SK98999A3 - A transformer/reactor and a method for manufacturing a transformer/reactor - Google Patents

Abstract

The present invention relates to a transformer or a reactor and a method of manufacturing a transformer/reactor. The transformer/reactor comprises a core and at least one winding, in which the core (1; 11; 21; 31) consists of at least two segments (4; 14; 24, 25; 33, 34, 36, 37), and the winding is flexible and comprises an electrically conducting core (7) surrounded by an inner semiconducting layer (8), an insulating layer (9) surrounding the inner semiconducting layer and consisting of solid material, and an outer semiconducting layer (10) surrounding the insulating layer, said layers adhering to each other.

Description

Technical field

The present invention relates to a transformer / reactor comprising a core and at least one winding.

The present invention also relates to a method of use in manufacturing a corresponding transformer / reactor.

BACKGROUND OF THE INVENTION

Transformers / reactors are available in all power ranges from several W to 1000 MW. The term 'power transformer / reactor ** generally refers to transformers / reactors having a rated power ranging from a few hundred kW to more than 1000 MW and a rated voltage ranging from 3-4 kV to extremely high transmission voltages.

A conventional transformer comprises a transformer core, hereinafter referred to as a core, of laminated oriented sheet metal, usually of an iron-silicon alloy. The core consists of several nuclear legs connected by a caliper. Many windings are placed around the nuclear feet, which are commonly called primary, secondary and regulatory windings. In the case of power transformers, these windings are almost always arranged concentrically and distributed along the nuclear legs. The core ¹ and 1 'of the transformer has a rectangular "window" through which the winding. This rectangular window is essentially the result of manufacturing techniques that are used when the core is laminated.

The use of transformer cores of various shapes is known, for example, from DE 40414, US 2,446,999, GB 2,025,150, US 3,792,399, US 4,229,721. Some of these documents also disclose cores made of segments. However, none of these documents relates to high-voltage power transformers and would not be applicable to such transformers according to the current oil cooling technique discussed below.

Conventional power transformers at the bottom of said power range are sometimes equipped with air cooling to eliminate natural heat losses that cannot be avoided. However, the most common power transformers are oil cooled, generally by compressed oil cooling. This is mainly used in high-power transformers. Oil-cooled transformers have several well-known drawbacks. For example, they are large, cumbersome and heavy, causing particularly significant transport problems, while imposing great demands on safety and attachments.

However, it has been shown that oil-cooled power transformers can be replaced in many cases by new type of dry transformers. This new dry transformer is equipped with a high-voltage cable winding, i. insulated high-voltage electrical conductor. Dry transformers can thus be used at considerably higher power ranges than hitherto possible. The terms "dry transformer" and "dry reactor" thus refer to a transformer / reactor that is not oil-cooled but preferably air-cooled.

As for reactors, these include a core that is usually equipped with only one winding. In other respects, as mentioned in the case of transformers, it is also important for reactors. In particular, even large reactors are oil-cooled.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a transformer or reactor that allows to overcome some of the drawbacks inherent in a conventional power transformer / reactor as well as to provide a method for use in the manufacture of such a transformer / reactor.

The objects are achieved by means of a transformer / reactor having the features defined in claim 1 and means of a method for producing such a transformer / reactor in accordance with the features defined in claim 25.

According to the first feature of claim 1, the core comprises at least two segments. The corresponding method comprises a core manufacturing feature that comprises at least two segments. The term "segment" or "segmented core" means that the core of the transformer / reactor is constructed from segments substantially identical, or from parts joined together to form a core.

Many advantages are obtained by the core being built from segments. First, even relatively large cores may be substantially annular in shape, offering significant advantages, which will be described below.

Secondly, this makes the core winding easier, since each segment can be wound separately

A third advantage of segmented cores is that the core parts can be disassembled or assembled at any time during production.

The advantages are also obtained in terms of production, since the core can be built in the form of modules, each comprising one or more segments. This also offers considerable advantages in terms of transport, since the core can be transported in segments and can then be assembled at the site where it will be used. If necessary, the winding can also be wound in place.

According to another feature of claim 1, the winding is flexible and comprises an electrically conductive core surrounded by an inner semiconductive layer, an insulating layer that surrounds the inner semiconducting layer and is comprised of a solid material, and an outer semiconducting layer that surrounds the insulating layer, on the second. According to a further feature of the method, said method comprises the step of installing a winding into the core, the winding being defined in accordance with claim 1.

