OA11907A

OA11907A - Transformer core.

Info

Publication number: OA11907A
Application number: OA00100054A
Authority: OA
Inventors: Lennart Hoeglund
Original assignee: Lennart Hoeglund
Priority date: 1998-09-02
Filing date: 1999-09-02
Publication date: 2006-04-10
Also published as: ZA200101707B; EE04406B1; PL346275A1; CA2342331A1; EP1110227B1; EE200100137A; CN1178234C; NO20011043L; JP2002524866A; HK1039827A1; AP2001002081A0; AU757893B2; CZ297230B6; NO20011043D0; EA004162B1; YU17101A; KR100613751B1; CA2342331C; AP1302A; HU225832B1

Abstract

A transformer core comprises at least one leg and at least one yoke part, wherein the cross section of the leg or the legs is regularly multi-edged with more than four edges. The core is made up of rings rolled from strips of constant width, whereby good electrical properties are achieved. The transformer is also easy to manufacture and avoids waste of material.

Description

1 119 ο 7

TRANSFORMER CORE

FI SEP O F INVENTION

The présent invention relates generally to transformercores and especially to three-phase and one-phase corescomprising regularly multi-edged legs.

BACKGROUND

Three-phase transformer cores are usually made oftransformer places eut to Ξ I shape for small trans-formera and to rectangular plates, which are laid edgeto edge, in larger transformers. They hâve the drawback that the magnetic field has to oass via edges fromy* plate to plate and that the magnetic field must go anunnecessarily long way and not always alcng a magneticorientation.

Designers of transformer cores hâve striven to obtainlegs with an essentially circular cross-section becausethat gives the best efficiency of the final trans-former. However, there is always a trade-off betweenefficiency and production requirements, leading to non-optimal transformer cores with non-circular legs.

Strip ccres for three-phase transformers hâve hithertobeen difficult to manufacture. The efficiency of thecore can be increased by cutting strips to variablewidth and winding rings, which are given a circularcross-section for single-phase transformers and semi-circular cross-section for three-phase transformers'.This method results in a great deal of waste and thewinding process is time consuming. 119 07 US 4,55",039 (Manderson) discloses a method cf manufac-turing transformer cores using electrical Steel stripshaving approximately a linear taper. 3y selecting asuitabïe taper, a hexagonal or higher order approxima-tion of a circular cross section for the legs of thecores is produced. However, the tapered strips are dif-ficult and time-consuming to produce and the design isnot well adapted to large-scale production.

In figs. la-c is shown a prior art three-phase trans-former core according to Manderson, generally desig-nated 10. The core has a general delta-shape, as isseen in the isométrie view of fig. 1, with three legsinterconnected by yoke parts. In fig. la, a cross-sectional view of the core is shown before final assem-bly. The core comprises tree identical ring-shapedparts 12, 13, and 14, the general shape of whichappears from fig. 1. Each ring-shaped part fills up onehalf of two legs with hexagonal cross-sections, seefig. la, thus totalling the three legs of a three-phasetransformer. The ring-shaped parts are initially woundfrom constant width strips to three identical rings12a, 13a, 14a with rhombic cross-sections comprisingtwo angles of 60 degrees and two angles of 120 degrees.These rings 12a-14a consticute the basic rings. Theorientation of the strips also appears from figs. laand 1b.

Outside of the basic ring in each ring-shaped partthere is an outer ring 12b, 13b, 14b of a regular tri-angular cross-section. The outer rings are wound fromstrips with constantly decreasing width. 119 0 7

When the three ring-shaped parts 12-14 are put to-gether, see fig. 1b, they form three hexagonal legs onwhich the transformer windings are wound. A drawback with this solution is that every size of5 transformer requires its own cutting of the strips.

Also, the outer rings 12b-14b are made of strips withdecreasing width, leading to waste and it aise makesthe transformer according to Manderson difficult tomanufacture. IC Transformer cores are also described in the followingdocuments: SE 153797, US 2,458,112, US 2,498,747, US2,400,184 and US 2,544,871. However, the above men-tioned problems are not overcome by the cores describedin these documents.

