaining material always remains in the metal sheet. This residual material can be used favorably for the production of the stray shielding (ie for the production of the laminations 4 ', 4 ") by first winding up the web-shaped rest material, then pressing it and finally cutting it to shape in the stack Laminate 3 equal to the lamella thickness D4 of the stray field screen 4 ', 4 ". The laminated core 3 and the stray field shield 4 ', 4 "are made of the same soft magnetic material.

In the FIG. 3 a second embodiment of the invention is sketched, in which the cross section of the core leg is circular. The laminated core 3 is here composed of partial laminated cores 3 ', 3 ", 3"', etc., and combined with the shroud cores 4 'or 4 "to form a leg-laminated corrugated metal.The peripheral contour of the laminated core 3 extends in the region of the partial laminated cores 3', 3 (See steps 18 in area 17) In each cylinder section 10, which is arranged by an end plate 7 ', or 7 "and by the concentric with the leg axis 12 arranged inside surface of the winding 13 (in FIG. 3 is indicated by a circle) is limited, each is a stray field screen 4'bzw. The stratification levels in the laminated core 3 and in the stray field shield 4 'and 4 "are also in FIG. 3 perpendicular to each other. Each laminated core 4 'and 4 "is according to the invention in each case with the end faces 9' and 9" of the fins 40'bzw. This makes it possible that the leakage flux 11 entering from the air space is largely absorbed by the "magnetic shield" 4 ', 4 "and by this in the axial direction 12 of a core leg 2', 2 ", 2"'can be performed without significant eddy currents and thus a corresponding heating in the laminated core 3 is caused.

The advantage of the construction according to the invention is, in particular, that the stray field shield 4 'or 4 "is an integral part of the core of the transformer 1. The adhesive connection eliminates the generally solid fastening devices known from the prior art for the" magnetic shield " is from the cross-sectional view of FIG. 3 good to see: the laminations 4 'and 4 "are directly to the respective Endlamellen 7'bzw 7" of the (core leg) laminated core 3 at. Since there are no clamping strips or clamping wedges in the winding window, no additional space is required. The electrical winding 13 therefore does not have to be dimensioned larger.

As in the embodiment of FIG. 1 sketched, the stray field shield 4 ', 4 "connects seamlessly at the joint to the lower yoke 4 and to the upper yoke 5. The same applies to the in FIG. 3 sketched second embodiment. In both cases, the stray field screen 4 ', 4 "also carries a part of the main flow, that is, it performs a dual function, namely the leadership of the main flow and the shielding of the leakage flux.

Since the individual lamellae 40 ', 40 "of the laminated core 4', 4" are held together by adhesive, also fastening devices for these sheets, i. There are no solid support plates, which are unfavorable in terms of the formation of eddy currents and are also expensive to manufacture.

A further advantage of the present invention is the fact that the emission of operating noise due to the elastic material closure of the adhesive bonds is lower.

From the FIG. 3 is a further advantage of the illustrated embodiment can be seen: when the viewed in the radial direction extension of the individual fins 40 ', 40''of the laminated core 4' or 4 "to the peripheral contour 19 of the winding 13 (arc) is adjusted, the by the Cylinder section 10 predetermined volume in the winding window can be used very efficiently for guiding the magnetic flux.

Of course, the width of the individual sheet metal laminations 40 'or 40 "of a stray field shield laminated core 4' or 4" can also be the same size or stepped (in FIG FIG. 3 not shown).

It is understood that the invention is not limited to a specific design of a transformer or a choke core.

Compilation of the reference numbers used

• 1 transformer core
• 2 ', 2 ", 2"' core legs
• 3 (core leg) laminated core
• 4 ', 4 "stray field screen
• 5 lower yoke
• 6 upper yoke
• 7 ', 7 "end lamella
• 8 ', 8 "outer wide area of 7' or 7"
• 9 ', 9 "lamination face
• 10 cylinder section
• 11 field line (leakage flux)
• 12 leg axis
• 13 winding arrangement
• 14 layer plane of 3
• 15 layer plane of 4
• 16 cohesive connection
• 17 area peripheral contour of 3
• 18 level
• 19 area circumferential contour of 4 ', 4 "

  40 ', 40 "

  Laminations of the stray field screen 4 ', 4 "

  D3

  Slat thickness of 3

  D4

  Slat thickness of 4 ', 4 "

Claims (10)

1. Transformer core having a stray field shield which has at least one core limb (2', 2'', 2"') bearing a winding arrangement (13) formed from a laminated core (3) and a yoke (5, 6), with the laminated core (3) being closed off by end lamellas (7', 7"), with each end lamella (7', 7") being assigned a stray field shield (4', 4"), which features layered metal laminations (40', 40"), the layer planes (15) of which are arranged at right angles to the layer planes (14) of the laminated core (3), wherein the metal laminations (40', 40") with lamination end surfaces (9', 9") pointing towards the laminated core (3) are arranged adjacent to each other on an outer width surface (8', 8") of an assigned end lamination (7', 7''), characterised in that the transition between the metal laminations (40',40") and the yoke (5, 6) is embodied flush.
2. Transformer core according to claim 1, characterised in that an adhesive is present between adjacent metal laminations (40', 40'') of a stray field shield (4', 4'').
3. Transformer core according to claim 2, characterised in that the stray field shield (4', 4'') is attached to the width surface (8', 8") of an assigned end lamination (7', 7") by means of adhesive.
4. Transformer core according to claim 1, 2, or 3, characterised in that each metal lamination (40', 40") has a thickness (D4) which is as great as a lamination thickness (D3) of a metal lamination of the laminated core (3).
5. Transformer core according to claim 4, characterised in that the laminated core (3) and the stray field shield (4', 4") are made from the same soft magnetic material.
6. Transformer core according to claim 5, characterised in that the laminated core (3) is composed of laminated core sections (3', 3", 3") so that, when viewed in cross-section, the circumferential contour in an area (17) of the laminated core (3) has steps (18) (Fig. 3) and in an area (19) of the stray field shield (4', 4") is the arc of a circle which is concentric to a core limb axis (12).
7. Transformer core according to claim 4, characterised in that the adhesive is embodied to cover part of the surface between width surfaces of the metal laminations (40', 40") lying adjacent to one another.
8. Transformer core according to claim 4, characterised in that the metal lamination end faces (9', 9") pointing towards the laminated core (3) are arranged lying in the plane of a width surface (8', 8'').
9. Transformer core according to claim 4, characterised in that the metal lamination end faces (9', 9") are ground.
10. Transformer core according to claim 2 or 3, characterised in that the adhesive is a cyanoacrylate adhesive.

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