US2145703A - Shell type transformer - Google Patents

Description

jan. 31, 1939. E WIRZ 2,145,703

SHELL TYPE TRANSFORMER Filed Aug. 4, 1937 @fa Z's il? v An Patented Jan. 31, 1939 PATENT OFFICE SHELL TYPE TRANSFOBLIER Emil Wirz, Biel, Switzerland Application August 4,

1937, Serial N0. 157,412

In Switzerland July 5, 1937 9 Claims.

This invention relates to shell type transformers, and particularly to shell type transformers provided with means for intentionally increasing the magnetic leakage thereof, for the purpose of protecting the windings against overload.

There are known shell type transformers in which leakage control members are inserted between the windings. Such transformers include, however, either open air gaps or else the necessary butt joints between the leakage control members and the yoke, on the one hand, and the core on the other hand, are so arranged, that by this means the same can no longer be influenced by the main field. In other known shell type transformers the arrangement is so chosen that the cross section of the butt joints is made so small in accordance with the cross section of the inserted leakage control members, that in spite of the influence of the main field still a much too great number of butt joint loss reducing ampere-turns is necessary for the passage of magnetic flux, so that the leakage control member can, in principle, no longer be considered as being devoid of an air gap.

According to the present invention, the magnetic leakage of a shell type transformer, in which the iron body of rectangular or other shape is divided, in a suitable known manner, for example, in a plane Whose trace extends through the leakage control members at right angles to the core, whereby two symmetrical comb-like iron body portions are provided, is intentionally increased, in such a Way that between the symmetrical portions a leakage control member composed of I-shaped sheet metal elements and having a smaller cross section than the main core is so inserted in recesses that the unavoidable air gaps to be crossed by the leakage eld are crossed by the main eld also. By increasing the cross sections of leakage control member enlargements, which are inserted in recesses, the inuence of the butt joint loss reducing ampereturns can be decreased to such a considerable extent that the iniiuence of these turns is negligibly small in which way savings in copper and a much smaller drop in voltage together with a greater degree of efficiency obtains.

By stamping the recesses out of tenons on the plate element portions of the iron body into which recesses the leakage control members are inserted, the butt joints between the latter and the yoke and the core respectively are shifted to the middle of the iron body, so that in the yoke as well as in the core the butt joints of the leakage control member are traversed by the main flux completely in consequence of which the magnetic resistance of the butt joints is decreased.

For certain purposes, even this arrangement still presents a relatively too high value of drop in voltage which can, however, be further decreased by stamping the plate elements of the lateral yokes, the cores and the leakage control members out of a single piece of material, the connecting yokes being, however, inserted perpendicularly to the cores as separate stampings in overlapping relation with recesses and tenons of the respective core and lateral yoke portions. For facilitating the assembling of the transformer the leakage control member elements are set in place centrally of the transformer, whereupon the normal trident-like plates are joined with the upper and lower sides of these members.

In shell type transformers of relatively large size, the stamping tools for which would be too expensive, the iron body may be composed of rectangularly cut strips, the leakage control plate elements which are here generally I-shaped in plan are inserted in recesses which are disposed centrally of the lateral yokes and cores and provide for increased butt joint cross sections.

In the accompanying drawing two embodiments of the invention are illustrated by way of example only, these embodiments representing shell type transformers for monophase and three-phase current respectively each having a different leakage control member arrangement. In the drawing Fig. l is a schematic elevational view of a shell type transformer showing the leakage control plate elements intertting with recesses, the windings and the course of the various leakage fluxes;

Fig. 2 is a cross section of the transformer shown in Fig. l as taken through the cores, the yokes and the leakage control plate elements interiitting with recesses;

Fig. 3 shows an elevation of a complete plate element for the part of the iron body including the leakage control members;

Fig. 4 shows an elevation of a complete plate element for the part of the iron body which is devoid of leakage control members, the hatched portions c to be stamped out indicating in which Way from these plates the plates shown in Fig. 3 can be made with the aid of special tools;

Fig. 5 shows a schematic elevation of a shell type transformer having leakage control members interiltting with recesses as indicated in Fig. 1, but with the two windings connected for economizing current;

