EP2251875A1 - Transformer core - Google Patents

Abstract

The core (70) has transformer core disks (52, 72), which are congruently arranged adjacent to each other, with horizontal projections. Passage openings are provided in the horizontal projections. The transformer core disks predominantly consist of amorphous ferromagnetic material. Cooling channels (64, 88, 90, 94) are arranged between the transformer core disks. The cooling channels are partially formed of distance elements (80-86) or a hollow element. The cooling channels partially consist of an electrically insulating material.

Description

The invention relates to a transformer core for a power transformer and a power transformer with such a transformer core.

It is well known that transformers are used to power transfer the power supply by voltage adjustment from a first voltage level to a second one. Instead of previously widely used power transformers with oil filling, power transformers in dry construction, so-called dry-type transformers, are increasingly being used.

The structure of a power transformer in dry construction is very similar to that of the power transformer with oil filling, as well as power transformer in dry construction, the respective winding body are applied to cores made of ferromagnetic material, which are connected at both ends with yokes and form a magnetic circuit.

However, in the case of the dry-type transformers, the heat loss, which was absorbed by the oil in the case of power transformers filled with oil and discharged via suitable cooling surfaces or separate coolers, is removed by air convection. The lower specific heat capacity of the air compared to oil means a performance limitation for dry-type transformers.

Ohmic losses occur in the windings of a loaded transformer due to the winding currents and eddy currents in the conductor material. These ohms Losses are superimposed by no-load losses and possibly short circuit losses as well as hysteresis losses.

The no-load losses are mainly determined by the induction and nature of the core and are approximately independent of the operating temperature of the transformer. The short-circuit losses are temperature-dependent and increase at constant load with the temperature or the resistivity of the conductor material. In order to keep the hysteresis losses as small as possible, preferably core materials with a very narrow hysteresis loop are used.

In order to reduce the resulting heat losses of a dry-type transformer and thus to improve its load capacity, amorphous core material is used in place of grain-oriented core material in recent times.

However, the use of amorphous materials requires new constructions and processing because, on the one hand, because of the lower flux density compared to a conventional transformer core, larger core cross-sections are required and, on the other hand, an amorphous core material is more sensitive to higher temperatures than a grain-oriented core sheet.

In addition, the amorphous material, which is usually available as a flat strip material, is mechanically very sensitive, which is why the available widths of the strip material are limited, for example to 200 mm. The mechanically realizable sizes of a transformer core are thus limited. The achievable ratings of amorphous core transformers have therefore been limited since then, for example, to 1 MVA, while conventional core dry type transformers have power ratings up to and over 20MVA.

Based on this prior art, it is an object of the invention to provide a transformer core of amorphous material, which increases the achievable since then nominal power of a power transformer with amorphous core. The object of the invention is also to provide a corresponding power transformer.

This object is achieved by a transformer core of the type mentioned in the introduction. This is characterized in that it has at least two transformer core disks arranged parallel to one another and at least approximately congruently adjacent to one another with an at least similar plan, that in the floor plan at least one through hole is provided, that the transformer core plates at least predominantly consist of an amorphous ferromagnetic material and that at least one cooling channel is disposed between the transformer core.

The at least one passage opening serves as a winding window for one or more later to be arranged transformer windings. A transformer core disk preferably extends perpendicular to its ground plan into a certain height. The height is limited by the mechanically achievable size and is for example 15cm to 25cm or even higher. If transformer core sizes are too large, even the dead weight of the core could lead to a risk of breakage due to the mechanical sensitivity of the amorphous ferromagnetic core material. In addition, the problem of core heating during operation of the power transformer becomes more critical with increasing height or thickness of the transformer core disk.

Similar floor plans do not necessarily mean an identity of the floor plans. Rather, it is also conceivable, for example, in the arrangement of three transformer core plates, to provide the two outer discs with a slightly larger passage opening and a slightly smaller outer floor plan than the middle disc.

Due to the modular division of the transformer core into a plurality of transformer core disks, each core disk is to be manufactured separately and, after production, forms a mechanically at least stabilized unit, which as such can also be transported and combined with other components to form a larger transformer core.

An arrangement of a plurality of such transformer core disks with cooling channels therebetween increases the cooling surface for the transformer core assembled in this way, so that excessive heating of the temperature-sensitive core material can also be counteracted.

The combination of a modular arrangement of transformer core disks and cooling channels therebetween thus advantageously makes it possible to construct and operate a transformer core made of amorphous ferromagnetic material, which is significantly larger in size.

