US3416110A - Fluid cooled transformer having casing supported coils and core - Google Patents

Description

Dec. 10, 1968 R. D. MORRIS ETAL FLUID COOLE 3,416,110 D TRANSFORMER HAVING CASING SUPPORTED COILS AND CORE Filed April 14. 1967 4 Sheets-Sheet 1 Q 9 3 NQ ow INVENTORS WITNESSES MM 0 s H i 0 am 0 MH T 0w %A no l M W MORRIS ETAL 3,416,110 RANSFORMER HAVING CASING SUPPORTED COILS AND CORE R. D. FLUID COOLED T Dec. 10, v1968 4 Sheets-Sheet 2 Filed April 14. 1967 Dec. 10, 1968 R MQRRIS ETAL 3,416,110

FLUID COOLED TRANSFORMER HAVING CASING SUPPORTED COILS AND CORE 4 Sheets-Sheet 3 Filed April 14. 1967 FIG.4.

FIG.5.

10, 1968 R D. MORRIS ETAL 3,416,110

FLUID COOLED TRANSFORMER HAVING CASING SUPPORTED COILS AND CORE Filed April 14, 1967 I 4 Sheets-Sheet 4 FIG.8.

United States Patent 3,416,110 FLUID COOLED TRANSFORMER HAVING CASING SUPPORTED COILS AND CORE Robert D. Morris and Robert H. Hollister, Sharon, Pa,

assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 14, 1967, Ser. No. 630,877 12 Claims. (Cl. 336-57) ABSTRAfIT OF THE DISCLOSURE An electrical transformer having a form-fit casing and a magnetic core-winding assembly disposed therein. The sidewall portions of the casing support and maintain the integrity of the magnetic core, and the top and bottom portions of the casing support the electrical winding assembly and restrain it against movement during short circuit stresses. The casing is completely filled with a fluid dielectric, which is force circulated through the winding assembly and external heat exchanger means.

Electrical transformers associated with electrically driven transit vehicles, such as trains and other tracktype transit systems, are usually mounted under the body of the driving car or cars. Thus, severe size and weight limitations are placed on the transformer. With the increased interest in high speed, electrically driven, tracktype transit vehicles for interurban transportation, the transformer ratings specified for these vehicles is being continually increased, without relaxing the restrictions on the size and weight of the transformer.

Accordingly, it is an object of the invention to provide a new and improved transformer for transit vehicles.

Another object of the invention is to provide a new and improved transformer for transit vehicles, which is smaller and lighter than similarly rated transformers of the prior art.

Briefly, the present invention accomplishes the above cited objects by providing a transformer having a magnetic core winding assembly disposed in a form-fit tank. The winding assembly (or assemblies if polyphase) is of the rectangular type, having concentrically disposed high and low voltage coils, two substantially flat opposed side portions, and cooling ducts which extend between opposite ends of the winding. The magnetic core is disposed intermediate the top and bottom portions of the tank or casing, and is supported by and has its integrity maintained by the side wall portions of the casing, dividing the casing into upper and lower sections. The magnetic core includes at least one leg portion disposed parallel with the top and bottom portions of the casing. The winding assembly is disposed on at least the one leg portion of the magnetic core, with one of its flat sides supported by the bottom portion of the casing, and its oppositely disposed flat side being restrained by the top portion of the casing. The casing is completely filled with a fluid dielectric, which is forced to flow in a predetermined path through the electrical winding assembly, and through external heat exchanger means. Thus, end frames for the magnetic core, and bracing means for preventing the electrical winding assembly from changing its dimensions during short circuit stresses, are eliminated, which allows a substantial reduction to be made in the size and weight of the transformer. The form fit casing also reduces the amount of fluid dielectric in the transformer, and the forced cooling arrangement makes it possible to adequately cool the transformer with this reduced amount of fluid dielectric.

