US2931993A - Magnetic core - Google Patents

Description

April 5, 1960 Filed April 18, 1956 H. w. DORNBUSH 2,931,993

MAGNETIC cons 5 Sheets-Sheet 1 INVENTOR. Henert 14 Darnbus/z Wttornqy April 5, 1960 H. w. DORNBUSH 2,931,993

MAGNETIC CORE Filed April 18, 1956 5 Sheets-Sheet 2 A? INVENTOR.

Herbert W .Dombus/z P 5, 1960 H. w. DORNBUSH 2,931,993

MAGNETIC cons- Filed April 1a, 1956 ,5 Sheets-Sheet a IN V EN TOR. 7ier6er 74! .Dombus/z April 5, 1960 H. w. DORNBUSH MAGNETIC CORE 5 Sheets-Sheet 4 Filed April 18, 1956 INVENTOR. Herbert if. .DQrnAus/z a, a

fltarnsr April 5, 1960 H. w. DORNBUSH MAGNETIC CORE 5 Sheets-Sheet 5 Filed April 18, 1956 INVENTOR. Herbert W Darnbus/z fig/ V fittorngy qwwm 95m 7. an i I 1 8m QM wow 8m QM NR 3m 1% 8m QQM I I I 5 4: mum, QR Q m \\k\m .9 MK 7 m9 9mm 3 wb 5 .m nu

United States Patent MAGNETIC CORE Herbert W. Dornbush, Can0nsburg,

Pa., assignor to McGraw-Edison Company,

a corporation of Delaware Application April 18, 1956, Serial No. 579,052 12 Claims. (Cl. 336-217) States Patent No. 2,489,625, having the same assignee as the present invention, the lap joints of the turns have been placed in radial alignment. As a consequence, in making such a core, while the winding legs particularly have been compact, the interleaving of the lamination ends and the alignment of the lap joints has occasioned a relatively open core structure in the core side containing the aligned lap joints.- Consequently, for cores like the illustrated example, relatively more core strip metal was required, which was relatively expensive especially when using oriented grain steel strip of the kind usually supplied with an insulating coating thereon for transformer cores. Closely related to the present invention is the magnetic core illustrated in Fig. 16 of U8. Patent No. 2,614,158 to Sefton et al., having the same assignee as the present invention, wherein respective pairs of adjoining turns are disposed with the intermediate turn ends in one layer, but the resulting core also has radial alignment of the lap joints and a relatively open core structure on the top and bottom necessitating additional core steel for the core build-up. In addition, in such prior core construction the alignment of the lap joints involved care in the interleaving of the lamination ends to provide an individual lap joint in each turn, particularly when a plurality of turns were inserted simultaneously through the window of an electrical winding. Further, such a relatively open core structure necessitates larger transformer tanks and a greater quantity of dielectric liquid, with corresponding trouble and expense.

In the core construction of the present invention such difl'iculties are markedly reduced or overcome. In my invention the advantages of a magnetic lap joint in each magnetic turn are retained while using much less core strip rnetaland providing a thickness in the core side containing the joints practically the same as the thickness of the adjoining core sides. Moreover, the magnetic core of my invention seems to have a further favorable magnetic quality because of my new progressive lap joint construction, for example, tending to suppress irregularities in flux distribution among laminations in the core.

It is an object of the invention to provide a magnetic core having lap joints and method of construction wherein the core side having the lap joints is not appreciably thicker than the remaining core sides.

It is a further object of the invention to provide a closed magnetic core having lap joints and method of construc- 2,931,993 Patented Apr. 5, 1960 tion therefor wherein the mean length of magnetic turn is a minimum.

Another object of the invention is to provide a closed magnetic core having lap joints and method of construction therefor which requires a minimum amount of steel.

A still further object of the invention is to provide a closed magnetic core having lap joints and method of construction therefor wherein the laminations may be collectively inserted through the window of an electrical winding and the laminations inherently assume the desired overlapped relation without the necessity of an operator interleaving the lamination ends.

Other objects and advantages of the invention will be apparent from the following description when taken in conjunction with the accompanying drawing wherein:

Fig. 1 is a profile view of one embodiment of the core of the invention;

Fig. 2 is a view of a preferred mode of providing a series of core strips of progressively different lengths, before shaping, for embodiment in a core such as that illustrated in Fig. 1;

Fig. 3 is an enlarged schematic view of a part of a progressive lap joint flight as shown in the embodiment of Fig. 1;

Fig. 4 is a view of a preferred embodiment of the new magnetic core construction of the invention having a single lap joint in each core turn;

Fig. 5 is a view of one end of another embodiment of the invention wherein the direction of the lap joint flight is reversed;

Fig. 6 illustrates still another embodiment of the invention suitable for multiphase transformers;

Fig. 7 is a plan view of the laminations of Fig. 2 assembled into a closed loop with lap joints progressively displaced in accordance with a step of one embodiment of the method of constructing the core of Fig. 4;

Fig. 8 is an auxiliary view showing the ends of the outermost lamination of Fig. 7 in overlapped relation and the rivets for holding the lamination in a closed loop;

Figs. 9 and 10 illustrate method steps in shaping the laminations of Fig. 7 into the rectangular configuration of the finished core; I

Fig. 11 shows the method step of inserting the laminations through the winding window of a preformed electrical winding;

Fig. 12 illustrates the blocks upon which the laminations of a cruciform-in-cross-section magnetic core are supported during the construction of the core;

Fig. 13 illustrates an embodiment of the magnetic core of the invention wherein the flights of lap joints are provided in a winding leg; and

Fig. 14 illustrates a further embodiment wherein the lap joints are provided in both winding legs, thereby permitting preformed windings to be assembled over the winding legs before the ends of the magnetic strip lengths are overlapped.

