US2836802A - Fluid cooled transformers - Google Patents

Description

May 27, 1958 M. J. GELPI ETAL FLUID COOLED TRANSFORMERS Filed Aug. 23, 1956 4 Sheets-Sheet 1 n O 3mm Re... w NJ W E Vw mnm m H M- W WITNESSES May 27, 1958 M. J. GELPI ETAL 2,336,802

FLUID COOLED TRANSFORMERS Filed Aug. 23, 1956 4 Sheets-Sheet 2 Fig.2.

May 27, 1958 M. J. GELPI ETAL FLUID COOLED TRANSFORMERS 4 Sheets-Sheet 3 Filed Aug. 23, 1956 M. J. GELP! ETAL FLUID COOLED TRANSFORMERS May 27, 1958 4 Sheets-Sheet 4 Filed Aug. 23, 1956 Fig.5.

United States Patent Ofiice FLUID COGLED TRANSFORMERS Maurice J. Gelpi and Wiliiam D. Wilkinson, Catonsviilo, Md assignors to Westinghouse Eleeiric Qorporation, East Pittsburgh, Pa, a corporation of Penusyivania Application August 23, 1956, Serial No. 6 35,33?)

6 Claims. (Cl. MiG-62) This invention relates to electrical transformers and more particularly to high current, high etficiency transformers of the type used in induction heating apparatus and in which part or all of the windings are made of a heavy hollow conductor through which a cooling fluid may be circulated in order to dissipate the heat generated in the transformer.

in induction heating apparatus where the current in the load often has a magnitude in the order of 20,000 amperes the resistance losses in the load connection conductors make it necessary to locate the load supply transformer as closely as possible to the work station. It is, therefore, highly desirable that the transformer be as small and as light as economical design will allow. in reducing the size and weight of the transformer, the dissipation of heat generated therein becomes a primary problem.

In the art of induction heating, it is conventional to use high frequency electrical power. Most high frequency generators of the type used have a relatively high output impedance as compared to the input impedance of the work processing induction coils. It is, therefore, necessary in order to achieve efi'icient power transfer to the Work coil to provide a load matching transformer or step-down transformer connected between the high frequency generator and the work coil. Thus, it is necessary to provide transformers capable of handling extremely high currents in the order of 20,000 amperes and having the smallest possible weight, dimensions, and losses.

Because of weight and space considerations, the use of fluid immersed apparatus in the conventional manner is impractical and it has become common practice to provide water cooling of the transformer coils and interconnecting leads. In the use of water cooled leads which must handle extremely high currents, the provision of variable ratio taps either on the primary or secondary of the transformer is difficult. In the prior art, it has been conventional to use flexible leads which are selectively connected to spaced taps on the transformer windings. In the art of the present invention, it is desirable to provide large gauge connector members which may be selectively positioned in conductive relationship with one of a plurality of taps on the transformer winding and which may be so connected as to provide optimum heat conduction from the connector.

Accordingly, it is an object of this invention to provide an improved transformer for operation at very high current densities.

It is another object of this invention to provide a tran former for high frequency, high current operation such as, for example, for impedance matching between a high frequency generator and an induction heating load coil.

It is a further object of this invention to provide a fluid cooled transformer for high current operation of a rugged, reliable and efficient construction.

it is an additional object of this invention to provide Patented May 27, 19555 a transformer having optimum coupling between its re spective windings so as to substantially decrease leakage It is a different object of this invention to provide a transformer having interleaved primary and secondary windings and having means for circulating fluid through as many as possible of the current conducting elements so that the apparatus may be operated at exceptionally high current densities without overheating.

it is still another object of this invention to provide a transformer for operation at high current densities in which some winding sections are made of hollow conductor and are interconnected so as to be in electrical parallelism and simultaneously interconnected so that a cooling fluid may be circulated serially therethrough without the use of insulating fluid conduit means.