Further objects and advantages of the invention will become apparent from the following detailed description,

taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a transformer constructed according to the teachings of the invention;

FIG. 2 is an end elevational view of the transformer shown in FIG. 1;

FIG. 3 is a plan view of the transformer shown in FIG. 1;

FIG. 4 is a view of the transformer shown in FIG. 1, partially cut away, and partially in section;

FIG. 5 is an elevational view of the transformer of FIGS. 1, 2 and 3, partially cut away, and partially in section;

FIG. 6 is a pictorial view of a coil and duct former constructed according to the teachings of the invention;

FIG. 7 is a plan view of the duct former shown in FIG. 6;

FIG. 8 is an end view of the duct former shown in FIG. 7;

FIG. 9 is an elevational View of a transformer, partially cut away, and partially in section, which illustrates another embodiment of the invention; and

FIG. 1'0is a side elevation of the transformer shown in FIG. 9, shown partially cut away, and partially in section.

Referring now to the drawings, and FIGS. 1, 2 and 3 in particular, there is shown side and end elevations, and a plan view, respectively, of a transformer 10 constructed according to a first embodiment of the invention. Transformer 10 includes a form-fit casing 12, having top and bottom portions 14 and 16, respectively, connected by first and second oppositely disposed substantially vertical side wall portions 18 and 20, and first and second oppositely disposed side wall portions 22 and 24, which are substantially contoured to the shape of the enclosed magnetic core-winding assembly.

A plurality of high and low voltage bushing assemblies are disposed through the vertical side wall portions 18 and 20, respectively, with the number of bushings depending upon whether the transformer is single or polyphase, and the number of secondary circuits required by the particular application. For example, if transformer 10 is single-phase, it may include two high voltage bushings 2-6 and 28, and if the particular application requires five electrical circuits, ten low voltage bushings 30, 32, 34, 36. 38, 40, 42, 44, 46 and 48 may be used.

Transformer 10 also includes an expansion tank 50, mounted on top portion 14, which is in communication with casing 12 through piping means 52. If transformer 10 includes a tap changer, its operating mechanism may be enclosed in housing 54, disposed on one of the side wall portions of casing 12, such as side wall portion 18.

The casing 12 of transformer 10 is completely filled with a fluid dielectric, such as oil, or one of the synthetic insulating fluids, with the expansion tank also including a predetermined quantity of the fluid, to insure that the casing 12 will remain completely filled with the fluid over the operating temperature range of the transformer 10. This dielectric fluid is forced to flow through the transformer 10 by pumping means 60, which includes a pump 62 having inlet and outlet pipes 64 and 66, respectively, and driven by suitable driving means, such as electric motor 68.

Suitable heat exchanger means 70 is disposed external to transformer 10, for cooling the fluid dielectric disposed within casing 12. Heat exchanger means 70 includes radiator means 73 having an inlet in communication with the dielectric fluid in casing 12 via piping means 72, and an outlet 74 connected to the inlet pipe 64 of pumping means 60. Cooling of the fluid dielectric in radiator means 73 may be accelerated by providing one or more fans, such as fan 76, directed to move a high velocity of air over the heat exchanger means.

FIGS. 4 and 5 are side and end elevations, respectively, of transformer 10, with the casing 12 partially cut away to more clearly illustrate the internal details of a transformer constructed according to a first embodiment of the invention. Specifically, transformer 10, which for purposes of illustration is shown as being of a single-phase type, includes a winding assembly 80 disposed in inductive relation with a magnetic core structure 82, which has first and second similar sections 84 and 86.

Electrical winding assembly 80 has a construction similar to that common of certain core-type power transformers, having concentrically disposed high and low voltage coils 88 and 90, respectively, separated by high-low insulation 89. However, instead of being disposed on the vertically disposed leg portion of a core-type magnetic core, i.e., a single section magnetic core, in this embodiment of the invention it is disposed on the horizontally disposed leg portion formed by adjacent portions of magnetic core sections 84 and 86. Thus, while winding assembly '80 is similar to that used in certain transformers of the core-form type, it is disposed in inductive relation with the magnetic core assembly 82 of the type generally used in transformers of the shell-form type, in which the high and low voltage coils are disposed in side-by-side relation.