Fig. 6 is a schematic elevation of a three-phase transformer with ve legs and leakage control members which interflt with recesses and are inserted between the windings, the cores and yokes, the windings, the leakage iluxes and the course of the latter being shown for an arrangement in which the iron body is composed of symmetrical plate element halves for two collateral mono-phase transformers as indicated in Fig. 1;

Fig. 7 is a section through the cores, the yokes and the leakage control plates, interiltting with recesses, all as provided in the live-legged threephase transformer;

Fig. 8 shows an elevation of a complete plate element for the part of the iron body including the leakage control member provided that the lateral yokes, the leakage control members and the cores are all stamped out of the same work blank and that the connecting yokes, which are formed by separate stampings, are joined with the lateral yokes and the cores in overlapping relation, by means of tenons and recesses;

Fig. 9 shows an elevation of a complete plate element for the part of the iron body in which the leakage control plates intertting with recesses are situated provided .that the cores andy the yokes are formed by rectangular strips;

Fig. 10 is a schematic elevation of a complete plate element for a ilve-legged three-phase transformer in which the leakage control plates interflt with recesses in the cores and yokes and the cores and yokes are composed of plates cut into rectangular shape, and

Fig. 111s a schematic elevation of a shell type transformer, as illustrated in Fig. 1, showing the leakage control plates interfitting with recesses, the windings and the course of the leakage fluxes for cases where the primary or the secondary Winding or both are divided in two parts for being connected in series or in parallel, to which end several leakage control members are required.

'Ihe shell type transformer representing the constructional example of the invention as shown in Figs. 1 to 5 is provided with a core k and yokes i which parts are assembled of bi-partite stamped transformer plate elements each consisting of two symmetrical halves provided with interiltting members at the jointing portions of the cores and yokes. On the central core two windings are so arranged that the primary winding Pr is disposed on one side and the secondary winding Sek on the other side. The leakage control members St are composed of a plurality of plate elements each of which is generally I- shaped in plan and has a medial portion of such width that the effective cross section of the member is less than the normal average cross sectional area of the ux path in the .iron body. 'Ihe enlarged terminal portions A11, are so inserted in this transformer that the leakage control members St enter the stamped out recesses between the cores and yokes. 'I'he enlargements An. on the leakage control plates serve the purpose to enlarge the cross sectional area of the joint and to reduce the number of butt joint loss reducing ampere-turns. This arrangement thus provides for improving the passage of flux from the leakage control member tothe yoke and from the leakage control member to the core and, consequently, results in increasing the influence of plied to the constricted portion of such core-leg.-

The tenon Z1 in consequence interts with "a similar tenon Zz'on the complementary half of the plate element.

Now, if an alternating voltage is impressed on the primary winding, in the core portion carrying the primary winding a magnetic, ilux p1 is generated the major part of which flows through a circuit, extending through the secondary core portion and carrying a magnetic flux, 1,029, and thence through the yokes. This delivers, at noload, a leakage flux pso through the leakage control members St, in accordance with the magnetic resistancewso of the path of the lines of force through the leakage control member and the magnetic resistance w20 of the secondary path of lines of force of the secondary circuit. The re- Y lation between the magnetic flux passing through the secondary path of the lines of force and that passing through the leakage path of the lines of force follows the rule t15m/1520 02 nl'wm that is, the magnetic fluxes of the leakage path of the lines oi force-and of the secondary path of the lines lof force are inversely proportional to the respective magnetic resistances or reluctances of these paths. In the event that the secondary winding is loaded up to the point of inviting short-circuiting, the magnetic flux generated by the secondary current counteracts the main magnetic flux passing through the secondary core until, on short-circuiting arising, the relation between the magnetic fluxes passing through the leakage control member and through the secondary core is inversely proportional to the relation between the magnetic resistances of these paths of the lines of force at this load. Therefore, the secondary current, on short-circuiting arising, can rise in value only so much until steady conditions obtain, so that by adequately choosing the cross sectional areas of the leakage control member, and of the butt joints, and selecting the material to be used the secondary current can be controlled so as to assume any desired'value.

