HRP20010153A2 - Transformer core - Google Patents

Description

The field of invention

The present invention relates in general to transformer cores and in particular to three-phase and single-phase cores which usually contain arms with multiple edges.

The basis of the invention

Three-phase transformer cores are commonly made from transformer plates cut to form E I for small transformers and cut into edge-to-edge rectangular plates in large transformers. These cores have the disadvantage that the magnetic field has to pass over the edges of the plate to the plate and so the magnetic field has to travel an unnecessarily long way and it does not twist along the magnetic orientation.

Designers of transformer cores strove, in essence, to realize arms with a circular cross-section, because they provide the best efficiency of the final transformer. However, there is always a trade-off between efficiency requirements and manufacturing requirements, leading to non-optimized transformer cores with legs that do not have circular cross-sections.

Strip cores for three-phase transformers have so far been difficult to produce. The efficiency of the core can be increased by cutting the strips to have a variable width and winding rings, which gave a circular cross-section for single-phase transformers and a semi-circular cross-section for three-phase transformers. This method results in a large amount of waste material, and the winding process is slow.

US 4,557,039 (Manderson) discloses a method of manufacturing transformer cores using electrical steel strips, which have approximately linear cuts. By choosing a suitable cut of hexagonal or higher order, an approximation of a circular cross-section for the arms of the core is created. However, the production of cut strips is difficult and slow to produce and the construction is not sufficiently adapted for mass production.

Figures 1 a-c show, according to the existing state of the art, a three-phase transformer core, according to Manderson, and marked with 10. The core has a general delta shape, as seen in the isometric view in Figure 1, with three arms interconnected with connecting parts. Figure 1 a shows a cross-sectional view of the core before final assembly. The core contains three identical ring parts 12, 13 and 14, the general shape of which is given in Figure 1. Each ring part fills one half of the two arms of the hexagonal cross-sections, see Figure 1 a, which means completely three arms of the three-phase transformer. The annular parts are wound from initial strips of constant width into three identical rings 12a, 13a and 14a of diamond-shaped cross-sections at two angles of 60° and two angles of 120°. These rings 12a, 13a and 14a form the basic rings. The orientation of the strips can also be seen from Figure 1a and 1b.

Outside of the base ring in each ring section there is an outer ring 12b, 13b and 14b of usual triangular cross-section. The outer rings are wound from the strip with a constant reduction in width. When the three ring parts 12 - 14 are assembled, see Figure 1b, they form hexagonal arms on which the transformer windings are wound.

The disadvantage of this solution is that each transformer size requires its own tape cutting. Likewise, the outer rings 12b - 14b are made from strip with decreasing width, which leads to material loss and makes the Manderson transformer difficult to manufacture.

Transformer cores are also described in the following documents: SE 163797, US 2,458,112, US 2,498,747, US 2,4000,184 and US 2,544,871. However, the previously mentioned problems are not overcome with the kernels described in these documents.

Subject of the invention

The object of the present invention is to provide a transformer core in which energy losses are minimal.

Another object is to provide a transformer core that is easily manufactured and prevents material loss.

A special object of the invention is to provide a method of producing transformers that is suitable for multi-series production.

The essence of the invention

The invention is based on the creation of such a transformer core with one or more, as a rule, multi-edge arms, with more than four edges that can be wound from a strip of material of constant width.

According to the invention, a transformer core is provided which contains at least one arm and at least one connecting part, wherein the cross-section of said at least one arm is usually multi-edged, with more than four edges and it is indicated that the core is made of rings obtained by winding tape constant width.

Further recommended examples are defined in the dependent Requirements.

Brief description of the drawing

The invention is described by way of example with reference to the corresponding drawings, in which:

Fig. 1 represents an isometric view of, according to the existing state of the art, a transformer core made of rings of diamond-shaped cross-sections and triangular cross-sections;

Figures 1 a and 1 b are cross-sections of the core shown in Figure 1, before and after assembly, respectively;

Fig. 2 is an isometric view of a three-phase transformer core, according to the invention, with arms of hexagonal cross-sections;

Figures 2a and 2b are cross-sections of the core shown in Figure 2, before and after assembly, respectively;

Figures 3a and 3b are cross-sections of one alternative transformer core, with legs of hexagonal cross-section, before and after assembly, respectively;

