Patent Description:
In the field of transportation of electricity where transmission and distribution networks are used, the energy losses in the European Union (EU) are around <NUM>% of generated power. Almost half of this relates to the transformers and <NUM>% of all energy losses come from no-load losses (stand-by) in transformer cores. In the world the transformer losses amount to over <NUM> TWh, which is about <NUM> times the power generation in Sweden. <NUM> % of these <NUM> TWh comes from no-load losses. (United4efficiency. org (UN Environment <NUM>)).

EU Commission Regulation No <NUM>/<NUM> of <NUM> May <NUM>, which stipulates Minimum Efficiency Performance Standard (MEPS) in max values or Peak Efficiency Index for losses in transformers, is now in force. This regulation is in <NUM> tiers; one for <NUM> and the next for <NUM>. The regulation has two purposes: <NUM>) to limit the transformer losses and <NUM>) to stimulate the industry to be innovate in new ways of manufacturing transformers.

Since <NUM> the core steel material in transformer and reactor cores has gone through a radical development where the losses have been reduced with almost <NUM> % from <NUM> W/kg (Armco <NUM>) to <NUM> W/kg (NSC <NUM>). However, the design of transformer and reactor cores have been almost the same in about <NUM>-<NUM> years. Therefore, there is a great need for improvements in the transformer and reactor core technology to further reduce the losses.

Furthermore, with the current process for manufacturing three-phase transformer cores the amount of material scrap can be from <NUM>% up to <NUM>%.

Today the total global volume of Grain Oriented Electrical Steel (GOES) produced for use in transformer manufacturing is around <NUM>. <NUM> tonnes, which means that the scrap created can be about <NUM> tonnes at a value of nearly <NUM>. These volumes are expected to increase with about <NUM>% a year for the next <NUM> years.

<CIT> discloses magnetic cores for stationary electrical induction apparatus and more particularly to three-phase stacked lamination cores having five legs.

Therefore, there is also a great need for improvements in the process for manufacturing transformers in order to reduce the amount of material wasted.

It is an object to provide magnetic cores for electrical power transformers or reactors with reduced energy losses and/or reduced scrap, and methods for manufacturing such cores.

These and other objects are met by embodiments of the proposed technology.

According to a first aspect of the invention, there is provided a method for manufacturing a magnetic core for an electrical power transformer or reactor. The method comprises cutting a symmetric cut-out from the middle of a long side of a rectangular yoke plate made of electrical steel such that a symmetric gap is formed in the yoke plate, forming building elements of grain oriented electrical steel either from the symmetric cut-out if the yoke plate is made of grain oriented electrical steel or from an end cut from a short end of a rectangular limb plate made of grain oriented electrical steel, where the building elements have the same size and shape as the symmetric gap divided into two equal parts, repositioning the building elements such that at least some of the building elements get a new orientation and/or position in relation to the yoke plate or the limb plate after the repositioning, and building a magnetic core by assembling at least yoke plates and repositioned building elements such that the repositioned building elements fit into the symmetric gaps formed in the yoke plates at the positions and with the orientations the building elements got after the repositioning.

According to a second aspect of the invention, there is provided a magnetic core for an electrical power transformer or reactor. The magnetic core comprises two parallel and spaced-apart yokes, where the yokes comprise rectangular yoke plates made of electrical steel. Each yoke plate has a symmetric gap at the middle of a long side of the yoke plate, the symmetric gap facing towards the other yoke. The magnetic core further comprises building elements made of grain oriented electrical steel, positioned in the symmetric gaps in the yoke plates, where the building elements have the same size and shape as the symmetric gap divided into two equal parts. In particular, magnetic hybrid cores with grain oriented electrical steel and amorphous steel are provided.

According to a third aspect of the invention, there is provided an electrical power reactor comprising a magnetic core according to the above.

According to a fourth aspect of the invention, there is provided an electrical power transformer comprising a magnetic core according to the above.

According to a fifth aspect of the invention, there is provided an apparatus configured to manufacture a magnetic core for an electrical power transformer or reactor. The apparatus comprises a high power laser equipment, HPL, configured to cut a symmetric cut-out from the middle of a long side of a rectangular yoke plate made of electrical steel such that a symmetric gap is formed in the yoke plate, and/or an end cut from a short end of a rectangular limb plate made of electrical steel, and to divide the cut-out and/or the end cut into building elements, where the building elements have the same size and shape as the symmetric gap divided into two equal parts, a positioning equipment configured to reposition the building elements such that at least some of the building elements get a new orientation and/or position in relation to the yoke plate or the limb plate after the repositioning, and a stacking equipment configured to build a magnetic core by assembling at least yoke plates and repositioned building elements such that the repositioned building elements fit into the symmetric gaps formed in the yoke plates at the positions and with the orientations the building elements got after the repositioning.

With the presently disclosed technology, electrical power transformer and reactor cores can be manufactured with almost no scrap, and at the same time the core losses and noise levels in the new cores will be significantly reduced compared to prior art technology.

Other advantages will be appreciated when reading the detailed description.

The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:.

The present invention generally relates to electrical power transformers and reactors, and more particularly to new designs of transformer and reactor cores with reduced energy losses, and new methods which reduce the amount of scrap produced when manufacturing such cores.

Throughout the drawings, the same reference designations are used for similar or corresponding elements.

As mentioned above, the core steel material in transformer and reactor cores has gone through a radical development where the losses have been reduced with almost <NUM> % since the <NUM>, whereas very little improvement has been made on the core design itself. This is mainly because of limited knowledge of the electromagnetic behaviour in the three-dimensional cores built up from strongly anisotropic electrical steel. This limited development is valid for both stacked, planar cores and wound cores of different forms. One major reason is the lack of computerized magnetic simulation models where neither different 3D reluctance paths nor joints have been fully described, together with their impact on magnetic flux patterns and thereby the magnetic losses from the frequency dependence of hysteresis part, eddy current loss part and the anomalous loss part.