Preferably, a plurality of cooling channels extend along the entire floor plan. The available cooling surface is exploited here in high degree and thus allows a correspondingly high cooling effect. It is both natural cooling, so for example, a flow through the cooling channels with ambient air, which passes through lower inlet openings in the cooling channels and in the heated state escapes again at the upper outlet openings, as well as forced cooling possible.

According to a preferred embodiment, the amorphous ferromagnetic material is band-shaped and arranged in several adjacent layers transversely to the plan around the at least one passage opening, so that a thickness of a transformer core results from a width of the band-shaped material.

Ribbon-shaped amorphous core material is well transportable on rolls despite its mechanical sensitivity and also allows a flexible manufacturing process of a transformer core or a transformer core. Preferably, the band material is applied in ring-like layers around the at least one passage opening. One layer comprises an angle of, for example, 360 °, with which a metal sheet encloses exactly the at least one through opening. An adjacent layer is then formed by another sheet.

360 ° are particularly advantageous in that, in the case of a hanging assembly of a transformer core or a transformer core disk, the mechanically sensitive metal sheet, which has a thickness of 15-50 μm, for example, can be hung over the upper edge of the core to be manufactured or via a holding device. On the sides of the plate then depends on each gravitational down and can then under the greatest possible avoidance of mechanical stress be joined at the lower edge of the transformer core to be manufactured at its two ends.

In the presence of a plurality of through openings or winding windows, a metal sheet in the respective outer layers preferably encloses all passage openings so as to ensure increased mechanical stability of the manufactured transformer core.

In a particularly preferred embodiment of the transformer core according to the invention, the plan view of the at least two transformer core disks is approximately rectangular in each case and the respective at least one through opening likewise forms so that at least two transformer core legs and at least two transformer core yokes are formed. The term rectangular is to be interpreted such that in each case the material-related bending radii of the strip material are taken into account, for example 100mm - 300mm and over, so that in general no sharp edges are formed.

This shape corresponds approximately to the shape of a conventional transformer core and allows a simplified arrangement of windings on the transformer legs thus formed. A preferred form here includes two rectangular through-openings or winding windows, so that three legs are formed, which allow the use of the transformer core for a three-phase power transformer.

In a further variant of the transformer core according to the invention, at least two transformer core disks can be opened and closed in layers on at least one leg and / or yoke, so that in the opened state, a cylindrical hollow body can be pushed over at least one leg, which is then penetrated by the leg.

Such a possibility of layer-wise opening consists, for example, in that the transformer core is arranged hanging vertically and the sheets forming the transformer core or the transformer core disks are in each case joined together in the part then located at the bottom. After opening the respective hang Sheets, which previously formed the lower yoke, each as an extension of the respective transformer leg down and it is from below a cylindrical hollow body, in particular a winding, pushed.

Advantageously, the at least one cooling channel is at least partially formed by spacer elements which space the transformer core disks. This type of cooling channel avoids additional thermal resistance between the cooling medium, such as air, and the adjacent transformer core disks,

Alternatively, the at least one cooling channel is at least partially formed from at least one hollow element. This is advantageous if, for example, a liquid is used as the cooling medium. In this case, the core surface is protected from direct contact with the cooling medium and a closed coolant circuit can be formed.

In a variant of the transformer core according to the invention, the at least one cooling channel consists at least predominantly of an electrically insulating material, for example a resin-impregnated hard fiber material.

In a further embodiment of the invention, a common supply connection and / or a common discharge connection is provided for a cooling medium flowing through the at least one cooling channel, which proves to be advantageous in particular in forced cooling with a liquid cooling medium.

In a preferred variant of the invention, the transformer core is also arranged in a hanging manner with a vertically oriented ground plan during operation. The mechanical loads on the transformer core are thereby further reduced.

According to a further variant of the transformer core, at least one electrical winding arranged about a winding axis is arranged on a limb of the transformer core, wherein the winding is penetrated by the limb along its winding axis. This corresponds to a typical winding arrangement on conventional transformer cores.

The object is also achieved by a power transformer with a transformer core of the type described above. In a preferred embodiment, this is a three-phase transformer, each having at least three primary and three secondary windings. The above-described advantages of the transformer core according to the invention are accordingly also applicable to such a transformer.

Further advantageous embodiment possibilities can be found in the further dependent claims.

Reference to the embodiments illustrated in the drawings, the invention, further embodiments and other advantages will be described in detail.