15 OBJECT OF THE INVENTION

An object of the présent invention is to provide atransformer core wherein the energy losses are mini-mised.

Another object is to provide a transformer core, which 20 is easy to manufacture and avoids material waste.

Another object is to provide a met’nod of manufacturinga transformer that is well adapted for large-scale pro-duction. 25 The invention is based on the réalisation that a trans-former core with one or more regularly multi-edged legswith more than four edges can be wound of strips ofmaterial with constant width. 119 0 7

Acccrding to the invention there is provided a trans-former core, comprising at least one ieg and at leastone voke parc, wherein the cross-section of said atleasc one leg is regularly multi-edged with more thanfour edges, characterised in that the core is made upof rings rolled from strips of conscant width.

Furcher preferred embodiments are defined in che dé-pendent daims.

BRIE? DESCRIPTION OF DRAWINGS

The invention is now described, by wav of example, withreference to the accompanying drawings, in which: fig. 1 is an isométrie view of a prier art three-phasetransformer core made of rings with rhombic and trian-gular cross-sections,· figs. la and 1b are cransverse cross-sections of thecore shown in fig. 1 before and after assembly, respec-tively; fig. 2 is an isométrie view of a three-phase trans-former core according to the invention with legs withhexagonal cross-sections; figs. 2a and 2b are transverse cross-sections of thecore shown in fig. 2 before and after assembly, respec-tive lv; figs. 3a and 3b are transverse cross-sections of analternative three-phase transformer core with legs withhexagonal cross-section before and after assembly, re-spectively; 1 119 0 7 5

Fig. 4 is an isométrie view of a three-phase trans-former core with octagonal legs;

Fig. 4a is a transverse cross-section of the core shownin fig. 4; 5 Fig. 5 is a cross-section of a transformer leg with tenedges;

Fig. 6 is a cross-section of a transformer leg withtwelve edges;

Figs. 7-9 show an arrangement for influencing the leak-10 âge inductance and the harmonies in a three-phase transformer;

Fig. 10 is a transverse cross-section of a three-phasetransformer core with specially shaped yoke parts forimproving the magnetic flux; 15 Fig. 11 shows a three-phase transformer core with linedup legs;

Figs. 12-14 show one-phase transformer cores accordingto the invention; and

Figs. 15-17 show further improvements of the shape of20 the transformer core cross-section.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of a three-phase transformer coreaccording to the invention will now be described.

Fig. 1 has already been discussed in connection with25 prior art and will not be explained further. δ

In fig. 2 is shown a three-phase transformer coreaccording to the invention, generally designated 20. Inits general shape it is similar to t’ne prior art trans-former core shown in fig. 1 with a general delta-shapebut is designed in an entirely different way.

The core is made up of three ring-shaped parts 22, 23,24 comprising severai rings. These corne in two widtns,broad or narrow wherein the narrow rings are made up ofstrips of half the width of the broad rings. Also, theycorne in two heights, low or high wherein the low ringshâve half the height of the high rings. Unless other-wise stated, these définitions will be used throughoutthis description. The strips are preferably made oftransformer plate.

Each of the ring-shaped parts 22-24 comprises a broadhigh basic ring 22a-24a, respectively, similar to thosedescribed with reference to fig. 1. Thus, these ringsform in pairs four of the sides in the hexagonal legs.The remaining rhombs in the legs are built in differentways, see figs. 2a and 2b.

In the first leg 25 in the background, the additionalrhombic cross-section is composed of two rhomboids. Thefirst one, designated 24b and belonging to ring-shapedpart 24, is a broad low ring. The second one, desig-nated 22b and belonging to ring-shaped part 22, is anarrow high ring.

In the second leg 26 to the right in fig. 2, the addi-tional rhombic cross-section is composed of one rhom-boid and two rhombs. The rhomboid is filled by the nar-row high ring 22b belonging to the ring-shaped part 22. 119Q7 7

The rhombs are filled bv two narrow low rings 23b, 23cbelonging to the ring-shaped part 23.