As illustrated in <FIG>, a typical three-phase transformer planar core <NUM> comprises two outer limbs <NUM>, a centre limb <NUM> and two yokes <NUM>. The limbs and the yokes are stacked from rectangular plates of electrical steel. To get the transformer function, windings (not shown in the figure) around the core limbs are needed. <FIG> illustrates such a transformer core <NUM> with typical mitre joints of <NUM>° in the T-joint (centre joint between the centre limb <NUM> and the yokes <NUM>) and <NUM>° in the L-joint corner (corner joint between the outer limbs <NUM> and the yokes <NUM>). Three-phase transformer planar cores have been stacked the last <NUM> years with mitre joints of <NUM>° in the T-joint and <NUM>° in the L-joint corner. In the latest <NUM> years those cores have multi-step lap joints with some offset between pairs of laminations, normally in a vertical direction. The ongoing climate crisis has led to No-Load Loss Regulation by governments in many regions of the world, e.g. EC regulation by Eco Designs. Those regulations are either stipulating maximum losses or minimum energy efficiency indexes in steps for coming years. This forces the manufacturing plants of transformers to use highly anisotropic material in the cores. Those sharper energy efficiency laws force manufacturers to use much more material in order to reduce the flux-densities, since new transformer technologies are not available. 3D electromagnetic simulation tools as FEM are not magnetically strong enough to lead innovation. The permeability variations in all 3D directions locally and in time are too complex still today to be simulated for full understanding in computers. As the full electromagnetic theory is not fully understood the core design and core manufacturing technology can however be improved by experience and model experiments. The core steel has its specific iron loss, but built into the core the losses increase, expressed by a building factor. So far, some historical traditions have been the base to explain the cause of the building factor and the loss pattern in cores.

The present innovation aims to reduce the building factor for cores, where:<MAT>.

The invention also seeks to meet sustainability goals by providing a method for manufacturing <NUM>-phase cores, without any scrap, of Grain Oriented Electrical Steel (GOES) of anisotropic type, or of amorphous electrical steel/metal (AM), or of combinations of both.

Electrical steel made without special processing to control crystal and domain orientation, non-oriented steel, has similar magnetic properties in all directions, i.e., it is isotropic. Grain-oriented electrical steel (GOES) is processed in such a way that the optimal properties are developed in the rolling direction, due to a tight control of the crystal orientation relative to the sheet. It is mainly used as the core material in electrical transformers that require high permeability and low power losses. The magnetic properties are highly anisotropic and the easiest magnetization direction or magnetic orientation is parallel to the magnetic field direction. <FIG> illustrates the magnetic orientation <NUM> in the limbs <NUM>, <NUM> and the yokes <NUM> of a typical three-phase transformer planar core <NUM> made of GOES steel plates, i.e. the magnetic orientation <NUM> is parallel to the long side of the rectangular plates.

Amorphous electrical steel/metal is a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal so fast that crystals do not form. Since many years AM cores are of wound core types in Evan form or five leg (four ring) cores. Amorphous steel is limited to foils of about <NUM> thickness. It has poorer mechanical properties than conventional electrical steels, the AM plates have fewer widths and the maximum width of the plates is about <NUM> which limits the size of the AM cores. The AM material has a lower magnetic saturation level than conventional electrical steels, which means that more material (about <NUM>%) is needed to make an AM core. Therefore, an AM core is slightly more expensive than a core of conventional electrical steel, but on the other hand the magnetic losses are much lower. Transformers with amorphous steel cores can therefore have core losses of about one quarter of that of conventional electrical steels.

Reactor cores are using anisotropic material in the yokes together with anisotropic material in the core segments in the limbs for larger power ratings. They have looked the same in <NUM> years. The design of transformer and reactor cores have looked almost the same in about <NUM>-<NUM> years.

The shipping and logistics of the master coils for the core steel are done from big electrical steel mills (about <NUM> big mill sites) around the world. Very often slitting centres are set up in some continents to spread core widths in slit bands to all transformer manufacturers. Some manufacturers have their own slitting machines together with cutting machines. Those slitting and cutting machines are very heavy mechanical equipment. Shipping of bands and storage of bands are all around the globe, which leads to loss of energy efficiency. All slitting and cutting are done by inflexible mechanical means by roller cutting and punching machines developed in the <NUM>. Some manufactures of transformers don't have that equipment and buy smaller cores from core manufacturers who use above core technologies. Smaller cores up to some <NUM> tonnes are made by E-stackers almost automatically. An E-stacker is a stacking equipment after the cutting line.

Some of the major drawbacks of today's technology are:.

A solution to the above problems is to employ High Power Laser (HPL) technology for manufacturing of transformer and reactor cores. HPL technology has been used for around <NUM> years and this technology increases in the industrial world. The HPL technology is widely spread in all industry. Some advantages of this technology are:.

Historically the use of new oriented electrical steel (Grain Oriented Electrical Steel, GOES) discovered during the <NUM> meant that three-phase cores needed to be designed and manufactured with a new stacking pattern; from <NUM>° with overlap to new cutting angles in the corners (L-joints) and the centre joints (T-joints) with smaller overlaps. The cutting angle has been set based upon empirical evidence and machining tools to be <NUM>°. This is now an accepted industry tradition with known characteristics in losses and sound level. Huge investments are done in heavy inflexible punching machines all over the world.

According to the current technology, as illustrated in <FIG>, the ends of the centre limb <NUM> plate are symmetrically cut at a <NUM>° angle starting at the middle of the limb <NUM> plate, so that two identical, but mirrored, right-angle triangles are removed from the end, thereby forming an outward <NUM>° corner or an "arrow" at the end of the plate. The yoke <NUM> plates have a corresponding symmetric cut-out forming a half of a quadrat, i.e. a triangle with one <NUM>° corner and two <NUM>° corners (therefore, one often talks about <NUM>° cuttings within this field of technology), where the <NUM>° corners are located at the edge of the yoke <NUM> plate so that the <NUM>° corner is "pointing" towards the opposite edge of the yoke <NUM> plate, see <FIG>. The ends of the centre limb <NUM> fit into the cut-outs in the yokes <NUM>, thereby forming "T-joints" between the yokes <NUM> and the centre limb <NUM>.

The dashed areas in <FIG> represent scrap <NUM> from the cutting and will be thrown away. Typical design-dependent scrap and other process scrap is around <NUM>-<NUM> %, depending on size of the cores, for these <NUM>° mitre joints. The ends of the outer limb <NUM> plates are cut at a <NUM>° angle to fit with the ends of the yoke <NUM> plates which are also cut at a <NUM>° angle, thereby forming mitre joints of <NUM>° or "L-joints" between the yokes <NUM> and the outer limbs <NUM> at the corners of the core <NUM>, as shown in <FIG>.

