Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0206—Manufacturing of magnetic cores by mechanical means
  • H01F41/0213—Manufacturing of magnetic circuits made from strip(s) or ribbon(s)
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F27/00—Details of transformers or inductances, in general
  • H01F27/24—Magnetic cores
  • H01F27/25—Magnetic cores made from strips or ribbons
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0206—Manufacturing of magnetic cores by mechanical means
  • H01F41/0213—Manufacturing of magnetic circuits made from strip(s) or ribbon(s)
  • H01F41/0226—Manufacturing of magnetic circuits made from strip(s) or ribbon(s) from amorphous ribbons

Definitions

• This invention relates to strip wound transformer cores and method of their manufacturing.
• a transformer is a known electrical device widely used for transferring the energy of an alternating current in the primary winding to that in one or more secondary windings through electromagnetic induction. It typically contains two or more electrical circuits comprising primary and secondary windings, each made of a multi-turn coil of electrical conductors with one or more magnetic cores coupling the coils by transferring a magnetic flux therebetween.
• Electrical transformer cores are typically formed of high grain oriented silicon steel laminations. The most common procedure for manufacturing such a transformer is to wind the core independently of a preformed coil or coils with which it will ultimately be linked. To this end, the core is formed with a joint at which the core laminations can be separated to open the core and thus accommodate insertion of the core into the coil window(s).
• the wound core joints are typically of the so-called step-butt joint or step-lap joint types.
• US Patent No. 1,164,288 discloses a technique of fabricating a cylindrical magnetic core for a power transformer.
• the magnetic core is made from coiled strips, wherein the core is of greater axial dimension than the width of the strip.
• To manufacture the core a plurality of layers of the magnetic steel strips is simultaneously coiled to form the cylindrical core. The sum of the width of the strips in each layer is equal to the axial dimension of the core, and at least one longitudinal edge of each strip is staggered is relation to those in adjacent turns of the resultant coil.
• the main idea of the present invention consists in the use of a desired number of layers of magnetic strips to be simultaneously wound so as to form a substantially cylindrical, toroid-like transformer core of a desired height for carrying a coil block mounted thereon.
• the construction is such that each layer is formed of a desired number of strips arranged along the longitudinal axis of the core, and the layers of a desired number are specifically arranged with respect to each other.
• This construction is aimed at providing the optimal distribution of magnetic flux inside the strips in the layers.
• the number of strips in the layer is dictated by the height of the transformer core and by the available widths of the magnetic strips.
• the number of layers is dictated by the magnetic properties of the magnetic material of which the strips are made.
• the thickness of the resultant winding it is dictated by the electrical and mechanical parameters of the transformer, such as the height and cross section of the core, and frequency and rate power of the transformer.
• a transformer core to be used in a power distribution transformer having a desired height and being of a substantially cylindrical toroidal shape, wherein: - the transformer core is in the form of a multi-layer structure wound about a central axis of the toroid;
• each layer in the structure is composed of a predetermined number of magnetic strips arranged along said central axis with air gaps naturally existing between each two adjacent strips of the layer, the predetermined number of the strips being such that the sum of the widths of said strips is substantially equal to said desired height of the core;
• n of layers in said structure is defined by the magnetic properties of the strips, and the layers are shifted with respect to each other a predetermined distance along said central axis such that each of the air gaps in one layer is overlapped by (n-1) strips of the other layers of the structure.
• the commercially available strips made of amo ⁇ hous metals are characterized by a working value of magnetic induction, B w , about 1.35T, and the saturation value of magnetic induction, B sat , about 1.55T
• B w working value of magnetic induction
• B sat saturation value of magnetic induction
• n the number of layers should satisfy the following relation: n>BJ(B sar B w ), n being integer. Considering the above parameters of the commercially available amo ⁇ hous strips, the minimal value of n is 7.
• the predetermined distance defining the shift between each two adjacent layers is such that each of the air gaps in one layer is overlapped by (n-1) strips of the other layers of the structure.
• the number of strips in the layer is defined by the desired height of the transformer core, namely, the sum of the width of the strips in the layer is substantially equal to the height of the core. It should be understood that, in order to planarize the top and bottom surfaces of the core, the number of strips in the extreme layers of the entire structure (I s and 7 layers) differs from that of the intermediate layers. The two opposite extreme strips in each of the intermediate layers are of a smaller width than that of the other strips in the layer.