Figure 4 is an isometric view of a three-phase transformer core, with octagonal arms;

Figure 4a is a cross-section of the core shown in Figure 4;

Figure 5 is a cross-section of a transformer arm with ten edges;

Figure 6 is a cross-section of a transformer arm with twelve edges;

Figures 7 – 9 show the construction that affects inductive losses and harmonics in a three-phase transformer;

Figure 10 is a cross-section of a three-phase transformer core with specially designed connecting parts for improving magnetic flux;

Figure 11 shows a three-phase transformer core with a series of arms;

Figures 12-14 show a single-phase transformer core according to the invention; and

Figures 15 – 17 show further improvements in the cross-sectional shape of the transformer core.

Detailed description of the invention

Recommended examples of a three-phase transformer core according to the invention will now be described.

Figure 1 has already been discussed in connection with the existing state of the art and will not be further explained.

Figure 2 shows a three-phase transformer core according to the invention, marked 10. In its general form, the core is similar to the previous transformer core, shown in Figure 1, with a general delta-type shape, but which is constructed in a completely different way.

The core is made of three ring parts 22, 23 and 24, which contain more rings. They come in two widths, as wider or narrower, the narrower rings being made from a strip twice as wide as the wider rings. They also come in two heights, small or large, with the smaller rings having twice the height of the large rings. These definitions will be used further during the description, unless stated otherwise. Tapes are primarily made from transformer panels.

Each of the ring parts 22 - 24 comprises a wide and tall base ring 22a - 24a, respectively, similar to those described in Fig. 1. This means that these rings form in pairs four sides of the hexagonal legs. The remaining rhombuses in the legs are formed in different ways, see Figures 2a and 2b.

In the first arm 25 in the background, an additional cross-section in the form of a rhombus consists of two rhomboids. The first, which is marked with 24b and belongs to the annular part 24, is a wide ring of small height. The second, which is marked 22b and belongs to the annular part 22, is a narrow ring of great height.

In the second arm 26, on the right side of Figure 2, an additional diamond-shaped cross-section consists of one rhomboid and two rhombuses. The rhomboid is filled with a narrow ring of large height 22b, which belongs to the ring part 22. The rhombuses are filled with two narrow rings of small height 23b, 23c, which belong to the ring part 23.

In the third arm 27, on the left side of Figure 2, the additional diamond-shaped cross-section also consists of one rhomboid and two rhombuses. The rhomboid is filled with a wide ring of small height 24b, which belongs to the annular part 24. The rhomboids are filled with two narrow rings of small height 23b, 23c, which belong to the annular part 23. The reason why the annular part 23 contains two narrow rings of small height instead of one larger ring is the fact that this larger ring could not be both narrow and high at the same time, as required for the left arm 27, and wide and small at the same time, as required in the right arm 26. This is why two narrow rings are used small height.

All the upper or lower links, which connect the arms 25-27, have different shapes, but they are all derived from one basic ring with a large cross-section of a rhombus along with one ring with a cross-section of a rhomboid or two rings with a small cross-section of a rhombus. This ensures that all ties have the same total cross-sectional area.

The diamond-shaped space outside the basic rings could of course be filled according to the basic pair of principles. Another example will be described with the help of Figures 3a and 3b. The core, which in the general case is labeled 30, has the same general shape as the first example described earlier. However, in this example the core contains three identical annular parts 32-34 of which only the rightmost 32 will be described. The annular parts 32-34 are similar to the part 23 described in connection with Figure 2. In the first arm 35, the part 32 comprises two narrow rings 32b,c with the ring 32 being wound outside the ring 32b. In the second arm 36, the part 32 has two rings 32b, 32c placed next to each other, see Figure 3a.

Two other parts 33,34 are identical to the first 32. It means that the production of the core can be simplified as a rule, depending on the production process, because all three ring parts 32-34 can be made from the same mold.

A further possibility is to make wide rings of low height and rotate the arm parts by 60°, causing a corresponding bending of the connecting parts. The connecting parts then require more space and bending is not easy to cause. By making narrow rings of great height, turning and bending is, as stated, also possible, but difficult. Additional variants, including those with small divisions, are also possible.