This stacking pattern seems to have the lowest no-load losses or core losses.

The inventor has made model tests on cores built with different qualities and with <NUM>°, <NUM>° and <NUM>° yoke cut-outs. The cut-outs with <NUM>° and <NUM>° have <NUM>-<NUM>% higher no-load losses than the <NUM>° cut-out. It is anticipated from those measurements that a <NUM>° cut-out is optimal for the core losses and sound levels in three-phase cores.

But the real drawback from the core punching and building of today is the amount of scrap for all three-phase cores, from the smallest < <NUM> kVA up to the biggest possible > <NUM> MVA. The technical scrap can be from <NUM>% up to <NUM>%. Today the total yearly global GOES volume produced is around <NUM>. <NUM> tonnes and thereby those "triangles" as cut-outs create scrap of about <NUM> tonnes at a value of nearly <NUM>. <NUM> EUR per year. These volumes and costs increase by about <NUM> % per year.

Based upon the apparently optimal <NUM>° cut-out most embodiments of the present invention utilize the symmetry of a <NUM>°-<NUM>°-<NUM>° triangle, and some embodiments similarly utilize the symmetry of a half-circle.

According to the present disclosure, a method for manufacturing a magnetic core for an electrical power transformer or reactor is schematically illustrated in <FIG>. The method comprises a step S10 of cutting a cut-out from the middle of a long side of a rectangular yoke plate made of electrical steel such that a gap is formed in the yoke plate, a step S20 of forming building elements from the cut-out or from an end cut from a short end of a rectangular limb plate made of electrical steel, a step S30 of repositioning the building elements such that at least some of the building elements get a new orientation and/or position in relation to the yoke plate or the limb plate after the repositioning, and a step S50 of building a magnetic core by assembling at least yoke plates and repositioned building elements such that the repositioned building elements fit into the gaps formed in the yoke plates at the positions and with the orientations the building elements got after the repositioning.

With this technology, the cores can be built without scrap, or almost without scrap since the cut-outs are re-used as new building elements in the core instead of being thrown away as scrap. Furthermore, by cutting out, turning and moving building elements from core plates of GOES material, the magnetic orientation in parts of the core can be changed, so the magnetic flux can be guided in the core in a way that reduces the harmonics in the local flux paths, and thereby also reduces the losses and noise in the core.

With this method, a magnetic core for an electrical power transformer or reactor can be made, where the magnetic core comprises two parallel and spaced-apart yokes built from rectangular yoke plates made of electrical steel, where each yoke plate has a gap at the middle of a long side of the yoke plate, the gap facing towards the other yoke, and building elements of electrical steel which are positioned in and fit into the gaps in the yoke plates.

An apparatus for manufacturing a magnetic core for an electrical power transformer or reactor may then comprise e.g. a high power laser equipment, HPL, configured to cut the above-described cut-outs from the yoke plates and/or the end cuts from the limb plates, and to divide the cut-outs and/or the end cuts into building elements. The apparatus may also comprise a robot or some other positioning equipment configured to reposition the building elements in the manner described above, and a stacking equipment configured to build the magnetic core by assembling at least the yoke plates and the repositioned building elements, as described above. The apparatus may in a particular embodiment also comprise a welding equipment such as e.g. an electron-beam welding equipment, a gas welding equipment, or preferably a laser welding equipment, configured to attach the building elements to the yoke plates and/or the limb plates.

In the following, some non-limiting embodiments of the present invention will be described.

As described above, a lot of material scrap is produced with the current methods for manufacturing transformer cores. An innovative solution to make scrap-less three-phase cores is shown in <FIG> and <FIG>, which are schematic illustrations of a T-joint in a three-phase transformer core according to different embodiment of the present disclosure.

In the embodiment shown in <FIG>, an isosceles right-angle triangular cut-out <NUM>, i.e. a symmetric cut-out, is cut from the middle of the long side of the yoke <NUM>, such that a symmetric gap is formed in the yoke plate. In one embodiment, a HPL laser beam is used to make the cut-out, and in another embodiment the cut-out can be mechanically punched out, as it is done in the current technology. The magnetic orientation <NUM> in the cut-out <NUM> is parallel to the long side or hypotenuse of the triangle. Instead of throwing away the triangle as scrap, it is handled as a new building block. The magnetic orientation <NUM> of this building block can be changed by cutting/dividing the triangle in half through its right angle, to form two new smaller and equal isosceles right-angle triangular building elements <NUM> of half the size of the original triangle, and with the magnetic orientation <NUM> along one of the short sides or legs of the triangles. Then the two smaller triangles are separated from each other, turned/rotated <NUM>° towards each other around the normal of their plane, and the two short sides with the same orientation and the orientation directed along the short sides are attached together, e.g. by laser welding in an embodiment, or other types of welding technologies such as electron-beam welding or gas welding in other embodiments, or by some other attaching means in another embodiment, to form a new building block in the form of a triangle of equal size as the original cut-out, but with a new magnetic orientation <NUM> perpendicular to the long side of the triangle.

With the technology according to the present disclosure there is no need to cut the centre limb at <NUM>° at each short end to create the "arrows" to fit into the yokes. Instead, the centre limb can be cut - with laser in one embodiment or mechanically in another embodiment - with a simple <NUM>° cut to the length that fits between the yokes, and the triangular building blocks from the upper yoke and from the lower yoke with their new orientation can be attached to the ends of the centre limb, e.g. with laser welding in an embodiment, or other types of welding technologies in other embodiments, or by some other attaching means in another embodiment. Thus, the complete assembled centre limb will have the same magnetic orientation as a centre limb according to prior art, but the centre limb according to the present invention is manufactured without scrap.

Then the stacking of laminations can be continued, but without any scrap.

According to an embodiment, an example of a new machining sequence can be:.