• each air gap of the intermediate layer in turn is overlapped by the (n-1) strips of other layers.
• some of the overlapping strips are of the structure in the same turn and the others are of the structure of an adjacent turn.
• the strip layers are wound simultaneously being fed from a corresponding number of bobbins (e.g., 7 bobbins). Namely, the bobbins are aligned in an array, each bobbin feeding a corresponding one of the seven strip layers. The strips are fed from the bobbin with the predetermined shift between the layers.
• the bobbins may be prepared such that the strips layer wound on each of the bobbins is arranged with respect to the strip layer wound on the other bobbins in a manner corresponding to the arrangement of layers in the resultant core.
• the bobbins may be identically wound with the strip layers, but mounted with the desired shift with respect to each other.
• a method of manufacturing a transformer core to be used in a power distribution transformer wherein the transformer core has a desired height and is formed of a multi-layer structure of magnetic strips wound so as to create a resultant substantially cylindrical toroidal winding of the core, the method comprising the steps of:
• an apparatus for manufacturing a transformer core to be used in a power distribution transformer wherein the transformer core has a desired height and is formed of a multi-layer structure of magnetic strips wound so as to create a substantially cylindrical toroidal winding of the core, the apparatus comprising:
• - a required number of bobbins, each carrying a predetermined number of magnetic strips for a corresponding one of the layers, the strips being wound on the bobbin and arranged along an axis thereof with small air gaps naturally existing between each two adjacent strips, wherein the required number of the layers is defined by magnetic properties of the strips; - a drive assembly for driving the simultaneous movement of the strips layers from the bobbins onto a mandrel supporting the transformer core; and
• a guiding assembly for guiding the winding of the fed layers about a central axis of the mandrel with a required density between the layers, wherein the layers of the core are shifted with respect to each other a predetermined distance along said central axis of the mandrel such that each of the air gaps in one layer is overlapped by (n-1) strips of the other layers
• the present invention may be used for manufacturing a three-phase transformer.
• a magnetic circuit of such transformer is composed of three transformer cores, each constructed as described above (for carrying three coil blocks, respectively) and two spaced-apart, parallel, plate-like elements attached to the top and bottom surfaces of the transformer cores, respectively.
• the transformer cores with the coil blocks mounted thereon are enclosed between the upper and lower plates of the magnetic circuit.
• the transformer cores are spaced at intervals of 120 degrees about a central vertical axis of the entire transformer structure.
• the cores are spaced from each other and from the plate-like elements by insulating spacers. All the spacers may be formed of plastic with filler of a magnetic powder with the concentration of 20-50%.
• the plates and the cores may be formed of amo ⁇ hous strips.
• the plate may be of a substantially triangular shape with rounded edges, or of a circular shape that simplifies the technological process of its manufacture.
• the plate-like element may be a toroid manufactured similar to that of the transformer core, as described above.
• the advantages of the above construction of a three-phase transformer consist of the following.
• the provision of the plate-like elements of a triangular shape with rounded corners allows for effectively transferring the magnetic flux between the three column-like elementary circuits enclosed between the plates.
• the provision of the column-like elementary circuits formed by one or more toroids produced by wounding the amo ⁇ hous strips enables to obtain a desired height of the column irrespectively of the limited width of the strip.
• the dimensions of the elements of the magnetic circuit i.e., the diameter of each transformer core and each of the plate-like elements
• FIG. 1A schematically illustrates a transformer core according to the invention
• Fig. IB partly illustrates a cross section of the transformer core of Fig. 1A taken along a plane A-A;
• Fig. 2 more specifically illustrates the principles of arranging layers in the core of Figs. 1A-1B;
• FIG. 3 schematically illustrates the main components of an apparatus for manufacturing the transformer core of Figs . 1 A- 1 B ;
• Fig. 4 is a schematic illustration of a three-phase transformer utilizing the transformer core of the present invention.
• a transformer core 10 to be used in a power distribution transformer (not shown here).
• the core is in the form of a cylindrically shaped toroid of a desired height L.