Referring to Figs/1 to 3 of the drawing, a new magnetic core 10 may be generally rectangularly shaped so as to provide a left-hand leg 11 and a right-hand leg 12 as one pair of legs'on opposite sides of core 10. One or both of legs 11 and 12 may be linked with one or more coils respectively denominated 13 and 14. The remaining pair of legs of core 10 may be dominated as an upper yoke leg 15 and a lower yoke leg 16 joining winding legs 11 and 12 to complete the magnetic path around the closed core 10. The innermost turn 17 has the shortest periphery, as will be well understood, around the central or transverse axis 18 of the window 19 bordered by turn 17. The central axis 18 is normal to the"plane of core 10, which plane for the purpose of this description may be taken as the plane of the drawing paper on-which ,Fig. 1 appears. However, substantially each turn in core in Fig. 1 is concentric relative to the other turns and has therein two lengths of the core steel strip laminations. The sides of the respective laminations in adjoiningturns are in a sideby-side arrangement. The respective laminations are preferably straight throughout the major portions of each'leg up to the bends forming corners in the core 10. All the laminations are parallel to axis 18. In the drawings, the lamination present in each turn, whether as one or more lengths of core strip, is usually schematically represented by a single line, although it will be recognized that in actually practicing this invention, such laminations will have the respective thickness of the core strip employed and the respective number of turns in a new magnetic core corresponding to the particular performance specifications for which the new core is being constructed. Althoughiin this description reference is made to left and right hand and to top and bottom, it will be recognized that those terms are relative and used for purposes of this description since any core may be usedin other than a vertical position or may be viewed, for example, from an opposite side.

Turn 17 in general forms a single lamination in core 10 and may. comprise two equal lengths of cold-rolled core strip metal respectively denominated 17L and 17R. In the embodiment being described, the upper end 17Ru and the lower end 17Rb of strip length 17R are on the uppersides respectively of ends 17Lu and 17Lb. The overlap area between ends 17Ru and 17Lu and between ends 17Rb and 17Lb, respectively, comprise an upper lap joint in yoke leg 15 and a lower lap joint inlower leg 16. Both of said lap joints are in turn, or lamination, "of core 10 and have a relatively 'lowmagnetic reluctance so as to essentially constitute turn 17 an independent and self-suflficient magneticpath for fiuxflow in a transformer in which core 10 may be used. Further, it may be noted that the radially outer upper end '17Ru and the radially outer lower end 17Lb of turn lamination 17 are respectively situate nearer and about the same distance from digonally opposite corners of lamination 17. Further, those ends 17Ru and 17Lb point away from their adjacent corners and generally in the direction of the respective flights of which the lap joints formed in part by those ends are a part. In other words, the innermost flights or series of hip joints in the innerrnost group of laminations in core 10 extendingbetween lamination-17 and lamination 21, inclusive will prefer- .ably start adjacent a corner of a yoke leg so as to permit the progressive displacement of the respectively radially outer successive lap joints in the flight under discussion, to take place, toward the other corner in that same .yoke leg as shown in Fig. 1. A second group of laminations may comprise those between lamination 22 and lamination 23in which a second series of flights 24 in the upper yoke leg 15 and a second series of flights25 in the lower yoke leg 16 restart the flight pattern and extend in the same direction along their respective yoke legs. In that way, a plurality of successively outer se- .ries of. flights may be provided with the displacement of the lap joints in each extending only along the respective yoke leg or legs as far as desired with both ends of all flights terminating short of the bends at the corners of the respective turns. In general, the lap joints in the new flights will-generally be confined to an intermediate portion of the core side in which they occur .such as a one-third length of the entire yoke leg to each side of the middle of that yoke leg.

As shown in Fig. 3, turn 26 is the lamination adjoining lamination 17 around the outer sides thereof in the same manner that substantially all of the laminations in core 10 are concentric relative to one another around axis 18. Turn 26 is made up of a left-hand length 26L and a right-hand length 26R of core steel strip and forms an upper lap joint in the. overlap area between ends 26Lu and 26Ru. Similarly, in yoke. leg 16 the ends 26Lb in Figs. 1 and 3, the lap joint between ends 26L u and 26Ru is the second lap joint in the first group'flight and is displaced to the left of the lap joint formed between the ends 17Lu and 17Ru. 17Ru and 26Lu are in a common layer in yoke leg 15 and substantially abut; 17Ru, 26Lu and 26Ru constitute but three, instead of four, radiallayers parallel to axis 18, in the make up of yoke leg 15. A new resultis that yoke leg15 and,

in the embodiment of Fig. 1', yoke leg 16 are far more compact than prior constructions and a material saving is eflected in the amount of core steel strip required. As shown, the next outer lamination adjoining lamination 26 around the outer sides thereof has its upper lap joint progressively displaced still further to the left and upwardly along yoke leg 15 and so on to upper lap joint in turn 21. Since the two lengths of core strip in'cach turn are equal and are preshaped as shown in .Fig. l, the flight in the group of turns between turns 17 and 21, along yoke leg 16,'which in practice will embrace farmore laminations than'the numerical difference of five laminations or the illustrated showing of eight laminations, will have its successive lap joints progressively displaced downwardly and to the right. The upper and lower flights 24' and 25 respectively in the succeeding radially outer group of turns between turns 22 and 23 restart and repeat the new lap joint interfitting construction of this invention in that group. Still further groups with corresponding interfitting flights may be provided radially outwardly of and adjoining the group 22--23. In cross section the respective legs of core 10 may be rectangular or cruciform or have any othershape produced by a selection of particular turns of appropriate width as will be understood by those in the art.