In the third leg 27 to the left in fig. 2, the addi-tional rhombic cross-section is also composed of onerhomboid and two rhombs. The rhomboid is filled by thebroad low ring 24b belonging to the ring-shaped part24. The rhombs are filled by two narrow low rings 23b,23c belonging to the ring-shaped part 23. The reasonthat the ring-shaped part 23 comprises two low narrowrings instead of one larger ring is that this largerring can not be both narrow and high, as recuired inthe left leg 27, and broad and low, as required in theright leg 26. Thus, instead two narrow low rings areused.

Ail upper or lower yokes connecting the legs 25-27 hâvedifferent shapes but ail are built from one basic ringwith a large rhombic cross-section plus one ring with arhomboidal cross-section or two rings with a smallrhombic cross-section. This gives ail yokes the sametotal cross-section area.

The rhombic space outside of the basic rings could ofcourse be filled in accordance with a couple of basicprinciples. A second embodiment will now be describedwith reference to figs. 3a and 3b. The core, generallydesignated 30, has the same general shape as the firstembodiment described above. However, in this embodimentthe core comprises three identical ring-shaped parts32-34, of which the rightmost one 32 will be described.The ring-shaped parts 32-34 are similar to the part 23described in connection with fig. 2. In the first leg35, part 32 comprises two narrow low rings 32b, c 119 0 7 3 wherein ring 22c is wound outside of ring 32b. In thesecond leg 36, part 32 nas the two rings 32b, 32cplaced one beside the other, see fig. 3a.

The two other parts 33, 34 are identicai to the firstone 32. Thus, the production of the core can as a rulebe simplifiée, depending on the production volume, be-cause ail three ring-shaped parts 32-34 can be madefrom the same mould. A further possibility is to make broad low rings andturn the leg parts 60 degrees, forcing a correspondingbending of the voke parts. The yoke parts then requiremore space and the bending is not so easy to effect.Making narrow high rings and turning and bending asmentioned is also possible, but difficult. Additionalvariants, including those with smaller divisions, arealso possible. A core with octagonal legs, generally designated 40,wili now be described with reference to figs. 4 and 4a.In an octagonal cross-section, see e.g. the back leg45, the sides turn 45 degrees, which means that theyhâve a relative angle of 135 degrees to each other.Three rhombs, each with an angle of 45 degrees, thusget space in the innermost edges of the legs of thecore. Outside of these rhombs, two squares are filledby rings with quadratic cross-sections. Finally, arhomb fills the rest of the octagonal cross-section ofthe leg.

From these .six cross-subsections, three subsectionscompose the cross-section of a profiled ring going tothe second leg 46. The remaining subsections compose 119 07 the cross-section of a profiled ring going to the thirdieg 47. There is also a profiled ring connecting thesecond and third legs 46, 47.

The three profiled rings ail contain two rings withequal leg parts. A first ring 42a, 43a, 44a has a rhom-bic cross-section and the yoke parts bent 15 degrees. Asecond ring 42b, 43b, 44b outside of the first ring iscuadratic and follows the form of the first ring 42a-44a.

Usina a solution from the embodiments with hexagonallegs described with reference to figs. 2 and 3, twoouter rhombs compose the cross-section of an outer ringwith the yoke parts bent 15 degrees. Alternatively, twoinner rhombs compose an inner ring but bent 60 degrees.The next ring must now give an outer rhomb in one legand an inner rhomb in the other leg and be bent 30degrees. One type of profiled ring is to be preferredbecause it is difficult to bend a ring 60 degrees andone car. not avoid a ring with both an outer rhomb andan inner rhomb.

In part 42, the third ring 42c has a rhombic cross-section in the leg parts and is placed outermost in theback leg 45 but inside the right leg 46. These rhombsof the leg parts are obtained by displacing the outerstrips of the ring to the right at the right leg 46 andto the left at the back leg 45. Furthermore, the legsare turned asymmetrically 30 degrees and the yoke partsare bent accordingly. The ring is given such a circum-ference that'it will lie outside of the other rings.