It is a still different object of this invention to provide a winding for a transformer in which a plurality of single induction turns are made from a hollow conductor and are in the form of a plurality of interrupted annuli connected together by hollow conductive bridge members so that all said single inductive turns are electrically in parallel while providing a serial cooling fluid pathway therethrough.

lt is a still additional object of this invention to provide a variable ratio transformer having hollow fluid cooled winding turns with a plurality of taps in longitudinal registration therealong and having a fluid cooled bus bar spaced from said winding turns such that a selectively positionable connector member to be connected selectively between one of said taps and said bus bar will be adequately cooled by conduction of heat from said connector member to the fluid cooled winding and the bus bar.

These and other objects of this invention will be apparent from the following description taken in accord ance with the accompanying drawings, in which like reference characters indicate like parts, which drawings form a part of this application and in which:

Figure l is a plan view of a fluid cooled variable ratio transformer in accordance with the present invention.

Fig. 2 is a front elevation of the transformer of Fig. 1 taken partially in section approximately on the line lI-ll of Fig. 1.

Fig. 3 is an end view of Fig. 1 showing in detail the connections of the secondary windings to the secondary terminal bus bars.

Fig. 4 is a plan view similar to Fig. 1, but showing a modification of the interconnection of the secondary winding turns.

Fig. 5 is a perspective view of one of the secondary coils with an interconnection bridge member connected thereto.

According to the present invention, there is provided a magnetic core 7 having a winding leg 8 with a primary winding 10 positioned about the winding leg in axial alignment therewith.

The core used in the present invention is preferably that of the wound core type which is made by winding a continuous ribbon or strip of magnetic sheet material on a substantially rectangular mandrel, annealing the strip after the winding and subsequently cutting the formed core loop transversely of its longer legs so that the core halves may be reassembled with a coil peripherally enclosing one of the longer legs. The wound core 7 is preferable in this invention as compared with conventional stacked lamination cores in that losses due to leakage flux are greatly reduced, cooling of the core is simplified, and the size and weight of the core and coil assembly are appreciably decreased.

The primary winding 10 mounted on the winding leg 2,see,so2

8 comprises a plurality of turns 12 axially spaced from each other in the form of an uninterrupted helix. This winding is normally made from a rectangular hollow copper tubing or other high conductive material. The tubing is preferably edge-wound so that the radial dimension of the conductor is substantially greater than its axial dimension. At each end of the primary winding helix, appropriate fluid conduit connectors 14 are soldered or brazed to the conductive tubing to provide means for circulating a cooling fluid serially through all the primary turns 12. Along one side of the primary winding it), a bus bar is provided for making electrical connection to a selected plurality of the primary turns 12.

Fig. 3 shows in detail the structure of these primary winding connections. The connector means for each turn consists of a flat rectangular block 6% having one concave edge 62 thereof soldered or brazed to the outer edge of a secondary turn 12.

Fig. 3 shows these connector blocks 66 on selected turns 12 near each end of the primary winding 1%. To the outer edge of the connector block 69 is securely fastened as by soldering a L-shaped bracket member 64 which includes a horizontal extending flange 66 having a threaded opening 68 therein. The above-described primary winding connector flanges are preferably aligned in longitudinal registration with each other at a peripheral location on the primary winding 19 spaced above the winding leg 8 of the core and spaced between the wind ing leg 8 and the other leg of the core 7. Above the core and adjacent the primary winding connector blocks 59 are positioned a pair of primary bus bars 16 spaced from the winding 12. The two primary bus bars 16 are aligned in end to end relation to each other with their adjacent ends 17 and 18 spaced a small distance apart. Each of the two primary bus bars 16 have a longitudinal opening 19 therethrough and have appropriate connectors 13 soldered or brazed to the bus bars 16 at each end of the longitudinal opening 19. The openings 13? at the adjacent ends of the bus bars are each connected to one of a pair of hollow conductive members to a source of cooling fluid. These hollow conductors 15 also serve as leads for connection to a source of primary energizing voltage as, for example, a high frequency generator (not shown). The hollow connectors 13 at the outer ends of the primary bus bars are joined to the fluid conduit connectors 14 at each end of the primary helix winding by means of appro priate insulating tubing 11.

