Transformer core

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to transformer cores and especially to three-phase cores comprising three frames of rings of transformer plate defining yokes in, for example, horizontal triangles and vertical legs extending between corners of the yokes. The invention also relates to single-phase shell cores having many rings, frame cores having two frames and two yokes, inductors, and components for the foregoing and transformers.

2. Description of the Prior Art

Transformer cores are almost solely made of transformer plates laid edge to edge to an EI form or ring. Some of them are made of cut rings and called C-cores. Others are wound to two rings inside a larger ring and cut to two E-core parts used for three-phase transformers.

Toroid transformers have a ring core which is not cut and is the only practical exception to the EI form. Small shell single-phase transformers and large three-phase transformers use the EI form of core.

A common three-phase transformer core will now be described. Virtually all have six coils, which by means of wires are wound on a cylinder forming three rod-shaped windings. The cores are composed of a multitude of thin, rectangular plates of electromagnetic material, which are stacked side-by-side with their long sides in alignment to form each of the legs.

The E-shaped plates form one yoke, and three short legs each extending its body into one of the transformer coils. Each leg faces a leg from a yoke at the opposite end of the coil. Thus, there is a core leg extending through each of the three sets of wound coils encircling the legs. The coils are bridged by one yoke at each side of the coils.

The plates of the core are thin sheets of metal, assembled in place, one sheet at a time, until an entire core is put together. This is a slow, labor intensive process.

The EI cores are inefficient to operate, and electrical losses occur at the juncture of many mating edges between the plates. That is, EI stacked cores in general have the drawback that the magnetic field has to cross small gaps between the edges from plate to plate.

There are further losses in the four outer corners of a complete three-phase transformer where field radiation occurs, since there is no ready path for the magnetic fields to flow. Further, the yokes are made of core material that is not encircled by coils and therefore does not contribute to the efficiency of the transformer, but to the contrary the consequence is that material and labor to form the yokes can be regarded to be wasted.

When the operation of a standard three-phase transformer is commenced, there are very high current losses. There are thus high losses during start-up as well as under load for standard three-phase transformers due to the conventional three-phase transformer cores.

The EI cores used in three-phase transformers have numerous other shortcomings. They vibrate and hum during operation. They set up electromagnetic radiation that is easily detectable at about five feet from typical three phase transformers. Due to e.g. electromagnetic forces in the space between the edges of the plates, there [is] will be noise in the core. Conventional three-phase transformers generate excessive amounts of heat, and means must be employed to cool them, requiring an excessive amount of cooling fluid.

As noted above, the inefficiencies of three-phase transformers requires each of them to have a large size. This requires them to be larger in both width and height. Large transformers are difficult and expensive to transport, due both to their size and height. In addition, shipping large transformers sometimes results in damage due to their instability. For example, large transformers have at times been unable to be shipped to offshore installations, and such shipping if possible is expensive. Designers of transformer cores have striven to obtain legs with an essentially circular cross-section because that gives the best efficiency of the final transformer. That is, transformer windings are nearly always cylindrical, having an interior void within the windings with a circular cross section. The core designer wants to fill that void. This is true for both three-phase and single-phase transformers. However, there is always a trade-off between efficiency and production requirements, leading to non-optimal transformer cores with non-circular legs.

U.S. Pat. No. 4,557,039 (Manderson) discloses a method of manufacturing transformer cores using electrical steel strips having approximately a linear taper. By selecting a suitable taper, a hexagonal or higher order approximation of a circular cross section for the legs of the cores is produced. However, the tapered strips are extremely difficult and time-consuming to produce, and the design is particularly not well adapted to large-scale commercial production.

In

FIGS. 1

,

1

a-b

is shown a prior art three-phase transformer core according to Manderson, generally designated

10

. The core has a general delta-shape, as is seen in the isometric view of

FIG. 1

, with three legs interconnected by yoke parts. In

FIG. 1

a

, a cross-sectional view of the core is shown before final assembly. The core comprises three identical ring-shaped parts

12

,

13

and

14

, the general shape of which appears in

FIG. 1

Each ring-shaped part fills up one half of two legs with hexagonal cross-sections, see

FIG. 1

a

, thus totaling the three legs of a three-phase transformer. The ring-shaped parts are initially wound from constant width strips to three identical rings

12

a

,

13

a

,

14

a

with rhombic cross-sections comprising two angles of 60° and two angles of 120°. These rings

12

a

-

14

a

constitute the basic rings. The orientation of the strips also appears from

FIGS. 1

a

and

1

b.

Outside of the basic ring in each ring-shaped part there is an outer ring

12

b

,

13

b

,

14

b

of a regular triangular cross-section. The outer rings are wound from strips with constantly decreasing width. When the three ring-shaped parts

12

-

14

are put together, see

FIG. 1

b

, they form three hexagonal legs on which the transformer windings are wound.

A drawback with this solution is that every size of transformer requires its own cutting of the strips. Also, the outer rings

12

b

-

14

b

are made of strips with decreasing width, leading to waste and also making the transformer according to Manderson very difficult to manufacture. Another drawback is that the design is not self-supporting, i.e. the ring-shaped parts tend to move in respect of each other.

U.S. Pat. No. 2,544,871 (Wiegand) discloses a transformer core with three legs, each leg being made from two ring-shaped parts and an auxiliary ring shaped part. There are thus nine ring shaped parts, three of which are used in an inefficient way, making Wiegand an expensive and impractical device.

Transformer cores are also described in the following documents: Swedish Patent No. 163797, U.S. Pat. No. 2,458,112, U.S. Pat. No. 2,498,747 and U.S. Pat. No. 2,400,184. However, the above mentioned problems are not overcome by the cores described in these documents.

The difficulty and expense of making transformer cores having a ring with a decreasing width has rendered this proposed transformer core construction totally impractical, and no such cores are known to exist in commercial use. Despite the recognition that transformer cores should nearly fill the circular interior of transformer windings, none has hitherto been proposed which is practical and economical. The design of such a transformer core would be of tremendous importance with respect to both three-phase and single-phase transformers. In addition, the provision of similarly designed inductors would be a most significant contribution to the art.

The electromagnetic and mechanical shortcomings of present three and a single-phase transformer core is very significant considering the number of transformers sold and in use throughout the world. The following figures demonstrate this. They were taken from the “The World Market for Transformers 2000” published by Golden Reports, of 109 Uxbridge Road, Ealing, London W5 5TL, United Kingdom. In 1999, the market in the United States for transformers was 2,664 units. The total for the rest of the world was about 4,828 transformers. The world market for transformers from 1994 through 1999, was as follows:

1994

$9,287,920,000

1995

$10,107,530,000

1996

$10,491,770,000

1997

$10,782,230,000

1998

$11,163,650,000

1999

$11,339,030,000

The World Market for transformers is growing, as shown in the following table:

1994 to 1995

8.8%

1995 to 1996

3.8%

1996 to 1997

2.8%

1997 to 1998

3.5%

1998 to 1999

1.6%

with an average annual growth of 4.1%. The sales of transformers is extremely large, as the following demonstrates:

1997

$10,782,000,000

1998

$11,164,000,000

SUMMARY OF THE INVENTION

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

Another object of the present invention is to provide a transformer core wherein the energy losses are significantly reduced.

Another object of the invention is to provide a transformer core for a transformer winding which is electromagnetically efficient.

It is yet another object of the invention to provide a transformer core for a transformer winding which substantially fills the void in the winding.

A still further object is to provide a transformer core for substantially filling a transformer winding comprising an assembly of wound metal strips, each of the metal strips having constant widths.

It is an additional object to provide a ring shaped core for transformers made of a combination of rings of wound strips of ferromagnetic material, each component ring having an equal width.

It is still a further object of the invention to provide ring shaped transformer cores for three-phase transformers made of set of wound metal strips, the metal strip of each component of the set having an equal width.

Another object is to provide a ring-shaped transformer core having straight legs and yokes curved at their intersection with straight legs for rendering the flow of magnetic fields efficient, the legs having polygonal cross sections and being made of wound metal strips, each strip having a constant width.