The core with octagonal arms, marked 40, will be described with the help of Figures 4 and 4a. In an octagonal cross-section, see, for example, the back of arm 45, the sides rotate by 45°, which means that they have a mutual relative angle of 135°. Three rhombuses, each with an angle of 45°, means that they give space furthest inside the edges of the core arms. Outside these rhombuses, two squares are filled with rings of cross-square section. Finally, the rhombus fills the rest of the octagonal cross-section of the arm.

Of these six cross-sections, three sub-sections form the cross-section of the profiled ring which is directed towards the second arm 46. The remaining sub-sections form the cross-section of the profiled ring which is directed towards the third leg 47. There is also a profiled ring which connects the other and the third leg 46,47.

All three profiled rings contain two rings with the same arm parts. The first ring 42a, 43a, 44a has a diamond-shaped cross-section and the connecting parts are bent by 45°. The second ring 42b, 43b, 44b outside the first ring has a square cross-section and follows the shape of the first ring 42a-44a.

Using the solution of the example with hexagonal legs, described with the help of Figures 2 and 3, the two outer rhombuses form the cross-section of one outer ring with the connecting parts bent at an angle of 45°. Alternatively, the two inner rhombuses form an inner ring but bent by 60°. The next ring must now form an outer rhombus in one leg and an inner rhombus in the other leg and must be bent at an angle of 30°. One type of profiled ring can be recommended, because it is difficult to bend the ring by 60° and a ring with both an external diamond and an internal diamond cannot be allowed.

In section 42, the third ring 42c has a diamond-shaped cross-section in the arm sections and is placed farthest in the back of the arm 45, but inside the right arm 46. These arm section diamonds are achieved by displacing the outer bands of the ring to the right in the right arm 46 and to the left in the back of the arm 45. Furthermore, the arms are turned symmetrically by 30° and the connecting parts are bent accordingly. The ring is now given as a peripheral so it will be located outside the other rings. The final result can be seen in Figure 4.

The ten-sided arm, marked 50, will now be described with the help of Figure 5. The profiled rings contain all four rings with the same parts of the arm. The first ring 50a, the second ring 50b and the third ring 50c with a diamond-shaped cross-section in its arm parts are added to the ten-sided cross-section. This means that they have angles of 36, 72 and 108° and that their connecting parts are bent at an angle of 24°. The fourth ring 50d, which has a cross-section of a rhomboid with an angle of 36°, lies highest on the first ring 50a. Its arm parts are turned outwards by an angle of 24°, causing a 48° bend in the connecting parts. The fourth ring causes the same with the connecting parts of the third ring 50c making a larger arc to create space. The fifth ring 50e has a diamond-shaped cross-section in its leg portions with an angle of 144° when outside the third ring 50c, but the ring has a diamond-shaped cross-section with an angle of 72° when outside the fourth ring 50d. The ties are only bent at an angle of 12°. The arrows "i" in the figure indicate that the cross-sections 50e belong to differently profiled rings. There is also channel 51 suitable for cooling the arms. In an alternative example, the channel is filled with an annulus. This is an advantage when the ring cooperates by allowing the magnetic field to move between them. The space can, for example, be designed in such a way that the upper part of the rings 50c realizes new cross-sections in the shape of a diamond with an angle of 72°, causing the channels 52a and 52b to be formed. The other parts of the ring 50c on the right side can be pushed towards the ring 50e, which forms the spaces 53a and 53b.

It is possible to provide three-phase transformer cores with multiple edges. Figure 6 shows a 12-sided core, marked 60. The profiled rings are composed of four rings 60a-d with diamond-shaped cross-sections with angles of 30, 50, 90 and 120°, which are added to the twelve-sided cross-section and turned by 15° . Within these rings there are two rings 60e, 60f with diamond-shaped cross-sections with angles of 30 and 60°, respectively, and turned outwards by 15°. Next to the fifth and sixth rings 60e, 60f there is a space for a ring 60g with a cross-section in the form of a diamond with an angle of 30° turned outwards by 45°. Its other arm parts are at right angles outside the sixth ring 60f and facing outwards by an angle of 15. Just above the ring 60d there is a space for a ring 60h with a cross-section in the shape of a diamond with an angle of 150° and the other part of the arm is at right angles connected to ring 60d and outside the ring 60f. The entire cross-section is then filled. The connecting parts are separated making some wider arcs to create space for other connecting parts.