Winding assembly 80 is generally referred to in the art as being rectangular, having a rectangular opening for receiving a leg of a magnetic core structure, and a generally rectangular outer configuration, including two oppositely disposed, substantially flat side wall portions 92 and 94, and two oppositely disposed side wall portions 96 and 98, which are usually curved or rounded. The side wall portions 92, 94, 96 and 98 extend between first and second oppositely disposed end portions 100 and 102, with electrical leads 104 extending from the high voltage coil 88 at end portion 100 for connection to high voltage bushings 26 and 28, and with leads 106 extending from the low voltage coil 90 at end portion 102, for connection to the plurality of low voltage bushings. Winding assembly 80 also has a plurality of cooling ducts or openings, such as duct 108 in high voltage coil 88 and duct 110 in low voltage coil 90, which extend between its ends 100 and 102. Ducts 108 and 110 are formed by duct formers disposed between predetermined turns of the high and low voltage coils 88 and 90, which duct formers will be described in detail hereinafter.

Winding assembly 80 is disposed within casing 12, with its flat side portion '94 resting on solid insulating means 112, which is disposed directly on the bottom portion 16 of casing 12. Solid insulating means 112 may be wood, pressboard, cast resinous insulating members, or any other suitable type of solid insulation.

The magnetic core assembly 82, which is generally formed of a plurality of stacked or superposed metallic laminations 114, such as silicon steel, completely surround winding structure 80, and is supported by the side wall portions 18, 20, 22 and 24, or extensions therefrom, along with cooperating solid insulating members. For example, the formed side wall portions 22 and 24 conform as closely as possible to the contour of winding assembly 80 and magnetic core assembly 82, in order to support the magnetic core assembly, to reduce the volume of fluid dielectric disposed in the transformer, and to direct all of the fluid dielectric through the cooling ducts, instead of around the outer sides of the winding assembly. Side wall portions 22 and 24 have vertical members 116 and 116', respectively, which are fixed to bottom portion 16 in predetermined spaced relation, which spacing substantially corresponds to the width of winding assembly 80. Vertical members 116 and 116' extend upwardly to substantially the start of the magnetic core assembly 82. Horizontal members 118 and 118' are fixed to the upper end of members 116 and 116', respectively,

and they extend outwardly therefrom to form supports for magnetic core assembly 82. Side wall portions 22 and 24 are completed by vertical members 120 and 120, which are fixed to horizontal members 118 and 118, respectively, and extend upwardly just beyond the height of the magnetic core assembly 82, by horizontal members 122 and 122' which are fixed to vertical members 120 and 120', respectively, and which extend inwardly to the start of winding assembly 80, and by vertical members 124 and 124' which are fixed to horizontal members 122 and 122', respectively, and which extend upwardly to just beyond the vertical height of winding assembly 80, where they are fixed to the top portion 14.

Side wall portions 18 and 20 are adjacent ends 100 and 102, respectively, of winding assembly 80, and thus the plurality of cooling ducts 108 and 112 in the high and low voltage coils 88 and are also disposed adjacent ends and 102. Headers for the cooling fluid are thus required adjacent the ends of winding assembly 80, and side wall portions 18 and 20, in cooperation with magnetic core assembly 82, form these headers. More specifically, instead of side wall portions 18 and 20 conforming with the contour of the winding assembly and the magnetic core assembly, in a manner similar to side wall portions 22 and 2-4, they are substantially vertical, being fixed to bottom portion 16, and spaced to enclose the magnetic core assembly 82. Side wall portions 18 and 20 include vertical members 126 and 126, respectively, which are fixed to bottom portion 16, and extend upwardly to substantially the start of magnetic core assembly 82, horizontal members 128 and 128', which are fixed to the upwardly extending ends of members 126 and 128, respectively, and which extend inwardly to form a support structure for magnetic core assembly 82, and vertical members 130 and 130 which are fixed to members 128 and 128', respectively, which extend upwardly to just past the top of winding assembly 80, where they are fixed to cover portion 14.