. The interfitting of adjoining lap joints in any flightso that there is a common layer between any two succeeding the case of four adjoining and progressively displaced lap joints, the eight lap joint layers will actually occupy the spaceof five layers as shown in Fig. 1, and so onto the end of that flight series and successive flight series, each flight having an echelon character. Moreover, in such new interfitting relation it would appear that any tendency of the flux to follow an irregular pattern or distribution seems to be inhibited apparently because in the new flight arrangement described each turn end and joint therein is so encased in an adjoining end or ends ofan adjoining turn or turns as to provide efiicient crossover paths in addition to its own main flux path through its own lap joint.

One convenient mode of constructing a core such as the one'illustrated in Fig. 1 may include the use of a progressive cutting machine to shear magnetic strip into progressively different lengths as shown in Fig. 2 which may form the righthand lengths of the laminations shown in Fig. 1. An identical bundle of strips would be cut for the left-hand lengths. Each pair of strip lengths in each progressively outer turn are longer to take care of the increase in the peripheral length of the core laminations which are positioned farther from the center. Such strip lengths may be assembled in a jig beginning with the pair of lengths in the outermost turns somewhat in the manner showniin the aforementioned UnitedStates Patent No. 2,614,158 (Figs. 5 to 8 thereof) except that provision will be made to offset the successive lap joints in each Moreover, the ends Hence, the respective ends 17Lu,

added provision may be made to secure the relative positions of each such length in each such turn during the stacking, blocking, binding, and annealing of the core. After such annealing the core has a permanent set as shown in Fig. 1. Following the annealing operation, the blocking and binding strips may be removed and either leg 11 or 12 or both such legs may be linked with a coil or coils as shown in the last-mentioned United States patent. In such linking, because of the set and progressive offset of succeeding lap joints in the respectively outer turns of the core, the interleaving labor of the prior aligned lap joint construction is greatly reduced, particularly in the case of a magnetic core such as that shown in Fig. 4.

Because of the greater number of pieces in the embodiment shown in Fig. 1, the construction thereof has been described first, However, the embodiment shown in Fig. 4, with a single lap joint per turn or lamination, is a preferred construction. The construction of the embodiment of Fig. 4 is generally the same in character and functioning to that provided in the embodiment of Fig. 1 except that each turn comprises but a single length of core steel strip and all of the lap joints occur along the upper yoke leg. For convenience, parts of the embodiment of Fig. 4 corresponding in construction and functioning to the parts of the core of Fig. 1, are given the same reference designations with the addition of a prime factor thereto. It may also be noted that the steps of constructing the embodiment of Fig. 4 may be similar to the construction of the Fig. 1 embodiment except that the core steel strip may initially be wound on a circular or polygonal mandrel instead of being cut by a progressive cutting machine as described above. If wound on a mandrel, the winding and radial cutting steps to provide suitable progressively greater lengths of core steel may be performed as generally described in the aforesaid Patent No. 2,614,158. In such winding, suitable spacing provision, for example, as mentioned in that patent or as shown, in my aforementioned Patent No. 2,489,625 should be provided, although one of the advantages of this invention is that not as much attention has to be devoted to spacing because the increases in mean turn length between adjoinfing turns throughout the full thickness of the core is not -as great as in prior cores, other conditions being similar. However, in stacking the turns of the embodiment of Fig. 4, such stacking will be practiced to provide the offset lap joints for the flight shown without carrying any lap joint or flight into any corner bend or any yoke leg or into any winding leg. Of course, after such stacking the steps of blocking, binding and annealing are carried out as described to provide a core permanently set as shown in Fig. 4.

In the embodiment of Fig. 5, a zig-zag flight arrange ment is shown which may be provided preferably in one yoke leg only, or in both the top and bottom yoke legs if so desired. The innermost group of turns in the embodiment of Fig. 5 and the flight or flights appertaining thereto are similar in general construction and functioning to the corresponding portion of the inner flight or flights respectively in the embodiment of Fig. 4 or Fig. 1. Hence, for convenience, the same reference designations have been employed in Fig. 5 with a double prime factor. However, the next outwardly succeeding flight in yoke leg 15 between the turns 22" and 23" is reversed producing, in edge profile, a back-and-forth or zigzag character which achieves the new features and ad, vantages of the other embodiments disclosed herein. Thus, in the case of the outer group of turns in yoke leg 15", end 22Lu"is above end 22Ru, thereby initiating the flight 24" immediately above the lap joint provided between the ends 21Lu" and ZLRu". In the case of the lap joint between the ends of lamination 22", its end 22Lu" becomes the one which points the direction which the new flight is to take, which is, in the case of flight 24", upwardly and to the right. Succeeding outer groups beyond group 2 "-23" in a construction like Fig. 5, may continue and repeat the interfitting flight pattern established by the two innermost groups. In the event the laminations in the core of Fig. 5 are provided with flights of lap joints in the lower yoke leg which is not illustrated, then preferably such lower flights will be reversed right and left from the flights in yoke leg 15". In that case, the innermost lower flight would extend downwardly and to the right while the next outer flight in the lower yoke leg would extend downwardly and to the left from the vicinity of the outermost lap joint in the innermost of the lower flights.

