US2556602A - Electrical coil structure for transformers - Google Patents

Description

C. A. SCHWA RTZ ELECTRICAL COIL STRUCTURE FOR TRANSFORMERS June 12,' 1951 2 Sheets-Sheet 1 Filed April 10, 1948 4 INVENTOR.23 CHARLES A.SCHWARTZ R AT T ORNFY l l I l I l l I l I I I l l l I 4 I I I l l l I Tli Z T x R 2 w 4 MM W w m H m h T 5 V 5, m A 2 m 6 A h s S 2 a m F m Hw -v-w 4 C. A. SCHWARTZ ELECTRICAL COIL STRUCTURE FOR TRANSFORMERS Patented June 12, 1951 UNITED STATES PATENT OFFICE ELECTRICAL COIL STRUCTURE FOR TRANSFORMERS Charles A. Schwartz, Elyria, Ohio Application April 10, 1948, Serial No. 20,283

8 Claims. 1

This invention relates to the coil structure of electrical power devices and apparatus and more particularly to the arrangement and structure of the coils in electrical transformer units.

In any device or apparatus containing electric ity conducting media, the passage of the electrical current therethrough,-in some degree, results in heat energy which is dissipated. In power applications, where the electrical energies involved are substantial, the generation of heat which is inherent in electrical devices, greatly influences the design and size of the devices and the rapid dissipation of the heat becomes an important factor in preventing the attainment of critically high temperatures which would impair or destroy these devices.

In apparatus such as alternators and induction coils, but more particularly in heavy duty transformers, forced cooling of the apparatus must be employed, and the size of the electrical conductors employed in such appartus is to a large ex tent determined by the efiiciency of the cooling system is dissipating the heat which is evolved.

For example, it is common practice in the construction of transformers for welding machines to employ water cooling coils for the secondary coil of the transformer. The heat which is generated by the primary coil must pass through the electrical insulation on the individual conductors and then must pass through the electrical insulating barrier between the primary and secondary coils before it is able to be absorbed by the cooling medium. As the electrical insulators are inherently also good thermal insulators, the heat generated by the primary coil is dissipated much less rapidly than that of the secondary coil and the primary will attain much higher temperatures than the secondary coil.

It is a primary object of my invention to provide a coil structure which encourages the rapid passage of heat from the electrical coils to the cooling medium.

' Another object of my invention is to provide a transformer construction in which the primary coil is formed in a matrix of either thermally or thermally and electrically conductive material.

Still another object of my invention is to provide a transformer construction in which the coils form a substantially rigid unitary mass whereby vibration of the conductors is inhibited.

A further object of my invention is to provide a transformer structure which will permit a reduction in the physical size of a transformer as compared to the size of transformers ciu'rently used for equivalent output rating.

A still further object of my invention is to provide an electrical coil construction which due to its efficiency in heat dissipation permits the use of smaller conductors than presently used at stated amperage ratings.

Other objects and advantages of my invention will become apparent during the course of the following description.

Although, for purposes of illustrating an embodiment of my invention, I refer generally throughout the description to welding transformers, I wish to emphasize that my invention is applicable to and equally effective in a broad class of coil wound electrical appartus, including but not limited to alternators, electro-magnets, induction heating coils and rotary transformers.

In the accompanying drawings, forming a part of this specification and in which like numerals designate like parts throughout the same.

Fig. 1 is a longitudinal cross-sectional view taken on line ll of Fig. 2, of a transformer embodying my invention, portions thereof being broken away to show certain details of the in vention.

Fig. 2 is a cross-sectional View, taken on line 22 of Fig. 1.

Fig. 3 is a fragmentary cross-sectional view, taken on line 33 of Fig. 1.

Fig. 4 is a fragmentary cross-sectional view, taken on line 44 of Fig. 1, showing the insulating barrier across the secondary coil of my transformer.

Fig. 5 is a plan view of a modified form of my invention, portions thereof being broken away to show certain details.

Fig. 6 is a cross-sectional view, taken on line of Fig. 5, showing the modified coil structure.

7 is a view in elevation showing the applicat on of my transformer to a welding machine.

Referring more particularly to Figs. 1 to 4 of the drawings, the numeral I designates generally a welding machine transformer which embodies the features of my invention. In the form shown, the transformer comprises a shell 2 formed of electrically conductive material such as copper, a primary coil 3, a secondary coil 4 and a laminated iron core 5.