In constructing transformer 10, the casing 18 should preferably be pre-assembled into upper and lower halves or sections, with the lower half including the bottom portion 16, upwardly extending members 116, 116', 126 and 126, and support members 118, 118', 128 and 128'. Solid insulating means 12 is placed on bottom portion 16, and winding assembly 80 is disposed thereon with its fiat side 94 against solid insulating means 112. Solid insulating members 132, 132, 134 and 134' are disposed on the support members 128, 128', 118 and 118, respectively, and magnetic core assembly 82 may then be stacked, or built-up, through the opening in winding assembly 80, and on the support members. After magnetic core assembly 80 is stacked to the desired build dimension, solid insulating members, such as members 136, 138 and 140 are disposed about the outer vertical surfaces or edges of the magnetic core assembly, and solid insulating members 142, 144, 146 and 148 are disposed on the upper horizontal surfaces of the magnetic core assembly, Solid insulating member 150 is also disposed on the flat top surface 92 of winding assembly 80. Then, the preassembled upper half of casing 18, comprising members 130, 130', 120, 120', 122, 122', 124 and 124', and top portion 14, may then be disposed over the magnetic core-winding assembly and presesd to tightly secure the winding assembly 80 between the top and bottom portions 14 and 16 and associated solid insulating members 112 and 150, and to also tightly wedge or secure the magnetic core assembly between side wall members 118 and 122, and 118' and 122, including the associated solid insulating members 134, 142, 134' and 144. Side wall members 130 and 130 may have additional horizontal members secured thereto (not shown) which will contact the upper surface of solid insulating members 146, and 148, to further compress magnetic core assembly 82 between solid insulating members 146 and 132, and 148 and 132. After the top half of casing 12 is pressed firmly into position,

it may be welded to the bottom half of the casing with a continuous weld bead 152. The high and low voltage bushings may then be placed in the openings provided in the casing for this purpose, and their respective elec trical leads attached thereto. Access to the inside of the casing may be made through suitable coverable openings. Or, low voltage bushings 40, 42, 44, 46 and 48 may be placed in position and connected to their respective electrical leads before the magnetic core is stacked, and the upper half of the casing may be placed in position and welded at 152, without the top portion 14. The high and low voltage bushings 26 and 28, and 30, 32, 34, 36 and 38, respectively, may then be placed in position and connected to their respective electrical leads before the top portion 14 is welded to the side members 130, 130, 124 and 124'. It should be noted that the magnetic core assembly 82 divides the casing 12 into upper and lower sections, and that the electrical winding assembly 80 divides the upper section into first and second compartments 160 and 162, and the lower section into first and second compartments 164 and 166. Compartments 160, 162, 164 and 166 thus form. the headers for the cooling fluid. The cooling fluid may be any suitable dielectric, such as oil, and it should completely fill the casing 12. In order to insure that there will be no air space in the casing 12, an expansion tank 50 is disposed on top 14, which is in communication with the fluid in casing 12 through piping means 52. Expansion tank 50 has fluid dielectric 168 disposed therein to a predetermined level, which level is free to move as the fluid within the transformer heats and cools due to the normal operating temperature of transformer 10. The amount of fluid dielectric in the casing 12 and the expansion tank is chosen to always maintain fluid dielectric in the expansion tank, without completely filling the expansion tank, over the operating temperature range of the transformer 10. Thus, when the fluid dielectric is forced through the cooling ducts in winding assembly 80, there will be no danger of any air being circulated, which would reduce the dielectric strength of the fluid.

In order to provide a closed loop through the upper and lower halves of the winding assembly, and through the heated exchanger means 70, suitable duct means 170 is disposed to connect compartments 162 and 166, and baflles 172, formed of a suitable solid insulating means, are disposed at each of the rounded outer corners of the winding assembly, as shown in FIG. 5, to confine the fluid dielectric flow path to the cooling ducts in the winding assembly.

The pumping means will thus pump the cooled fluid dielectric from heat exchanger means into the first upper compartment 160, through the cooling ducts in the upper half of the winding assembly to the second upper compartment 162, and then through duct means into the second lower compartment 166, through the cooling ducts in the lower half of winding assembly 80 to the first lower compartment 164, and then through heat exchanger means 70. It will also be understood that the direction of the fluid flow path may be reversed by reversing the pumping directions of the pumping means.

A rectangular type winding assembly, such as winding assembly 80, when subjected to a short circuit, tries to assume a round configuration. Since this type of winding assembly has two substantially flat side wall portions 92 and 94, and two substantially rounded side wall portions 96 and 98, most of the short circuit forces will be concentrated on the flat side wall portions 92 and 94, as the remaining sides are already substantially rounded. These flat side wall portions 92 and 94, being snugly held between solid insulating members 150 and 112, and top and bottom portions 14 and 16, respectively, are prevented from moving, thus eliminating the boxed channel members normally utilized in the prior art to brace the winding assembly and restrain the flat sides from moving during short circuit stresses. The top and bottom portions of the casing thus perform these bracing functions, which eliminates the cost, weight and volume of dielectric fluid which would be necessitated when using extra bracing members, and which also allows the height of the assembly to be reduced.