Laser cutting has the advantage over mechanical cutting/punching in that it is very flexible and can cut almost any desired geometry at approximately the same speed as mechanical cutting. This flexibility is illustrated in <FIG> in which the cut-out pattern origins from a half-circle, which can be divided into two quarter-circles which are turned, shifted and attached (e.g. welded) in analogy with the embodiment shown in <FIG>. In the embodiment illustrated in <FIG>, the radius r of the half-circle is half the width D of the centre leg, and the width D' of the yoke is equal to or slightly larger than 2r, i.e. D'≥2r, which can also be expressed as D'=2r+x%. Similarly, the cut-out illustrated in <FIG> is also based on quarter-circles but where the arc of the quarter-circles are "inverted" as compared to <FIG>, i.e. the cut-out is formed as two adjacent squares where a quarter-circle has been removed from each square and where the arced edges of the cut-out are curving towards each other instead of away from each other. In other words, the cut-out may be considered as an isosceles concave circular triangle with one straight side, where the straight side is positioned along the long side of the yoke plate. The cut-out can be divided into two equal building blocks which are turned, shifted and attached in analogy with the embodiment shown in <FIG> and <FIG>. The cut-out pattern of <FIG> may be particularly beneficial for guiding the flux from the centre legs into the yoke, lowering the reluctance in the joint and thereby the magnetic losses.

<FIG> illustrates another possible embodiment of a T-joint, where an isosceles right-angle triangular cut-out <NUM> with the hypotenuse positioned along the long side of the yoke plate is cut from the yoke plates of each of the yokes <NUM> such that triangular gaps are formed in the yoke plates. The cut-outs <NUM> are used as new building elements <NUM> as they are, without dividing/cutting them further. The building elements <NUM> are then turned <NUM>° and inserted into the gaps formed in the yoke plates of one of the yokes <NUM> with the bases of the triangular building elements <NUM> facing each other, i.e. such that they mirror each other. The magnetic orientation <NUM> of the building elements <NUM> is now <NUM>° from the magnetic orientation <NUM> of the yoke plates. The centre limb <NUM> is cut in a scrap-less manner by cutting the ends of the limb plates in a triangular shape such that a <NUM>° "arrow" or protrusion with the same size and shape as the building elements <NUM> is formed at one end of a limb plate and a corresponding triangular gap is formed at the other end of the limb plate. The end with the "arrow" is then inserted into the triangular gap in a yoke plate of one of the yokes, and the triangular building elements <NUM> are inserted into the gap formed at the other end of the limb plate, i.e. the building elements <NUM> will fit exactly into a space which is formed by the gap in the yoke plate and the gap at one of the ends of the limb plate, when the limb plate is placed adjacent to the yoke plate with the respective gaps facing each other.

The embodiment illustrated in <FIG> follows the same principle, but the cut-outs <NUM> are formed as half-circles with the diameter line positioned along the long side of the yoke plate, so that the shape of the building elements <NUM>, as well as the gaps in the yoke plates and the gaps and protrusions at the ends of the limb plates are instead formed as half-circles. The half-circular building elements <NUM> are turned <NUM>° and inserted into the space formed by the gap in the yoke plate of one of the yokes <NUM> and the gap at one of the ends of the limb plate, with the diameter lines of the half-circular building elements <NUM> facing each other. The embodiment illustrated in <FIG> also follows the same principle but the cut-outs <NUM> as well as the building elements <NUM> are formed as isosceles concave circular triangles with one straight side, where the straight side is positioned along the long side of the yoke plate, i.e. the cut-outs are based on quarter-circles but the arced edges of the cut-outs are curving towards each other instead of away from each other. The building elements <NUM> are turned <NUM>° and inserted into the space formed by the gap in the yoke plate of one of the yokes <NUM> and the gap at one of the ends of the limb plate, with the straight sides of the building elements <NUM> facing each other. The cut-out pattern of <FIG> may be equally efficient for lowering the magnetic losses as the cut-out pattern of <FIG>. Other symmetric shapes of the cut-outs, building elements, gaps and protrusions may also be possible.

The patterns in <FIG> and/or <FIG> can be combined with a new L-joint in the corners of the transformer core, in order to guide the <NUM>-phase fluxes in the <NUM>-phase core to minimize harmonics in the local flux paths. An example of a new L-joint in a three-phase transformer core according to an embodiment is schematically illustrated in <FIG>, where an end element <NUM> in the form of an isosceles right-angle triangle is cut from the end of a yoke <NUM> lamination. The short sides of the triangle are positioned along the sides of the yoke <NUM> and have the same length as a short side of the yoke <NUM>. In another embodiment, as illustrated in <FIG>, the end element <NUM> may instead have the form of a quarter of a circle where the straight sides of the quarter-circle are positioned along the sides of the yoke and have the same length as a short side of the yoke. Other forms of end elements may also be possible in other embodiments. An example is illustrated in <FIG> where the shape of the end element <NUM> is also based on a quarter-circle but where the arc of the quarter-circle is "inverted" as compared to <FIG>, i.e. the end element is formed as a square where a quarter-circle has been removed, so that the arced edge of the end element is concave instead of convex. The straight sides of the end element are positioned along the sides of the yoke and have the same length as a short side of the yoke. Thereby, a bevelled end is formed at the end of the yoke such that the side of the yoke facing the other yoke is shorter than the opposite side of the yoke. The change of the orientation is done in two steps: First the end element <NUM> is turned <NUM>° in the plane, i.e. it is rotated around the normal of the plane, to get the new orientation direction and then turned <NUM>° outside the plane to get the element into a position such that a new rectangular end, with a magnetic orientation <NUM> which is <NUM>° from the original magnetic orientation, is formed at the end of the yoke <NUM>. The end element <NUM> is then attached to the yoke <NUM> or to the outer limb <NUM> which has been cut at <NUM>°. The result is a scrap-less L-joint which guides the flux towards the outer part of the yoke. Other symmetrical forms can also be cut by laser to get a new orientation which can change the local flux pattern.

Accordingly, the additional steps of the method shown in <FIG> required to create the L-joints of <FIG> are shown in <FIG>, i.e. the method also comprises a step S15 of cutting an end element from an end of the yoke plate such that a bevel is formed at the end of the yoke plate, a step S35 of repositioning the end element to fit with a bevel of a yoke plate such that a <NUM>° angle is formed at the end of the yoke plate, and such that the magnetic orientation of the end element after repositioning is <NUM>° from the magnetic orientation of the yoke plate. Then, in this embodiment the step S50 of building the magnetic core further comprises assembling the yoke plates and repositioned end elements.