Thus, windings in a transformer / reactor according to the invention are preferably of the type corresponding to the cables having fixed extruded insulation, of the type now used for power transmission, such as XLPE cables or EPR insulated cables. Such a cable comprises an inner conductor composed of one or more core parts, an inner semiconducting layer surrounding the conductor, a solid insulating layer that surrounds the semiconducting layer, and an outer semiconducting layer surrounding the insulating layer. Such cables are flexible, which is an important feature in this context, since the technology of the device of the present invention is essentially based on winding systems in which the winding is formed from a cable that bends (or curves) during assembly. The flexibility of the XLPE cable usually coincides with a radius of curvature of approximately 20 cm for a 30 mm diameter cable and approximately 65 cm for an 80 mm diameter cable. In this application, the term "flexible" is used to indicate that the winding is flexible up to the radius of curvature, about four times the cable diameter, preferably eight to twelve times the cable diameter.

The winding should be designed to retain its properties even when bent and when subjected to thermal stress during operation. It is essential that the layers retain their mutual adherence in this respect. The material properties of the layers are crucial here, in particular their elasticity and coefficients of thermal expansion. In the XLPE cable, the insulating layer consists, for example, of low density crosslinked polyethylene and the semiconducting layers consist of polyethylene with carbon black in which metal particles are mixed. Volume changes as a result of temperature fluctuations are completely absorbed as changes in cable radius and, due to the relatively slight difference between the coefficients of thermal expansion in the layers relative to the elasticity of these materials, radial stretching can take place without losing adhesion between the layers.

The material combinations mentioned above should be considered as examples only. Other combinations meeting the specified conditions as well as being semiconductive, i.e. have a resistivity in the interval 10 ' ¹ -10 ^<s Qcm, e.g. 1-500 Hcm or 10,200 Ωαη, of course, are also within the scope of this invention.

For example, the insulating layer may consist of a rigid thermoplastic material such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polybutylene (PB), polymethylpentene ("TPX"), crosslinked materials such as crosslinked polyethylene (XLPE), or rubber, such as ethylene-propylene rubber (EPR), or silicone rubber.

The inner and outer semiconductive layers may be of the same base material, but with conductive material particles such as carbon black or metal powder mixed therein.

The mechanical properties of these materials, in particular their coefficients of thermal expansion, are influenced relatively little by whether or not the carbon black or metal powder is mixed in them - at least in the proportions required to achieve the conductivity required by the present invention. The insulating layer and semiconducting layers thus have substantially the same coefficients of thermal expansion.

Ethylene-vinyl acetate copolymers / nitrile rubber (EVA / NBR), butyl grafted polyethylene, ethylene-butyl acrylate copolymers (EBA) and ethylene-ethyl acrylate copolymers (EEA) may also form suitable polymers for semiconducting layers.

Even when different types of material are used as a basis in different layers, it is desirable that their coefficients of thermal expansion be substantially the same. This is the case with the combination of materials mentioned above.

The materials mentioned above have a relatively good elasticity with an elastic modulus E < 500 MPa, preferably < 200 MPa. The elasticity is sufficient for small differences between the coefficients of thermal expansion of the materials in the layers in the radial direction of elasticity, so that no cracks or other damages occur and therefore the layers do not loosen each other. The material in the layers is resilient and the adhesion between the layers is at least as great as the weakest material.

The conductivity of the two semiconducting layers is sufficient to sufficiently equalize the potential along each layer. The conductivity of the outer semiconductive layer is sufficiently high to equalize the electric field within reach of the cable, but low enough not to increase the considerable losses caused by currents induced in the longitudinal direction of the layer.

Thus, each of the two semiconducting layers essentially forms one equipotential surface, and these layers substantially enclose the electric field between them.

Of course, nothing prevents one or more additional semiconducting layers from being formed in the insulating layer.

Other characteristics and advantages will be apparent from the other dependent claims.

In addition to the above-mentioned advantages obtained from a winding consisting of a cable, there are fewer problems with magnetic stray fields when using a cable. This has the advantage that the toroidal core can be used even in high-voltage transformers, provided that the problem of arranging a sufficiently large core is solved and this is done according to the invention using a segmented core. An important advantage is the fact that technology which has so far been known only from the low-voltage field of electronics can be used.