It is yet another object of the invention to produce a three-phase transformer core with rings made from transformer plate of a constant width for the respective rings and with a controlled thickness, the core having legs whose cross-section is composed of rhombs and/or rhomboids, including squares and rectangles, forming a polygon.

Another object is to provide a three-phase transformer core made of rings of offset transformer plate, the core having legs composed in cross-section of rhombs and/or rhomboids, forming a regular polygon having at least six sides.

It is an object of the invention to provide the foregoing transformer cores that can be produced in commercial volumes having high quality as transformer cores and being produced in a practicable manner.

Another object is to provide a transformer core that does not suffer from the relatively high electromagnetic losses at junctures of adjoining sheet metal plates, end corners and angled corners of EI cores presently used in three-phase transformer cores.

Still yet another object is to reduce the noise from electromagnetic forces between the plates.

A further object is to provide a transformer core that does not hum or vibrate, as do transformer cores in current use.

Another object is providing a transformer core that does not suffer start up losses, as do conventional transformer cores.

A further object is to provided a practical and efficient transformer core for three-phase transformers which enables the windings to be arranged in a compact orientation, i.e. at the corners of an imaginary triangle.

It is yet still another object of the invention to provide a three-phase transformer core made from rings of offset transformer plate, the rings cooperating to define legs in a delta arrangement for extending through transformer windings in a delta arrangement.

It is an additional object of the invention to provide a three-phase transformer core which is more effective and efficient than prior transformer cores for three-phase transformers, yet does not require the manual labor to assemble the core as do conventional EI cores.

Still another object is to provide an improved single-phase transformer core having as a cross-section a polygon of at least six sides.

An additional object is to provide a single-phase transformer core having in cross-sections rhombs and/or rhomboids, defining a polygon having at least six sides.

Yet another object is to provide an improved inductor core having a polygonal cross section with wound rings, each ring being made of a metal strip with equal width.

A further object of the invention is to provide an improved inductor core having yokes of polygonal cross section made of offset laminates of transformer plate, each of equal width, and made from metal of constant width.

It is a general object to make inductors of excellent electromechanical efficiency that can be made economically using metal strips of constant non-varying widths.

It is another object of the present invention to provide an improved frame (as explained below) for transformer cores.

An additional object is to provide an improved frame for inductor cores.

A further object is to provide an improved transformer.

A still further object of the present invention is the provision of an improved inductor.

Another object is to provide a method of manufacturing a transformer that is well adapted for large-scale production.

Other objects will occur to those skilled in the art from the description to follow and from the appended claims.

The invention is based on the realization that a transformer core with one or more regularly multi-edged legs with more than four edges can be assembled from rings of strips with constant width.

An important aspect of the present invention with respect to three-phase transformer cores is to make or fill rhombic cross-sections in three legs in a triangular pattern using three frames, each frame being composed of at least two rings of wound offset transformer plate, where each frame forms part of two legs. Each leg has a polygonal cross-section made of rhombs and in some cases, rhomboids. The straight or leg portion of two frames cooperate to form a transformer core leg, the leg having the polygonal cross-section. The leg portion of the cooperating parts of two frames each define one half of the desired polygonal cross-section, and together they form the desired full polygonal cross-section. While the simplified polygonal cross-section is a hexagon, any number of even sides, six or above, can be prepared pursuant to the invention. Moreover, while the combined leg portions can cooperate to form the desired polygonal cross-section, with each of the two frames forming one half of the desired polygonal cross-section, it is also possible pursuant the invention to form the desired rhombic cross-section using frames to each contribute one third of one desired rhombic cross-section.

Another important aspect of some of the preferred forms of the invention is that the transformer core is made of frames of rings of offset or splayed material as defined below, each ring being made of wound sheets of transformer plate of a constant width. Each frame has surfaces which match corresponding surfaces of another frame, and they connect and lock the frames together. This differs from the prior art as shown in

FIG. 1

where the surfaces are flat or even, because such surfaces can slip apart and make it difficult to keep the frames in a tight fixed position during subsequent manufacturing stages and also makes such transformer cores less stable and shock resistant during transport and installation. The traditional E-shaped core of stacked thin sheets is very vulnerable and is likely to loose some of its initial efficiency when moved around in the factory and during transport and installation. The edges of the prior art plates separate somewhat when a core or transformer is moved around, as is well known in the art—and the preferred embodiments do not suffer this disadvantage.

This differs from U.S. Pat. No. 2,544,871 to Wiegand where three cores and three auxiliary cores cooperate to form three transformer legs, since it takes two rings and an auxiliary ring to form one transformers leg. The three auxiliary cores are not necessary in the present invention.

BRIEF DESCRIPTION OF DRAWINGS

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

FIG. 1

is an isometric view of a prior art three-phase transformer core made of rings with rhombic and triangular cross-sections;

FIGS. 1

a

and

1

b

are transverse cross-sections of any of the legs of the core shown in

FIG. 1

before and after assembly, respectively;

FIG. 2

is an isometric view of a three-phase transformer core according to one embodiment of the invention with legs having hexagonal cross-sections, showing the cross-section of each of the legs;

FIGS. 2

a

,

2

b

and

2

c

are transverse cross-sections of each of the legs of the core shown in FIG.

12

.

FIG. 3

is an isometric view of another preferred embodiment of the invention, the cross-section of the legs thereof being regular hexagons;

FIGS. 3

a

and

3

b

are transverse cross-sections of an alternative three-phase transformer core with legs with hexagonal cross-section before and after assembly, respectively;

FIG. 3

c

is an isometric view of one of the frames of the transformer core shown in

FIG. 3

;

FIG. 3

d

is an exploded view of the frame shown in

FIG. 3

c;

FIG. 3

e

is a cut away isometric view of the frame shown in

FIG. 3

c;

FIG. 3

f

is a cross-sectional view of the frame shown in

FIG. 3

c;

FIG. 3

g

is a transverse cross-sectional view of the three-phase transformer core as shown in

FIG. 3

before assembly;

FIG. 3

h

is a transverse cross-sectional view of the three-phase transformer core as shown in

FIG. 3

after assembly;

FIG. 3

i

is a front view of one of the rings forming part of the frame shown in

FIG. 3

c;

FIG. 3

j

is a side view of the ring shown in

FIG. 3

i;

FIG. 3

k

is a cross-sectional view taken in the direction of arrows

3

k

—

3

k

in

FIG. 3

i;

FIG. 3

l

is a front view of another of the rings forming part of the frame shown in

FIG. 3

c;

FIG. 3

m

is a side view of the ring shown in

FIG. 3

l;

FIG. 3

n

is a cross-sectional view taken in the direction of arrows

3

n

—

3

n

in

FIG. 3

l;

FIG. 3

o

is a front view of another of the rings forming part of the frame shown in

FIG. 3

c;

FIG. 3

p

is a side view of the ring shown in

FIG. 3

o;

FIG. 3

q

is a cross-sectional view taken in the direction of the arrows

3

q

—

3

q

in

FIG. 30

;

FIG. 4

is an isometric view of a three-phase transformer core with legs that are octagonal in cross-section;

FIG. 4

a

is a transverse cross-section of the core shown in

FIG. 4

, taken in the direction of the arrows

4

a

—

4

a;

FIG. 5

is a cross-section of a transformer leg according to the invention whose legs have ten edges;

FIG. 6

is a cross-section of a transformer leg pursuant to the invention with twelve edges;

FIG. 7

is a top view of an arrangement for influencing the leakage inductance and the harmonics in a three-phase transformer;

FIG. 8

is a cross-section of a leg in the middle of the core for leakage inductance correction;

FIG. 9

is another cross-section for leakage inductance correction;

FIG. 10

is a transverse cross-section of a three-phase transformer core with specially shaped yoke parts for improving the magnetic flux;

FIG. 11

shows in isometric form a three-phase transformer core with legs in a generally flattened or planar arrangement;

FIG. 11

a

is a cross-sectional view of the transformer core shown in

FIG. 11

taken in the direction of arrow

11

a

-

11

a;