In a particular embodiment, as illustrated in <FIG>, the method of <FIG> also comprises a step S40 of attaching the repositioned building elements and/or the repositioned end elements to the yoke plate or the limb plate before building/assembling the magnetic core.

This different form of L-joint in combination with the patterns of <FIG> and/or <FIG> could change the reluctance network in the three-phase core to level out the difference of the inner reluctance path with the outer reluctance path. This change of reluctance network might reduce the building factor which is caused by harmonics of the flux in all parts of the core. The different reluctance paths in wound and planar cores are one of the biggest contributors to local flux harmonics in cores. With the present innovations, designers can reduce losses by reducing flux harmonics.

<FIG> is a schematic illustration of a normal three-phase reactor core <NUM> of GOES with core limb segments <NUM> of GOES according to prior art. A reactor does not have full limbs as a transformer but may instead have "gapped" limbs or limb segments between the spaced-apart yokes. Smaller cores have no core limb segments but only windings between the yokes <NUM>. Bigger reactors have core limb segments. The present disclosure is valid for both types.

As illustrated in <FIG>, in the prior art reactor core the three-phase magnetic flux enters the yokes <NUM> from the segments <NUM> in a perpendicular direction with regard to the core steel orientation <NUM> in the yokes <NUM>. This causes large extra losses and an increase of magnetostriction, which causes high sound level and large reactor core vibrations, as the flux must pass the planar lamination in cross direction causing <NUM>-<NUM> times higher losses than in the direction of orientation <NUM>.

<FIG> is a schematic illustration of a three-phase reactor core <NUM> according to an embodiment of the present disclosure. The principle of the new design and manufacturing method of this new reactor core follows the same pattern as for the three-phase transformer core described above, i.e. cutting out building elements <NUM> from the yokes, turning and/or moving the building elements <NUM> and attaching them again to the yokes with new orientations and/or in new positions. However, for the transformer cores the object of the invention is to reduce the scrap, but since reactor cores are already built in a scrap-less manner, the object for the reactor cores is instead to lower the energy losses and magnetostriction movements in the reactor core by creating flux guiding effects in the building elements <NUM>.

<FIG> is a schematic illustration of manufacturing logistics of the three-phase reactor core of <FIG> according to an embodiment of the present disclosure. The ends of the yokes <NUM> are cut at a <NUM>° angle to form bevelled ends as for the transformer core described above, and the end elements <NUM> are then turned <NUM>° and moved e.g. to the other yoke <NUM> and attached there, in order to change the magnetic orientation <NUM> at the ends of the yokes <NUM>. Alternatively, in another embodiment as illustrated in <FIG>, the end elements <NUM> can instead be attached to the same end of the same yoke as they were cut from, but flipped around so that the opposite surface of the plate is facing the viewer of the figure, with the hypotenuse of the triangle still against the same end of the same yoke as it was cut from. A right-angle triangular cut-out is cut at the centre of the yokes <NUM>, the triangle is cut into half into two building blocks <NUM> in the same manner as for the transformer core described above, the halves are turned <NUM>°, their places are switched and the halves are put back together again to change the magnetic orientation <NUM> in a triangular segment at the middle of the yokes <NUM>.

The building elements <NUM> in the centre of the yokes <NUM> and the end elements <NUM> at the ends of the yokes can be cut by laser cutting in an embodiment or by traditional mechanical punching in another embodiment. The building elements <NUM> in the centre of the yokes <NUM> can be built together by laser welding in an embodiment, or by other welding technologies in another embodiment, or by gluing or some other attaching means in yet another embodiment, and then used as building blocks which can e.g. be put and forced together with the yoke between yoke clamps with butt joints with small airgaps. Airgaps is an integrated part of a reactor.

Reactor yokes have a tradition to be made of one lamination width to reduce flux density and thereby reduce losses. As mentioned above, the losses are mainly caused by planar cross fluxes. The present embodiments of the reactor core use the anisotropy to better match the three-phase flux coming from the three limbs with segments and the three windings, and allow the flux lines to be guided into the yokes, as similar as possible to a transformer core with L-joints at the outer limbs and T-joints at the centre limbs. <FIG> illustrates the new magnetic orientations in the corners and centre joints of a three-phase reactor core according to an embodiment of the present disclosure. The flux and loss situation will thereby be more like a three-phase transformer core in the present embodiments of a three-phase reactor core. Thus, the reactor core according to the present embodiments has lower energy losses than the prior art reactor cores. With the new orientations in the building blocks to match the flux direction, the fluxes will follow the orientation. This will reduce the magnetostriction in those parts as compared to prior art cores with a large magnetostriction. With the present innovation a significant reduction of noise is expected.

<FIG> is a schematic illustration of a part of a single-phase shunt reactor core <NUM> design according to prior art and shows the T-joint between the centre limb segments <NUM> of GOES and the top yoke <NUM> of GOES, and the two top L-joints between the top yoke <NUM> and the outer limbs <NUM>. The prior art design shown in <FIG> has two yokes <NUM> (only the top yoke is shown in the figure) with the same width D/<NUM>. The main flux from the centre limb with a width of D has to be guided via the T-joint into the yoke <NUM> and then divided into two paths flowing towards the L-joints and into the outer limbs <NUM>. This design has the drawback that the main flux has to penetrate into the yoke in the wrong direction, i.e. <NUM>° from the main orientation <NUM> of the yoke <NUM>. That causes extra losses in the whole shunt reactor and increases also the magnetostriction in a transverse direction which causes increased noise levels.

<FIG> is a schematic illustration of manufacturing logistics of a new T-joint in a single-phase shunt reactor core according to an embodiment of the present disclosure. As illustrated in the bottom part of <FIG>, the drawback of the prior art is solved by introducing core building elements <NUM> with the same orientation as the centre limb segments <NUM>, thereby guiding the main flux from the centre limb into the yoke <NUM> and out in the two outer loops through the outer limbs <NUM> with much less reluctance than today's design. Thus, the reactor core according to the present embodiments has lower energy losses and lower sound levels than the prior art reactor cores.

The core building elements <NUM> are made by cutting a triangular cut-out <NUM> from the yoke <NUM> lamination, and with the same methodology as described above it is cut into two halves which are turned <NUM>°, their positions are switched and then they are attached back into the yoke lamination for stacking. As above, the triangle can be cut by laser in an embodiment or mechanically punched in another embodiment, and it can be attached by laser welding in an embodiment, or other types of welding technologies in other embodiments, or by some other attaching means in another embodiment.