The primary coil 3, which in this instance is the high voltage winding, is formed of conductor wire 6 which is coated with a high temperature insulating material 1 such as woven glass fiber impregnated with silicone varnish or, preferably, a material of the ceramic type. The primary coil 3 is formed by winding the individual turns of 3 the conductor wire 6 on a specially formed bobbin, so as to form a space-wound coil, relatively large and uniform spaces being left between the respective turns and layers of the coil.

The space-wound primary coil 3 is adapted to be placed and contained within the shell 2. The shell is generally rectangular in shape, and has a channel-like cross-section consisting of a bottom 8, an exterior wall 9 and an interior wall it). For convenience, the four interior walls are designated as Illa, Nib, We and Hid, and the exterior walls are designated as 9a. 9b, and 90. No exterior wall is provided along the side of the shell opposite the interior wall id, as to this portion of the shell are firmly aflixed, as by brazing, solid copper blocks 4 i and [2, which as will hereinaftermore fully appear, serve as the electrical terminals of the secondary coil 4.

It will be noted that the blocks II and I2 are separated from each other by a narrow gap I3, which is' fi'lleol with insulating material 1, and that the'electrical continuity of theshell 2 is likewise interrupted by atransverse gap [4 in the .interior wall Hid and the bottom 8'of the shell, the gap l4 being in effect acontinuation of the gap [3.

Theb'loclrs I land 52 are provided with recesses I5 and lirespectively, these recesses serving to accommodate portions of a copper tube l'l'which is formedto' serve as a cooling 'coil l8 when liquid coolant, such as water, is passed therethrough. The: wall 95 of the shell'2 is provided with an opening Hithrough which theinlet end 20 andthe'outlet'end 2i ofthe cooling coil 18 may pro ject.

The primary coil 3 and the cooling coil l8 are of such-size .andform that the primary coil. 3 can be placed betweenthe upper and lower turns of theicooling coil, the copper tubing l1 thereby lying in close proximity to the end turns'of the primary coil. The primary coil 3 and cooling coil l8,lassembled as aforesaid, are placed within the shelli2, the ends .22 of the 00113 being disposed inproxirnity to circularopenings 24 provided in the exterior wall 9a of the shell.

It is well to state at this point, that the spacers (not shown) which were originally utilized in winding. the coil'3? may all be removed with the exception of one which is: designated by the numeral 25; Dabs of ceramic slurry or the like at spaced points within the coil will, when set, serve to'maintain the turns in spaced relationship after the spacers are removed. The spacer 25' is so disposedas tobe in registry with the gap [4 in the shell-2: when the assembly of the coil 3 and cooling coil [8 are placed withinthe shell 2' as aforesaid. The spacer 25 is completely covered with the' insulating medium 7 so as to form an insulating barrier 26 which extends completely across the. portion ofithe shell 2 which is defined hyithegap l4. The layers of conductorwire 6, of: course, extend through the barrier 26 due to themanner inwhich. the primary coil 3 wasoriginally formed;

Iwill now describe my method of forming the secondary coil, which inthis instance is the low voltage coil. The secondary coil 4 may be formed in general of any low-melting metallic alloy such as those of lead, silver ortin of the group commonly. referred to. as solders. Those alloys which have relatively better characteristics of electrical conductivity being, of course, preferred. I havexfound thatI am able to improve theelectri'cal and. thermal conductivity of some of these solders by mixing therewith granular or powderedcopper: particles.

The secondary 4 is formed by pouring the molten metal into the shell 2, completely filling the shell and the spaces between the turns of the coil 3. A copper cover plate 23, which con.- forms to the shape of the shell 2, is placed over the shell to further increase the strength and conductivity of the secondary 4. The molten metal bonds the copper cover plate to the shell 2 and to the secondary coil 4. When the metal has cooled and solidified, it forms a solid matrix for the primary coil 3, completely enveloping the turns of the coil 3 and firmly supporting the conductorwire B and-the copper cooling coil l8.

Although I have found the casting method of forming the secondary coil 4 to be the most practicable, it is also possible to utilize other methods for forming. the matrix, such as, for example, metal spraying, electroplating, and sintering (powdered metals) Prior to the casting of the secondary coil 4, I secure-theaends. 22 0i the-primary coil 3 to ter minal posts; 2.1 which are securedto the wall 9a of: the ,shellby means of the insulator bushings 28 andlretainers1r29, the postsZl, of course, being insulated fromthe shell 2 andthesecondary; coil'4.