Fig. 1

eine exemplarische erste Transformatorkernscheibe in dreidimensionaler Ansicht,

Fig. 2

eine exemplarische zweite Transformatorkernscheibe mit Distanzelementen in einer Draufsicht,

Fig. 3

einen exemplarischer Transformatorkern in einer Seitenansicht und

Fig. 4

einen Transformatorkernschenkel mit elektrischer Wicklung in einer Schnitt- ansicht.

Show it:

Fig. 1

an exemplary first transformer core in three-dimensional view,

Fig. 2

an exemplary second transformer core disk with spacers in a plan view,

Fig. 3

an exemplary transformer core in a side view and

Fig. 4

a transformer core with electrical winding in a sectional view.

Fig. 1 shows an exemplary first transformer core 10 in a three-dimensional view, wherein the alignment of the three-dimensional coordinates by the coordinate system 42 is indicated. The transformer core 10 has a rectangular plan in the z-direction 44 and two rectangular passage openings 12, 14 perpendicular to the plan in the y-direction, which serve as a winding window. The transformer core disk 10 is formed from a plurality of layers 16, 18, 20, 22, 24 of a band-shaped amorphous ferromagnetic material, the actual number of layers being unequally higher than the five layers indicated here, for example due to their small thickness of approximately 15-50 μm several thousand. It should be noted in the presentation that due to a Minimum bending radius of the sheets, the edges of the floor plan are not formed as angular, as indicated in the figure, but for example with a radius of 100mm - 300mm.

Each layer is formed in this example exactly by a circumferential sheet having a width designated by the reference numeral 36, the two ends are joined together in the representation in the lower yoke region of the transformer core. At just these points, which are indicated in the figure as opening points 26, 28, 30, 32, 34, the transformer core is required to open again, for example, to push in a further production step, a winding from below over the then accessible transformer core plate legs ,

The respectively indicated three inner layers of strip material 16, 18, 20 each enclose one of the two passage openings or winding windows 12, 14. The two indicated outer layers 22, 24 enclose both passage openings 12, 14 with the respective inner layers 16, 18, 20. This is particularly useful for reasons of mechanical stability of the transformer core 10, which is shown hanging on the two hangers 38, 40. The hanging arrangement is particularly advantageous during production but also during later operation, because the mechanical load for the transformer core or the transformer core disk 10 is thus reduced.

Fig. 2 shows an exemplary second transformer core plate 52 with spacers in a plan view 50. The plan view of the second transformer core plate 52 is also rectangular in this figure, rectangular and has two also rectangular passage openings 54, 56, which serve as a winding window. Thus, three transformer core legs 58, 60, 62 are pronounced, which are connected at their two ends in each case via a yoke 66, 68.

Arranged on the second transformer core disk 52, rectangular spacer elements are indicated, which are drawn as rectangles filled in black. Cooling channels, whose height corresponds to the preferably uniform height of the spacer elements, result between these spacer elements. In a real arrangement, the corresponding transformer core is arranged upright, so that with natural cooling, a flow through the cooling channels, one of which is exemplified by the reference numeral 64, with air from bottom to top, as indicated by the arrows.

Fig. 3 shows an exemplary transformer core 70 in a side view, this from the already in Fig. 2 shown second transformer core plate 52 with the associated spacer elements and a structurally identical third transformer core plate 72 is formed. Visible in this sectional view and provided with a reference number are the cooling channels 88, 90, 92, 94, 96 and the already in Fig. 2 characterized first cooling channel 64, which are formed between the spacer elements 80, 82, 84, 86 and the other unmarked spacer elements. Also visible are the opening points 76 and 78 of the two transformer core disks, to which the peripheral outer plates are joined together.

Such an assembly of the transformer core or the transformer core plate forming sheets is possible for example by a layer-wise gearing and wrapping the legs or yokes formed with a suitable band-shaped fastening material.

Fig. 4 1 shows a transformer core leg with electrical winding in a sectional view 100. The transformer core leg is formed by the three transformer core disk shanks 102, 104, 106 and the hollow elements 108 and 110 arranged therebetween whose inner region forms the cooling channels 112 and 114. Such hollow elements are useful in particular when using a different cooling medium than the ambient air, because in such a case preferably a closed circuit of the cooling medium is to be formed. The width and height of the leg cross sections of the transformer core disks are selected such that an ellipse-like cross section of the transformer core leg results, which corresponds to the high-cylindrical inner cross section of the winding 116. In addition, the cooling effect is homogenized over the entire leg cross-section, because the outer transformer core disks 102, 106 adjoining only one cooling channel 112, 114 are thinner than the central transformer core disk 104 surrounded by cooling channels 112, 114 on both sides.

