EP2395521A1

EP2395521A1 - Method for manufacture of triangular transformer cores made of amorphous metal

Info

Publication number: EP2395521A1
Application number: EP10005874A
Authority: EP
Inventors: Martin Dr. Carlen; Lise Dr. Donzel; Stephane Dr. Schaal
Original assignee: ABB Technology AG
Current assignee: ABB Technology AG
Priority date: 2010-06-08
Filing date: 2010-06-08
Publication date: 2011-12-14
Anticipated expiration: 2030-06-08
Also published as: CN102364642A; BRPI1103036A2; CN102364642B; KR20110134316A; ES2406808T3; KR101867947B1; EP2395521B1; PL2395521T3

Abstract

The invention relates to a method for manufacture of cores for three phase transformer (10) whereas the core (14) is composed of three frames (16) designed to be combined so that each transformer core leg (18) is composed of two frame legs (18), whereas the transformer core legs (16) are arranged in a triangular configuration, and the cross-section of the core legs (20) have a circular or polygonal shape, and where the core frames (16) are made of layers of at least one continuously wound band (22) of low-loss magnetic material, whereas the width of the bands (22) is adjusted according to the respective layer of the core leg (20) by means of laser (24) cutting.

Description

The invention relates to a method for manufacture of cores for three phase power transformers whereas the core is composed of three frames designed to be combined so that each transformer core leg is composed of two frame legs, and the transformer core legs are arranged in a triangular configuration.

