Title:
Transformer core structure
United States Patent 2142066


Abstract:
My invention relates to electrical apparatus of w a class known as reactors, and more particularly acso to electrical transformers and core structures at therefor. Cores for electrical transformers are ti material, which may be of a high grade of silicon f steel, although alloys having similar...



Inventors:
Daniel, Eppelsheimer
Application Number:
US17776737A
Publication Date:
12/27/1938
Filing Date:
12/02/1937
Assignee:
Daniel, Eppelsheimer
Primary Class:
Other Classes:
29/609, 336/60, 336/212, 336/213, 336/214, 336/216, 336/218, 336/234
International Classes:
H01F27/25; H01F41/02
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Description:

My invention relates to electrical apparatus of w a class known as reactors, and more particularly acso to electrical transformers and core structures at therefor. Cores for electrical transformers are ti material, which may be of a high grade of silicon f steel, although alloys having similar characteristics and containing nickel and cobalt have also h 10 been used. Such laminations are built up to form tV the transformer cores, and the ndividuallaminae p are generally insulated from each other in order to reduce eddy current losses. f There are certain objections to such construe- t tions among which are that the punching of odd q shaped laminae from sheet material involves a considerable scrap loss; and since the material of high magnetic properties is usually relatively ex20 ably increased. Furthermore, it is known that a working of the metal forming the cores has a deleterious effect upon the magnetic properties thereof, so that in accordance with present practice the laminae after they are sheared and punched from the sheet material have to be annealed or heat treated in one way or another to eliminate these deleterious effects.

Another objection to this construction is that the labor cost is high because of the large number of pieces which have to be assembled to constitute a single core. This number may be of the order of several thousand. Furthermore, in the assembly of the core pieces care must be taken that the laminae are properly superposed and the joints must be arranged in such a way that the magnetic circuit is not seriously affected.

Nevertheless the magnetic reluctance due to the joints in the magnetic circuit is generally such that considerably more magnetic core material must be provided in the design of such transformers in order that they will perform according to the specifications of the users. o With the above difficulties and objections in mind, it is an object of my invention to provide a novel core structure for reactors and more particularly for electrical transformers which will be free, at least to a great extent, of the objections above noted.

It is an object of my invention to provide a core structure in which the laminae are continuous, and in which the direction of the magnetic path coincides with the direction of rolling of the material constituting the core. It is a further object of my intention to provide a core struc65 ture of what is known as the three-leg type, hich is nevertheless composed of only two pieces Sthat a great simplicity of manufacture is thieved. It is a still further object of my invenon to cut down the amount of shearing and unching to an absolute minimum, so that the ectrical properties will not be deleteriously afected.

These and other objects which will be set forth ereinafter or will be apparent to one skilled in he art upon reading this specification, I accomlish by that certain construction and arrangeient of parts of which I shall now describe a preerred embodiment. Reference is now made to he drawing which forms a part hereof, and in 1 rhich: Figure 1 is an elevational view of a transformer ccording to my invention.

Fig. 2 is a plan view of the same.

Fig. 3 is a horiontal cross sectional view of the 20 -enter leg member.

Fig. 4 is a view similar to Fig. 1 showing a different form of loop.

Fig. 5 is a view similar to Fig. 4 showing another form of loop.

ig. is a view similar to Fig. 3 showing a different form of center leg..

Fig. 7 is a view similar to Fig. 3 showing another form of center leg.

Briefly, in the practice of my invention, I provide a core structure of the three-leg type in which the two outer legs and the yokes are formed from a strip of sheet material wound upon itself to form a loop as indicated at 8 in Fig. 1. The member 8, of course, may be formed from more than a single strip; for example, it might be formed by winding two or more strips into a loop or by winding a plurality of strips welded end-toend into a loop. The strips forming the member 8 when made of materials having marked directional properties are taken with their length parallel to the ajis of rolling of the original sheet from which they have been sheared, or that of greatest permeability if it differs from the direction of rolling, so that in the finished transformer the magnetic path will be coincident with the direction which results in the most effective use of the material. The shearing of the strip material to form the member 8 will not ordinarily affect its properties very much; but any effects so produced may be removed by annealing after slitting. The member 8 may of course be annealed after complete fabrication, and the whole ferrous part of the transformer may be annealed to remove strains caused in 5 shearing, coiling or the like.

Although I have shown In Figs. 1 and 2 a circt lar member I, it will be understood that depend Ing upon the shape of the bobbin upon which th strip is wound, the member I could be oval c 6 elliptical, as shown in ig. 4, or rectangular, wit rounded corners, as shown in ig. 5, or indeed o any desired shape. In the winding of the stri; an appropriate tension may be maintained 1c any desired way; and the strip is prevented fron unwinding by means of one or more tensioi bands 8a.

The center leg, indicated In the drawing at 8 I prefer to form by spirally winding a sheet o magnetic material into a roll form. If the cente leg is so formed it may be rolled so that the axi of the roll will correspond to the direction o rolling of the sheet. I prefer to roll the centei leg 9 in such a way as to leave a central bore 9c for purposes which will be described hereinafter For assembling the two parts together I pro. vide for forming a taper on each end of the member B, and I provide a tapered recess in the member I adapted to make a perfect seat for the tapered portion of the leg 9. The two parts may readily be assembled by compressing the loop I to increase its diameter on the axis of the recesses 10, and the member 9 may then be simply slipped into place and will be held in position by the natural resiliency of the loop I in returning to its original form. In the embodiment of ig. 3, if desired, the center leg may be of such length that a bolt and nut (11, 12) may be used to contract the loop 8 on its long axis until it is circular.