The final resuit appears in fig. 4. 10 11907 A 10-sided leg, generally designated 50, will now bedescribed with reference to fig. 5. The profiled ringscontain ali four rings with equal leg parts. A firstring 50a, a second ring 50b and a third ring 50c withrhombic cross-sections in their leg parts are attachedto the 10-sided cross-section. Thus they hâve theangles 36, 72, and 108 degrees and their yoke partsbent 24 degrees. A fourth ring 50d having a rhomboidcross-section with the angle 36 degrees lies mainlyupon the first ring 50a. Its leg parts are turned out-wards 24 degrees, causing a 48 degrees bending of itsyokes. The fourth ring also causes the yoke parts ofthe third ring 50c to make a larger bow to give space. A fifth ring 50e has a rhombic cross-section in its legparts with the angle 144 degrees when it lies outsideof the third ring 50c, but the ring has a rhombiccross-section with the angle 72 degrees when it liesoutside of the fourth ring 50d. The yokes are bent only12 degrees. The arrows i the figure indicate that thecross-sections 50e belong to different profiled rings.T'nere will also be a channel 51 suitable for coolingthe legs. In an alternative embodiment, the channel isfilled with a ring. This is an advantage when the ringsco-operate by letting the magnetic field go betweenthem. The space can e.g. be disposed of in such a waythat the upper part of the rings 50c obtains new rhom-bic cross-sections with the angle 72 degrees, causingthe channels 52a and 52b to be formed. Further parts ofring 50c to the right can be pushed to ring 50e, whichforras the spaces 53a and 53b.

It is possible to provide three-phase transformer coreswith even more edges. Fig. 6 shows a 12-sided core, 119 0 7 11 generally designated 60. The profiled rings are com-posed of four rings 60a-d with rhombic cross-sectionswith the angles 30, 60, 90, and 120 degrees, which areattached to the 12-sided cross-section and are turned15 degrees. Inside of these rings there are two rings60e, 60f with rhombic cross-sections with the angles 30and 60 degrees, respectively, and turned outward 15degrees. Attached to the fifth and sixth rings 60e, 60ft'nere is space for a ring 6Cg with a rhombic cross-section with the angle 30 degrees turned outward 45degrees. Its other leg part is a rectangle outside ofthe sixth ring 60f and turned outward 15 degrees. Uponthe ring 60d there is space for a ring 60h with a rhom-bic cross-section with the angle 150 degrees and theother leg part is a rectangle attached to ring 60d andoutside ring 60f. The whole cross-section is thenfilled. Yoke parts are separated by giving sorae widerbows to give space for other yoke parts.

The gocd properties of these transformer cores can bemade even better for some transformer application, seefig. 7. The leakage inductance can easily be increasedby an additional core 29 of strips between the primaryand secondary windings of the transformer. The stripsare brought together at the top and bottom. The stripscan be spread around the entire primary winding or beconcentrated to one place, making the secondary windingeccentric.

The non-linear magnetic properties of iron resuit inharmonies in the magnetic fields, voltages and cur- rents. 119 0 7 12

An abdicional leg placed in the centre of the core willnot get any magnetic field under perfectly symmetricaland distortion-free three-phase conditions. Common com-ponents in the phase voltages, like the third harmon- 5 ics, will be influenced by a centre leg.

Also a combination of strips between the windings and acentre leg is possible.

In one embodiment, the centre leg is made of three rec-tangular pôles 80 from strips given a height three IC times the width, laid on each other to a quadratic cross-section, see fig. 8. This is preferably triangu-lar and a custom-raade solution contair.s pôles with arhombic cross-section, of which three are put togetherto form a packet with the strip edges toward each other 15 in a wave form, see fig. 9. Three packets are put to-gether with small distances to form a leg with a cross-section approximating a triangle. The ends of the pôlesare bent outward to reach the yokes. To make the bendspossible spacers between the pôles are necessary. The 20 spacers do not influence the magnetic properties be-cause one pôle from each packet 91a-c; 92a-c; 93a-c isbent to each yoke. Also the strips are, at least on oneside, parallel to the spacers. A rod, wound of strips in spiral form or as coils, is 25 useful, especially if there are to be air gaps betweenthe centre leg and the yokes. The spiral can be madewider at the ends to reduce the air gaps to the yokes.