When concentric coils are subjected to short circuit stresses, they are forced apart laterally, or perpendicular to the axis of the coils, and any axial separation of their electrical centers, i.e., that point which divides the ampere turns of a coil into two equal portions, produces an axial component of the lateral force which tends to force the coils apart axially. The top and bottom portions 14 and 16 restrain the winding assembly against movement due to the lateral forces. Axial components of the force are reduced by forming the coils of sheet or strip conductor, instead of wire conductor, thus providing one turn per layer and making it possible to more accurately de termine the location of the electrical centers of the various coils, and thus align the electrical centers of the coils, than it is with wire wound coils. Thus, as shown in FIG. 6, the low voltage coil 90 may be wound with a strip of a good electrical conductive material, such as copper or aluminum. The conductor turns of coil 90 may be insulated from one another with a coating of insulating enamel applied to the strip conductor, such as an epoxy, or the turns may be separated by a sheet of separate insulating means wound at the same time as the conductor turns 180.

In order to provide a more effective transfer of the heat from the conductor turns of the various coils which make up the winding assembly, to the fluid dielectric being circulated through the cooling ducts of the winding assembly, the duct formers may be formed as shown in FIGS. 6, 7 and 8. More specifically, the duct formers, such as duct former 190, which are placed between predetermined turns of the coils while they are being wound, may be formed of corrugated solid insulating means, such as pressboard, having a succession of connected furrows 191 and waves 193. However, instead of disposing the duct formers with the direction of the openings formed by the furrows and waves perpendicular to the direction of winding the coils, which would form straight through ducts between the ends of the winding assembly, the duct former is cut to provide an angle 192, as shown in FIG. 7, between the direction 194 of winding the coils, and the direction of the furrows and waves, which angle should be substantially equal to 45. Then, the furrows and waves are provided with openings 196-, the direction of which is at a predetermined angle 198 with the direction of the furrows and waves, which angle is preferably 90. Openings 196 are relatively narrow, and may be made by a plurality of spaced saw cuts across first one side of duct former 194 and then the other. Thus, when the corrugated duct former 190 is disposed between turns of the coils, such as coil 90- as shown in FIG. 6, the fluid dielectric will be forced to flow a tortuous path through the openings provided by the waves and furrows, and through the openings 196 out in the waves and furrows, which causes the desired turbulent flow across the complete area of the duct and provides excellent heat transfer from the conductor turns to the fluid dielectric.

In addition to bracing the winding structure with the casing 12, the casing 12 and cooperating wedging solid insulating means also support and compress the laminations which make up the magnetic core assembly 82, completely eliminating the end frames normally associated with transformers having concentrically disposed high and low voltage coils. Eliminating the end frames reduces the overall transformer size and weight.

Further, the high and low voltage bushing assemblies are disposed completely within the insulating fluid within the casing 12, without passing through an air space. This reduces the size and weight of the bushings. Still further, since the inner terminals on the bushings are inherently disposed in a close relationship with their associated electrical leads and coils, conventional superstructures for supporting the leads are eliminated.

A transformer rated 1500 kva. was constructed according to the teachings of this embodiment of the invention, and, without the heat exchanger, it weighed 12,000 lbs., was 30 inches high, 68 inches wide, and 88 inches long. A 1500 kva. transportation type transformer of the prior art, also without heat exchanger, weighs 15,000 lbs., is 32 inches high, 68 inches wide, and 232 inches long. Thus, a very substantial savings in weight and length have been achieved by utilizing the teachings of the invention, as well as a reduction of 2. inches in the critical height dimension.

While the teachings of this embodiment of the invention have been specifically illustrated with respect to a single phase transformer, it will be understood that they may be applied with equal advantage to polyphase transformers. Thus, a polyphase transformer would utilize rectangular concentrically disposed high and low voltage coils of the conventional core-form type, and would use magnetic cores of the shell-form type, which completely surrounds the winding assemblies.

FIGS. 9 and 10 are front and elevational views, respectively, of a transformer 200 constructed according to another embodiment of the invention. FIGS. 9 and 10 are partially cut away, and partially in section, and since the heat exchanger means, storage tank and electrical bushings for this embodiment of the invention are the same as already shown and described relative to the first embodiment of the invention, they are not shown.