According to a particularly advantageous feature, it is noted that the winding consists of a high-voltage cable.

As a further feature, it is noted that the high voltage cable preferably has a diameter of 20-250 mm and a conductor area of 80-3000 mm ² .

According to a particularly preferred characteristic, the core is substantially annular. This shape has the advantage of providing a shorter magnetic path than a rectangular core and better distribution of fluxes in the core. The advantages of an annular core with a shorter magnetic path than that of a conventional core are that less material is used, the core is lighter and cheaper, resulting in lower energy losses and higher efficiency.

According to another particularly advantageous characteristic, the core has a substantially toroidal shape. In the toroidal core, the coil can be evenly distributed around the entire core, reducing problems with unwanted magnetic fields. A high degree of symmetry is also advantageous because the magnetic field attenuates more quickly as a function of distance.

In one embodiment, the core of the transformer / reactor has a window that is substantially circular in shape and the annular shape of the core is circular. Alternatively, the core may comprise a window that is substantially elliptical and the annular shape of the core is elliptical. The core may also be rectangular.

According to a preferred embodiment, the core consists of two segments. In many cases, this is, of course, the simplest alternative that is in itself an advantage.

According to a further preferred embodiment, the core consists of four segments, two straight segments and two segments having a semicircular shape, wherein the two semicircular segments are connected to each other by two straight segments. This design, as well as the elliptical design, has the advantage that it can be used even in tight spaces.

Advantageous features include that each segment comprises a plurality of sheets and that the core is formed as a laminated core.

According to further advantageous features, the sheets may consist of magnetically oriented steel and several segments are sufficiently large to prevent the direction of magnetic orientation being lost. Alternatively, the sheets may be made of amorphous steel. ¹ , ''

According to one embodiment, adjacent segments are held together by one segment having at least one protruding sheet that fits into a corresponding gap between the sheets formed on the corresponding side of the nearest adjacent segment, thereby forming a lap joint. This creates the advantage that no special attachments are required to hold the segments together to form a core together. However, alternatively or by means of an additional device, the transformer / reactor may comprise additional devices.

According to yet another preferred feature, the segment core comprises internal tubes which can be used for the cooling medium. Depending on the particular embodiment of the cooling tubes, the core segments can be connected.

Finally, the method according to the invention is characterized by the advantageous feature that the core windings are wound on the segment before the segment is assembled to form the core.

The invention is preferably intended for single-phase transformers.

In summary, it should be pointed out that by using a combination of winding as defined in claim 1 and a segment core, the present invention can provide high voltage dry transformers / reactors with large cores of substantially annular shape and preferably of toroidal shape.

Image overview

For a better understanding of the invention, four segments will be described in detail with reference to the accompanying drawings, in which:

Fig. 1 is a schematic perspective view of a first embodiment of the invention, f

Fig. 2 is a schematic view of a second embodiment of the invention; FIG. 3 is a schematic view of a third embodiment of the invention; FIG. 4 is a schematic view of a fourth embodiment of the invention; FIG. Fig. 5 shows a cross-section of a core segment according to the invention; 6 shows a cross-sectional view of a high voltage cable.

Examples'

A schematic diagram of the present invention, which also constitutes a first embodiment, is schematically shown in FIG. The figure shows a transformer core 1, which could equally well be a reactor core, provided with a winding 2 which passes through a substantially circular window 5. The core is made up of a relatively large number of segments 4 for which only one reference number is used. The segments are preferably the same as this is advantageous in terms of manufacture, but may, if appropriate, have a partially different shape. The diagram shows eighteen segments, each segment consisting of several plates 3, which are built on top of each other in a known manner. An example of how these sheets can be stacked on top of each other is shown in FIG. 5, showing a cross-section of a core segment. Sheets are usually glued together. By stacking the sheets, a so-called laminated core is obtained. Various bonding methods may be used, of which only one is shown in FIG. 5. Another possible method is known, for example, as step lap technology.

The individual sheets shown in the embodiment of FIG. 1 have a shape corresponding to a parallel trapezoid. This means that the “annular” shape of the core is actually polygonal. However, with a relatively large number of segments, as in this case, the annular shape or the toroidal shape, such as the case with a core cross-section, approaches a polygonal shape.