The flexibility of building cores like this is good andis shown in fig. 10. The figure shows the core de- 30 scribed in connection with fig. 4. A major part of the 1 19 0 7 13 magnetic flux can pass from one profilée rang toanother in che legs where ohey are touching each other.This enables the rooatron of larger fluxes in the yoketriangle.

With the présent invention, in is also possible to pro-vide a three-phase transformer cors with lined up legs.This has the advantage that the transformer is narrowerthan with the delta shaped core. This type cf trans-former is idéal for placement on e.g. train wagons.

Fig. lia shows the transverse cross-section cf a trans-former with octagonal legs. Ali legs comprise fourrhombs with an angle of 45 degrees and two squares.Rings running between adjacent legs are shown in thefigure while those running between the outer legs arealmost entireiv hidden.

In order to make transformer cores of this kind, theleg parts musc be bendable and that the yoke parts canbe bent and pass each other. There are several solu-tions, of which one is shown in the figure. The legparts of the rings are bent outward and the yoke partinward or vice versa. The shape of the yoke parts islimited by the limited possibilities of plastic defor-mations but otherwise the yoke parts can hâve anyshape. The principle shown in fig. 11 is to hâve sharpbends and straight yoke parts.

The rings can also be placed on each other givingrounded bends in order to save materiai.

The yokes bètween the left leg 115 and the centre leg116 are built up of a ring 112a with a rhombic cross-section in the leg part, a ring 112b with a square 4 119 0 7 cross-section and both bent 22.5 degrees and a rhombicring 112c turned 67.5 degrees in the leg parts. Therings 112a and 112b fit into the octahedrons close tothe yoke side while the ring 112c fits into the oppos- 5 ing side.

The yoke between the centre leg 116 and the right leg117 can only be placed in the centre leg in the remain-ing positions: 114a-c. The cross-sections of the leftand right legs 115, 117 are mirror images to the centre 10 leg 116 so that the rings running in che centre leg aresymmetric. The inner rings 114a, 114b hâve their clos-est positions in the right leg 117. Kowever, the ring114c with a square cross-section in the leg parts runsto the closest square-shaped position in the right leg. 15 The reason behind that is that the ring 113a with asquare cross-section between the outer legs is in anouter position on the yoke parts already présent inorder to reach the left leg.

The turning of the yokes can be impossible to achieve. 20 In an alternative embodiment, a heavily sloping fold isused instead. This is.shown for the ring 114c havingthe shortest yoke. The fold starts at one end of theyoke and ends at the other end, marked by 118a for thelower yoke and 118b for the upper yoke in fig. 11. 25 Also, the yokes can be subdivided into several narrowrings.

Also single-phase transformers will be more efficientif they are given polygonal cross-sections. Fig. 12shows a transformer with an octagonal cross-section 30 composed of rings with the same cross-sections as inthe three-phase transformers but with the retum loops 15 11907" going the closest way outside of the windincs. Therings car. be transposed and yet given an octagonalcross-seccion. A small réduction cf the amount of platecan e.g. be obtained by looping up to the left of the 5 ring looping rightmost in the figure. There must itscross-section be changed to a rhombic form close torectanguiar form. A core with two legs can be made from the t'nree-phasedesigns by bending the rings from one leg together to 10 form only one more leg. A core is shown in fig. 13 withan octagonal cross-section in its legs. The turning ofthree lec-parcs is 45 degrees and the bending is 90degrees. A ring with a rectanguiar cross-seccion andthe two rings outside of that ring are not deformed. 15 Cores with hexagonal legs need only three rings made ofstrips with the same width.

If that octagon edge where three rhomb edges meet, isput innermost in the core, the turnings will only be 22.5 degrees except for the rhomb in the middle, which 20 must be tumed 67.5 degrees. Replacing this rhomb with Λ,. a ring, with steps approximatif the rhomb, is morerealistic and is shown in fig. 14. A further improve-ment is made by letting the strips reach the circle,thus increasing the total cross-section. 25 The segments outside of a polygonal leg can be filledby a thin rhombic ring of a strip with about half thewidth and the full height of the segment and wound toits total width. Folds in the strips along the middleof the rhomb as in fig. 15 make two sides to one fiat 30 side giving a triangle, the sides of which are in con-tact with the core. With about 2/3 width and 8/9 119 0 7 15 height, a fold at the edge of the innermost strip makesa crapezoid cross-section as in fig. 16. The cross-seccion can also be rounded. 3y aieans of strips of constant width the leg parts can5 be given a cross-section shape doser to the shape of a circle, see fig. 17, 17a and 17b. The right leg 172 infig. 17 wiil be described as .an example with referenceto fig. 17a, wherein a transverse cross-section of thatleg is shown. Innermost, there are rings 173 of e.g. 10 80% of full width and to a height of 9% of its width.