Along the side of the primary bus bars 16, adjacent the transformer coil 10, are provided a plurality of threaded openings 70 which are positioned on the bus bars 16 so as to be transaxially adjacent the threaded openings 68 in the horizontally positioned flanges 66 of the primary connector blocks 60. As shown in Fig. l, a pair of flat strap members 72 of conductive material are provided for selectively connecting a flange 66 at each end of the primary winding to one of the bus bars 16. These strap mem bers 72 constitute conductive means for selectively completing electrical paths between the primary bus bars 16 and selected turns 12 of the primary winding 10. Clamping means, as for example, a bolt 74 of highly conductive material are provided for clamping or securing one end of the connector member 72 to the bus bar 16 and for securing the other end of the connector member 72 to one of the flanges 66 on the primary winding. Because of the relatively small length of the connector members 72, and because of the rigidly secured connection to the bus bars 16, all heat generated in the connector members 72 will be conducted therefrom, in both directions, to the fluid cooled bus bars 16 and to the fluid cooled turns 12 of the primary winding 10. It is to be noted that the connector members 72 and the bus bars 16 are positioned above the plane of the transformer core 7 and at one side of the transformer coil 12 so as to provide convenient access to the clamping means 74. The connector members '72 therefore be readily moved from one selected primary ing 64 to another primary lug 64 without in any way disturbing the assembly of the transformer and the bus bars.

The primary bus bars 16 may be supported relative to the transformer coils 12 in any convenient manner, but are preferably mounted on top of an elongated strip of insulating material which is fastened at each end to a transformer support frame (not shown). Such a transformer support frame may comprise a plurality of beams with one of said beams being positioned under each of the shorter legs of the core and with one positioned on top of each of the shorter legs, as is usual practice in the transformer art. The primary winding helix 10 has its respective turns 12 spaced apart axially with a distance between each consecutive pair of turns suflicient to allow a single turn secondary winding section, such as 22 or 29, to be inserted between successive primary turns 12. Thus, the transformer winding, as shown in Fig. 1, comprises a generally cylindrical structure made up of alternate primary and secondary turns. As shown in Fig. 5, each secondary turn 22 is formed of a rectangular hollow conductor, preferably of copper, which is edge-wound to form a substantially circular turn 22 having a helical pitch slightly greater than the thickness of the hollow conductor.

As shown in Fig. 5, each secondary turn has both its ends cut off at an angle of approximately 50. A plurality of U-shaped fluid conduit bridge members 80, formed of hollow conductive tubing similar to that of which the secondary turns 22 are formed, are provided for interconnecting the secondary turns 22 to 35 one to another. Each of the bridge members has ,a pair of legs 81 and 82 extending from the base of the U-shaped end and spaced apart a distance equivalent to the helical pitch of the secondary turns 22. Each leg or" the U-shaped bridge member 80 is cut off in a tapered manner at an angle of approximately 50 or at an angle corresponding to the angle at which the ends of the secondary turns 22 are tapered. Each of the secondary winding sections 22 has one of the bridge members 80 attached to each of its ends as by brazing or soldering so as to provide a fluid tight joint between the secondary turn 22 and the bridge member 849.

As best seen in Fig. 2, the U-shapecl bridge members 86 extend in opposite directions from each turn and are similarly joined to the corresponding ends of the next adjacent secondary turns. That is to say the first or upper end of a first turn 21 is connected to the first or upper end of the next adjacent turn 22 to the right of said first turn 21. The second or lower end of the second turn 22 is connected by one of the U-shaped bridge members 80 to the second or lower end of the next adjacent secondary turn 23 to the right of said second turn 22. The U-shaped bridge members 80 are connected to the secondary turns with the longitudinal axis of the bridge member 89 extending from the secondary turns substantially parallel to a diameter of the coil taken between the upper and lower bridge members. The bridge members 80 are connected to the cut-off ends of the secondary turns 22 so that an insulating space is provided between the upper and lower bridge members.