FIG. 12

shows a single-phase shell-type transformer core with one leg in cross-section according to the invention;

FIG. 12

a

is a variation of the single-phase transformer core according to the invention;

FIGS. 13 and 14

show single-phase core-type transformers with two legs in cross-section according to the invention;

FIGS. 15 and 16

show side views of further improvements of the shape of the transformer core;

FIG. 17

is an isometric view of a three-phase transformer core according to another embodiment of the invention;

FIG. 17

a

is a cross-section of one of the legs shown in

FIG. 17

;

FIG. 17

b

is a cross-section of an alternate leg for the core shown in

FIG. 17

;

FIGS. 18

,

19

,

20

a

,

20

b

and

21

a show alternative embodiments of a three-phase core with alternatively shaped legs according to the invention;

FIG. 21

b

is a plan view of the transformer core shown in

FIG. 21

a;

FIG. 21

c

is a top view of an alternative embodiment of the invention showing a three-phase transformer core with rings added to help in cooling the core;

FIG. 22

is a plan view of another transformer core according to the invention;

FIG. 22

a

is cross-sectional view of the core shown in

FIG. 22

, also including in exploded form the respective frames, and in a second exploded view showing each of the combined legs;

FIG. 23

is a single-phase transformer core with ten sides in cross-section according to the invention;

FIG. 24

is a single-phase transformer core with ten sides in cross-section according to the invention constructed for improved cooling;

FIG. 25

is a inductor core according to another embodiment of the invention, shown in isometric form;

FIG. 26

is an alternative leg for the inductor shown in

FIG. 25

;

FIGS. 27

a

-

27

w

are cross-sectional views of various transformer or inductor legs according to the invention;

FIG. 28

is a schematic view of a transformer according to the invention; and

FIG. 29

is a schematic view of an inductor according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

FIGS. 1

,

1

a

and

1

b

has already been discussed in connection with prior art and will not be explained further.

In

FIG. 2

is shown a three-phase transformer core according to the invention, generally designated by the numeral

20

. In its general shape it is similar to the prior art transformer core shown in

FIGS. 1

,

1

a

,

1

b

with a general delta-shape but is designed in an entirely different way. The core is made up of three frames

22

,

23

,

24

, each comprising several rings. (The word “ring” means a strip of material which is wound as a cylinder of many layers of the strip (to give the ring its thickness) and then slid over, offset or splayed as explained below. Rings are primarily circular but can have any shape with generally rhombic or rhomboidal cross sections, which include in some special cases quadratic and rectangular cross-sections. The term “frame” as used herein, means a ring-shaped part composed of two or more rings of laminated transformer plate, that is preferably wound strips of sheet metal. The frame is composed of rings of strips of transformer plate with a cross-section, which is a combination of the rhombic cross-sections of the rings. The frame, as well as the rings of which the frames are composed, is preferably generally rectangular. As used herein, the terms “offset”, “profiled” or “splayed” means the layers or laminates of transformer plate sheet metal are shifted so that edge of each layer is laterally displaced from the adjacent layer, the displacement being in the same direction for any ring. Since the rings preferably wound strips of sheet metal, the layers are slid over and are almost coaxial. Thus, an offset, profiled or splayed ring is a truncated core. Since the metal is of small dimension, the surface looks and feels smooth. The term “rhomb angle” means the bottom angle in a rhomb when the innermost edge of a leg is directed downwards. Although the figures herein show the layers schematically, they are in fact thinner than shown. The terms “delta” or “triangular” shaped means that three legs are extendable through parallel cylinders, such as are defined by windings of conductive wire, at three corners of an imaginary triangle or “delta.” (Three non-aligned parallel legs are in a delta arrangement.) Each frame

22

-

24

has a pair of opposed, parallel yokes. A set of three legs

25

-

27

extends between the respective yokes. Straight portions of two of the frames are arranged to form to legs

25

-

27

. That is, one straight portion of frame

22

cooperates with a straight portion of frame

24

to form leg

25

, straight portions of frames

22

and

23

form leg

26

, and straight portions of frames

23

and

24

form leg

27

. The yokes have at their respective ends rounded corners. The legs should fill the interior of the transformer windings through which they extend. The frames

22

,

23

and

24

are each composed of different rings. The rings of each frame come in two widths, broad or narrow wherein the narrow rings are made up of strips of half the width of the broad rings. The term “width” is the transverse dimension between the longitudinal edges; the width of the broad strips is, shown as “w”, and that of the narrow strips is shown as “w/2” in some of the figures. Also, they come in two thicknesses, thin or thick wherein the thin or low rings have half the thickness or height of the thick rings. (The thickness refers to the number of layers of sheet metal, each layer having a constant thickness.) From the shape of a hexagon,

t=w

·sin 60

=w

·2/2

=w

·0.866.

Unless otherwise stated, these definitions will be used throughout this description. The strips are preferably made of transformer plate, the plate being sheet metal.

Frame

22

comprises a broad, thick ring

22

a

having a width w and a thickness t, and a narrow thick (or high) ring

22

b

having a width w/2 and a thickness t, equal to that of the broad, thick basic ring

22

a

. The cross-section of leg

25

is shown in

FIG. 2

a

, and the cut away portions of rings

22

a

and

22

b

are shown. Frame

23

is composed of a broad thick ring

23

a

, identical to ring

22

a

, a narrow thin (or low) ring

23

b

and another narrow thin ring

23

c

. Narrow thin rings

23

b

and

23

c

have a width w/2 and a thickness t/2, one half the width and one half the thickness of rings

22

a

and

23

a

. The cross-section of leg

26

is shown in

FIG. 2

b

. Frame

24

is composed of a broad thick ring

24

a

and a broad thin ring

24

b

. Ring

24

b

has the same width w as rings

22

a

,

23

a

and

24

a

, and the same thickness t/2 as ring

23

b

and

23

c

. The cross-section of leg

27

can be seen in

FIG. 2

c.

The cross sections of legs

25

,

26

and

27

each form a regular hexagon. The hexagons substantially fill the cylinders defined by transformer windings. The hexagons can be described in terms of the rhombs and rhomboids therein.

Each of the frames

22

-

24

comprise a broad, thick basic ring

22

a

-

24

a

, respectively, similar to those described with reference to FIG.

1

.

Still referring to FIG.

2

and

FIGS. 2

a

,

2

b

and

2

c

, rings

22

a

-

24

b

form in pairs, four of the sides in the hexagonal legs. The remaining rhombs in the legs are built in different ways.

Still referring to

FIGS. 2

,

2

a

,

2

b

and

2

c

, rings

22

a

-

24

b

form, in pairs, four of the sides in the hexagonal legs. The remaining rhombs in the legs are built in different ways.

In the first leg

25

, the additional rhombic cross-section is composed of two rhomboids. The first one, designated

24

b

and part of frame

24

, is a broad thin ring. The second one, designated

22

b

and part of ring

22

, is a narrow thick ring.

In the second leg

26

to the right in

FIG. 2

, the additional rhombic cross-section is composed of one rhomboid and two rhombs. The rhomboid is filled by narrow thick ring

22

b

belonging to the frame

22

. Two narrow thin rings

23

b

,

23

c

belonging to frame

23

, fill the rhombs.

In third leg

27

to the left in

FIG. 2

, the additional rhombic cross-section is also composed of one rhomboid and two rhombs. The broad thin ring

24

b

belonging to the frame

24

fills the rhomboid. Two narrow thin rings

23

b

,

23

c

belonging to the frame

23

, fill the rhombs. The reason that frame

23

comprises two thin narrow rings instead of one narrow thick ring is that this larger ring can not be both narrow and thick, as required in the left leg

27

, and broad and thin, as required in the right leg

26

. Thus, instead two narrow thin rings are used.

All upper or lower yokes connecting the legs

25

-

27

have different shapes but all are built from one basic ring with a large rhombic cross-section plus one ring with a rhomboidal cross-section or two rings with a small rhombic cross-sections. This gives all yokes the same total cross-sectional area.