The embodiments of Figs. 1, 4, and 5 may be utilized in either single phase or multi-phase transformers. A multiphase transformer magnetic core embodying the invention is illustrated in Fig. 6 and has winding legs denoted A, B, and C, each of which may respectively be linked with one or more coils denominated D, E, and F. Inner cores and 101 may be constructed in accordance with the embodiment of Fig, 4, or in accordance with one of the other embodiments, and disposed side-byside. The outer winding legs A and C may be completed by the use of an encircling core 102 which, except for change in dimensions, may be constructed, as shown, in accordance with the embodiment of Fig. 4 hereof, or core 102 may be made in accordance with the construction shown either in Fig. 1 or Fig. 5. In a multiphase magnetic core, such as that shown in Fig. 6, the new interfitting lap joint construction disclosed herein is of even greater advantage while maintaining the superior electrical characteristics of lap joint cores utilizing wound or bent strips of grain oriented steel.

The steps of a method particularly suited for constructing the embodiment of Fig. 4 for transformers above 167 kva. rating are illustrated in Figs. 7 to 11 wherein parts corresponding to those of the embodiments of Figs. 1 to 5 are given the same reference numerals with the addition of a zero. For example, lamination 17 of Figs. 1 to 5 is shown as element 170 in Figs. 7 to 11. This method includes the step of providing a group of magnetic strip laminations of progressively increasing length similar to the laminations of Fig. 2. The laminations are assembled in a closed loop with a single lap joint in each lamination and successive lap joints in a radial direction progressively displaced circumferentially. Only two groups of laminations 128 and 129, each comprising a plurality of successive laminations, are illustrated in Figs. 7 to 11, but it will'be appreciated that a finished core may comprise tens, or even hundreds, of such groups. .To retain the loop 130 closed the overlapped ends of the longest lamination in each group are fastened together, preferably by hollow rivets or metal grommets 131. The radially outermost group 129 is illustrated as comprising eight laminations and extends from outermost lamination 230 having the greatest peripheral length to lamination 220 which has the shortest peripheral length. Apertures are provided adjacent both ends of lamination 230 to receive rivets 131 for fastening the ends of lamination 230 in overlapped relation as shown in Fig. 8. Lamination 229 is then inserted within closed lamination 230 with the respective ends thereof overlapped and circumferentially displaced to the right of the lap joint in lamination 230 as shown in Fig. 7. In a similar manner successive radially inward laminations are inserted within the closed radially outermost laminations 230 and 229 to build up the closed loop 130 with the respective ends of the laminations overlapped and with each lap joint circumferentially displaced to the right of the next radially outer lap joint to form a flight, or series of lap joints, similar to those of the embodiments of Figs. l to 6. It will be appreciated that the ends 230Lu and 229Ru of the laminations 230 and 229 respectively are in a common layer and substantially abut. The flight in the group 129 of laminations 230 to 220 has its successive lap joints progressively ditlamination 220 to receive rivets 132 for securing the ends thereof in overlapped relation. The interfitting of the adjoining lap joints in the. flight so that there is a common layer between any two succeeding lap joints decreases the mean length of turn in comparison to prior art cores having lap joints and provides 'a=core' side containing the joints of a thickness practically the same as the thickness of the adjoining core sidese A second, radially inward group 128 of laminations may comprise those between lamination 210 and lamination 170 in which a second series of lap joints restart the flight patttern and extend in the same direction as the first, group. Apert-ures are provided near the ends of the radially outermost lamination 210 to receive rivets 133 for securing the ends of lamination 210 in overlapped relation and preferably in alignment with the lap joint in lamination'230. of the outermost group 129. Successive, radially inward laminations are. thenv inserted within closed lamination 210 with the respective ends overlapped and theylap. joints circumferentially displaced to the, rightand downward as in the outer group 129 to further build up the. closed loop .130. Preferably the ends of the radially innermost lamination 170 in this group aresecured in. overlapping relation by rivets 134.

In this manner a plurality of successively inner groups may be provided adjoining groups 128 with the displacenient of the lap joints in each extending circumferentially only as far as desired and with ends of all flights prefcrably; in alignment. In cross section the closed loop 130 may be rectangular as illustrated orcruciform or have any other shape by a selection of particular turns of appropriate width as will be understood by those in the art.

Although the method has been illustrated and described as overlapping the respective ends of individual laminations, the invention is not so limited and comprehends the arrangement of the laminations in sections each comprising a plurality of successive laminations and the overlapping of the respective ends of each section. Tests indicate that exciting current and core loss are not appreciably different if the ends of individual laminations, are overlapped or if each section comprises two, or three successive laminations and the ends of each section are overlapped.

Pressure is then applied against surfaces of the periph- -ery of; the closed loop 130 to shape the laminations to the configuration ofthe finished core. Although the de sired shape for some cores is obtained by applying pressure only against the inner periphery of the closed loop 130, in the illustrated method for constructing larger sizecores, pressure is applied against both the inner and .theouter-periphery and-a five piece mold is used to shape the annular closed-loop 130into approximate rectangular configuration. As seen in Fig. 9 two rectangular end mold; pieces 136, preferably S-shaped, are inserted within the axial window in the annular loop 130. The longer the inner-periphery of the portion of the closed loop 130 containing the lap joints and the other end mold piece is' positioned diametrically oppositethereto. G- clamps 139 each having one leg acting against the outer periphery of the closed loop 13 and the otherleg abutting against an inner surface of an 8-shaped end mold piece 136; are then tightened to draw the end mold pieces 136. against: the inner periphery of the loop 13$! and flatten the laminations against the longer side 137 thereof. Preferably a plate Mil-approximately as long as side 137 of piece 136 is interposed between the C-clamps 139 and theexternal periphery ofthecore to prevent damage to. the outermost laminations and to distribute the appliedpressure. Hydraulic or other pressure'means, preferablya jack screw 141,, is. then utilized todiametrically est tes he ast madnes 6.; until h des ed; a s.