Transformer 200, for purposes of illustration, is shown as being of the single phase type, having first and second rectangular type winding assemblies 208 and 210 disposed in inductive relation with a magnetic core 202 of the core-form type having winding legs 204 and 206, upon which winding assemblies 208 and 210 are disposed, respectively. This magnetic core-winding assembly is disposed within a casing 201, which has a bottom portion 212, a top portion 214, a sidewall portion which includes members 216 and 220, a sidewall portion which includes members 21 8 and 222, a sidewall portion which includes members 250 and 254, and a sidewall portion which includes members 252 and 256.

Each of the winding assemblies 208 and 210 are similar in construction, and each may have concentrically disposed high and low voltage coils, such as high and low voltage coils 288 and 290 respectively, in winding assembly 210, 292 and 294, respectively, in winding assembly 208. The high and low voltage coils, such as coils 288 and 290 in winding assembly 210 may be separated by high-low insulation 282.

Magnetic core assembly 202, instead of being of the shellform type as in the first embodiment of the invention, is of the core-form type, having a plurality of superposed or stacked laminations 286 arranged to form the two leg portions 204 and 208, and connecting yoke portions 296 and 298. The winding assemblies 208 and 210 are disposed within-casing 201, with their flat side portions disposed uponsuitable solid insulating means 224, and separated by solid insulating means 284. The directions of the major openings in the winding assemblies 208 and 210 are parallel to the bottom and top portions of the casing 201, and they are also parallel with one another. The winding assemblies 208 and 210 are disposed with their greater cross sectional dimension parallel with the top and bottom portions of the casing 201.

The casing 201 may be made in two sections, a lower section which includes bottom portion 212 and upwardly extending portions or members 216, 218, 250 and 252, and an upper section which includes top portion 214 and downwardly extending portions 220, 222, 254 and 256. The winding assemblies 208 and 210 may then be disposed within this bottom portion of the casing, upon the solid insulating means 224, and the upwardly extending portions 250 and 252 may each include a horizontal member 258 and 260, respectively, upon which the magnetic core assembly 202 may be stacked and supported. After the magnetic core 202 has been stacked or built up to the desired build dimension on suitable solid insulating members 262 and 264, suitable bafiles formed of solid insulating means, such as baffies 232, 234, and 300 are disposed to continue or extend the barrier elfect of the magnetic core assembly 202 across the front and back surfaces of the winding assemblies, in order to divide the casing 201 into upper and lower compartments, when the upper section of the casing is disposed in its proper position. These baffles were not necessary when utilizing the shell form magnetic core structure in the first embodiment of the invention, since the shell form structure inherently completely separates the casing into upper and lower sections. Additional baflles may be disposed at the corners of the rectangular winding assemblies to prevent the circulation of cooling fluid around the outside of the winding assemblies, instead of through the cooling ducts, such as duct 280 in winding assembly 210. For example, baffies 236, 238, 240, 242, 244 and 246 may be placed at each of the outer and adjacent corners of the winding assemblies 208 and 210, as shown in FIG. 9.

After the winding assemblies 208 and 210 have been placed in position in the bottom section of the casing 201, the magnetic core assembly 202 built up to its build dimension, and the hereinbefore mentioned baffles placed in position, solid insulating means 228 and 230 are disposed at each end of the winding assembly, and solid insulating means 226 is placed on the upper flat side portions of the winding assemblies. The upper section of casing 201 may then be placed in position over the winding assemblies. The upward extending portions of the lower section of casing 201 may each include a flange or outwardly extending projection, which mates with a similar outwardly extending projection on the sidewall portions of the upper section of casing 201. The upper portion of the casing is then pressed tightly into position, and the outwardly extending projections on the upper and lower sections of casing 201 may be welded to secure the upper and lower sections of the casing in fixed, assembled relation.

The upper section of casing 201 may have inwardly extending projections 268 and 272 which, along with solid insulating means 266 and 270, respectively, cooperate with the similar projecting members 258 and 260 and their associated solid insulating means 262 and 264, respectively, to tightly compress the laminations 286 of the yoke portions 298 and 296 of the magnetic core assembly 202. Thus, the end frames normally associated with this type of magnetic core structure are completely eliminated, which substantially reduces the size and weight of the overall transformer assembly.