A second preferred embodiment is described with reference

FIGS. 3 and 3

a

-

3

q

. This embodiment is for a three-phase transformer core having three frames

32

-

34

arranged in a triangular or delta pattern. (It should be noted that in a three-phase transformer core with hexagonal legs and yokes in a triangle, the innermost parts of the cross sections of the rings must be 60°. This is the definition of the orientation of the angle notations in this application.) As explained below, the core has three legs, each of which extends through a transformer coil. The frames are composed of rings, each ring being a wound sheet of transformer plate sheet metal, the layers of each of which are offset, i.e. splayed or profiled. In cross-section, the legs form regular hexagons. The terms referred to earlier (broad, narrow, thick, thin, etc.) have the same meaning as they did earlier.

Referring first to

FIG. 3

, a three-phase transformer core

30

is shown. Core

30

has frames

32

,

33

,

34

. Each frame has vertically extending portions that run between opposite ends of a pair of opposed yokes. As explained below, the legs of each frame cooperate with legs of adjacent frame frames to form legs

35

,

36

and

37

of transformer core

30

. Since each frame is identical to the other frames, only frame

32

will be discussed.

Frame

32

has a broad, thick ring

32

a

, a narrow thin ring,

32

b

which goes partly over ring

32

a

, and a narrow thin ring

32

c

which goes partly over ring

32

b

. Ring

32

is shown alone in

FIG. 3

c

.

FIG. 3

c

is a rear view of frame

32

a

, viewed from inside core

30

. It can be seen in

FIG. 3

c

that broad, thick ring

32

a

is lying in one plane, that ring

32

b

has an edge lying on the forward edge of ring

32

a

as viewed on the left portion of

FIG. 3

c

, but is located so that the right edge of ring

32

b

is sitting near the rear edge of ring

32

a

. Ring

32

c

has its left hand surface flush against the left hand surface of ring

32

b

, and then is arranged so that it crosses over ring

32

b

and that its offset or splayed surface, labeled

301

is aligned with the offset or splayed surface

302

of ring

32

b

. The right hand edge of ring

32

a

is forward of the splayed portion of ring

32

b

. The splayed surface

303

of ring

32

a

angled in the opposite direction of surfaces

301

and

302

.

Frame

32

is shown in exploded form in

FIG. 3

d

. It can again be seen that broad thick ring

32

a

is a wound ring, with its layers being skewed or inclined so that its innermost strip in the profile extends forwardly, out of the plane of the paper. Narrow thin ring

32

c

has its layers skewed inwardly, towards the plane of the paper, that is, opposite to the direction of the offset of ring

32

a

, as noted above. Ring

32

b

is narrow and thin, and the direction of the offset of its layers is the same as that of ring

32

c

.

FIG. 3

e

shows a portion of frame

32

in cross-section. Ring

32

a

is at the innermost part of frame

32

, ring

32

b

is close to the forward edge of ring

32

a

when viewed in the left hand corner of

FIG. 3

e

, and then extends partly through ring

32

a

as can be seen from the direction of the windings of

32

b

in

FIG. 3

e

. The latter is indicated by the angle μ in

FIG. 3

n

. Narrow, thin ring

32

c

is rearward of ring

32

b

as shown in

FIG. 3

e

, but is wound around and sits on ring

32

b

as can be seen in the right hand portion of frame

32

.

The cross-section shown in

FIG. 3

e

on the left-hand portion shows a rhombus

32

a

and two rhomboids

32

b

and

32

c

. A cross-section showing all three frames

32

,

33

, and

34

is shown in

FIG. 3

a

. This will be discussed, briefly, below.

FIG. 3

f

is a top cross sectional view of frame

32

in

FIG. 3

c

. It shows broad thick ring

32

a

, narrow thin ring

32

b

, and narrow thin ring

32

c

. The offsetting or splaying of the profiled rings

32

a, b

and

c

is clear from this view. Ring

32

a

is lower in the foreground and higher in the background. Rings

32

b

and

32

c

are higher in the foreground and lower in the background. The dimension “w” shows the width of ring

32

a

, and the width of rings

32

b

and

32

c

are “w/2”. The thickness of ring

32

a

is shown as “t” and the thickness of each of rings

32

b

and

32

c

are “t/2”.

FIG. 3

g

is similar to

FIG. 3

a

, and

FIG. 3

h

is similar to

FIG. 3

b

, and they will be described together. Transformer core

30

is composed of legs

35

,

36

and

37

. Frame

32

includes broad, thick ring

32

a

and narrow, thin rings

32

b

and

32

c

. Frame

33

has broad, thick ring

33

a

, and narrow thin rings

33

b

and

33

c

. Frame

34

includes broad, thick ring

34

a

, and narrow rings

34

b

and

34

c.

FIGS. 3

a

and

3

g

shows transformer core

30

in exploded form, and core

30

is shown in assembled form in

FIGS. 3

b

and

3

h

, with a cross-section through each of the legs depicted. The cross-section of leg

35

is composed of rhomb

32

a

, rhomb

32

b

, rhomb

32

c

, rhomb

34

a

, rhomb

34

b

and rhomb

34

c

. The cross-section of leg

36

is made of rhomb

32

a

, rhomb

32

b

, rhomb

32

c

, rhomb

33

a

, rhomb

33

b

and rhomb

33

c

. Finally, leg

37

has rhomb

33

a

, rhomb

33

b

, rhomb

33

c

, rhomb

34

a

, rhomb

34

b

and rhomb

34

c

. Each of the cross-sections of legs

35

,

36

and

37

is regular hexagons. The hexagon of leg

35

is defined by the bottom side and right edge of rhomb

32

a

, the right side edge of rhomb

32

b

and the right side edge of rhomb

32

c

(the last two edges are aligned to form one side of the hexagon), the edge of rhomb

32

c

and the aligned edge of

34

c

, the left edge of rhomb

34

a

and the lower edge of rhomb

34

a

. The hexagon of leg

36

is defined by the bottom side and right hand edge outside of rhomb

32

a

, the aligned right hand edges outside of rhombs

32

c

and

33

c

, the lower aligned edges of rhombs

33

b

and

33

c

, the lower edge of rhomb

33

a

and the left hand edge of rhomb

33

a

. Finally, the hexagon of leg

37

is defined by the upper right hand side and edge of rhomb

34

a

, the inner side of rhomb

33

a

, the bottom edge of rhomb

33

a

, the aligned bottom edges of rhombs

33

b

and

33

c

, the aligned left-hand of rhombs

34

c

and

34

b

, and the upper left hand edge of rhomb

34

a.

Turning next to

FIGS. 3

i

-

3

k

, ring

32

a

, which is identical to rings

33

a

and

34

a

, is shown in its front, side and cut away views taken in the direction of arrows

3

k

—

3

k

. Ring

32

a

includes opposite, parallel leg portions

305

,

306

, opposing yoke portions

307

,

308

and rounded corners

309

-

312

. The offset or splaying is shown in the profile

303

.

Narrow thin ring

32

b

, which is identical to

33

b

and

33

c

, is shown in

FIGS. 3

l-n

.

FIG. 3

l

shows a front view of

32

b

,

FIG. 3

m

shows a side view of

32

b

and

FIG. 3

n

shows a cross-sectional view taken in the direction of

3

n

—

3

n

. Ring

32

b

has opposing, parallel legs

314

,

315

, and opposing yokes

316

,

317

. Ring

32

b

has rounded corners

318

-

321

. Ring

32

b

is turned as it passes partly through broad thick ring

32

a

, and this is shown by the angle μ in

FIG. 3

n

. The offsetting or splaying of the wound layers of

32

b

is shown at

323

. It should be observed that the offset of the profile shown in

FIGS. 3

l

-

3

n

is in the opposite direction from that of ring

32

a

shown in

FIGS. 3

i

-

3

k.

Front and side views of ring

32

c

(which is identical to rings

33

c

and

34

c

) are shown in

FIGS. 3

o

and

3

p

.