As best seen in Fig. 1, all of the bridge members 80 extend outwardly from the coil assembly at the side thereof opposite from the two legs of the magnetic core 7. All of the secondary winding sections 21 to 35 are circumferentially oriented with respect to the core 7 and primary winding 10 so that all of the first or upper ends of the secondary turns 21 to 35 are aligned in longitudinal registration with each other at a first peripheral location parallel to the axis of the winding leg 8 of the core 7. All of the second or lower bridge members 80 are similarly aligned in longitudinal registration with each other at a second peripheral location adjacent to and below that of the first bridge members 80. Thus, the extremities of the U-shaped portion of the bridge members 80 all lie substantially in a single plane outside the peassasoe riphery of the coil structure and on the opposite side of the coil structure from the second core leg.

A pair of parallel spaced bus bars 84 and 86 of highly conductive material, are positioned in conductive relation against each set of the U-shaped bridge members 80. One of the bus bars 86 is positioned adjacent the lower set of bridge members and is conductively connected thereto as by brazing. The other bus bar 84 is positioned longitudinally adjacent all of the first set of bridge members 80 in edge to edge alignment with the first bus bar 86 with a slight space for insulation purposes therebctween and is securely and conductively connected to all of said first bridge members 80 as by brazing.

As best shown in Fig. 3, the first and second bus bars are L-shaped in cross section so that each has a flange 85 of appreciable thickness extending horizontally away from the transformer coil. A layer 87 of insulating material such as mica sheet is provided between the two flanges 85 to insulate them from each other. The respective flange 85 of the first and second bus bars 84 and 86 are each provided with a longitudinal opening 88 therethrough from one end to the other for circulation of a cooling fluid therethrough to dissipate the heat generated in the bus bars 84 and 86. Appropriate hose connections (not shown) may be provided at each end of each of the secondary bus bars for connection to a source of cooling fluid. Thus, it is seen that the secondary turns 21 to 35 of the transformer coil, by connection of fluid conduit bridge members 80 therebetween, are all provided with means for circulating a cooling fluid so that no current carrying member of the secondary circuit is without provision for dissipating heat generated therein.

Along the outer edge of the first and second bus bars 84 and 8a? is a plurality of threaded openings 89 for connection of high current circuits such as fluid cooled induction heating coil. It is to be noted, as best shown in Figs. 1 and 3 that all of the first ends of the secondary coils 21 to 35 are electrically joined together by the upper or first secondary bus bar 84. Likewise, all of the second or lower ends of the secondary coil sections 21 to 29 are joined electrically together and are rigidly attached to each other by the second or lower secondary bus bar 86. A circuit is thus provided in which all of the secondary winding sections 21 to 29 are connected to supply current to a single load with the secondary turns being in a parallel connected network so as to have a minimum resistance and a maximum current carrying capacity.