Power line cables (not shown) are connected tothe terminal posts 21 and it .willbe apparent that the? primary circuit of the transformer is thus established: through the coil 3.

It will .also be'apparent that the solid matrix,.

the-continuity of. whichis broken by the barrier 2e; forms: the secondary circuit orcoil 4 consisting of asingieturn, the terminals-bf which are theblocks l i andlZ; Intheillustrated form, I have shown weldingelectrodes 39 afiixed to adapters 3! in the blocks II and I2.

The transformer construction above described hasconsiderable advantageover the transformer structure whichgiscurrentlyemployed in the art.

'- The intimate relationship of the primary and secondary coils:v results ingreater efficiency; of transformer operation due tovery low leakage reactance; Heat: generated in the primary'coil 3- passes rapidly through the thin insulating coating. 1 and: is conducted through the solid matrix tortheycooling coil l8 which is imbedded therein. I havefound that heat dissipation can be'eirected sorapidly in a transformer embodying my invention, thatI can readily employ conductor wire. 6 having a cross-sectional area equivalentto 25 circular mils per ampere and still maintain thepperating temperature or" the transformer well below the point where it would become, injurious to the transformer. By cos;- parison; it is'tobe noted that-it is conventional practice in transformer; construction to employ conductors having areasin the range-oi 300 to 1000 circular mils per ampere;

The fact that" I, am thusable" to efliciently utilize from one-fortieth to one-twelfth themass of conductor wireemployed for theprimary coil in transformers of conventional construction, in turn, results in a substantial reduction in the overall size of'a transformer embodying my invention as compared to one of conventional design. The decreased size of my transformer, apart from its obvious economical advantage, permits its use directly on a resistance welding machine, the electrodes 30 being mechanically secured directly to the terminal blocks II and I2 ofthe transformer. This integration of the transformer with the welding machine, has heretofore, due to space limitations, been possible only in.very special applications. It will be obvious that, if, for. example, a series of spot welds two inches apart is desired, the pairs of welding electrodes can be integrated with the transformer terminals only when the physical space occupied by the transformers will permit them to be aligned side by side on four inch centers. Welding transformers, as presently constructed, are'required to be so large as generally to prohibit the integration of the transformers with the welding machine. Therefore, it is in most cases necessary to place the transformer at some distance from the Welding machine, and to electrically connect the welding electrodes to the low voltage terminals of the transformer by means of conductor cables.

The connector cables themselves use large quantities of copper and add to the cost of welding installations. However, this initial expense is greatly overshadowed by still another factor of cost. This second factor is the cost of the excess electrical energy which must be purchased to overcome the energy losses which occur as the weld current flows through the cable connectors. To handle this additional flow of elec tricity, the transformer, in .turn, has to have a higher rating, and is, therefore, larger than is actually necessary to supply the desired weld. current through the electrode tips.

The reduced size of a transformer embodying my invention, permits, in most applications, the mounting of the transformer directly on the welding machine, integrally with the welding electrodes, and is of great importance in that it eliminates the use of cable connectors between the welding electrodes and the terminals of the secondary coil. The energy losses, which occur when the weld current flows through the cable connectors are likewise eliminated and the transformer terminal voltage may thereby be reduced to less than one-half of that which is required when cable connectors are necessary. Thus a transformer of lower output rating can be em ployed to produce welding currents which are in all respects equivalent to those obtained with the use of a cable connected transformer 01' higher load rating and larger size.

The lower output voltage required not only reduces the overall cost of the electrical power supply charges. but also permits the physical size of the transformer to be decreased still more.

Referring now to Figs. 5 and 6 of the drawings,

The modified form represents two major denartures from the structure shown in Figs. 1 to 4. Firstly, the secondary coil and terminal blocks are a unitary casting formed of relatively high-melting alloys having good characteristics of mechanical strength. Secondly, the spacing between the layers and turns of the primary coil is modified so as to dispose a series of insulating barriers across the layers of the coil, as will more fully hereinafter appear.