FIG. 3

q

is taken in the directions of arrows

3

q

—

3

q

in

FIG. 3

o

. Ring

32

c

has leg portions

325

,

327

, which are opposing and parallel to each other. Parallel yoke portions

328

,

329

oppose each other. Rounded corners

330

-

333

join the yokes and legs. The rings of transformer plate are offset or splayed are shown in

FIGS. 3

o

-

3

q

at

335

. It can be seen that the direction of the profile of offset portion

335

is to the right as viewed in

FIG. 3

p

, which is the same as the direction of the profile of ring

32

b

shown in

FIG. 3

m

. The turning is in the opposite direction reversed with respect to ring

326

.

The rhombic space outside of the basic rings described with reference to

FIGS. 2

,

2

a

and

2

b

, could thus be filled in accordance with a couple of basic principles. The second embodiment was just described with reference to

FIGS. 3 and 3

a

through

3

q

. In other words, the core, generally designated

30

, has the same general shape as the first embodiment described above. However, in this embodiment the core comprises three identical frames

32

-

34

, as explained above of which the rightmost one

32

will again be briefly described. The frames

32

-

34

are similar to the part

23

described in connection with FIG.

2

. Referring to

FIGS. 3

a

and

3

g

in the first leg

35

, the leg part of frame

32

comprises the broad thick ring

32

a

and two narrow thin or low rings

32

b

,

32

c

wherein ring

32

c

is wound outside of ring

32

b

, and the leg part of frame

34

with broad thick rings

34

a

, and side-by-side narrow thin rings

34

b

and

34

c

. In the second leg

36

, the leg part of frame

32

has the broad thick ring

32

a

, and the two narrow thin rings

32

b

,

32

c

placed one beside the other. Leg

37

has the leg part of frame

33

with broad thick ring

33

a

, narrow thin rings

33

b

,

33

c

, and leg part of frame

31

with broad thick ring

34

a

and narrow thin rings

34

b

,

34

c.

The two other frames

33

,

34

are identical to the first one

32

. Thus, the production of the core can as a rule can be simplified, depending on the production volume, because all three frames

32

-

34

can be made from the same mould.

A further possibility is to make broad thin rings and turn the leg parts 60°, forcing a corresponding bending of the yoke parts. The yoke parts then require more space and the bending is not so easy to effect. Making narrow thick rings and turning and bending as mentioned is also possible, but difficult. Additional variants, including those with smaller divisions, are also possible.

A core with octagonal legs, generally designated

40

, will now be described with reference to

FIGS. 4 and 4

a

. In an octagonal cross-section, see e.g. the back leg

45

, the sides turn 45°, which means that they have a relative angle of 135° to each other. Three rhombs

42

a

,

44

a

,

44

c

each with an angle of 45°, thus get space in the innermost edges of the legs of the core. Outside of these rhombs, rings

42

b

,

44

b

with quadratic cross-sections fill two squares. Finally, a rhomb fills the rest of the octagonal cross-section of the leg shown at

42

c.

From these six cross-subsections, three subsections compose the cross-section of a leg part of frame

42

going to the second leg

46

. The remaining subsections compose the cross-section of a frame

44

going to the third leg

47

. There is a frame

43

connecting the second and third legs

46

,

47

.

The three frames all contain two rings with equal leg parts. A first set of rings

42

a

,

43

a

,

44

a

each has a rhombic cross-section and the yoke parts bent 15°. A second set of rings

42

b

,

43

b

,

44

b

, outside of the respective first rings

42

a

,

43

a

,

44

a

is a quadratic and follows the form of the first set of rings

42

a

-

44

a.

Using a solution from the embodiments with hexagonal legs described with reference to

FIGS. 2

,

2

a

,

2

b

and

3

,

3

a

-

3

q

two outer rhombs compose the cross-section of an outer ring with the yoke parts bent 15°. Alternatively, two inner rhombs compose an inner ring but bent 60°. The next ring must now give an outer rhomb in one leg and an inner rhomb in the other leg and be bent 30°. One type of profiled ring is to be preferred because it is difficult to bend a ring 60° and one can not avoid a ring with both an outer rhomb and an inner rhomb.

In frame

42

, the third ring

42

c

has a rhombic cross-section in the leg parts and is placed outermost in the back leg

45

but inside the right leg

46

. These rhombs of the leg parts are obtained by displacing the outer strips of the ring to the right at the right leg

46

and to the left at the back leg

45

. Furthermore, the legs are turned asymmetrically 30° and the yoke parts are bent accordingly. The ring is given such a circumference that it will lie outside of the other rings. The final result appears in FIG.

4

.

A 10-sided decagon leg, generally designated

50

, will now be described with reference to FIG.

5

. The profiled (or offset or splayed) frames contain all four rings with equal leg parts. A first ring

50

a

, a second ring

50

b

and a third ring

50

c

with rhombic cross-sections in their leg parts are attached to the 10-sided cross-section. Thus they have the angles

36

,

72

, and 108° and their yoke parts bent 24°, causing a 48° bending of its yokes. A fourth ring

50

d

having a rhomboid cross-section with the angle 36° lies mainly upon the first ring

50

a

. Its leg parts are turned outward 24°, causing a 48 degrees bending of its yokes. The fourth ring

50

d

also causes the yoke parts of the third ring

50

c

to make a larger bow to give space. A fifth ring

50

e

has a rhombic cross-section in its leg parts with the angle 144° when it lies outside of the third ring

50

c

, but the ring has a rhombic cross-section with the angle 72° when it lies outside of the fourth ring

50

d

. The yokes are bent only 12°. The arrows in the figure indicate that the cross-sections

50

e

belong to different frames. There will also be a channel

51

suitable for cooling the legs. In an alternative embodiment, the channel is filled with a ring. This is an advantage when the rings co-operate by letting the magnetic field go between them. The space can e.g. be disposed of in such a way that the upper part of the rings

50

c

obtains new rhombic cross-sections with the angle 72°, causing the channels

52

a

and

52

b

to be formed. Further parts of the ring

50

c

to the right can be pushed to ring

50

e

, which forms the spaces

53

a

and

53

b.

FIG. 5

shows one-third of the core. There are two other identical legs, but rotated 120° and 240°, respectively.

It is possible to provide three-phase transformer cores with even more edges.

FIG. 6

shows a 12-sided dodecagon leg generally designated

60

. The core has two other equal legs, and yokes similar to those shown in

FIGS. 4

a

and

5

. The frame is composed of four rings

60

a-d with rhombic cross-sections with the angles

30, 60, 90, and 120°, which are attached to the 12-sided cross-sections with the angles 30 and 60°, respectively, and turned outward 15°. Attached to the fifth and sixth rings

60

e

,

60

f

there is space for a ring

60

g

with a rhombic cross-section with the angle 30° turned outward 45°. Its other leg part is a rectangle outside of the sixth ring

60

f

and turned outward 15°. Inside of these rings there are two rings

60

e

,

60

f

with rhombic cross-sections with the angles 30 and 60°, respectively, and turned outward 15°. Upon the ring

60

d

there is space for a ring

60

h

with a rhombic cross-section with the angle 150° and the other leg part is a rectangle attached to ring

60

d

and outside ring

60

f

. The whole cross-section is then filled. Yoke parts are separated by giving some wider bows to give space for other yoke parts. Giving some wider bows to give space for other yoke parts separates yoke parts.

The good properties of these transformer cores can be made even better for some transformer applications, see FIG.

7

. The leakage inductance can easily be increased by an additional core

70

of strips between the primary and secondary windings of the transformer. The strips are brought together at the top and bottom. The strips can be spread around the entire primary winding or be concentrated to one place, making the secondary winding eccentric.

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

An additional leg placed in the center of the core will not get any magnetic field under perfectly symmetrical and distortion-free three-phase conditions. Common components in the phase voltages, like the third harmonics, will be influenced by a center leg.

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

In one embodiment, the center leg is made of three rectangular poles

80

from strips given a height three times the width, laid on each other to a quadratic cross-section, see FIG.

8

. This is preferably triangular and a custom made solution contains poles with a rhombic cross-section, of which three are put together to form a packet with the strip edges toward each other in a wave form, see FIG.