There are tnree rings reaching a circumscribed circle,see fig. 17a.

Four of the six segments hâve been filled with magneticmacerial and strips outside of the assembled core can 15 fill the other segments. A ring 174 can be placed on the outer sides of thehexagons.

Another embodiment is shown in fig. 17b, wherein thering 174 has been replaced by broader strips in the 20 other rings.

Some of the advantages of the inventive transformercore hâve already been mentioned. Among the otheradvantages can be mentioned: lower no load losses, lessweight, less volume, lower electrical leakage, a reduc- 25 tion of harmonies due to the symmetry of the phases ofthe three-phase transformer, easy maintenance etc.

Preferred embodiments of a transformer core accordingthe invention hâve been described. The person skilled

1 19 07 17 in the art réalisés that these can be varied within thescope of the daims.

Claims

ο 18 119 0 7

1. A transformer core, comprisinç three legs and5 yoke parts connecting said legs, wherein the cross- section cf said legs is regularly multi-edçed with morethan four edges, characterised in thatthe ccre is made up of rings rolled from strips ofconstant width, wherein each of said rings make'up'part 10 of twc of said legs. \
2. A transformer core accordinç to claim 1,characterised in that said legs hâvehexagonal cross-section.
3. A transformer core accordinç to claim 2, 15 characterised in that it comprises ninerings.
4. A transformer core accordinç to claim 3,characterised in that it comprises threerings of a first width and a first heiçht and six rings 20 of a second width corresponding to half the first widthand a second height corresponding to half the firstheight.
5. A transformer core accordinç to claim 4, characterised by 25 a first (32), a second (33) and a third (34) ring-shaped part, wherein each ring-shaped part comprises a first ring (32a, 33a, 34a) wound from strips of afirst width to a first height, the cross-sections ofsaid rings being rhombic with two angles of 60 degrees, O. 119 0 7 19 a second ringseccr.c wcdthcirst width,correspcncinçring having ron said first (32b, 33b, 34bi wcu.nc from a strip cf aessentially correspcncinç cc haie crieco a second height essentially co haie the cirst height, said secondhombic cross-section and beinç positicned ring (32a, 33a, 34a), a third ring (32c, 33c, 34c) wound from a strip of thesecond width to the second height, said second ringhaving rhombic cross-section and being positicned in 10 one position on said firsc ring (32a, 33a, 34a) adja-cent Co said second ring and in anccher position onsaid second ring, said first, second and third rinç-shaped part beingassembled whereby a three-phase transformer core withthree legs with hexagonal cross-sections is formed. ιη
6. A transformer core accordinç to claim 2,characterised in t h a t it comprises sevenrings.
7. A transformer core accordinç to claim 6, 20 characterised b y a fi.rst (22a), a second (23a) and a third (24a) ringwound from strips of a first width to a cirst height,the cross-sections of said rings being r'nombic with twoangles of 60 degrees, said first, second and third 25. rings forming yoke parts together forming a triangle, a fourth ring (24b) wound from a strip of said firstwidth to a· second height essentially corresponding to • 4 half the first height, said fourth ring having rhomboi- 20 119 0 7 dal crcss-section and beinç positioned on said thirdrinç (24a), a fifth rinç {22b} wound from a strip or a second widthesser.tially correspondinç to haif the first width, to 5 said firsr heiçnt, said fifth rinç having rhomboidal crcss-section and being posirioned on said first ring(22a;, a sixth ring (23b) wound from a strip of the secondwidth ro said second height, said sixth ring havinç 13 rhcmbic cross-section and. being positioned on said .second rinç (23a), and a seventh rinç (23c) wound from a strip of the secondwidth ro said second height, said seventh ring havingrhombic cross-section and being positioned on said 15 second ring (23a) and on said sixth ring (23b), whereby a three-phase transformer core with three legswith hexagonal cross-sections is formed.