Description of the State of the Art

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors - the transformer's coils. To transform power three phase transformers have been developed long time ago. Three phase transformers have a core comprising three or five limbs arranged in line and in parallel and both ends of each limb are connected to common yokes, In case of a five leg core the three inner limbs are provided with windings of the coils while the outer limbs only serve as conductor for the magnetic flux as well as the inner limbs, too. In case of three leg cores, all three legs are provided with windings. Regularly transformers are formed by means of sheet metal which sheets are stacked or wound to form the transformer core.
A special transformer arrangement is the one where the transformer legs and coils are arranged at the corners of a triangle. Those limbs have been connected to yokes having the form of triangles. This arrangement allows to save space, provides a symmetrical set-up for the magnetic flux and offers benefits with respect to transformer core losses. Those triangular transformers have become known as Hexaformer or as Delta transformer. Here the core is assembled from three sub-cores each being formed as a quasi-rectangular frame whereas each of the three sub-cores is made from continuously wound steel laminations. The adjustment of the lamination width to obtain the required cross-section is done by slitting, which is a mechanical process.
Though these transformers are space saving its efficiency could be better. Furthermore the manufacture of such transformer is complex and laborious.
Hence it is an object of the invention to design a method for manufacture a space-saving transformer core which is more efficient than those of the state of the art while the manufacture of such cores is less complex and laborious.
Accordingly the method according to the invention is characterized by the fact that the width of the steel tape is adjusted to obtain the desired circular or polygonal shape of the cross-section to the by means of laser cutting.
Accordingly the method according to the invention is characterized by the fact that the tape provided for forming the transformer's core is an amorphous metal tape, in particular an amorphous steel tape. Cores made from amorphous steel have lower losses. However due to the amorphous structure slitting and/or cutting of amorphous metal is difficult and requires some knowhow.
The basic idea according to the invention is to provide the core members made from amorphous metal which is usually available as foils having a thickness of about 25 micron provided as an endless ribbon. Those foils are utilized for manufacturing of said frames by coiling the ribbon continuously. Thereby it is provided pursuant to the invention to trim the ribbon to the desired shape of the frame cross-section by means of laser cutting.
Accordingly the winding of the ribbon and its trimming is effected preferably simultaneously thus the desired shape of the frame member is achieved exactly by form cutting the ribbon. Consequently the cutting tool is positioned close to the winding mechanism in order to define the width of the ribbon according to the respective layer with regard to the cross-section of the core leg.
Pursuant to an embodiment of the invention the winding of the ribbon layers to form a frame is effected by a winding mechanism which preferably is operating partly automatically or fully automatically.
A further essential feature of the method according to the invention is characterized in that the sheet metal layers are made from amorphous metal. Alternatively the sheet metal layers are made from steel alloyed with silicium which steel is relatively brittle, too, but less brittle than the amorphous metal.
Finally it is a preferred object of the invention to provide for a triangular transformer having a core manufactured according to the method illustrated before which is characterized in that the coils are wound on the core legs when the manufacture of the triangular core has been finished.
While the coil winding with conventional transformers is done separately whereas the finished coils are shifted easily on the respective core leg before the yoke is mounted thereon, with the triangular transformers the winding is effected directly since the closed loop of the frames do not allow to open it and thus there is no possibility of pre-fabricating the coil and shifting it on the core leg.
The big advantage of transformer cores made of amorphous metal is that such cores have still lower losses than cores made of Si-steel respectively than other low-loss iron alloys with respect to the magnetic flux. Hence the use of amorphous metal is rather essential for increasing the transformer's efficiency.
In case of amorphous metal ribbons, the cutting of the ribbons is difficult due to the amorphous structure of the material. Mechanical cutting is rather inefficient respectively imprecise compared to laser cutting so that according to the present invention a preferred embodiment is the use of laser beams for cutting the amorphous ribbon to an appropriate width.
In case of laser cutting the width to cut is easily and precisely adjustable. The process allows high speed. Single ribbon layers or a bundle of layers can be cut at a time. Preferably it is possible to place the laser cutting device close to the winding mechanism so that the respective cut is done to achieve the width of the metal tape according to the respective layer with regard to the desired shape of the cross-section of the limb member which may be semicircular or polygonal.
Preferably the laser used for trimming the brims of the amorphous ribbons is a CO₂ laser or it is a solid state laser whereas the power of the laser is at least 2 W, but it may be higher in case of tapes having greater thickness e.g. tapes made of Si-steel.
If a bundle of layers are cut the laser power can be chosen so that the layers weld together at the cut. This has the benefit that it fixes the layers together and they become easier to handle when winding the sub-cores. Hence it is a further advantage of the claimed method according to the invention to trim the ribbons according to its respective layer in order to get the desired shape of the cross-section of the frame member.
The laser cutting method pursuant to the invention can not only be applied for the manufacturing of Delta cores, but also for Hexaformer cores. With Hexaformer cores metal bands of two different widths are used for winding core loops, which provide a hexagonal core leg cross section, when they are adequately positioned. The second width is half of the first width, and can therefore easily be produced by slitting a band in the middle. For amorphous metal, laser cutting is also a preferred method for doing the cutting.
The use of laser cutting for the manufacturing of triangular cores is especially preferred in case of amorphous metal, but can also be applied to Si-steel.
These and further advantageous embodiments and improvements of the invention are subject matter of the dependent claims.
By means of examples of various preferred embodiments of the invention which are shown in the attached drawing the invention, advantageous embodiments and improvements of the invention as well as special advantages of the invention shall be illustrated and described in more detail.
It is shown in

Fig. 1: a lateral view of a transformer provided with coils wound on a transformer core according to the invention;
Fig. 2: a top view on the base section of the transformer core according to the invention and
Fig. 3: a schematic view of the trimming of the width of a ribbon for a transformer core according to the invention.