It should be stressed that the terms "annular, circular window and toroidal", which includes a circular cross-section, all referring to the core, refer in this context not only to a geometrically perfect circle, torus or ring, but should also be considered to include the approximate equivalents of these geometrical figures due to the fact that the core may have a cross-section across both directions, transverse and longitudinal, which is in fact a polygon. 1

Figure 2 shows a second embodiment of the invention in the form of a core 11 with segments 14 as shown above. According to the embodiment of Figure 2, the segments have a shape similar to a circular cut-out with a cut-off end so that they can be joined into an approximate circle, preferably a toroidal shape. Each sheet 3 in Figure 5 is thus cut to form the circular cutout shown in Figure 2. In this case, the core 11 is composed of eight segments 14. The segments in this core are formed of sheets of magnetically oriented steel, as shown by arrows on the Figure. When using magnetically oriented steel, it is important that several segments are sufficient to not lose the magnetic direction of orientation. Here, the core also has a circular window 15 through which the winding or winding should pass.

A third embodiment of the core is shown in Figure 3. The segmental core 21 is composed of only two segments in the form of two semicircles 23, 24 which have been connected to the core with a substantially circular window 25.

A fourth embodiment is shown in Figure 4, from which it can be seen that the core 31 preferably consists of four segments: two straight segments 36, 37 and two segments 33, 34 in the form of semicircles. The two segments 33, 34 in the form of semicircles are connected by two straight segments 36, 37. The core has a window 35.

The segments may be held together or joined together in various ways to form an annular core. Thus, it is possible to arrange segments with a plurality of sheets that protrude out from the useful side of the segment, i. a side that faces the adjacent segment and that are inserted into corresponding gaps between the sheets arranged on the corresponding side of the adjacent adjacent segment, and vice versa that the sheets in the adjacent segments overlap. This provides a joint between the sheets in two adjacent segments, which is formed in the same manner as the example of the joints formed within the segment shown in Figure 5. Alternatively, special attachments such as clamps, yokes, screws and the like can be used.

One advantage of the segment core is that it may comprise internal coolant tubes. These tubes may be comprised of gaps 12 that have been formed between the sheets during the formation of the layers. Alternatively, coolant tubes may be installed in segments during lamination of the sheets. Another alternative is to subsequently drill the tubes through the segments. It is also possible for the segments to be held together by internal cooling tubes in such a way that adjacent segments are held together by at least one segment that is provided with a cooling tube terminating in a projecting end of the tube which is shaped to fit into the corresponding end of the tube terminating the cooling tube. pipe in the adjacent segment.

Finally, Figure 6 shows a cross-section of a high voltage cable 6 which is particularly suitable for use in the present invention. The high voltage cable 6 comprises a plurality of cores 2, which are made, for example, of copper (Cu) and has a circular cross-section. These veins are arranged in the middle of the high voltage cable. The first semiconductor layer 8 surrounds the veins 2. This first semiconductor layer S is surrounded by an insulating layer 2, for example XLPE insulation. The insulating layer 9 is surrounded by a second semiconductive layer 10. The cable shown differs from a conventional high-voltage cable in that the external mechanical protective sleeve and the metal shielding which usually surround such cables is omitted. Thus, the term "high voltage cable" in this patent application does not necessarily include metal shielding or sheathing that usually surround such power transmission cables.

The embodiments shown and described above may be considered merely as examples and the invention should not be limited thereto, but may be varied within the scope of the invention as defined in the appended claims. Thus, the core window in three of the illustrated examples has been shown essentially only in a circular form, but can of course also be elliptical or of another shape. Similarly, the annular core shape may be elliptical instead of circular. This may be more advantageous, for example, when the available space is limited in width. Furthermore, of course, nothing prevents the segmented core from having a rectangular shape with a rectangular window.

The number of segments can vary greatly depending on many different considerations, with regard to production technology, winding technology, transmission distance, etc. The sheets may also be made of steel other than magnetically oriented steel, e.g. of amorphous steel.

Finally, it should be noted that the invention is of course also applicable to a three-phase transformer / reactor by a combination of three cores constructed in accordance with the invention.