Experiments have shown that the more completely the butt joint loss reducing ampere-turns for the leakage control members can be compensated for, or reduced in number, and depending upon which material is selected for these members and upon the manner in which the said members are inserted and, accordingly, the cross sectional areas of the butt joints are increased, the course of the curves representing the secondary drop in voltage is kept down to a widely varying extent. Experiments have further shown that by increasing the cross sectional areas of the leakage control members, as indicated in the drawings, the number of butt joint loss reducing ampere-turns is reduced to a minimum, so that the drop in voltage at the rated secondary current is accordingly considerably smaller as compared with that presented by the transformer types hitherto used.

For certain cases, where it is required to keep the drop in voltage down to an extremely small value and increasing of the cross sections of the copper is undesirable, a further drop in voltage can be obtained by stamping the plate elements of the lateral yokes, the cores and the leakage control members out of a single piece of material, as indicated in Fig. 8. The connecting yokes i1 between the cores k and the lateral yokes i2 must then be intertted with the aid of overlapping butt joints within the extent of the iron body to be provided with leakage control members, prior to applying the windings. For the remaining portions of the iron body, where no leakage control members are provided, normal plate elements are used, as shown in Fig. 4.

For larger specimens of shell type transformers for which trimming of the plate element portions by means of a cutting tool would no longer be economical for some reason or other, the cores and yokes may be cut out of rectangular sheet metal strips, as indicated in Figs. 9 and 10 for monophase and three-phase transformers respectively. In this case, the recesses for the leakage control plate enlargements An are stamped out of the plate element portions, whereupon the leakage control plate elements provided with the enlargements are inserted in these recesses. The connecting yokes i1 and i2 for these arrangements are made from plates of different widths and interfitted by means of alternately overlapping portions. Such an arrangement can also be used for manufacturing a transformer in which the drop in voltage becomes small, whilst the cross sectional areas of the copper are substantially reduced.

For producing the iron body of shell type transformers by means of shop methods, symmetrical plate element halves having intertting projections may be used, the hatched areas c corresponding to the recesses for receiving the leakage control members being stamped out of the plate element halves A, by means of special tools, as this is indicated in Fig. 4 for the part of the iron body provided with leakage control members. The plate element halves B thus produced, inclusive of the leakage control plate elements, are indicated in Fig. 3.

The iron body of the shell type transformer for monophase current, as illustrated, is also applicable for transformers connected up for current economizing (autotransformer), as shown in Fig. 5. Experiments have shown that in providing for edonomizing current by applying a magnetic by-pass between portions of an integral winding and adequately choosing the dirnensions of the leakage control member, apart from obtaining safety against short-circuiting, also the phase displacements between the currents and the potentials can be varied which holds out hopes of great advantages for certain purposes.

Further economies in current consumption may be effected in shell type transformers made in accordance with the present invention if the material of the leakage control members employed has diierent magnetic properties from that of the core and yoke. For example, the control members St shown in Fig. 5 may be of transformer steel having a higher permeability than has the symmetrical halves of the plate element, this being indicated by broken hatches in Fig. 5.

The iron body of the shell type transformer for monophase current, as illustrated, is also applicable when it is desired to arrange two equal iron bodies side by side for obtaining a tive-legged three-phase transformer having leakage control plates interfitting with the yokes and cores by means of recesses, as shown in Figs. 6 and 7, the leakage control plates being provided with enlargements to the eiect that the cross sectional areas of the butt joints are increased and thus a reduced drop in voltage is obtained.

With five-legged three-phase transformers, the iron body may, alternatively, be composed of trimmed sheet metal strips, the leakage control plates provided with enlargements being inserted in recesses in the core and yoke plate elements, as shown in Fig. 10. The provision of leakage control members which are provided with increased cross sectional butt joint areas for reducing the short-circuiting currents and are inserted in recesses is applicable to all practical cases of constructing monophase shell type transformers and five-legged three-phase transformers of any ratings, it being, however, necessary to subdivide the windings and the leakage control members as the rating increases, in a manner similar to that shown in Fig. 1l for monophase current.