. window dimension before the jack screw 141 is removed. It will be appreciated that with a core comprising a largev window dimensions are obtained and, thus'cause-ithe laminations to assume an approximately rectangular shape. J

After the S-shaped end mold pieces 136 have been spread apart by the jack screw 141, rectangular center mold blocks 143, 144 and 145 (see Fig. 10) are inserted between the end mold pieces 136 to hold the laminations in approximately rectangular shape with the desired core number of lamination groups, tension will be greatest in the radially innermost group 128 causing the laminations of this group to assume an almost exact rectangular shape whereas the tension in the groups outward therefrom Will progressively decrease in, a radially outward direction. An attempt has been made in Fig. 9 to illustrate this condition, although with only the few laminations shown an almost exact rectangular shape would probably attained in all of the groups. 1 w Pressure is then applied against the external periphery of the closed loop 130 to shape the laminations to the rectangular configuration of the finished structure. As shown in Fig. 10, end plates 150 disposed against the external periphery of the loop 130 opposite the S-Shaped end mold pieces 136 are connected by threaded tie rods 151 both above and below the core, and nuts 152 engaging the threaded tie rods 151 are tightened to apply ex,-

- ternal pressure against the yokes of the core. Side plates 154 disposed against the winding legs of the core are connected by threaded tie rods 155, also both above and below the closed loop 130, and nuts 156 are tightened on the threaded tie rods 155 to clamp the winding legs of the core between the center mold pieces 143 and 145 and the side plates 154. In order to remove all deleterious strains and give the laminations a permanent set in the positionthey will occupy in the final core, the laminations, comprising the core structure illustrated in Fig. 10 are then given a suitable strain-relief anneal, preferably by heating in a suitable atmosphere to a temperature of approximateloy 1500 degrees F. The laminations take a permanent set as a result of the annealing and thereafter remain in place without the necessity for binding or compression. r v

After annealing, the laminations are stacked a second time in linking the core with a preformed winding. The end plates 150 and side plates 154 are removed and the mold pieces 136, 143, 144 and 145 are removed from the window in the core. The rivets 131, 132, 133- and 1341-securing the ends of the innermost and outermost laminations in each group are then broken. In the sec;-

' ond stacking operation the core is built up radially outside 13 7; of one end mold piece 136 is disposed adjacent I ward. The step of assembling the core with preformed transformer windings is illustrated in Fig. 11. In order to assemble a core type transformer, preformedwindings 13 and 14 are disposed side-by-side. One of these windings may be the primary and the other the secondary, or the primary and secondary winding maybe divided into two groups. The innermost lamination group 128 of the core is first separated from the remaining lamination groups and its lapped ends opened slightly, The ends of the laminations comprising the group 128 are then collectively inserted through the. central openings in the windings 13 and 14. It will be observed that slight bending of the laminations in the yoke leg'of the core is necessary to permit this insertion, but the deformation does not exceed the elastic limit and consequently, the mag netic properities of the magnetic strip material are not impaired. beenpassed entirely through the openings of the windings 13 and 14.- they inherently assume the overlappingrelation inwhichthey were annealed. In prior art methods of construction it was necessary for an operator to shuttle the ends of the lamination lengths into individually overlapping, relation. I Because thelaminations areperinanenty, etiw h. e h t p ph lly. a ge e it is, possib e 7 When the open ends of the group 128 have to collectively assemble the entire group 128 of laminations in one operation without requiring an operator to peripherally displace the lap joints and to shuflle the lamination ends into overlapping relation beyond the far edge of the preformed winding.

In order to provide added mechanical strength, the ends of the innermost lamination 170 are riveted in overlapped relation after being linked with the preformed windings 13 and 14. As illustrated in Fig. 11 the innermost group 128 of laminations has been linked with the windings 13 and 14 as above described, the overlapped ends of lamination 170 have been secured by rivets 158, and the second group 129 is being threaded through the openings in the windings 13 and 14 so that the lap joints occur in the yoke of the core containing the lap joints of the innermost group 128. Although only two groups 128 and 129 of laminations are illustrated, it will be appreciated that any desired number of lamination groups each having a flight of peripherally displaced lap joints may be utilized to build up a finished core substantially identical to that illustrated in Fig. 4. If desired, the ends of the radially innermost or the radially outermost lamination in each group, or both, may be riveted to hold the laminations securely in position.

Although the method has been described and illustrated for the construction of a core having a rectangular cross section, it will be appreciated that by the selection of laminations of appropriate width, at cross section of cruciform or any desired shape may be provided. When a cruciform-in-cross section core 160 is constructed in accordance with the present invention, the various lamination widths thereof are supported on the steps 161 of stepped support blocks 162 peripherally spaced apart beneath the core as shown in Fig. 12.

Magnetic cores embodying the invention for transformers having ratings of 5000 kva. have been constructed in accordance with the method illustrated in Figs. 7-12 and successfully operated. It will be appreciated that if every group of laminations comprises n laminations, the radial thickness of the core side containing the lap joints is increased by only the thickness of one magnetic ribbon for every n laminations. Thus, if each joint has a onehalf inch overlap and a series of ten overlap joints in one group are staggered over a peripheral length of five inches, the radial thickness of the core side containing the lap joints is only one-tenth thicker than the adjoining core sides. Thus, the mean length of lamination of the magnetic cores of the present invention is decreased considerably in comparison to conventional cores. Inherent with the decrease in mean length of turn is a reduction in'the amount of core steel while retaining the low reluctance and low core loss advantages of a magnetic lap joint in each core turn.