In fig. 1 a lateral view of a transformer 10 is shown which is provided with coils 12 wound on a transformer core 14 according to the invention. The transformer 10 is formed by three identical frames 16 which frames 16 form core members.
The three frames 16 are put together in order to form a triangular column 14 which is the transformer core according to the invention.
Each core member 16 has two long sides and two small sides whereas the two long sides are straight and form limb members 18 where each is put in parallel to the respective limb member 18 of an adjacent frame 16 and thus form a core leg 20.
Furthermore the cross-section of each limb member 18 is either semicircular or polygonal in order to complete the cross-section of the core leg 20 to full circle or polygon.
The coils 12 are wound on the core legs 20 after the triangular transformer core 14 has been finished.
Fig. 2 shows a top view on the base section 15 of the transformer core 14 according to the invention which discloses the triangular layout of the transformer core 14. besides that this design of the transformer 10 is space saving due to the little base the transformer core 14 requires. As can be seen from fig. 2 the cross-section of each limb member 18 is semicircular and forms together with the limb member 18 of the adjacent core member 16 a core leg having a circular cross-section.
Fig. 3 is a schematic top view on a ribbon or tape 22 which is provided for being wound layer by layer of the transformer core 14. In order to achieve the desired shape of the cross-section of the limb members 18 the tape needs to be trimmed accordingly since otherwise the shape cannot be achieved by a lamination configuration where the ribbon or tape 22 is laminated in a plurality of layers.
Hence the trimming of the width of a ribbon 22 is necessary to achieve the shape of the limb member 18 of a frame 16 for a transformer core 14 according to the invention. According to the invention the trimming is done by means of a laser 24 having a laser beam 26 whereas preferably a CO₂ laser is being used for cutting or trimming the ribbon or tape 22 and having a power of at least 10 W.
The laser beam 26 is guided on the ribbon or tape 22 along the desired cut line 28 which corresponds to the width of the ribbon or tape 22 required for the respective layer of core loop 14 where the ribbon or tape 22 is forwarded (flash 30) for winding the frame 16 as a core member.

Reference list

10: transformer
12: coil
14: transformer core
15: transformer base
16: frame, core member
18: limb member
20: core leg
22: ribbon, tape, band
24: laser
26: laser beam
28: cut line
30: forwarding direction for winding

Claims

Method for manufacture of cores for three phase transformer (10) whereas the core (14) is composed of three frames (16) designed to be combined so that each transformer core leg (18) is composed of two frame legs (18), whereas the transformer core legs (16) are arranged in a triangular configuration, and the cross-section of the core legs (20) have a circular or polygonal shape, and where the core frames (16) are made of layers of at least one continuously wound band (22) of low-loss magnetic material,
characterized in that
the width of the bands (22) is adjusted according to the respective layer of the core leg (20) by means of laser (24) cutting.
Method according to claim 1 characterized in that the laser (24) cutting of the tape or band (22) is done at the same time as the winding of the band (22) in order to form the frame (16).
Method according to claim 2 characterized in that the manufacture of the core frames (16) is effected by winding a first band (22) on a mandrel and at least a second band (22) on the first wound band (22).
Method according to claim 2 or 3 characterized in that the manufacture of the core frames 816) is effected by winding at least a second band (22) of different width on the first wound band (22).
Method according to claim 1 characterized in that the manufacture of the core frames (16) is effected by assembling at least two loops of wound bands (22).
Method according to at least one of the preceding claims characterized in that the laser (24) used for trimming the bands (22) has a power of at least 10 W.
Method according to claim 1 or 6 characterized in that the laser (24) is a CO₂ laser.
Method according to claim 1or 6 characterized in that the laser (24) is a solid state laser.
Method according to at least one of the preceding claims characterized in that the band (22) of low-loss magnetic material consists of amorphous metal.
Method according to at least one of the preceding claims 1 to 8 characterized in that the band (22) of low-loss magnetic material is made from steel alloyed with silicon
Method according to any of the above claims characterized in that multiple bands (22) are simultaneously cut and weld together by means of a laser (24) which results in a certain mechanical stability of the frame (16).
Method according to any of the above claims characterized in that the transformer core (14) is annealed for improving its magnetic characteristics.
Method according to any of the above claims characterized in that the transformer core (16) is coated with a polymeric material for providing mechanical stability.
Transformer core manufactured according to the method according to at least one of the preceding claims characterized in that it consists of three frames (16) arranged to form a triangular configuration.
Transformer having a core according to claim 14 which is provided with coils (12) on the core legs (20).