9

. Three packets are put together with small distances to form a leg with a cross-section approximating a triangle. The ends of the poles are bent outward to reach the yokes. To make the bends possible, spacers between the poles are necessary. The spacers do not influence the magnetic properties because one pole from each packet

91

a-c

;

92

a-c

;

93

a-c

is bent to each yoke. Also the strips are, at least on one side, parallel to the spacers.

A rod, wound of strips in spiral form or as coils, is useful, especially if there are to be air gaps between the center leg and the yokes. The spiral can be made wider at the ends to reduce the air gaps to the yokes.

The flexibility of building cores like this is good and is shown in FIG.

10

. The figure shows a core

100

described in connection with

FIG. 4

, each leg of which forming an octagon in cross-section. A major part of the magnetic flux can pass from one profiled (or offset or splayed) ring to another in the legs where they are touching each other. This enables the rotation of larger fluxes in the yoke triangle.

With the present invention, it is also possible to provide a three-phase transformer core with lined up legs. This has the advantage that the transformer is narrower that with the delta shaped core. This type of transformer is ideal for placement on e.g. train wagons.

FIG. 11

a

shows the transverse cross-section of a transformer core

110

with octagonal legs. All legs comprise four rhombs with an angle of 45° and two squares. Rings running between adjacent legs are shown in the figure while those running between the outer legs are almost entirely hidden. This core has the advantage that it is built with octagonal legs, which fill 90% of the circle in which it is inscribed. Thus, it is valuable to make it as good as possible in all respects, e.g., the possibility to cross over the flux within the legs.

In order to make transformer cores of this kind, the leg parts or portions must be turnable and the yoke parts must be bent and pass each other. There are several solutions, of which one is shown in the figure. The leg parts of the rings are turned outward and the yoke parts inward or vice versa. The shape of the yoke part is limited by the limited possibilities of plastic deformations but otherwise the yoke parts can have any shape. The principle shown in

FIG. 11

is to have sharp bends and straight yoke parts.

FIG. 11

is an isometric view of a flattened three-phase transformer core

110

, with the distances between the yokes enlarged for the purpose of clarity. The core is seen from a direction where the edge between ring

114

a

and

114

b

in leg

116

(described below) is seen in the middle of the leg.

The rings can also be placed on each other giving rounded bends in order to save material.

The yokes between the left leg

115

and the center leg

116

are built up of a ring

112

a

with a rhombic cross-section in the leg part, a ring

112

b

with a square cross-section and both bent 22.5° and a rhombic ring

112

c

turned 67.5° in the leg parts. The rings

112

a

and

112

b

fit into the octagon close to the yoke side while the ring

112

c

fits into the opposing side.

The yoke between the center leg

116

and the right leg

117

can only be placed in the center leg in the remaining positions namely,

114

a-c

. The cross-sections of the left and right legs

115

,

117

are mirror images to the center leg

116

so that the rings running in the center leg are symmetric. The inner rings

114

a

,

114

b

have their closest positions in the right leg

117

. However, the ring

114

c

with a square cross-section in the leg parts runs to the closest square-shaped position in the right leg. The reason behind that is that the ring

113

a

with a square cross-section between the outer legs is in an outer position on the yoke parts already present in order to reach the left leg.

The twisting of the yokes can be impossible to achieve. In an alternative embodiment, a heavily sloping fold is used instead. This is shown for the ring

114

c

having the shortest yoke. The fold starts at one end of the yoke and ends at the other end, marked by

118

a

for the lower yoke and

118

b

for the upper yoke in FIG.

11

. Also, the yokes can be subdivided into several narrow rings.

Thus, one variant is to also let the rings between legs

116

and

117

keep their shape in leg

117

as in leg

116

. This has the consequence that the ring with quadratic leg part between the outer legs

115

and

117

must take the innermost quadrate in leg

117

. In order to pass the ring with quadratic leg part between leg

116

and

117

, a fold on one of the yoke of the ring must be made. The other rings between the other legs

115

and

117

can chose rhombs in the legs, which are turned against each other in order to reduce the twisting of the yokes. It is worth mentioning that an advantage of this variant is that the flux can more easily pass between the rings within the legs.

Also single-phase transformer cores will be more efficient if they are given polygonal cross-sections. All legs in the cores in

FIGS. 4

a

and

10

can be used to make single-phase cores by removing the opposite frame and ignoring the bending of the yokes. These cores have the advantage that the rings extend in a 90° sector.

FIG. 12

shows a transformer core

120

with an octagonal cross-section composed of rings with the same cross-sections as in the three-phase transformers but with the return loops going the closest way outside of the windings. Core

120

has a leg

122

with the same cross sections as the three-phase transformer core legs shown in

FIGS. 4

,

4

a

and

10

. By removing one frame, single-phase transformer core legs are obtained. Letting the rings keep their position in the windings is easy to accomplish. Spreading the rings out makes the core lighter. The rings can be turned 45° or 90° within the leg and yet given an octagonal cross-section. A small reduction of the amount of the plate can e.g. be obtained by looping up to the left of the ring looping rightmost in the figure. Its cross-section would have to change to a rhombic form close to rectangular form.

A core with two legs can be made from the three-phase designs by bending the rings from one more leg. A core

150

is shown in

FIG. 13

with an octagonal cross-section in its legs. Three leg parts pass through the center of the leg which is suitable for strips resting on each other. The turning of three leg-parts is 45° and the bending is 90°. A ring with a rectangular cross-section and the two rings outside of that ring are not deformed. Cores with hexagonal legs need only three rings made of strips with the same width. By increasing the number of polygons in the legs of transformer cores according to the invention renders them easy to form.

If that octagon edge where three rhomb edges meet is put innermost in the core, as in

FIG. 4

a

, e.g. rings

42

a

,

42

b

,

42

c

,

43

a

,

43

b

and

43

c

, and the opposite frame

44

is removed, one obtains a single-phase shell core

140

shown in

FIG. 12

a

, the turnings will only be 22.5° except for the rhomb in the middle, which must be turned 67.5° to make the rings meet again.

FIG. 12

a

thus shows the development of a single-phase core from a three-phase core, i.e. from the core

40

of

FIG. 4

a

to the core

120

of FIG.

12

. Single-phase core

140

has a frame

142

showing in a leg

141

, rhombs

142

a

and

142

c

, and a square

142

a

. Frame

142

has another leg part with rhombs

142

a

,

142

c

and square

142

b

. Leg

141

further includes a leg part of frame

144

, and includes rhombs

142

a

and

142

c

, and a square

142

c

. Rings

144

a

and

144

c

have rhombs

144

a

,

144

c

and square

144

b

. Replacing this rhomb

144

c

with a ring, with steps approximating the rhomb, is more realistic and is shown in the core

152

in FIG.

14

. Letting the strips reach the circle, thus increasing the total cross-section makes a further improvement.

It is realised that the single phase transformers described herein also can have a cross-sectional shape deviating from a perfect regular polygon, like the three-phase cores described below with reference to

FIGS. 18-21

.

The segments outside of a polygonal leg can be filled by a thin rhombic ring of a strip with about half the width and the full height of the segment and wound to its total width. Folds

154

in the strips along the middle of the rhomb as in

FIG. 15

make two sides to one flat side giving a triangle, the sides of which are in contact with the core. With about ⅔ width and {fraction (8/9)} height, a fold at the edge of the innermost strip makes a trapezoid cross-section

156

as in FIG.

16

. The cross-section can also be rounded.

By means of strips of constant width the leg parts can be given a cross-sectional shape closer to the shape of a circle, see

FIGS. 17

,

17

a

and

17

b

. A core

170

shown in

FIG. 17

has a right leg

172

in which will be described as an example with reference to

FIG. 17

a

, wherein a transverse cross-section of that leg is shown. Innermost, there are rings

173

of e.g. 80% of full width and to a height of 9% of its width. There are three rings reaching a circumscribed circle, see

FIG. 17

a.

Four of the six segments have been filled with magnetic material, and strips outside of the assembled core can fill the other segments. A ring

174

can be placed on the outer sides of the hexagons. The addition of rings

174

over and under the yokes increases the cooling of the core.