Advantage is taken of the minimum radial buildup of the disclosed interfitting lap joints in the embodiment of magnetic core 300 illustrated in Fig. 13 wherein the flights 301 of peripherally displaced lap joints occur in a winding leg 302 of the core 300. The innermost group 303 comprises the whole turn laminations between lamination 304 and lamination 305, and the series of lap joints 301 between lamination ends extendsdownward and to the right; similarly the flight 301 of lap joints between the respective ends of the whole turn laminations of the radially outward group 306 extend downward and to the right. Inasmuch as the thickness of winding leg 302 is increased by only one lamination for every n laminations in each group 303 or 306, the space factor within the window of any winding encircling leg 302 is not substantially difiFerent from that of other embodiments of the invention.

The embodiment of the invention illustrated in Fig. 14 permits the electrical windings to be assembled over the winding legs rather than requiring the insertion of the laminations through the window of an electrical winding as inthe embodiments of Figs. 1, 4, 5, and 6. Flights 310 and 311 of lap joints occur substantially above the electrical coils l3 and 14 in the winding legs 312 and 313 respectively. Each lamination includes two lengths of magnetic strip in a manner analagous to the embodiment of Fig. 1. Radially innermost lamination 317 comprises two lengths of cold-rolled magnetic strip denoted 317U and 317L. Strip lengths 317U and 317L overlap in a first joint 318 in winding leg 312 and in a second joint 319 in winding leg 313. The next radially outer lamination 326 also comprises two lengths of magnetic strip 326U and 326L which overlap in a first joint 328 displaced peripherally upward from lap joint 318 and also in a second joint 329 displaced peripherally downward from lap joint 319. The end of strip length 326L partially forming lap joint 329 is in the same layer as the end of strip length 317U which partially forms lap joint 319. Similarly the end of strip length 326U which partially forms lap joint 328 is in the same layer as the end of strip length 317L which partially forms lap joint 318. In this manner the flights 310 of lap joints as shown in the drawing extend upward and to the left and the flights 311 of lap joints extend downward and to the right.

In reality the ends of the laminations are only overlapped approximately one-half inch, and consequently the series 310 and 311 of lap joints occupy a much smaller portion of the peripheral length of the winding legs 312 and 313 in an actual core than that represented in Fig. 14.

The magnetic strip lengths 317U, 326U, etc., in upper are assembled in overlapped relation with the: strip lengths 317L, 326L, etc., after the electrical wind-- ings 13 and 14 have been inserted over the winding legs- 312 and 313, and it will be appreciated that no bending; of the laminations occurs which would disturb the grain. and permanently setv yoke 330 orientation of the annealed laminations 317, 326, etc.

ners of the core. In this embodiment also the electrical coils can, be placed on the winding legs before the lami nation lengths are assembled in overlapped relation.

While there have been shown and described preferredi practices of the invention, it will be obvious to those: skilled in the art that changes and modifications may be made without departing from the invention, and it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention. The appended claims are intended to cover the aforementioned embodiment wherein the laminations are arranged in sections each comprising a plurality of radially successive laminations all having the same length, and the phrase lamination length used in certain of the claims is intended to cover either a single lamination or a plurality of laminations all having the same length.

It is claimed:

1. A magnetic core for stationary induction apparatus comprising, in combination, a plurality of concentric groups of lamination lengths of magnetic material forming a closed four-sided magnetic core having a pair of opposed legs and a pair of opposed relatively shorter yokes, one of said legs being a winding leg, each of said groups comprising a plurality of radially succesive lamination lengths, each lamination length constituting a closed magnetic circuit and having its ends overlapped a relatively short distance in one of said yokes, substantially all of said lamination lengths having those improved strain-free properties characteristic of magnetic material relief-annealed subsequent to mechanical working, radially successive lap joints. in each of said groups being circumferentially displaced along one of said yokes and hav- I mamas 11 ingoneend of each'adjoining pair of lap joints disposed in; a common layer with the end of one lamination length in said layer discontinuous from the endof the other lamination length in said layer to provide an interiitting flight of lap joints in said one yoke, whereby the lamination lengths of each group may be separated at their overlapped ends and collectively inserted through the window ofan electrical winding ands'aid lamination lengths in herently assume said overlapping relation. 2. A closed magnetic core for stationary induction apparatus comprising, in combination; a plurality of radially I nested, fiatwise curved laminations of magnetic materialhaving a preferred grain orientation lengthwise thereof; substantially all of said laminations having those improved strain-free properties characteristic of magnetic material relief-annealed subsequent ;to mechanical workingand having a permanent set of rectangular configuration with four sides joined at approximately right angle corners to form a hollow core havingoppositely disposed sides; and relatively shorter, oppositely disposed ends, oneof the sides of said core being, a winding leg, eachone of. said laminations being, of longer length than theadditive: length ofasaid sides and ends of. said magnetic corerneasured circumferentially atv said one of said lami nations, saidlaminations being in solid contact along substantially their entire length with the, corner bends compactly nested together and each lamination having the ends thereof overlapped a relatively short distance in one of the ends of said core,.the lap joints of'radially successive, laminations being progresively displaced peripherally along a. substantial portion of the circumferential length. of said one end of said core and the outermostle'nd of each laminationbeing'in theisamelayer as, butdi'scontinuone from, the innermost end of the lamination radially outward'therefrom to provide an interfitting. flight of lap joints along said one end, whereby's'aid laminations may" he collectively inserted through the window of anelectri-j cal windingand' said laminations' inherently resume said overlapping relation: w j