Ordinarily, in welding applications, the energy losses in the transformerthe so-called iron and copper losses-are but such a small percentage of the total losses which occur in the weldin circuit, that they merit little attention. Therefore. the structure shown in Figs. 1 to 4 would not be objectionable for most welding applications, even though the eddy current loss in the primary coil would be fairly high. However, in certain special welding applications and in many other transformer applications, such high eddy current loss may be objectionable and unde- H sirable.

In order to reduce this eddy current loss, I fabricate the primary coil 3 in the manner shown in Fig. 6. The coil is wound on a specially formed bobbin, as aforementioned, however the spaces 8 between the layers of the winding are made greater'than the spaces t between the turns of the coil. A large medial space m is also provided between the turns of the coil 3', for a purpose to be hereinafter described.

After the primary coil 3' has been wound, it is dipped in a semi-viscous slurry of ceramic insulation 1. Due to the cohesiveness of the slurry and the small space t between the turns of the conductor wire 6. the insulation forms a series of insulating barriers 32 which extend across each layer of the coil 3. The conductor wires 6 will therefore not be completely surrounded by the metallic matrix, as they were in the embodiment shown in Fig. 2. The insulating barriers serve to limit and restrict the eddy current paths and therefore serve to reduce the eddy current loss which, as previously stated, may in some cases be objectionable.

The ends 22 of the primary coil are secured to the terminal posts 22', which, in turn, are par tially enveloped in ceramic insulation 1, so as to insulate the posts from the secondary coil. An insulating barrier 26 is also provided on the coil 3'. as in the previously described embodiment.

The primary coil assembly is placed in a mold which is provided with suitable cores, and the secondary coil 4 is formed by pouring molten metal such as copper or aluminum alloys into the mold. Due to the high thermal and electrical conductivity of the metal used, and its relatively good characteristics of mechanical strength, it is unnecessary to utilize the copper shell 2 in this modified structure.

Through the use of cores, a circuitous conduit or channel 33 is formed in the cast metal in the space m and serves as a coolant path having its inlet as at 34 and its outlet as at 35. The terminal blocks II and I2 are formed integrally with the secondary coil 4' and may be sawed or otherwise machined or cast so as to form the gap l3 which is filled with insulation 1.

The blocks H and I2, as well as blocks I l and 12 shown in Fig. 1, may be strengthened by tiebolts 36 which are insulated from the blocks by insulating sleeves 31 and washers 38. The bolts 35 extend through openings 39 formed in the blocks and are secured by nuts 40.

The terminal posts 21 are supported by the solid secondary coil 4', thus eliminating the re-. quirement for the bushings 28 and 29, previously referred to. The transformer structure is completed by mounting thereon the laminated iron which my transformer structure could be uti-' lized for a spot welding application. The electrodes 30 are mounted directly on the terminal. blocks II and [2 of the secondary coil 4 of the transformer. The transformer, in turn, is resiliently secured as by insulated bracket 4! to a piston 42 of a pneumatic cylinder assembly 43. An insulated flexible joint 44 is interposed be tween the ends of the piston 42 and the blocks! I and 12. which, in combination with the resilient bracket mounting 4|, permits equalization of the pressure brought to bear on the blocks by the piston, thereby permitting proper registry of the electrodes with the work to bewelded. I

It is to be notedlthat the integration of the electrodes 30 with the transformer is made possible by the small physical size of a transformer constructed in accordance with this disclosure, and that I thereby eliminate the cable connectors 'and'obtain the several advantages heretofore enumerated.

It is to be understood that various features, of each of'theembodiments which I have shown are to a great.- extent applicable to both the transformers I and I. For example, the primary coil 3 maybe embodiedintransformer i and the primary. coil 3' may be embodied in the transformer I; or, the copper cooling coil is may be embodied'in .thetransformer I instead of formingthe cored out channel 33.

It is also to be understood that, in accordance with the common practicein the art, both the primary andsecondary coils, or either of them, may be tapped or supplied with leads at a p1urality of positions in order. to permit selective variation in the electrical. performance of the transformer. Additional variations may also be utilized, for examplathe coolant coil It may be secured exteriorly of the coil structure under circumstances where it may be expedientand further, the cooling circuit through the secondary coil can be connectedto and made continuous with acooling circuit through the welding electrodes, such. as. is commonly employed in the art;

The improvedstructure which I have disclosed, and which for purposes of illustration I have shown as a transformer, may with equal advantage beemployed in other types of coil-wound electrical apparatus, to which I have previously referred. Forexample, any large electro-magnet, such as used in av cyclotron, can effectively employ, my improved coil structure to obtain more efficient cooling of the coils. equally, applicable to the coils of large. alternators particularly to the armature windings, in which case the matrix serves only as a heat conductor and does not have to have good characteristics of. electrical conductivity. By short circuiting the secondary coil, the highly efficient cooling structure mayv also be utilized in induction heating coils to permit the heating of. large items at powerfrequencies. Numerous other applications of, my improved coil structure. willbe. apparent to those skilled in the art, without necessity for their detailed enumeration herein.