The good characteristics of these transformer cores can be further improved for some transformer applications, see Figure 7. The inductance loss can easily be increased by an additional core 29 of tape between the primary and secondary windings of the transformer. The strips are joined together at the top and bottom. The bands can be distributed around the entire primary thread or they can be concentrated in one place, making the secondary thread eccentric.

The non-linear magnetic characteristics of iron result in harmonics in magnetic fields, voltages and currents.

An additional arm placed in the center of the core will not produce any magnetic field in fully symmetrical and, without interference, three-phase conditions. Common voltage phase components, such as the third harmonic, will be affected by the center arm.

Likewise, a combination between the thread and the central arm is possible.

In one example, the central arm is realized by means of three rectangular poles 80 from strips of a certain height, which is three times the width, lying on top of each other, of a square cross-section, see Figure 8. This is recommended to be in the form of a triangle and the solution for the consumer, it contains poles with a diamond-shaped cross-section, three of which are placed together to form a bundle with banded edges facing each other in the form of waves, see Figure 9. The three packages are placed together at a small distance to form a leg with a cross-section of approx. triangular. The ends of the poles are bent outwards to reach the tie. In order to create an arc, spacers are needed between the poles. The spacers do not affect the magnetic properties, because the pole of each package is 91a-c; 92a-c; 93a-c bent to each link. Likewise, the strips are, at least on one side, parallel to the spacers.

A bar, obtained by winding the tape in the form of a spiral, or slit, is useful, especially where it is necessary to have a space between the central arm and the link. The spiral can be made to be wider at the ends, to reduce the air space to the link.

The flexibility of preparing cores such as these is good and is shown in Figure 10. The figure shows the core described in Figure 4. The main part of the magnetic flux can pass from one profiled ring to another in the arms, where they touch each other. This enables the rotation of larger fluxes in the connection triangle.

With the present invention, it is also possible to provide a three-phase transformer core with a series of arms. This achieves the advantage that the transformer is narrower than is the case with a delta-shaped core. This type of transformer is ideal for installation in, for example, railway wagons.

Figure 11a shows a cross-section of a transformer with octagonal arms. All arms contain four rhombuses with an angle of 45° and two squares. The rings located between the adjacent arms are shown in the picture, while those located between the outer arms are mostly completely hidden.

In order to create transformer cores of this type, the arm parts must be flexible and the connecting parts can be bent to fit each other. There are several solutions, one of which is shown in the picture. Parts of the arms of the rings are bent outward, and parts of the link are inward or vice versa. The shape of the connecting parts is limited due to their limited possibilities to deform plastically, whereas, in contrast, the parts of the link can have any shape. The principle shown in Figure 11 is characterized by sharp bends and straight connecting parts.

The rings can also be placed on top of each other, giving circular bends in order to save material.

The links between the left arm 115 and the central arm 116 are made of a ring 112a with a diamond-shaped cross-section in the arm part, and a ring 112b with a square cross-section and both are bent at an angle of 22.5° and the diamond-shaped ring 112c is rotated by 67.5° in parts of the arm. Rings 112a and 112b fill the octahedron near the bond faces, while ring 112c fills the opposite side.

The link between the central arm 116 and the right arm 117 can only be placed in the central arm in the remaining positions 114a-c. The cross-sections of the left and right arms 115, 117 are symmetrical with respect to the central arm 116, so that the rings around the central arm are symmetrical. The inner rings 114a, 114b have their closest positions in the right leg 117. However, the ring 114c with a square cross-section in the leg parts extends to the closest square-shaped position in the right leg. The basis for this is that the ring 113a with a square cross-section between the outer legs in the outer position on the connecting parts is already present in order to reach the left leg.

Turning the link is impossible. In an alternative example, a very steep pass was used instead of the usual one. This is shown for ring 114c which has the shortest bond. The bend starts at one end of the link and ends at the other end, which is indicated by 118a for the lower link and 118b for the upper link in Figure 11. Likewise, the links can be subdivided into several narrow rings.

Likewise, single-phase transformers would be more efficient if they had polygonal cross-sections. Figure 12 shows a transformer with an octagonal cross-section made up of rings with the same cross-section as three-phase transformers, but with the return connection in the closest way outside the threads. The rings can be moved to give an octagonal cross-section. A small reduction in the number of plates can be obtained, for example, by creating a loop to the left of the ring, bending the loop to the far right in the figure. Because of this, its cross-section would have to be changed to a rhombus shape, close to a square shape.