Another embodiment is shown in

FIG. 17

b

, wherein the ring

174

has been replaced by broader strips in the other rings.

The transformer cores described above have all in common that the legs are perfectly regular, i.e., the corners thereof can be inscribed in a circle. However, the invention also provides cores with legs that deviate slightly from the above-described regular shapes. Thus, in

FIGS. 18 and 19

, there are shown three-phase transformer cores with legs having corners that can be inscribed in two circles with different radiuses. Thus, every other corner protrudes from an inner circle. The outer corners can be inscribed in an outer circle. This is shown in

FIG. 19

, wherein the left lower leg is shown with two different circles touching the corners thereof.

Regularly octagonal legs, such as those used with the embodiment described with reference to

FIG. 4

, have adjacent edges with a mutual angle of 45° while the angle between the yokes in a transformer core with the yokes in a regular triangle of 60°. This results in bent yokes, such as those shown in

FIG. 4

, which can be a drawback.

However, if the legs are given a shape like the ones

185

,

186

,

187

shown in

FIG. 18

, this problem is overcome. In

FIG. 18

, every other angle between edges is 30° and the other 60°. This results in an irregular octagon. This can be inscribed in a 1.52° power:

x

1.52

+y

1.52

=r

1.52

wherein x and y are two-dimensional co-ordinates and r is the radius of the circle.

If an increase of the transition of the magnetic fields in the legs is desired, the core can be shaped like the core

190

shown in FIG.

19

. This core is made up of three rings

194

a-c

to the left in the figure, three lower rings

193

a-c

and five rings

192

a-e

to the right in the figure. The rings shown in

FIG. 19

are described in the Tables 1-3 below:

TABLE 1

Cross-section in

Cross-section in

Ring

leg 196

leg 195

Remarks

192a

rhombic 30°

Rectangular

outwards

192b

rectangular

Rectangular

Displaced 0.866 of

width inwards;

located on 192a

192c

rectangular

Rhomboidal 60°

Located outside of

outwards

192a

expanded 30°

outwards

192d

rhomboidal

Rhomboidal

Located on 192c

60° inwards plane

60° outwards

and outside of

expanded 30°

192b

outwards

192e

rhomboidal

Rhombic 30°

Displaced 0.616 of

60° inwards

outwards

width inwards

located on 192b

and 192d

193a

quadratic

193b

rhombic

Outside of 193a

60° outwards

TABLE 2

Ring

Cross-section

Remarks

193a

Quadratic

193b

rhombic 60° outwards

Outside of 193a

193c

rhombic 30° outwards

on 193a and 193b

TABLE 3

Ring

Cross-section

Remarks

194a

Rhombic 30° outwards

194b

Quadratic

on 194a

194c

Rhombic 60° inwards

on 194b

The magnetic field can now pass between rhomb and square and square and rhomb, respectively.

In an embodiment not shown in the figures, legs with twelve edges and angles of 60° and 12° are used.

The cross-sectional areas of polygons compared with the circumscribed circle and the hexagons are given in table 4 below:

TABLE 4

Shape of cross-

Relative cross-

Comparison with

Comparison with

section

sectional area

a circle

a hexagon

Circle

3.1416

100

120.9

Dodecagon

3

95.5

115.5

Decagon

2.9389

93.5

113.1

Octagon

2.8284

90.0

108.9

Hexagon

2.5981

82.7

100

Duo-decagon 60

2.5582

81.4

98.5

and 12°

Duo-octagon 60

2.5176

80.1

96.9

and 30°

Square

2

63.6

77

Where angles other than 60 and 30° are chosen in a duo-octagon, the comparison value will be between 96.9% and 108.9%.

Yet another embodiments are shown in

FIGS. 20

a

and

20

b

. The legs shown in

FIGS. 20

a

and

20

b

are essentially elliptical polygons, i.e., the cross-section can be inscribed in an ellipse. In

FIG. 20

a

, a core

200

with legs

201

,

202

and

203

is shown. The cross-section of each leg is a decagon essentially inscribed in an ellipse with the major axis radially out from the center line of the core. In

FIG. 20

b

, a three-phase transformer core

205

is also shown. Core

205

has legs

206

,

207

and

208

. The cross-section of each leg is an octagon essentially inscribed in an ellipse with the minor axis radially out from the center line of the core.

The magnetic field can to a large extent pass from one yoke to another in the legs.

In the embodiments described with reference to

FIGS. 18-20

a

,

20

b

the positions of the corners of each leg can be described as being essentially positioned on an imaginary generalised circle defined by orthogonal coordinates x and y according to the following formula:

(

x/a

)

n

+(

y/b

)

n

=1

wherein, a, b and n are positive numbers.

An embodiment with improved magnetic flux will now be described with reference to

FIG. 21

a

, which is a cross-sectional view of a three-phase transformer core

210

and

FIG. 21

b

, which is an end view showing a yoke part of a transformer core.

Three rings

212

a

,

213

a

and

214

a

are given a rhombic cross-section with an inner angle of 60° They can then be assembled to triangular yokes and legs with four of the sides and five of the edges of hexagons.

Six low narrow rings

212

b, c

,

213

b, c

and

214

b, c

are assembled outside of the rings

212

a

,

213

a

,

214

a

as shown in

FIG. 21

a

. This gives an end view of the yoke part as shown in

FIG. 21

b

. The leg portions are turned 60° when they are lying besides each other so that they can then transfer magnetic flux to neighboring rings. However, the bends can deviate slightly from those shown in the figure. The magnetic flux can go in all rings from one yoke to another.

Smoothing of the edges of the legs of the core provides for a smaller play between the core and the rotating bobbin because higher accuracy can be easily achieved during manufacturing. This in turn increases the space for the windings and decreases the load losses. The flow density in the yoke decreases slightly but is still an advantage.

A particularly advantageous three-phase transformer core

218

according to the invention is shown in

FIG. 21

c

, which is a combination of the embodiments shown in

FIGS. 17 and 21

a,b

. It shows how a three-phase transformer core which has had rings added can also help cooling the transformer. When putting rings on the legs to make its legs more rounded, one can also let the strips transfer heat to the air by connecting these rings at the top and/or bottom of the transformer to a radiator/cooler of strips as shown in

FIG. 21

c.

The core

218

can be provided with windings

220

with segment strips using the principle of

FIGS. 17

a-c

using used when strips for filling the segments, but also filling the adjacent segments. The ends of a pair of segment strips

221

and

222

are when necessary bent upwards for cooling and also bent downwards at the bottom. A strip of ferromagnetic material is closely wound to a cooling ring

223

at the top of the core. The ends of the segment strips

221

and

222

are spliced and connected to the strips

224

,

225

in the cooling ring

223

. Now both magnetic flux and heat are transferred.

Often the transformer is placed within a container. Sometimes the transformer is so hot that the container must be protected from the heat.

Cores of the invention are very silent. Thus they can be connected to heat transferring material

226

to e.g. the container

227

or part of it. This is of interest because the resistance increases with temperature and the power losses increase as well. The transfer of noise from the core will be reduced by bends on the material e.g. aluminum plate.

Also the ends of a set of wires or foils

228

from the windings, especially from a low voltage coil, can with advantage be attached to some cooling device

229

, e.g. cooled from water circulating within it via pipes

230

.

Another three-phase transformer core is shown in

FIG. 22

, and identified by the numeral

400

. Transformer core

400

is shown as a top view in

FIG. 22

having yokes

402

,

403

, and

404

. A cross-section of core

400

is shown in

FIG. 22

a

, which also shows the core, and the frames, in exploded form. Core

400

has three frames

406

,

407

and

408

. It can be seen that frames

406

-

408

are different from each other, but this may be better for large transformers for reducing the strain on the core. Frames

406

-

408

together form legs

409

,

410

and

411

. Considering the view shown in the center portion of

FIG. 22

a

and the exploded portion showing frame

406

, it can be seen that the latter includes a basic broad, thick ring

414

, and a narrow thick ring

416

. Frame

407

is composed of a narrow thick ring

418

, another narrow thick ring

420

, a narrow thin ring

422

and another narrow thin ring

424

.