In addition to the advantages of my improved structure, which I have previously enumerated, I wish to point outthat the rigidity of thecoil structure is such that substantially all of the audible vibration. customarily associated with transformer operationis. eliminated and the coil structure is itself more rugged and less susceptible to injury.

- Itis to be. understood ,thatthe .forms of myinvention, herein shown anddescribed, represent specific examples of the same and that various changes in the shape, sizeand arrangement of parts may be resorted to, without departing from the spirit of my invention or the scope of the subjoined claims.

Having thus described my invention, I claim: 1. An electrical coil structure for transformers and the like, saidstructure comprising a primary coil of insulated conductor wire consisting of a plurality of" layers of turns with the layers in spaced'rel'ation to each other, and a solid metallic matrix of good'electrical conductivity in which said primary, coil is embedded, the electrical con The structure is tinuity of said. matrix being interrupted trans.-

versely of said primary coil-to formtheterminals of a single turn secondary coil of'the structure. the layers of said primary coil being separated. from each other by said matrix and eachlayer being enveloped thereby, whereby to quickly'dise sipate the heat generated in said-primary coil.'.

2. An electrical coil structure fortransformers. and the like, said structure comprising aprimarycoil ofinsulated conductor wire'consisting of .a

plurality of layers of turns, with thefllayersin spaced'relation to each other, and a solid metallic matrix of'good electrical conductivity in which said primary coil is embedded, said matrixbeing interrupted transversely of said primary. coil to form theterminals of a single turn secondary coil of the structure, the. layers of said'primarycoil being separated from each: other by said matrix, with the matrix surrounding a substantially large portion of eachturn. of the primarycoil, whereby heatgenerated. in said. turns is. readily dissipated'insaid matrix, andaconduit extending through. said matrix for passage-of. acoolin medium for removing heat from the;

matrix.

3. An electrical coil. structure as defined. in.

claim 2 wherein each turn of: saidprimary coil is completely enveloped'hy said matrix.

d; An electrical coil structure as defined in claim 2 in which barriers of insulating materialare provided between adjacent turns .in eachof.

said layers, whereby to restrict the eddyv current paths in said solid matrix.

5'. An electrical coil structure,. as-defined in claim Z'including an iron core disposed about said coil structure.

6.- An electrical coil structure, as defined in claim 2, in which the secondary coil is of generally LJ-shaped form, theiarms andbight portion of.

said secondary coilencompassing three. sidesof said primary coil, the terminals of said secondary coil being disposed in proximity to the. fourth side of said primary coil, and solid-metallic blocks.

are'secured to the terminals of said secondary coil.

7. An electrical coil-structure for transformers the like, said structure comprising a, space wound primary coil of insulated'conductor wire consisting of a multiplicity of layers. of turns,.

with the layers in spaced relation to each other, a single turn secondary coil of generallyU -shaped form consisting of a solid metallic matrix of good electrical conductivity which envelopes said layers and fills the spaces between said layers and lies in intimate heat conducting relationship to. the turns of said primary coil, the arms and bight portion of said secondary coil encompassing three sides of said primary coil, said secondary coil having terminals arranged adjacent each other'at the fourth side of 'saidprimary coil, and a cooling conduit extending through said matrix for pas"- sage of 'a heat removing medium.

8. An electrical coil structure, as defined in claim 7, in which said matrix also fills the spaces between the turns of wire in each layer of said primary coil.

CHARLES A. SCHWARTZ.

(References on following page) REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Lightfoot Feb. 15, 1927 Number Number Name Date Eckman Feb. 3, 1931 Robinson Mar. 19, 1935 Guthrie July 18, 1939 Camilli Aug. 1, 1939 FOREIGN PATENTS Country Date Germany Sept. 8, 1928 Australia Apr. 17, 1942

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