As best seen in Fig. 1, the first turn 21 at the left end of the secondary winding is not provided with a U- shaped bridge member 8% as are the other turns 22 to 29, but is connected to the upper or first bus bar 84 by a short solid tap 2%? which is brazed to the outer edge of the secondary turn 21 and is brazed at its other end to the first bus bar 34 to thereby provide a highly con ductive connection between the first turn 21 and the first bus bar 84. The hollow conductive tube of which the first turn 21 is formed then extends a fractional part of a turn to a position between and below the legs of the core 7 where it is provided with an appropriate connector 90 for supplying a cooling fluid thereto. The ultimate turn 31 at the right end of a secondary coil is extended a fractional part of a turn from the final bridge member 80 to a similar position between the core legs where it is provided with an appropriate connection 93 to a source of cooling fluid. Thus, as seen in Fig. 2, a cooling fluid may be caused to flow into and through the fractional turn 31 at the right end of the secondary winding to a first one 89a of the lower bridge members 80 and therethrough to the lower end of a second turn 32. The fluid then flows counterclockwise as seen from the right end of Fig. 2, to the upper or first end of the second secondary turn 32 and through a first one of the upper bridge members 891; to the first or upper end of a third secondary turn 33 and thence clockwise t0 the second end of the third turn 33 and similar through all of the intercom nected secondary winding sections 21 to 35 in peripherally reversed directions through each successive turn. Since' the cooling fluid flows in successively reversed directions through the successive turns, any voltage induced in the fluid stream by a selected turn will be counteracted by the next adjacent turn so that the total additive voltage induced in the fluid stream between the cooling fluid supply connectors 91 and 99 at each end of the secondary winding is zero volts. Therefore, the secondary winding may be connected to a conventional cooling fluid supply without the use of insulating conduit or hoses.

Fig. 4 shows a modification of the present invention similar to the structure shown in Fig. 1 except that as shown in Fig. 4, each secondary winding section, such as 43, comprises a plurality of edge-wound turns having a helical pitch substantially equal to the pitch of the primary winding helix 10 and with each of said turns 41 to 49 being positioned between adjacent spaced turns 12 of the primary. It is necessary that the U-shaped bridge members 92 used with this modification have a dimension between the legs substantially greater than that of the U-shaped bridge members shown in Fig. 1.

As shown in Fig. 4, the upper end of a first coil section 41 and the upper end of a second next adjacent secondary coil section 42 have two primary turns 12 and one secondary turn 42 spaced therebetween. Each upper or first bridge member 92 spans from a first turn 41 to the fifth successively adjacent turn 42 and each lower or second bridge member 92 likewise spans from the lower end of section 42 to the lower end of the next adjacent section 43. In the embodiment of Fig. 4, each coil sec tion which is connected between the first or upper bus bar 84 and the second or lower bus bar 86 comprises two turns, so that the secondary circuit is a network comprising a plurality of two-turn winding sections 41 to 50, all connected in parallel between the first and second secondary bus bars 84 and 86. The embodiment of Fig. 4 will therefore have a turns ratio equal to one-half that of the embodiment shown in Fig. 1. For example, if the primary helix winding 10 has sixteen turns, the turns ratio of the embodiment of Fig. 1 would be sixteen to one, while the turns ratio of the embodiment of Fig. 4 would be eight to one.

While the invention has been shown in one form only it is to be understood that the same principle may be applied to transformers of various types and sizes, and that the invention is susceptible of various changes and modifications without departing from the spirit and scope thereof. For example, the secondary winding sections as shown in Fig. 4 need not be confined to any particular number of turns per section, but each section may comprise any number of turns. Also, in order to further increase or decrease the turns ratio of the transformer, a plurality of adjacent secondary turns 27, 28 and 29 in the secondaly portion of the winding may be omitted and replaced by primary turns thereby increasing the ratio of the transformer. Alternatively, a few of the primary turns 12 might be omitted and replaced by secondary turns with an elongated bridge member similar in structure to that shown in Fig. 4 being used to jump the primary winding across the space in which the primary turns are omitted.

We claim as our invention:

1. In an electric transformer a winding having a longitudinal axis, said winding comprising a continuous hollow conductor member forming a plurality of turns, each of said turns having a first end and a second end with all said first ends being aligned in a first peripheral location and being electrically connected together and with all said second ends being aligned with each other in a, second peripheral location and being electrically connected together, with portions of said hollow conductor member extending from the first end of a first turn to the first end Of a second turn and from the second end of said second turn to the second end of a third turn, in such a way that a cooling fluid may be caused to flow serially thro gh said first second and third turns in cir'cumferentially reversed directions through each serially successive turn.