A two-arm core can be made from a three-phase construction by bending the rings of one arm together, to form just one more arm. The core is shown in Figure 13 with an octagonal cross-section and its arms. The turning of the three parts of the arm is 45° and the bending is 90°. A ring with a square cross-section and two rings outside this ring is not deformed. Cores with hexagonal spokes require only three rings made of three spokes of the same width.

If this octagonal edge, where the three edges of the rhombus meet, is placed deepest in the core, the rotation will be only 22.5°, except for the rhombus in the middle, which must be rotated 67.5°. Replacing this diamond with a ring, with steps approximating the diamond, is more realistic and is shown in Figure 14. A further improvement is made by allowing the strip to reach the circle, which means increasing the overall cross-section.

Segments outside the polygonal step can be filled with thin diamond-shaped rings of tape about half the width and full height of the segment and wound to its full width. The bends in the strips around the center of the rhombus, as in Figure 15, make the two sides towards one straight side form a triangle, the sides of which are in contact with the core. With about 2/3 of the width and 8/9 of the height, the bend in the edge of the innermost strip forms a trapezoidal cross-section, as in Figure 16. The cross-section can also be rounded.

By means of a strip of constant width, the parts of the arm can also be given a cross-sectional shape that is close to a circle, See Figures 17, 17a and 17b. The right arm 172 in Figure 17 will be described as an example with the help of Figure 17a, where a cross section of this arm is shown. Deepest are the rings 173 of, for example, 80% of its full width and up to a height of 9% of its width. There are three rings that reach the bounding circle, see Figure 17a.

Four of the six segments were filled with magnetic material, and strips outside the assembled core can fill the other segments.

The ring 174 can be placed on the outer sides of the hexagon.

Another example is shown in Figure 17b, where ring 174 is replaced by wider bands in other rings.

Some of the advantages of the transformer core according to the invention have already been mentioned. In addition to other advantages, we can mention: lower losses or no losses due to load, lower weight, lower volume, lower electrical losses, reduction of harmonics due to the symmetry of the phases of the three-phase transformer, easier maintenance, etc.

Recommended examples of the transformer core according to the invention are described. A person skilled in the art will understand that they can be varied within the domain of the request.

Claims (17)