In <CIT> a three-phase hybrid transformer core is described. The hybrid transformer core comprises a first and a second yoke of amorphous steel and at least two limbs of Grain Oriented Electrical Steel (GOES) steel extending between the yokes. This transformer core has butt joints between the GOES steel in the limbs and the AM steel in the yokes. A drawback with this technology is that the butt joints cause airgaps. Even if the airgaps may be small, i.e. about <<NUM>, they cause large magnetizing currents with high current peaks. These current peaks set up similar H-field peaks in the core which cause localized distortion of the flux and thereby local harmonics in the flux increasing the eddy currents and eddy losses in the core. Also, the anomalous losses by harmonics in the domain movements will increase. Another drawback is the local flux saturation at the joint areas in the AM yoke when the flux in the limbs enter into the yokes. Even if the AM yoke has a larger cross-sectional area than the GOES limb, the local flux at the joint areas will be saturated. Both drawbacks will lead to extra core losses and sound level.

<FIG> is a schematic illustration of a new three-phase hybrid transformer core according to an embodiment of the present disclosure, with AM steel in the yokes and GOES in the limbs. AM material saturates at about <NUM>. 5T and GOES at about 2T, and therefore, in order to avoid saturation effects in the AM material, the flux density into the AM yokes must be reduced with a factor of > <NUM> (or preferably around <NUM>-<NUM> for some margin) as compared to the flux density in the GOES limbs. This can be accomplished by providing a joint between the GOES part and the AM part which has a length of ><NUM> times the width of the GOES part. Thus, in the embodiment illustrated in <FIG> the width of the AM yokes is about <NUM> times the width D of the GOES limbs, and the ends of the AM yokes <NUM> are cut at an angle of ><NUM>°, i.e. the bevels formed at the ends have an acute angle which is larger than <NUM>°, or preferably around <NUM>°. The outer limbs <NUM> are also cut at an angle so that the bevelled ends of the outer limbs <NUM> fit with the bevelled ends of the yokes <NUM> to form <NUM>° angles at the corners of the core <NUM> in <FIG>.

The centre limb <NUM> of the embodiment in <FIG> is provided with <NUM>° "arrows" at the ends, as described previously in relation to <FIG> and <FIG>, to fit into triangular cut-outs in the yoke <NUM>. This design also provides a reduction in flux density from the GOES centre limbs <NUM> into the AM yokes <NUM> of about a factor of <NUM>, since the joints between the centre limbs <NUM> and the yokes <NUM> have a length of about <NUM> times the width D of the centre limb due to the geometry (<NUM>. This factor is however not as critical in the centre T-joint as in the L-joints, since the flux from the centre limb is divided into two parts when entering the yoke, as described above.

Furthermore, to avoid the above described drawbacks with butt airgaps causing flux distortion, the new design shown in the embodiment in <FIG> has joints with step-lap overlaps. The overlap <NUM> of the step-lap joints are illustrated with dashed lines in <FIG>.

The three limbs <NUM>, <NUM> in the core <NUM> in <FIG> have GOES as material and can be either punched in a traditional steel cutter in an embodiment or cut by an HPL equipment in another embodiment. The yokes <NUM> are of AM material and should preferably be cut in an HPL equipment. The core can have several layers of steel sheets, which are shifted vertically in relation to each other, so there is an overlap <NUM> between the different layers. The ends of the AM yokes <NUM> and the ends of the outer limbs <NUM> are cut at an angle so that the bevelled ends of the outer limbs <NUM> fit with the bevelled ends of the yokes <NUM> to form <NUM>° angles at the corners of the core <NUM>.

In an example embodiment, from a production point of view there can be e.g. <NUM> GOES sheets of <NUM> each glued together, which overlap with <NUM> AM sheets, also glued together in pieces. This can be optimized in production to match manufacturing costs with extra joint losses. This will later simplify the automatic stacking and top-yoking after winding assembly. The top yoke can for example be assembled together with the whole core, and then be removed in the above pieces before winding assembly.

The centre limb can be cut at <NUM>°, and triangular building blocks can be attached at the ends of the centre limb, for example by HPL welding in an embodiment, or some other type of welding in other embodiments, to form the <NUM>° "arrows" as described above. For example, as shown at the bottom left in <FIG>, an end cut <NUM> in the form of a rectangle, or more precisely half a quadrat is cut from a short end of a rectangular GOES limb plate and this half-quadrat is divided into two small isosceles right-angle triangular building elements <NUM> of equal size and a large isosceles right-angle triangular building elements <NUM>' of twice the size of the small triangular building elements <NUM>. The small triangular building elements <NUM> are then repositioned and put together into a large triangle such that the short sides of the triangles that have a magnetic orientation parallel to them are facing each other, and attached along their other short sides to one end of the centre limb, and the large triangular building element <NUM>' is attached to the other end of the centre limb with its hypotenuse against the end, to form a <NUM>° "arrow" at each end of the centre limb. In another example, an end cut <NUM>' in the form of a complete quadrat can be cut from a short end of a rectangular GOES limb plate and divided into two large triangular building elements <NUM>' and four small triangular building elements <NUM>, as shown at the bottom right in <FIG>. This building block then has material enough for two centre limbs. Thus, the centre limb can be manufactured without scrap (the outer limbs are already manufactured without scrap in prior art technology). In these embodiments, the magnetic orientation <NUM> of the triangular building elements <NUM>, <NUM>' is the same as the magnetic orientation <NUM> of the centre limb.

The yokes of AM material must get a <NUM>° triangle cut-out <NUM> in the middle, such that the cut-out <NUM> from the yoke plate has the same size and shape as the second building elements <NUM>'. This cut-out will be scrap as it cannot be reused again.

The steps for cutting, repositioning and attaching the building blocks of the three-phase hybrid transformer core of <FIG> as described above correspond to the step S20 of forming building elements, the step S30 of repositioning the building elements and the step S40 of attaching the building elements according to the method of <FIG>. Then, in this embodiment the step S50 of building the magnetic further core comprises assembling yoke plates and limb plates with attached building elements with overlap joints between the yoke plates and the limb plates.