I do not limit myself to the particular size, shape, number or arrangement of parts as shown and described, all of which may be varied without going beyond the scope of my invention as shown, described and claimed.

What I claim is:

1. In a transformer having an intentionally increased magnetic leakage, a transformer iron body of the shell type consisting of a plurality of laminar elements each having yokes, outer legs, and an inner core arranged to form symmetrical legged portions lying on each side of a common medial plane whose trace passes transversely across said core and legs, said portions, when united, forming at least one recessed main core and two recessed yokes extending collaterally of said core and providing the terminal transformer leg members, windings surrounding said core on both sides of said plane, and leakage control members of laminations I-shaped in plan assembled to have an effective cross section smaller than that of said core extending through said plane between said windings, said control members having their end portions fitted into said recesses forming interiitting joints without intervening air gaps between said body and said leakage control members, thereby providing a magnetic circuit for the main flux of relatively low reluctance and independent shunt paths, with relatively low terminal reluctance by reason of the extended area of the gapless butt joints thus formed extending across the leakage field and the main eld of the transformer.

2. In a transformer having an intentionally increased magnetic leakage, a transformer iron body of the shell type consisting of a plurality of laminar elements each having yokes, outer legs, and an inner core arranged to form symmetrical legged portions lying on each side of a common medial plane whose trace passes transversely across said core and legs, said portions, when united, forming at least one recessed main core and two recessed yokes extending collaterally of said core and providing the terminal transformer leg members, windings surrounding said core on both sides of said plane, and leakage control members of laminations I-shaped in plan assembled to have an effective cross section smaller than that of said core extending through said plane between said windings, said control members having their endporuons fitted mm said recesses forming intertting joints extended in Z- shape without intervening air gaps between said leakage control members, on the one hand, and

said core and said yokes, on the other hand, thereby providing a magnetic circuit for the main ux of relatively low reluctance and independent shunt paths, with relatively low terminal reluctance by reason of the extended area of the gapless butt joints of increased cross section thus formed extending across the leakage field and the main field of the transformer.

3. In a transformer having an intentionally increased magnetic leakage, a transformer iron body of the shell type consisting of a plurality of laminar elements each having yokes, outer legs, and an inner core arranged to form symmetrical legged portions lying on each side of a common medial plane whose trace passes transversely across said core and legs, said portions,

when united, forming at least one recessed main. core and two recessed yokes extending collaterally of said core and providing the terminal transformer leg members, windings surrounding said core on rboth sides of said plane, and leakage control members of laminations I-shaped in plan assembled to have an eiective cross section smaller than that of said core extending through said plane between said windings, the material of said leakage control members having diierent magnetic properties from that of said core and said yokes for providing a certain magnitude of resistance for the individual control members, said control members having their end portions fitted into said recesses forming interfltting joints without intervening air gaps between said leakage control members, on the one hand, and said' core and said yokes, on the other hand, thereby ,providing a magnetic circuit for the main flux of relatively low reluctance and independent shunt paths, with relatively low terminal reluctance by reason of the extended area of the gapless butt joints thus formed extending across the leakage field and the main field of the transformer.

4. In a transformer having an intentionally increased magnetic leakage, a rectangular transformer iron body of the shell type consisting of a plurality of laminar elements each having yokes, outer legs, and an inner core arranged to form symmetrical legged portions lying on each side of a common medial plane whose trace passes transversely across said core and legs, said portions, when united, forming at least one recessed main core and two recessed yokes extending collaterally of said core and providing the terminal transformer leg members, a primary winding and a secondary winding forming a continuous coiled conductor, for economizing current, disposed on said core at the respective sides of said plane, and leakage control members of laminations I-shaped in plan assembled to have an effective cross section smaller than that of said core extending through said plane and subdividing said coiled conductor at a cer ain intermediate point thereof in two spaced coiA ed portions, said control members having their end portions fitted into said recesses forming interfltting joints without intervening air gaps between said leakage control members, on the one hand, and said core and said yokes, on the other hand, thereby providing a magnetic circuit for the main flux of relatively low reluctance and independent shunt paths, with relatively low terminal reluctance by reason of the extended areas of the gapless butt joints thus formed extending across the leakage field and the main eld of rthe transformer 5. In a transformer having an intentionally increased magnetic leakage, a rectangular transformer iron body of the shell type consisting of a plurality of laminar elements bach having yokes, outer legs, and an inner core arranged to form symmetrical legged portions lying on each side of .a common medial plane whose trace passes transversely across said core and legs, said rectangular lamination having a configuration such as to provide two symmetrical centrally jointed multi-legged body portions, said portions, when united, forming at least one recessed main core and two recessed yokes extending collaterally of said core, windings surrounding said core distributed on both vsides of said plane and connected to provide a multi-legged transformer, and leakage control members of laminations I- shaped in plan assembled to have an effective cross section smaller than that of said `cores extending through said plane between said windings, said control members having their end portions fltted into said recess forming intertting joints without intervening air gaps between said leakage control members and said iron body, thereby providing a magnetic circuit for the main flux of relatively lowreluctance and independent shunt paths, with relatively low terminal reluctance by reason of the extended areas of the gapless butt joints thus formed extending across the leakage field and the main iield of the transformer.