3. In'combination, a'closedmagnetic core havingfour sides surrounding a window and comprising aplurality ofconcentric groups of laminations of magnetic material, each group including a-plurality of'radiallysuccesive -lami- 7 nations, eachlamination comprisingga whole turn in said coreand substantially all of said laminations havingthose improved strainafree properties characteristic of magnetic material relief-annealed: subsequent to mechanical working and having a permanent set of rectangularconfiguration with :fonrgsides joined at approximatelyrrightangle corners toform-a hollow, closed corehaving oppositely disposed legs: and oppositely disposed, relatively shorter-yokes, oneof. said legsbeing a winding leg; said laminationsofeach group being in' solid contactialong-substantially? their entire-length with the cornerbends compactly nested together and each laminationof'saidgroup having its ends overlapped a relativelyshort distance in one of said yokes, radially; successive lap joints in each groupgbeing pro'gres sively displaced. in a circumferential direction along a substantial portion of the length of one of said'yokes and, the radially outermost end of each lamination being in the same layer as, but discontinuous from, theradially innermost end of the lamination radially outward therefrom toprovide an interfittingflight of lap joints in said group along, said one yoke, whereby the laminations. of each,

group maybe separated atutheir overlapped ends and collectively inserted through the window of'an electrical winding to link said one leg with said winding and saidlaminations inherently assume said overlappingrelation,

the-interfittinglap jointsin radially; succesive groups being similarly arranged .and. displaced al'ongziat least one yoke of said core.

4. A'magneticcore for stationaryinduction apparatus comprising; in combination, aplurality of radially nested, lengthwise bent lamination lengths of'magnetic material eachhavinga-ipreterred grain. orientation lengthwise there of, said lamination lengths having those improved strainannealed subsequent to mechanicalworking and having a permanent set of four-sided configuration to form a closed, hollow magnetic core having a pair of opposed legs and a pair of opposed, relatively shorter yokes sur rounding a window, one of said legs being a winding leg, each of said lamination lengths constituting a whole turn in said core and having its ends overlapped a relatively short distance in one of said yokes, radially-successive lap joints being progressivelydisplaced in a circumferential direction along said one yoke and'jhavin'g one end of each adjoining pair of lap joints disposed in a commonlayer in said one yoke with the end of one lamination length in said layer discontinuous from the end of the other lamination length in said layer, whereby saidlamination'lengths may be separated at their overlapped ends and collectively inserted through the window of an electrical winding and said lamination lengths inherently assume said overlapping relation.

5. Stationary induction apparatus comprising, in combination, an electrical winding having a window therethrough and sides of substantially rectangular cross section surrounding said window, a closed quadrilateral mag net-ic core including a plurality of concentric groups of lamination lengths, said core passing through said window and; closely embracing one of said sides of said winding and having a pair of opposed legs, one of which is disposedwithin said window, and a pair of'opposed, rela tively'shorter yokes, said lamination lengths having those improved strain-free properties characteristic of magnetic material relief-annealed subsequent to mechanical working and having a permanent set ofquadrilateral configuration, each said group including a plurality ofradially successive lamination lengths in solid contact along substantially their entire length and each of which comprises a whole, turn of said core and has its ends overlapped a relatively short distance in one of said yokesof said core,

individual closed magnetic circuits, the steps comprising,

in combination, providing a plurality of magnetic laminations of progressively different lengths, stacking said lamination lengths concentrically in order of length and overlapping the respective ends of each lamination length a relatively short distance to form a closed loop and progressively displacing the lap joints in a peripheral; direction along the circumferential length of said closed loop so that the radially innermost lamination length endat eachlap joint is'discontinuous from but in a common" layer with the radially outermostlamination length end of the lap joint of the succeeding radially inward closed magnetic circuit toprovide a step-like flight-of lap joints,

shaping said lamination lengths into a four-sided core having said'step-like flight of lap joints in one ofthe sides thereof, andannealing the core while so shaped to relieve strains'in the magnetic material and to give'said" lamination lengths a permanent set of four-sided con figuration with the ends of each lamination length overlapped, whereby=the ends of said lamination lengths'may be separatedat said lap jointsand said lamination 'lengths collectively inserted through the window of an electricalwinding and said lamination lengths inherently assume said overlapping relation.

7. In the'methodof constructing a magnetic'core, the

steps comprising, in combination, providing a plurality" of magnetic laminations of progressively different lengths,-

stacking said lamination lengths concentrically inforderl of lengthingroups eachcomprising a plurality of'radi-v 13 ally successive lamination lengths'and overlapping the ends of each lamination length to form a closed magnetic core and progressively displacing the lap joints of each said, group in a circumferential direction along said closed core so that radially successive lap joints have one end of eachdisposed in a common layer with the end of one lamination length in said layer discontinuous from the end of the other lamination length in said layer to provide a step-like flight of lap joints in said group, positioning said groups so that said flights of lap joints are in radial alignment in at least one peripheral portion of said core, shaping said lamination lengths into a quadrilateral core having a pair of opposed legs and a pair of opposed relatively shorter yokes and with said flights of lap joints in at least one of the yokes thereof, and annealing the core while so shaped to permanently set said lamination lengths in quadrilateral configuration with overlapped ends in one of said yokes and to relieve strains in said magnetic lamination lengths.

8. In the method of constructing a magnetic core of individual closed magnetic circuits, the steps comprising, in combination, providing a plurality of magnetic laminations of progressively difierent lengths, stacking said lamination lengths concentrically in order of length and overlapping the ends of each lamination length a relatively short distance to form a closed core and progressively displacing the lap joints of radially successive lamination lengths in a circumferential direction along a substantial portion of the peripheral length of said closed core and so that the radially innermost lamination length end at each lap joint is in a common layer with but discontinuous from the radially outermost lamination length end of the lap joint of the succeeding radially inward lamination length to form an interfitting flight of lap joints and said lamination lengths are in solid contact along substantially their entire length, shaping said lamination lengths into a quadrilateral core having a pair of opposed legs and a pair of opposed relatively shorter yokes and with said flight of interfitting lap joints in one of the yokes, and annealing the core while so shaped to relieve strains in said lamination lengths and to permanently set said lamination lengths in quadrilateral configuration with overlapped ends, whereby the ends of said lamination lengths may be separated at said lap joints and collectively inserted through the window of an electrical winding and said lamination lengths in herently assume said overlapping relation.