LIST OF REFERENCE NUMBERS

10

exemplary first transformer core disk

12

first passage opening

14

second passage opening

16

first layer of the band-shaped material

18

second layer of the band-shaped material

20

third layer of the band-shaped material

22

fourth layer of the band-shaped material

24

fifth position of the band-shaped material

26

first opening point

28

second opening point

30

third opening point

32

fourth opening point

34

fifth opening point

36

Width of the band-shaped material

38

first hanging device

40

second hanging device

42

coordinate system

44

vertical orientation

50

exemplary second transformer core disk with spacers

52

second transformer core disk

54

third passage opening

56

fourth passage opening

58

first transformer core leg

60

second transformer core leg

62

third transformer core

64

first cooling channel

66

first yoke

68

second yoke

70

exemplary transformer core

72

third transformer core disk

76

sixth opening point

78

seventh opening point

80

first spacer element

82

second spacer element

84

third spacer element

86

fourth spacer element

88

second cooling channel

90

third cooling channel

92

fourth cooling channel

94

fifth cooling channel

96

sixth cooling channel

100

Transformer core with electrical winding

102

fourth transformer core disk

104

fifth transformer core

106

sixth transformer core disk

108

first hollow element

110

second hollow element

112

seventh cooling channel

114

eighth cooling channel

116

electrical winding in the form of a cylindrical hollow body

Claims (13)

A transformer core (70) for a power transformer, characterized in that it has at least two transformer core disks (10, 52, 72, 102, 104, 106) arranged parallel to each other and at least approximately congruent with an at least similar plan, that in the plan view at least in each case a through opening (12, 14, 54, 56) is provided, that the transformer core disks (10, 52, 72, 102, 104, 106) at least predominantly consist of an amorphous ferromagnetic material and that between the transformer core disks (10, 52, 72, 102, 104, 106) at least one cooling channel (64, 88, 90, 92, 94, 96, 112, 114) is arranged. Transformer core according to claim 1, characterized in that a plurality of cooling channels (64, 88, 90, 92, 94, 96, 112, 114) are arranged along the entire floor plan. Transformer core according to one of claims 1 or 2, characterized in that the amorphous ferromagnetic material is band-shaped and in several adjacent layers (16, 18, 20, 22, 24) transversely to the plan around the at least one through hole (12, 14, 54, 56) is arranged so that a thickness of a transformer core disc results from a width (36) of the band-shaped material. Transformer core according to one of the preceding claims, characterized in that the floor plan of the at least two transformer core discs (10, 52, 72, 102, 104, 106) is approximately rectangular in each case and that the respective at least one passage opening (12, 14, 54, 56) is also approximately rectangular, so that at least two transformer core legs (58, 60, 62) and at least two transformer core yokes (66, 68) are formed. Transformer core according to Claim 4, characterized in that the at least two transformer core disks (10, 52, 72, 102, 104, 106) are opened in layers on at least one leg (58, 60, 62) and / or yoke (66, 68). and closable (26, 28, 30, 32, 34), so that in the opened state via at least one leg (58, 60, 62) a cylindrical hollow body (116) is slidable, which then by the leg (58, 60, 62) is penetrated. Transformer core according to one of the preceding claims, characterized in that the at least one cooling channel (64, 88, 90, 92, 94, 96, 112, 114) at least partially from spacer elements (80, 82, 84, 86) is formed, which the Spaced transformer core disks. Transformer core according to one of the preceding claims, characterized in that the at least one cooling channel (64, 88, 90, 92, 94, 96, 112, 114) at least partially from at least one hollow element (108, 110) is formed. Transformer core according to one of the preceding claims, characterized in that the at least one cooling channel (64, 88, 90, 92, 94, 96, 112, 114) consists at least predominantly of an electrically insulating material. Transformer core according to one of the preceding claims, characterized in that a common supply port and / or a common discharge port for the at least one cooling channel (64, 88, 90, 92, 94, 96, 112, 114) flowing through the cooling medium is provided. Transformer core according to one of claims 4 to 9, characterized in that the transformer core (70) is arranged hanging in a vertical (44) aligned plan. Transformer core according to one of claims 4 to 10, characterized in that at least one arranged around a winding axis electrical winding (116) on a leg (58, 60, 62) of the transformer core (70) is arranged, wherein the winding (116) along its Winding axis of the leg (58, 60, 62, [102 + 104 + 106 + 108 + 110]) is penetrated. Power transformer with a transformer core (70) and at least one winding according to one of claims 1 to 11. Power transformer according to claim 12, characterized in that it is a three-phase transformer, each having at least three primary and three secondary windings.

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