If the tapered recesses I are provided with holes extending completely through the member 8, the center leg may be cooled by fluid passing through the bore 9a. If it is desired to make a tighter fit by adding pressure to the joints between the member 9 and the member 8, a non-magnetic bolt II may be passedthrough thou te bore a and held in place by means of a nut 12. If it is still desired to provide for extra cooling the bolt II may, of course, be hollow.

In completing the transformer, the low voltage coils are wound onto the member 9, as Indicated at 14, and the high voltage windings are wound over the low voltage windings, as Indicated at 13, or in any manner which the results desired would indicate to be preferable.

60 It will thus be seen that I have provided a relatively simple core structure of the three-leg type in which the magnetic path Is continuous and uninterrupted throughout the outer legs and yokes. It will be seen that I have provided an 65 excellent magnetic joint between the yokes and the center leg and that I have provided for cooling if that is deemed necessary or advisable.

Furthermore, It will be noted that I have provided a transformer in which the magnetic path is always in the direction of rolling of the material constituting the core or the direction of greatest permeability thereof, and that I have reduced the working of the metal to an absolute -ninimum whereby the magnetic properties of the 5 hnaterial are not adversely effected.

It will be understood that the particular circular form of the member 8 shown in the drawing is not to be considered as constituting a limitation upon my Invention, and that other shapes may be used, provided the material is formed in accordance with the spirit of this invention.

Although I have shown as a preferred embodiment in Fg. 3, a center leg formed from a sheet of material spirally wound, it will be understood 76 that the same purpose would be served by a I- center leg formed simply from laminae of narL- row, flat strips aheared so that their length wau b In the direction, u shown in Pig. 6, in which the ir permeability would be highest at the operating h induction, or by more than one leg, the whole I if surrounded by the primary and secondary windp Ings, as shown In Fig. 7. It will, of course, be a clear that in th i e embodiment shown, the amount a of shearing necessary is greatly reduced. a The laminae may be insulated in any conventional or desired way either prior to or during I, winding; but the particular manner of insulating f the core laminae has not been described because r it forms no part of my invention.

s Having thus described my Invention, what I is f claim as new and desire to secure by Letters r Patent, is:t 1. A core structure for a transformer comprising magnetic material wound to form a laminated * loop-shaped member constituting a magnetic * yoke, and a center leg member bridging the yoke, - said leg being of laminated construction, and Smagnetic connections between the ends of said leg and s said yoke, said leg being tapered at its Sends substantially to a point, the yoke member Shaving at its opposite sides correspondingly shaped recesses to receive the ends of the leg, the said leg being less in its cross-sectional dimension than the width of the inner lamina of the yoke, whereby the nner lamina of thine of e yoke remains unsevered by the recesses therein, the recesses in successive laminae outwardly being of less and less area, whereby the yoke remains a strong unitary structure which may be sprung to receive the ends of the leg, the relationship 3 of the laminae in the leg and the laminae in the yoke being a substantially continuous one, lamina for lamina, so that lines of magnetic force traversing the leg and yoke traverse paths longitudinally of all laminae without cutting acros laminae.

2. A structure as claimed in claim 1 in which the direction of magnetic lines of force in an laminae coincides with the direction of rolling of said laminae.

3. A structure as claimed in claim 1, In which. the yoke is formed of a single strip of magnetic material having a high permeability longitudinally of the strip and a relatively lower permeability in other directions. 60 4. A structure as claimed in claim 1 In which said leg is formed of magnetic material wound upon itself spirally, in which the ends of the leg are tapered to a conical formation, and In which the yoke has corresponding conical receses. 5. A structure as claimed in claim 1 in which said leg is formed of magnetic material wound upon itself spirally, in which the ends of the leg are tapered to a conical formation, and in which the yoke has corresponding conical recesses, the central portion of said leg being hollow, and a bolt passing through said yoke and said leg to hold said parts in assembled relationship.

6. A structure as claimed in claim 1 in which " said leg is formed of magnetic material wound upon Itself spirally, in which the ends of the leg are tapered to a conical formation, and In which the yoke has corresponding conical recesses, said yoke being formed of a single strip of silicon steel having a high permeability in the direction of its length and a relatively lower permeability in other directions, and said leg being formed of similar material In which the direc- ?7 I_ tion of greatest permeability coincides with the direction of the axis of said leg.

7. A structure as claimed in claim 1 in which said leg is formed of magnetic material wound - upon itself spirally, in which the ends of the leg are tapered to a conical formation, and in which the yoke has corresponding conical recesses, said yoke being formed of a single strip of silicon steel having a high permeability in the direction of its length and a relatively lower permeability in other directions, and said leg being formed of similar material in which the direction of greatest permeability coincides with the direction of the axis of said leg, and fastening means passing through said yoke and said leg to hold said parts in assembled relationship.

DANIEL EPPELSHEIMER.