As mentioned above, single-phase and three-phase reactors have been built the same way during the last <NUM> years. For all typical units, there are two yokes which connect to one winding for a single-phase reactor or three windings for a three-phase reactor. At larger ratings the windings have several spaced-apart core limb segments inside, the segments dividing the magnetic energy by many airgaps.

As described above, the reactor cores shown in <FIG>, <FIG> and <FIG> reduce the cross and transfer losses in the GOES lamination by guiding the flux into the GOES yokes as similarly as possible to a transformer core with L-joints and T-joints.

<FIG> is a schematic illustration of a three-phase reactor core <NUM> according to an embodiment of the present disclosure, where the yokes <NUM> are built from GOES and the limb segments/elements <NUM> located between the yokes <NUM> are wound coils built from AM. <FIG> is a schematic illustration of a single-phase reactor core <NUM> according to an embodiment of the present disclosure, where the core limb segments/ elements <NUM> are wound coils built from AM and the yokes <NUM> and outer limbs <NUM> are built from GOES. In these embodiments the losses can be reduced even further by using segments of wound coils from AM instead of the core segments of GOES used in the previous embodiments shown in <FIG>, <FIG> and <FIG>. Otherwise, the manufacturing logistics of these cores is the same as for the previous embodiments shown in <FIG>, <FIG> and <FIG>. It is anticipated that the space factor for AM coils are the same as for the GOES pieces/segments. The AM coils containing several turns must be divided such that there are no close turns. All turns must be open and the coils must be provided with turn-to-turn insulation, i.e. all turns must be extra insulated by plastic film/foil. Such insulation film is usually ~<NUM> thick. That can be done in the same way that the AM cores are wound today. If this is not done properly there is a risk that the core segment will melt down due to induced currents in the turns.

The loss reduction in the AM segments compared to GOES segments is estimated to be about <NUM>%.

The sound level with less cross fluxes in the yokes and less other vibration patterns should also be reduced as compared to the prior art design.

GOES segments are usually formed in an epoxy process to a hard element in order to stand the compressive pressure. AM segments can be formed in the same manner after it is built as described above, so when the AM coil is delivered from the AM supplier it will be handled the same way as for a GOES segment. It goes into a form with vacuum and epoxy hardening process to be a hard element.

When building large reactor cores, the core may be provided with outer limbs connecting the yokes, for optimization reasons. Due to transportation issues there is a maximum total height for large reactors, and if the reactor is made with outer limbs the height of the yokes can be reduced, the height of the windings can be increased and hence the reactive energy is increased. Accordingly, <FIG> is a schematic illustration of a three-phase hybrid reactor core <NUM> with limb segments/elements <NUM> of AM, yokes <NUM> of GOES and outer limbs <NUM> of GOES (<NUM>-limb reactor) according to an embodiment of the present disclosure. The manufacturing logistics of the GOES yokes <NUM> is the same as for the reactor cores shown in <FIG>, <FIG> and <FIG> and <FIG>, with triangular core building elements <NUM> cut out at a <NUM>° angle. The width of the outer limbs <NUM> should be half the diameter of the AM coils. If the ends of the yokes <NUM> is cut at an angle larger than <NUM>° the height of the yokes will be larger than the width of the outer limbs <NUM>.

As mentioned above, the reactor cores of <FIG>, <FIG> and <FIG> are built with AM in the limb segments and GOES in the yokes, but it is also possible to have other combinations of materials, e.g. GOES in the limb segments, and AM or GOES in the yokes. If the yokes are built with AM material, no cutting of cut-outs or end elements from the yokes are needed.

In the hybrid reactor core described above the core segments are manufactured by amorphous core steel. In the following a hybrid transformer core is described where the amorphous material is used in the same manner. GOES material is an anisotropic material with very high magnetic orientation in the rolling direction, which means that the magnetization in the orientation direction takes about <NUM>-<NUM> times less magnetic energy (and losses) than when the material is magnetized in the transverse direction. Therefore, a core segment would never be made in the form of a wound GOES coil since it would then be magnetized at <NUM>° or in a direction transverse to the rolling direction, which would cause large losses. The amorphous material is an isotropic material which consumes the same magnetic energy or losses in all directions. When the amorphous material was invented in the beginning of <NUM> it was only used as a substitute for GOES material in wound transformer cores which is the case also today <NUM> years later. In the hybrid transformer cores described below the limbs are made as amorphous coils which are easily magnetized in a direction transverse to the coil direction since the magnetic energy is the same in all directions. This is a new and important innovation in the transformer industry.

<FIG> is a schematic illustration of embodiments of hybrid single-phase transformer cores <NUM> according to the present disclosure, and <FIG> is a schematic illustration of embodiments of hybrid single-phase transformer cores <NUM> not in accordance with the invention. The cores of <FIG> and <FIG> are similar to the reactor core of <FIG>, with yokes <NUM> built from GOES and AM in the limbs, but with whole limbs <NUM> of AM coils instead of spaced-apart limb segments of AM. The manufacturing logistics of the GOES yokes in the transformer cores of <FIG> and <FIG> is the same as for the reactor cores shown in <FIG>, <FIG> and <FIG> and <FIG>, with triangular core building elements <NUM> cut out at a <NUM>° angle. In an embodiment of the transformer cores of <FIG> and <FIG> the butt joints between the AM limbs and the GOES yokes are provided with insulation. The width T of the GOES yokes in these embodiments should be larger than the diameter of the AM limbs in order to take care of flux leakage from the windings in the AM coil to further minimize losses in the core.

Similarly to the AM limb segments described above, all turns in the AM limb coils must be open and the coils must be provided with turn-to-turn insulation, where the total turns shall be divided into a number of sub-turns, in order to avoid flashover/short circuit between the layers. A mechanically strong but thin AM-coil end insulation to the yoke must be added, and the usual grounding system of all core parts is to be applied. As mentioned previously, sheets of AM steel is limited in width, but to manufacture larger AM limbs several AM sheets can e.g. be placed next to each other with overlap and wound together into a larger interleaved coil. In this way this innovation can already today with the limited AM widths available be used to manufacture larger cores up to nearly about <NUM> MVA, thus covering half of the yearly global transformer needs.