Claims (26)

PATENT CLAIMS A transformer / reactor comprising a core and at least one winding in which the core (1; 11; 21; 31) consists of at least two segments (4; 14; 24, 25; 33, 34, 36, 37) and the winding is flexible and comprising an electrically conductive core (7) surrounded by an inner semiconductive layer (8), which is surrounded by an insulating layer (9) and consists of a solid material, and the insulating layer is surrounded by an outer semiconductive layer (10), on the second. Transformer / reactor according to claim 1, characterized in that the layers (8, 9, 10) consist of materials having such elasticity and such a relationship between the coefficients of thermal expansion of the materials that, despite the volume variations of these layers caused by fluctuations temperatures during operation, the layers retain adherence to each other. Transformer / reactor according to claim 2, characterized in that the materials in said layers (8, 9, 10) have a high elasticity, preferably with a modulus of elasticity of less than 500 MPa, even more preferably less than 200 MPa. Transformer / reactor according to claim 3, characterized in that the coefficients of thermal expansion of the materials in said layers (8, 9, 10) have substantially the same size. Transformer / reactor according to claim 4, characterized in that the adhesion between the layers (8, 9, 10) is at least as great as in the weakest material. Transformer / reactor according to claim 1 or claim 2, characterized in that each base semiconducting layer (8, 10) forms one equipotential surface. Transformer / reactor according to one of Claims 1 to 6, characterized in that the stator windings (4) consist of high-voltage cables (6). Transformer / reactor according to claim 7, characterized in that the high voltage cable (6) has a diameter of 20-250 mm and a conductor area of 80-3000 mm ² . Transformer / reactor according to one of the preceding claims, characterized in that the core (1; 11; 21) is substantially annular. Transformer / reactor according to claim 9, characterized in that the core (1; 11; 21) comprises a window (5; 15; 25) having a substantially circular shape and that the annular shape of the core is circular. The transformer / reactor of claim 9, wherein the core comprises a window having a substantially elliptical shape and that the annular shape of the core is elliptical. Transformer / reactor according to any one of claims 1-8, characterized in that the core (31) comprises four segments, two straight segments (36, 37) and two semicircular segments (33, 34), the two segments they are connected to each other by means of two straight segments. Transformer / reactor according to one of the preceding claims, characterized in that the core (1; 11; 21) has a substantially toroidal shape. Transformer / reactor according to any one of the preceding claims, characterized in that the core has a substantially rectangular shape. Transformer / reactor according to one of claims 1-11 or 13-14, characterized in that the core (21) consists of two segments (23, 24). Transformer / reactor according to one of the preceding claims, characterized in that each segment comprises a plurality of sheets (3) and that the core is constructed as a laminated core. Transformer / reactor according to claim 16, characterized in that the sheets (3) consist of magnetically oriented steel. 18. A transformer / reactor according to claim 17, wherein the plurality of segments is sufficiently large to not lose the magnetic orientation direction. Transformer / reactor according to claim 16, characterized in that the sheets (3) are made of amorphous steel. Transformer / reactor according to any one of claims 16-19, characterized in that the adjacent segments are held together by one segment having at least one protruding sheet which fits into a corresponding gap between the sheets formed on the corresponding side of the nearest adjacent segment to form a lap joint. Transformer / reactor according to one of the preceding claims, characterized in that it comprises fastening devices, preferably clamps or screws, for connecting the segments. Transformer / reactor according to any one of the preceding claims, Characterized in that the segmented core comprises inner tubes (17) for the coolant. Transformer / reactor according to claim 22, characterized in that the adjacent segments are held together by one segment which is provided with a cooling tube (17) ending at the end of the projecting tube which is shaped to fit into the corresponding end of the ending tube. in the cooling tube of the adjacent segment. Transformer / reactor according to any one of the preceding claims, characterized in that the transformer is a dry transformer / reactor. A method of use in the manufacture of a transformer / reactor comprising a core and at least one winding, comprising the step of producing a core comprising at least two segments that are connected to form said core, and comprising the step of installing the winding into the core, an electrically conductive core (7) surrounded by an inner semiconductive layer (8), an insulating layer (9) that surrounds the inner semiconductive layer and comprising a solid material, and an outer semiconductive layer (10) that surrounds the insulation layer, said layers adhering one to other. The method of claim 25, wherein the core windings are wound on the segment before the segment is assembled to form the core.