9. In the method of constructing an electrical transformer, the steps comprising, in combination, providing a plurality of magnetic laminations of progressively different lengths, stacking said lamination lengths concentrically in the order of length in groups each comprising a plurality of radially successive lamination lengths and overlapping the ends of each lamination length to form a hollow magnetic core and peripherally displacing the lap joints of each said group progressively along the circumferential lengths of said core so that radially successive lap joints have one end of each disposed in a common layer with the end of one lamination length in said layer discontinuous from the end of the other lamination length in said layer to provide a step-like flight of lap joints in said group, positioning said groups so that said flights of lap joints are in radial alignment in at least one portion of the periphery of said core, shaping said lamination lengths so stacked into a quadrilateral core having a pair of opposed legs and a pair of opposed relatively shorter yokes and with the flights of lap joints in at least one of the yokes of the core, annealing the core while so shaped to relieve strains in said lamination lengths and permanently set said lamination lengths in quadrilateral shape with overlapping ends, collectively bending the lamination lengths of each of said groups at positions including the corners at the ends of said one yoke to open said lap joints and collectively inserting said lamination lengths so opened through the window 14 of an electrical winding, whereby said laminations in herently assume the position in which they were annealed with the peripherally displaced lap joints reclosed to complete the linking of a leg of said core with said electrical winding.

10. In a method of constructing a magnetic core, the steps comprising, in combination, providing a plurality of magnetic strip laminations of progressively different lengths, securing the ends of the longest lamination length in overlapping relation to provide a closed magnetic turn, inserting the lamination lengths in order of decreasing length concentrically within said closed turn and overlapping the ends of each lamination length a relatively short distance to provide a hollow core and progressively displacing the lap joints in a circumferential direction along said hollow core so that the radially innermost end of each lamination length is in a common layer with but discontinuous from the radially outermost end of the succeeding radially inward lamination length to provide a step-like flight of interfitting lap joints along the periphery of said core, shaping said core into foursided configuration with said step-like flight of interfitting lap joints in one side thereof, and annealing the core while so shaped to relieve strains in said magnetic strip lamination lengths and to give said lamination lengths a permanent set of four-sided configuration with the ends of each lamination length in overlapping relation.

11. In the method of constructing a magnetic core, the steps comprising, in combination, providing a pluality of magnetic laminations of progressively different lengths, securing the ends of the longest lamination length in overlapping relation to provide a closed magnetic turn,

inserting the lamination lengths in order of decreasing length within said closed turn and overlapping the ends of each lamination length a relatively short distance to provide a hollow core of individual, closed magnetic circuits and progressively displacing said lap joints in a peripheral direction in a recurring pattern wherein the lap joints in each group comprised of a plurality of radially successive lamination lengths are displaced circumferentially in a step-like flight of lap joints along the periphery of said hollow core and so that radially successive lap joints have one end of each disposed in a common layer with the end of one lamination length in said layer discontinuous from the end of the other lamination length in said layer, positioning said groups so that said flights of lap joints are in radial alignment along at least one portion of the peripheral length of said core, applying pressure against the inner periphery of the portion of the core containing the lap joints and against the inner periphery of the portion diameterically opposed thereto to shape said lamination lengths into a quadrilateral core having opposed shorter sides forming yokes and opposed longer sides with the flights of lap joints in at least one of said yokes, and annealing the core while so shaped to relieve strains in said lamination lengths and to give said lamination lengths a permanent set of quadrilateral configuration with overlapped ends.

l2. In the method of constructing a magnetic core of individual closed magnetic circuits, the steps comprising, in combination, providing a plurality of magnetic laminations of progressively different lengths, securing the ends of the longest lamination length in overlapping relation to provide a closed turn, inserting said lamination lengths in order of decreasing length within said closed turn and overlapping the ends of each lamination length a relatively short distance to provide a hollow core and peripherally displacing said lap joints in a recurring pattern wherein the lap joints in each group comprising a plurality of radially successive lamination lengths are progressively displaced peripherally in a step-like flight of lap joints along the circumference of said hollow core and so that said lamination lengths are in solid contact along substantially their entire length with the radially innermost 15 lamination length end at each lap joint in a common IfaYenWith; but discontinuous from, the radially outermost end of the succeeding radially inward lamination length; positioning said groups so that said flights of lap joints are in radial alignment in at least one portion of said hollow core, shaping said core into a four-sided configuration having a pair of opposed legs one of which may be a winding leg and a pair of opposed relatively shorter yokes and with said flights of lap joints in at least one of said yokes, annealing the core while so shaped to relieve strains in said magnetic strip lamination lengths and to permanently set said lamination lengths in four sided configuration with the ends of each lamination length overlapped, wherebysaid lamination lengths of each said group may be opened at theiroverlapped ends 15 i ans col ct ve y s r th hl w w o an trical winding and said laminationlengths inherently as:

2,053,362 Smalley ....V Oct. 20, 1936' 2,595,820 Somerville ;Q.. May 6; 1952 2,614,158 Sef ton et al. Oct. 14, 1952 2,700,207 Zimsky Jan. 25, 1955' 2,702,936 H rin Mar. '1, 1955;

FOREIGN PATENTS

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