1. The transformer core, which contains three arms and connecting parts connecting said arms, where the cross-section of said arms is usually multi-edged, with more than four edges, is characterized by the fact that the core is made of rings wound from tape of constant width, where each of said rings forms part of two said arms. 2. The transformer core, according to Claim 1, is characterized by the fact that said at least one leg has a hexagonal cross-section. 3. The transformer core, according to Claim 2, is characterized by the fact that it contains nine rings. 4. The transformer core, according to Claim 3, is indicated by the fact that it contains three rings of the first width and the first height and six rings of the second width, which corresponds to half of the first width, and of the second height, which corresponds to half of the first height. 5. The transformer core, according to Claim 4, is indicated - the first (32), second (33) and third (34) annular part, where each annular part contains - the first ring (32a, 33a, 34a) wound from the strip of the first width to the first height, and the cross-sections of the said rings are rhombus-shaped with two angles of 60°, - a second ring (32b, 33b, 34b) wound from a strip of a second width, which essentially corresponds to half of the first width, and to a second height, which essentially corresponds to half of the first height, and said second ring has a diamond-shaped cross-section and is placed on said first ring (32a, 33a, 34a), - the third ring (32c, 33c, 34c) wound from the strip of the second width to the second height, and said second ring has a diamond-shaped cross-section and is placed in position on said first ring (32a, 33a, 34a) in the vicinity of said second ring and in the second position on the said second ring, - and the mentioned first, second and third annular parts when assembled form a three-phase transformer core with three arms of hexagonal cross-section. 6. The transformer core, according to Claim 2, is characterized by the fact that it contains seven rings. 7. The transformer core, according to Claim 6, is indicated - with the first (22a), second (23a) and third (24a) rings, wound from the strip of the first width to the first height, and the cross-sections of the said rings are rhombus-shaped with two angles of 60°, and the said first, second and third rings form connecting parts, and together a triangle, - the fourth ring (24b) wound from the strip of the first width to the second height, which essentially corresponds to half of the first height, and the said fourth ring has a cross-section of a rhomboid shape and is placed on the said third ring (24a), - a fifth ring (22b) wound from a tape of a second width, which essentially corresponds to half of the first width and up to the specified first height, and the said fifth ring has a cross section of a rhomboid shape and is placed on the said first ring (22a), - the sixth ring (23b) wound from the tape of the second width to the specified second height and the said sixth ring has a cross-section in the shape of a rhombus and is placed on the said second ring (23a), - the seventh ring (23c) wound from the tape of the second width to the specified second height and the said seventh ring has a diamond-shaped cross-section and is placed on the said second ring (23a) and on the said sixth ring (23b), - whereby a three-phase transformer core with three arms of hexagonal cross-section is created. 8. The transformer core, according to Claim 1, is characterized by the fact that at least one leg has an octagonal cross-section. 9. The transformer core, according to Claim 8, is indicated by the first, second and third profiled rings, each of which contains three rings (42a, 42b, 42c) with two arm parts and two connecting parts, where the first ring (42a) has a diamond-shaped cross-section in its leg parts at an angle of 45° and with the link parts bent by 15° in such a direction that the outer surfaces of their leg parts move in the direction of each other, the second ring (42b) has a square cross-section in its leg portions and is mounted on said first ring, and the third ring (42c) has a diamond-shaped cross-section in its arm parts, the first part of the arm, which is at 45°, lies mainly on said first ring (42a) and the second part of the arm, which is at 135°, lies on said first ring (42b), i said first, second and third profiled rings in the assembly create a three-phase transformer core with three arms with octagonal cross-sections. 10. The transformer core, according to Claim 1, is characterized by the fact that said at least one leg has a cross-section with ten edges. 11. The transformer core, according to Claim 10, is indicated by the first, second and third profiled rings, each of which contains five rings (50a-e) with two arm parts and two connecting parts, where the first ring (50a) has diamond-shaped cross-sections in its leg parts at an angle of 36°, the second ring (50b) has diamond-shaped cross-sections in its arm parts at an angle of 72°, the third ring (50c) has diamond-shaped cross-sections in its arm parts at an angle of 108°, the fourth ring (50d) has a diamond-shaped cross-section in its leg portions at an angle of 36° and rests substantially on the first ring (50a) and has its connecting portions turned outwards by 24°, and the fifth ring (50e) has diamond-shaped cross-sections in its leg portions at an angle of 144° when lying on the third ring (50c) and a diamond-shaped cross-section at an angle of 72° when lying outside the fourth ring (50d), and the channel (51 ) suitable for cooling the arm outside the fifth ring (50e), a said first, second and third profiled rings in the assembled state create a three-phase transformer core with three arms with ten-sided cross-sections. 12. The transformer core, according to Claim 11, is indicated by cooling channels (52a, 52b, 53a, 53b) caused by giving the outer parts of the third ring (50c) a cross-section in the shape of a rhombus with an angle of 72° and displacing the second outer part of the third ring in the direction of the fifth ring (50e) when moving within the complete arm. 13. The transformer core, according to Claim 10, is indicated by multi-edge cross-sections of their arms, and profiled rings containing a first group of rings with diamond-shaped cross-sections with different angles, but in their leg parts turned by the same angle and connected to the multi-edge cross-section and within the second group of rings of diamond-shaped cross-section with different angles, but in their leg parts turned by the same angle and connected to the first group, and so on, until the innermost ring space is reached, which is in one of their leg parts of the given cross-section and which is turned differently from those in the second part of the arm. 14. The transformer core, according to Claim 1, is characterized by the fact that all rings have a cross-section in the form of a rhombus with two angles of 60° and two angles of 120°. 15. The transformer core according to claim 1 is characterized by an additional strip core (70) between the turns connected together at the top and bottom of the core. 16. The transformer core, according to Request 1, is indicated by an additional core in the center line of at least one strip pole, and if there are more, placed in groups of three (Figures 8 and 9), the poles of which are bent towards each terminal. 17. The transformer core, according to Claim 1, is characterized by the fact that the segments between the cross-sections of the arms and the limited circuit are partially filled with thin rings and/or slightly wider strips.