8. A transformer core according to claim 1,characterised in t h a t said legs hâve 23 cctagonal cross-section.
9. A transformer core according to claim 8,characterised by a first, a second, and athird profile ring, each comprising three rings (42a,42b, 42c) with two leg parts and two yoke parts, 25 wherein a first ring (42a) having rhombic cross-section in itsleg parts'with an.angle of 45 degrees and with the yoke parts bent 15 degrees in such a direction that the n· ) 21 11907 ctter sid3 3 Ch ΟϋΠβ ss of les I êr:s are moved towards a second ring (42b) havinç çtadratic cross-sections inits leg parts and being positioned on said first ring,and a third ring (42c) havinç rhcmbic cross-sections in itsleg parts, a first ieg part having 45 degrees lyingmainiy on said first ring (42a) and a second leg parthavinç 133 degrees lying en said second ring (42b), 12 said first, second and third profile rings being assem-bled wherebv a three-phase transformer core with threelegs with octaçcnai cross-sections is formed.
10. A transformer core acccrding to daim 1,chaxacterised in that said legs hâve a 15 cross-section with ten edçes.
11. A transformer core according to claim 10,characterised by a first, a second, and athird profile ring, each comprisinç five rings (50a-e)with two leg parts and two yoke parts, w'nerein 20 a first ring (50a) having rhombic cross-sections in itsleg parts with an angle of 36 degrees, a second ring (50b) having rhombic cross-sections inits leg parts with an angle of 72 degrees, a third ring (50c) having rhombic cross-sections in its 25 leg parts with an angle of 108 degrees, a fourth ring (50d) having rhombic cross-sections in >its leg parts w.ith an angle of 36 degrees and lying 22 119 Q7 mar.tly 3*“. che first ring (50a; and havi.cg ins yokeparts turned cutwards 24 degrees, a.td a fifth ring (50e) having rhombic cross-sections in itsleg parts with an angle of 144 degrees when in lies on 5 the third ring (50c) dur rhombic cross-section with anangle cf 72 degrees when in lies outside the fourthring (50c), and a channel (51) suitable for cooling theleç outside of the fifth ring (50e), sait first, second and third profile rings being assem-10 bled whereby a three-phase transformer core with three lecs with ten-sided cross-semions is formed.
12. A transformer core accordinç no claim 11,characterised by cooling channels (52a, 52b, 53a, 53b) caused by givinç the outer part of the 15 third ring (50c) a rhombic cross-section with an angleof 72 degrees and by displacinç another outer leg partof the third ring toward the fifth ring (50e) when itgoes within the complété leg.
13. A transformer core according to claim 10, 20 characterised by muiti-edged cross-sectionsof their legs and profile rings comprising a firstcluster of rings with rhombic cross-sections withdifferent angles but in their leg parts turned the sameangle and attached to the muiti-edged cross-section, 25 and inside a second cluster of rings with rhombic cross-section with different angles, but in their legparts turned the same angle and attached to the firstcluster and so on until innermost there arises spacefor rings, which in one of their leg parts is given a 23 119 0 7 cross-sectton and tnrning differently frcm those in theother leç part.
14. A transformer cors according to claim 1,characterised in that ail rings hâve a 5 rhombic cress-secticn with two angles of 60 degrees andtwo angles cf 120 degrees.
15. A transformer core according to claim 1,characterised by an additional core (70) ofstries between windings brought toçether at the top and 10 the bottom cf the core.
16. A transformer core’according to claim 1,characterised by an additional core in thecentre line of at least one strip pôle, and if many,arranged three and three in a package (figs. 8 and 9), 15 which pôles are bent to each yoke.
17. A transformer core according te claim 1,characterised in that segments betweenthe cross-sections cf the legs and a circumscribedcircle are partly filled by thin rings and/or slightly 20 broader strips.