Finally, considering frame

408

, it can be seen that this leg includes a broad, thick ring

426

and a narrow, thick ring

428

.

Transformer core

400

is composed of a set of rings, all of which are made from transformer plate of one width for each ring, combined in such a manner as to provide the desired legs with a hexagon cross-section in each leg. The construction of core

400

is different from other cores described earlier having hexagon cross-sections, but they all can be made using conventional manufacturing techniques with transformer plate of one width, namely broad or narrow.

Another way to describe the embodiment shown in

FIGS. 22 and 22

a

is by way of the geometry of the cross-section of legs

409

-

411

of transformer core

400

. Accordingly, the cross-section of leg

409

shows that it is composed of rhombs

414

and

426

, and rhomboids

416

and

428

. Leg

410

is composed of rhombs

414

, rhomboids

416

,

418

and

420

, and has small rhombs

422

,

424

. Leg

411

has large rhomb

426

, rhomboids

418

,

420

and

428

, and small rhombs

422

,

424

. Each leg

409

-

411

has legs of regular hexagons, since the width and thickness of rhombs

414

are of equal length; the width of rhomboids

416

,

418

,

420

and

428

are one half the width of rhombs

414

and

426

; the thickness of the latter rhomboids is equal to that of rhombs

414

and

426

; and the width of small rhombs

422

and

424

are one quarter the corresponding dimensions of large rhombs

414

and

426

.

One would not expect that the provision of more rings in a transformer core could give simpler and better solutions to the problems noted earlier. A three-phase core with its legs in a row is relatively easy to assemble with octagonal legs, so one would not strive to make hexagonal legs. Single-frame cores can advantageously be made with decagonal legs. There are many decagons with inscribed rhombs. One of the decagons has the advantage that all but one of the rings for filling the rhombs have their axes in the three directions deviating with a minimum angle of 36°. A shell core

260

is shown in FIG.

23

. It has rings providing in the cross section of shell core

260

rhombs

261

-

270

.

By bending the yokes of core

260

shown in

FIG. 23

, a frame core

275

is obtained and shown in FIG.

24

. Rings can be wound with the distance between the turns so that air can pass through it. The rhombs within the leg innermost is a rhomb with an angle of 72°. The rhombs are in layers with the number of rhombs from innermost 4,3,2,1. They are marked from left to right

263

,

264

,

266

,

261

. In second row they are

265

,

267

,

262

. In third row they are

269

and

268

. Last is a rhomb marked

270

. In the first layer, the rhombs have all sides with the angle 72°. In the second layer, the rhombs have all sides with the angle 108°. In the third layer the rhombs have all sides with the angle 36°. In the fourth layer the rhomb has all sides with the angle 144°. This shows the systematic shape of this decagon with inscribed rhombs. The circle is so effectively filled that ring

263

could be omitted. A ring

271

having strongly turned out legs is especially good with respect to cooling because the yokes are also turned, so that air can rise when it passes between the strips. The foregoing tells us how to find the best shape of dodecagon etc. with inscribed rhombs. First the corresponding shell core was shown in FIG.

23

. The rings need not have their frames or leg parts turned or yoke parts bent and were shown in FIG.

24

. The surface of the strips with the air will be very large.

Some of the advantages of the inventive transformer core have already been mentioned. Among the other advantages the following can be mentioned: lower no load losses, less weight, less volume, lower electrical leakage, a reduction of the harmonics due to the symmetry of the phases of the three-phase transformer, easy maintenance etc. The mechanical stability of all of the cores can be improved by modifications to the cores to provide places for rings with octagonal legs as well as hexagonal, decagonal and other legs. The inventive core is insensitive to rough handling, as would occur during transport. It embodiment with interlocking frames are self-supporting. The weight saving over corresponding cores is very significant, amounting to about 40%; this is significant for large transformers whose weight is several tons. Transportation is facilitated in that the frames can be transported independently of each other.

Referring next to

FIG. 25

, an inductor according to the invention is shown. It can be seen that this inductor has a construction very similar to the transformer core

20

shown in FIG.

2

. However, the inductor, identified by the numeral

500

, has a pair of air gaps extending through each leg. Thus, inductor

500

includes three legs

501

,

502

and

503

, each having as a cross-section a hexagon as that shown in transformer core

20

in FIG.

2

. Each leg has a pair of air gaps identified as

504

,

505

for leg

501

, air spaces

506

and

507

for leg

502

, and air gaps

508

and

509

for leg

503

.

The hexagonal legs

501

-

503

could be replaced with cylindrical legs

550

shown in FIG.

26

. Each leg

550

is divided into two parts having an air space

554

between them. Air spaces

552

,

553

separate the opposite ends of leg

550

from the yokes of inductor

500

.

The concept of the present invention can be used to provide legs of various cross sections, such as to fit into conductor coils having round or elliptical shapes, where the cross section approaches such shapes. These are shown in

FIGS. 27

a

-

27

w

.

FIG. 27

a

is a quadrate

601

.

FIG. 27

b

depicts a hexagon

603

with three rhombs

605

.

FIG. 27

c

shows an octagon

607

with six rhombs

609

.

FIG. 27

d

illustrates a decagon

611

called a penrose having ten rhombs

613

. Another possibility is shown in

FIG. 27

q

, where there is a decagon

615

with ten rhombs

617

, having no new rhombs created but are rather redistributed.

FIGS. 27

r

through

27

u

are other examples of decagons

619

,

621

,

623

and

625

, respectively.

FIGS. 27

h

and

27

i

show the octagon

607

from two different corners.

FIGS. 27

j

and

27

k

show octagon

607

from different sides.

FIG. 271

depicts octagon

607

from a different direction.

FIGS. 27

m

through

27

n

show that it is possible to alter rhomboids to rhombs in hexagons

627

and

629

.

FIG. 27

v

illustrates that it is possible to inscribe rhombs in an ellipse, in a polygon

631

. A contour which can be divided into two curves, one with a 180° rotation with respect to the other curve, can have rhombs inscribed within it. Polygons with less number of sides will appear inside the original polygon. They can be mirrored or rotated 180° and make it possible to redistribute the rhombs. A rotated hexagon is marked with a circle in

FIG. 27

w

. Of course, matched irregular contours can circumscribe any form of collection of rhombs.

A three-phase transformer

600

according to the invention is shown in FIG.

28

. It includes a three-phase transformer core

602

as discussed earlier. Transformer

600

includes the primary windings and secondary windings as identified as winding assembly

604

. Transformer

600

operates in the conventional manner, but having improved operating capabilities due to the core.

FIG. 29

shows an inductor

620

according to the invention. It includes an inductor core

622

and a winding

624

. The core was described earlier. The inductor operates in the ordinary fashion, having an improved output resulting from the core.

The invention has been described in detail, with particular detail with respect to the preferred embodiment. However, variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains.

Number	Name	Date	Kind
523572	Hassler	Jul 1894	A
2305999	Steinmayer et al.	Dec 1942	A
2333464	Christensen	Nov 1943	A
2400184	Woolfolk	May 1946	A
2401952	Mayberry	Jun 1946	A
2414603	Nelson	Jan 1947	A
2458112	Steinmayer	Jan 1949	A
2498747	Weigand	Feb 1950	A
2544871	Weigand	Mar 1951	A
2561250	Treanor	Jul 1951	A
4325045	Mehl	Apr 1982	A
4497449	Lin et al.	Feb 1985	A
4504813	Strang	Mar 1985	A
4557039	Manderson	Dec 1985	A
4592133	Grimes et al.	Jun 1986	A
4761630	Grimes et al.	Aug 1988	A
4893400	Chenoweth	Jan 1990	A
5608371	Valencic et al.	Mar 1997	A
5791585	Knight et al.	Aug 1998	A

Number	Date	Country
957677	May 1964	GB
351420	Aug 1937	IT
163797	Jul 1958	SE

Transformer core

Information

Patent Number

Date Filed

Date Issued

Inventors

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

PCT Information

US Referenced Citations (19)

Foreign Referenced Citations (3)