6. In a transformer having an intentionally increased magnetic leakage, a transformer iron body of the shell type consisting of a plurality of laminar elements each having yokes, outer legs, andan inner core arranged to form symmetrical legged portions lying on each side of a common medial plane Whose trace passes transversely across said core and legs, said portions being severed to provide a joint and notched so that, when united, they form at least one recessed main core and two recessed yokes .extending collaterally of said core and providing the terminal transformer leg members, windings surrounding said core distributed on both sides of said plane, and leakage control members of laminations of material diiferent from that of the core body I- shaped in plan assembled to have an effective cross section smaller than that of said core extending through said plane between said windings, said control members having their end portions iitted into said recesses forming interfitting joints without intervening air gaps between said leakage controlk members and said iron body, thereby providing a magnetic circuit for the main flux of relatively low reluctance and independent shunt paths, with relatively low terminal reluctance by reason of the extended areas of Y the gapless butt joints thus formed extending across the leakage field and the main field of the transformer.

7. In a transformer having an intentionally increased magnetic leakage, a transformer iron body of the shell type consisting of a plurality of plate elements each having yokes, outer legs, and an inner core arranged to form symmetrical legged portions lying on each side of a common medial` plane whose trace passes transversely across said core and legs, said portions having a coniiguration such that, when united, they form at least one recessed main core and two recessed legsextendng collaterally of said-core and providing the terminal transformer leg members joining with two transverse yoke members, windings surrounding said core distributed on both sides of said plane, and leakage control members of laminations each having a configuration with enlarged terminal portions and a reduced medial portion such that said members when assembled have an effective cross section smaller than that of said core and positioned to extend through said plane between said windings and having the terminal portions entering said recesses in tight engagement respectively with said core and legs thereby forming joints without air gaps, each of said plate elements composing said iron body including a lamination for the leakage control member being stamped out of a single piece of material providing integral core, leg and yoke members, said core and leg portions being severed by broken cuts.

8. In a transformer having an intentionally increased magnetic leakage, a transformer iron body of the shell type consisting of a plurality of laminar elements each having yokes, outer legs, and an inner core arranged to form sym- Ametrical legged portions lying on each side of a core distributed on both sides of said plane, andl transverse leakage control members of laminations each having a coniguration with enlarged terminal portions and a reduced medial portion such that said members when assembled have an eiTective cross section smaller than that of said core and when in place are positioned to extend between said core and said legs and fit into said recesses forming joints Without air gaps in which the magnetic reluctance in the region of a joint is less than that of a medial portion of said control members.

9. In a transformer having an intentionally increased magnetic leakage, a transformer iron body of the shell type consisting of a plurality of assembled laminar elements each having yokes, outer legs and an inner core and of a shape involving portions which are substantially symmetrical with respect to a plane whose trace passes transversely across said core and legs, said core and at least one opposite leg being provided with recesses, windings distrlbutedongsaid core on both sides of said plane, and at least one laminated magnetic leakage control member disposed between said core and recessed leg and provided with a mid-portion whose average cross-sectional Aarea is materially less than the average cross-

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