• the toroid 10 is formed by coiling a multi-layer structure 12 of magnetic strips about a central axis 14 of a mandrel 16
• the multi-layer structure 12 is composed of a plurality of parallel layers - seven layers L ⁇ -L in the present example, which are arranged along an axis pe ⁇ endicular to the central axis 14.
• Several strips (ribbons) made for example of a soft ferromagnetic amo ⁇ hous alloy form each of the layers: layer Li is formed by strips Si, layer L 2 is formed by strips S , etc.
• the strips in the layer are arranged in an array extending along the central axis 14, with the unavoidable existence of an air gap, generally 18, between each two adjacent strips.
• the air gaps of each layer are shifted with respect to the air gaps of the adjacent layer, as will be described more specifically further below.
• the resultant winding of the core 10 is composed of a plurality of turns of regularly repeated multi-layer structure 12.
• the number of turns i.e., the thickness of the resultant winding
• each of the layers in the structure 12 is composed of several strips such that the sum of the widths of the strips (together with the gaps between the strips) is substantially equal to the height of the transformer core.
• strips Si of layer Li are arranged with air gaps 18a, strips S 2 of layer L - with gaps 18b, strips S 3 of layer L 3 - with gaps 18c, strips S 4 of layer L 4 - with gaps 18d, strips S 5 of layer L 5 - with gaps 18e, strips S 6 of layer L 6 - with gaps 18f, and strips S 7 of layer L 7 - with gaps 18g.
• Gaps of each layer are shifted with respect to those of the adjacent layer a predetermined distance along the central axis 14 such that each of the air gaps in one layer is overlapped by six strips of the other layers (generally, (n-1) strips).
• gap 18a of layer Li is overlapped by strips S 2 -S of layers L 2 -L of the same turn of the resultant winding
• gap 18c of layer L 3 is overlapped by strips S 4 -S and further by strips of Si- S of layers Li and L 2 of an adjacent turn of the resultant winding.
• magnetic flux F produced by the passage of an electric current through the strip Si flows across the strip Si, and while reaching the gap 18a, flows through the six strips S 2 -S of layer L 2 -L 7 overlapping this gap 18a.
• the shift between the layers is appropriately selected. For example, considering the equal width of the intermediate strips of the layer (i.e., strips between two opposite extreme strips), the sum of shift distances of all the layers in the structure should not exceed the width of the intermediate strip.
• Fig. 3 illustrates the main components of an apparatus 20 for manufacturing the transformer core 10.
• the apparatus 20 comprises seven bobbins B ⁇ -B (generally, n bobbins), each for carrying a corresponding strip layer to be fed to the mandrel 16.
• the layers are previously wound onto the bobbins in a manner, which will be described further below, and simultaneously fed onto the mandrel 16, by a suitable driving assembly, which is not specifically shown.
• the driving assembly may be of any known suitable kind, and may be associated with the mandrel 16 for driving the revolution thereof, while the bobbins are rotatably mounted on their shafts (not shown) to rotate against the tension of the feeding layers.
• the driving assembly may also be associated with the shafts of bobbins for driving the revolution thereof.
• the construction may be such that the bobbins are driven together for rotation about the mandrel, which, in this case, is mounted stationary.
• a guiding assembly 22 comprising one or guiding rollers, generally at 24, and a pair of width limiting rollers 26 accommodated at opposite ends of the mandrel 16 extending normally to the direction of movement of the layers onto the mandrel.
• the layers are prepared on the bobbins with the corresponding shift between the strips of each two adjacent layers as described above. To this end, either the corresponding arrangements of strips of different layers are previously determined, and the strips are wound on the bobbins accordingly, or identically wound bobbins are prepared and then cut by any suitable cutting tool.
• the layers of sufficient width could be wound on the mandrel, and the so produced core then cut at opposite ends.
• the bobbing and/or guiding means may be appropriately shifted.
• the transformer 30 comprises a magnetic circuit formed by an upper plate-like element 32a, a lower plate-like element 32b, and three parallel identical cores 10 (only two of them being shown in the drawing).