2. In a fluid cooled transformer a primary winding in the form of a helix with axially spaced turns, a plurality of single turn secondary windings formed of a hollow conductor and positioned between the primary turns with each secondary turn having a first and a second end with thefirst ends of a plurality of said secondary turns positioned adjacent the second ends of the respectively next axially adjacent secondary turns, a plurality of hollow conductive bridge members connected respectively to the ends of a plurality of said. secondary turns, with a first one of said members being connected between the first end of a first secondary turn and the first end second turn, a second of said members being connected between the second end of said second turn and the second end of a third secondary turn, and with a third one of said members being connected between the first end of said third turn and the first end of a fourth one of said secondary turns, and means for circulatingra cooling medium serially through the hollows of said secondary turns and the hollows of said conductive bridge members, with said bridge members being adapted to direct said coolant through serially successive turns insuccessively reversed circumferential directions.

3. In a fluid cooled transformer the combination with a core having a winding leg of a plurality of winding sections positioned about said leg and having axially spacedturns formed of a hollow conductor, each of said winding sections having a first end and a second end with a plurality of said first ends being aligned with each other at a first peripheral location relative to said core leg and with a plurality of said second ends being aligned at a second peripheral location, a plurality of fiuid conduit bridge members formed of a hollow conductor, with a first set of said bridge members being connected individually between selected pairs of said first ends and aligned in longitudinal registration with each other ada cent said first peripheral location and with a second set of said bridge members being aligned with each other at a position radially adjacent said second peripheral location, and individually connected between selected pairs of said second ends, and a pair of parallelrspaced bus bars positioned adjacent one side of said winding sections with one of said bus bars being rigidly and conductiveiy connected to said first set of bridge members and with the other of said bus bars being connected to said second set of bridge members.

4. In a fluid cooled transformer the combination with a core of a primary winding having axially spaced turns in the form of an uninterrupted helix and positioned about one leg of said core, a plurality of secondary winding sections having axially spacedturns in the form of a helix and formed of a hollow conductor, each of said sections being interleaved between the spaced turns of a portion of said primary winding in substantially coaxial relation thereto, each of, said sections having a first end and a second end with said first ends being aligned in longitudinal registration with each other and with said second ends being aligned in longitudinal registration with each other at a difierent peripheral location from that of said first ends, and a plurality of hollow conductive bridge members with a first of said members being connected between a pair of said first ends to conduct a cooling fluid therebetween and with a'second one of said members being connected between a pair of said second ends, a first bus bar connected to said first member and bus bar connected to said second member so bus bars comprise terminals of an electrical network including a. plurality; of said secondary winding said one leg of said corebetween the primary turns. in.

interleaved relation thereto, all said first ends being. aligned in longitudinal registration with each other between said primary winding and said first bus, and all said secondends being aligned in longitudinal registration with each other between said primary winding and said second bus, a first plurality of fluid conduit bridge members. formed of a hollow conductor connected between selectedpairs. of said first ends to conduct a cooling fluid therebetween, and a second plurality of hollow conduit bridge members connected between selected pairs of said secured ends, with said first bridge members being electrically connected to said first bus and with said second bridge mernbers being electrically connected to said second bus.

6. in an electric transformer for use With induction heating apparatus and having a core including a Winding leg, a plurality of winding sections formed of a continuous hollow conductor with said sections being axially aligned along said winding leg and each having a first end and a second end, all said first ends being longitudinally aligned in a first peripheral location and electri cally con ected together, all said second ends being longitudinally aligned with each other at a second peripheral location and electrically connected together with a first and a second portion of said hollow conductor extending espectively in fluid impervious connection from the first end of a first winding section to the first end of a second section and from the second end of said second section to the second end of a third section so that a coolant fluid may be circulated serially through a plurality of said sections with the peripheral direction of flow in each section being opposite to that in the preceding section.

References Cited in the file of this patent UNITED STATES PATENTS 2,655,636 Pliske Oct. 13, 1953

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