<FIG> illustrates a core with a centre limb <NUM> of AM and two outer limbs <NUM> of GOES, similarly to the reactor core of <FIG>, whereas the core illustrated in <FIG> instead has two AM limbs <NUM>. The core with two AM limbs may have some advantages, e.g. since the two limbs can be connected in series to increase the voltage. Also, the yokes of the core with two AM limbs are simpler to manufacture, shorter and therefore more mechanically stable.

Analogously with the single-phase transformer cores illustrated in <FIG> and <FIG>, <FIG> is a schematic illustration of a hybrid three-phase transformer core <NUM> according to an embodiment of the present disclosure and is similar to the reactor core of <FIG>, but with whole limbs <NUM>, <NUM> of AM instead of spaced-apart limb segments.

Today all AM cores in distribution transformers are made by AM wound cores. Such single phase and three phase transformers are made in different ways with different loops as Evans cores and <NUM> limb cores and HEXA cores. They all have some major drawbacks:.

A way to avoid these drawbacks is to avoid wound cores and instead use planar stacked one phase or three phase cores. Also for planar stacked GOES cores there are differences in the length of the reluctance paths but the flux can level out a bit in the planar geometry as to reduce the distortion and the magnitude of harmonics in local fluxes. This is more pronounced in AM planar stacked cores which are not built today. There are measurements done showing the difference in building factor for planar cores and wound cores, where wound cores have higher building factors. Wound cores are very simple to make and by the different traditions in the USA and EU since <NUM> years the single phase transformers started to be used in the single phase Distribution System Operator (DSO) systems in the USA and the countries using the IEEE/ANSI standards. The EU DSO system started almost at the same time but then only with three-phase systems. When the world is now searching for energy efficiency in Distribution System and Transmission System components, innovations for new transformer designs are needed.

Building blocks for a planar stacked AM core can e.g. be cut in an HPL equipment, and a three-phase core can be built up with e.g. <NUM> rectangular blocks/cuboids with overlap joints and airgaps between the blocks. These rectangular blocks can be made of several layers of thin AM steel of about <NUM>-<NUM> layers. Since AM is isotropic the joints can be done without scrap. It is also possible to set other layers with smaller dimensions to form a possible circular limb.

A drawback with rectangular blocks is the final core will have many airgaps between the blocks which increases the build-up of magnetic energy. This leads to magnetizing current peaks and H-field peaks inside the core; all causing flux harmonics. This problem can be overcome by building very tight joints with similar overlaps as in a GOES core where the flux jumps from one layer to another layer. <FIG> is a schematic illustration of a stacked Amorphous Metal Distribution Transformer (AMDT) core <NUM> with overlap <NUM> joints between the yokes <NUM> and limbs <NUM>, <NUM> for single and three-phase according to an embodiment of the present disclosure. The core may be built without scrap by cutting the yokes <NUM> and outer limbs <NUM> at an angle so that the yokes <NUM> have bevels at the ends such that a side of the yoke plate facing the other yoke <NUM> is shorter than the opposite side of the yoke plate, and where the outer limb plates have bevels at the ends fitting with the bevels at the ends of the yoke plates, such that <NUM>° angles are formed at the corners of the magnetic core, where the bevels may have an angle of for example <NUM>° in a particular embodiment as illustrated in <FIG>, and the centre limb <NUM> at <NUM>°, e.g. by laser cutting in an embodiment, and attaching them together by e.g. laser welding in an embodiment or other types of welding technologies in other embodiments, or by some other attaching means in another embodiment.

In the design shown in <FIG>, the reluctance paths in the AM core have the same total permeability in all directions in the plane and in the same time moment. In <FIG> the outer limbs are fitted to the yokes by a <NUM>° joint with overlap. But it is also possible to make outer limb joints as in the T-joint with <NUM> ° cuts instead of <NUM>° cuts in another embodiment. Other angles of the cut are also possible in other embodiments. The optimal design, e.g. overlap size, and process may be fine-tuned during production start-up. Especially the outer limb joints can only be established after vibration and sound level measurements since the joints decide the oscillation pattern at different vibration harmonics. So, the reluctance is more or less only dependent on the path length, which should give less harmonics in the local fluxes and thereby a smaller building factor. If the GOES specific losses are set to <NUM> W/kg at <NUM> T, <NUM>, it can be estimated that the core losses for a GOES three-phase transformer core as illustrated e.g. in <FIG> are <NUM> x <NUM> = <NUM> W/kg at <NUM> T and <NUM> (<NUM> is the anticipated building factor). For the stacked AM core with overlap joints as illustrated in <FIG> we anticipate that the AM losses at <NUM> T and <NUM> are <NUM> W/kg with building factor <NUM>. We then get the core losses to <NUM> x <NUM> = <NUM> W/kg, which is an improvement of <NUM>% by switching from GOES to AM for distribution transformers.

Similarly to the hybrid transformer core illustrated in <FIG> the AM sheets can be built by pieces made from <NUM>-<NUM> sheets (=<NUM> to <NUM>) where the sheets in one embodiment may have a thin glue on the surface to bind them together for simpler handling, or in another embodiment be welded together by e.g. spot welding, or bound together by some other means in other embodiments.

Claim 1:
A method for manufacturing a magnetic core (<NUM>; <NUM>; <NUM>; <NUM>) for an electrical power transformer or reactor, the method comprising:
cutting (S10) a symmetric cut-out (<NUM>) from the middle of a long side of a rectangular yoke plate made of electrical steel such that a symmetric gap is formed in the yoke plate;
forming (S20) building elements (<NUM>; <NUM>') of grain oriented electrical steel, GOES, either from the symmetric cut-out (<NUM>) if the yoke plate is made of grain oriented electrical steel, or from an end cut (<NUM>; <NUM>') from a short end of a rectangular limb plate made of grain oriented electrical steel, where the building elements (<NUM>, <NUM>') have the same size and shape as the symmetric gap divided into two equal parts;
repositioning (S30) the building elements (<NUM>; <NUM>') such that at least some of the building elements (<NUM>; <NUM>') get a new orientation and/or position in relation to the yoke plate or the limb plate after the repositioning;
building (S50) a magnetic core (<NUM>; <NUM>; <NUM>; <NUM>) by assembling at least yoke plates and repositioned building elements (<NUM>; <NUM>') such that the repositioned building elements (<NUM>; <NUM>') fit into the symmetric gaps formed in the yoke plates at the positions and with the orientations the building elements (<NUM>; <NUM>') got after the repositioning.