• the magnetic circuit is arranged such that the plates 32a and 32b are parallel to each other, and the cores 10 serve as supports between the plates, thereby forming a cage-like structure spatially symmetrical about a central axis CA.
• each of the plates 32a and 32b is a toroid, and is made of amo ⁇ hous ribbons 34 wound about a central hole 35 to form the planar toroid.
• each of the coil blocks 36 includes a primary winding 36a and a secondary winding 36b.
• each phase of the transformer 30 is formed by the transformer core 10 with the corresponding coil block 36 mounted thereon.
• the transformer 30 has a modular structure, namely, the plates 32a and 32b, and the cores 10 can be easily assembled together and disassembled. When one of the plates 32a or 32b is removed, the coil blocks 36 can be removed as well, thereby enabling, for example, to repair the coil.
• each of the plates 32a and 32b has a generally triangular shape with rounded sides and corners.
• the amo ⁇ hous ribbon 34 is made of an alloy having soft ferromagnetic properties.
• Each of the cores 10 is a toroid manufactured as described above. This construction enables to achieve a desired height of the core 10, notwithstanding the fact that the width of amo ⁇ hous ribbon is typically limited.
• the entire structure is held together with three de-mountable bands 38 (only two of them being seen in the figure), each having a screw (or spider) 40 to tighten the band.
• Structural members 42 are provided, each located between the corresponding one of the bands 38 and each of the plates 32a and 32b.
• a base 44 supports the entire structure. An inner, upper surface of the plate 32b is brought into contact with lower surfaces of the cores 10 to transfer magnetic fluxes therebetween, as will be described more specifically further below.
• the transformer 30 operates in the following manner. As an electric current passes through each primary winding 36a of the coil block 36, a magnetic flux is generated and propagates along the corresponding core 10 between the upper and lower plates 32a and 32b. Arrows 46, 48 and 50 show fluxes generated in the three cores 10, respectively. The magnetic flux flowing through the column 10 generates an induced voltage in the secondary winding 36b of the corresponding coil block 36.
• the device having this structure thus functions as a three-phase transformer.
• the electric current for example, with the working frequency of 50Hz, is supplied from a power source (not shown) to a terminal of coil of the primary winding 36a, and, whilst passing through the coil turns, creates the basic magnetic flux 46.
• the flux 46 is divided into two identical fluxes 52 and 54 in the plate 32a. These fluxes 52 and 54 flow along two identical portions of the toroidal plate 32a, and, then, flow down through the two other cores 10.
• the flux 52 changes into flux 48
• the flux 54 changes into the flux 50 passing down through the cores 10.
• the fluxes 48 and 50 flow along two equal paths of the toroidal plate 32b. Whilst passing along the toroidal plate 32b, the flux 48 changes into a flux 56, and the flux 50 changes into a flux 58.
• the fluxes 56 and 58 are transferred into the core 10 - In ⁇
• the plates 32a and 32b could have a circular shape.
• the flux streams 52, 54, 56 and 58 will flow along circular paths therein.
• each of the plates 32a and 32b is shaped like an equilateral triangle with rounded sides and corners. This results in a shorter path for the flux streams in the plates between the cores 10, i.e., the shape of the flux streams is closer to a straight line. This enables to achieve a lower magnetic reluctance, or better conductance of the magnetic flux.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Manufacturing Cores, Coils, And Magnets (AREA)
• Coils Or Transformers For Communication (AREA)
• Coils Of Transformers For General Uses (AREA)

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Citations (5)

• 2000
  • 2000-04-27 DE DE60029640T patent/DE60029640T2/de not_active Expired - Fee Related
  • 2000-04-27 RU RU2002131940/09A patent/RU2241271C2/ru not_active IP Right Cessation
  • 2000-04-27 AU AU2000241411A patent/AU2000241411A1/en not_active Abandoned
  • 2000-04-27 ES ES00921014T patent/ES2269128T3/es not_active Expired - Lifetime
  • 2000-04-27 EP EP00921014A patent/EP1279177B1/en not_active Expired - Lifetime
  • 2000-04-27 AT AT00921014T patent/ATE334473T1/de not_active IP Right Cessation
  • 2000-04-27 WO PCT/IL2000/000243 patent/WO2001082316A1/en active IP Right Grant

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