In the prior art, the end frames which are disposed to compress the yoke portions of the magnetic core assembly are extended such that suitable bracing members may extend between the outer extremities of the end frames and thus restrain the rectangular winding assemblies from movement during short circuit stresses. In this embodiment of the invention, the rectangular winding assemblies 208 and 210 are completely restrained by two oppositely disposed sidewall portions, and the top and bottom portions of casing 201. For example, the sidewall portions which include members 216 and 220, and solid insulating means 228 are disposed snugly against the outer end surface of winding assembly 208, and the sidewall portion which includes members 218 and 220, and solid insulating means 230, are disposed snugly against the outer end surface of winding assembly 210.

In like manner, the bottom portion 212 with its solid insulating means 224, and the top portion 214 with its solid insulating means 226, snugly compress the fiat sidewall portions of winding assemblies 208 and 210. Thus, auxiliary bracing means for insuring that the winding assemblies retain their shape during short circuit stresses are completely eliminated. Similar to the winding assembly of the first embodiment of the invention, winding assemblies 208 and 210 may also be formed of electrically conductive sheet or strip material, in order to reduce any axial forces tending to separate the high and low voltage coils of the winding assemblies.

The cooling of transformer 200 may be similar to that described in the first embodiment of the invention, with the coolant being force circulated through the enclosure, starting at arrow 302, where it enters the front portion of the upper half of the casing through a suitable opening, it is circulated through the upper cooling ducts in the winding assemblies, such as duct 280, it leaves the upper cooling ducts at the other end of the winding assemblies, still in the upper portion of the casing, as shown by arrows 306, the coolant is then directed to the lower portion of the casing through duct means 248, the coolant, as shown by arrows 308, is then directed into the lower cooling ducts through the winding assemblies, the coolant emerges from these cooling ducts as shown at 310, and exits the casing through a suitable opening, as shown by arrow 312, where the coolant is circulated through external heat exchanger means.

The cooling ducts 280 and winding assembly 210* may be formed in the manner hereinbefore described relative to the winding assembly in the first embodiment of the invention.

While the teachings of this second embodiment of the invention have been specifically illustrated with respect to a single-phase transformer, it will be understood that they may be applied with equal advantage to poly-phase transformers. For example, a three-phase transformer would have a magnetic core assembly with an additional winding leg, and one additional winding assembly. Otherwise, the single and polyphase structures are similar.

In summary, there has been disclosed new and improved transformer structures in which end frames and bracing members have been completely eliminated. The casing of the transformer is form-fitting, sup-porting and compressing the laminations which make up the magnetic core assembly, and bracing the winding assembly or assemblies against movement during short circuit stresses. Eflicient, forced circulation of the cooling fluid through ducts in the winding assemblies enables the transformer to be adequately cooled with a minimum amount of coolant. Thus, the size and weight of the transformer structures have been reduced to a minimum, without adversely affecting the performance and operating life of the transformer.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative, and not in a limiting sense.

We claim as our invention:

1. An electrical transformer comprising a casing having top and bottom portions connected by side wall portions,

a magnetic core having a plurality of metallic laminations, said magnetic core being disposed in said casing intermediate said top and bottom portions to divide said easing into upper and lower sections, said magnetic core having at least one leg portion disposed substantially parallel to said top and bottom portions,

solid insulating means wedged between said magnetic core and said sidewall portions, to hold and maintain the integrity of said magnetic core,

at least one electrical winding assembly having first and second ends, said at least one electrical winding assembly being disposed on said at least one leg portion, dividing each of the upper and lower sections of said casing into first and second compartments,

said electrical winding assembly having openings therein which extend between its ends to connect the first and second compartments of both the upper and lower sections of said casing,

solid insulating means wedged between said electrical winding assembly and said top and bottom portions, to brace said electrical winding assembly against movement during short circuit conditions, duct means disposed to connect the second compartments of the upper and lower sections of said casing,

fluid dielectric means disposed within said casing,

and pumping means for forcing said fluid dielectric means to flow from the first compartment of one of the sections of said casing, through the openings in said electrical winding assembly to the second compartment of said one section, through said duct means itno the second compartment of the other section, and through the openings in said electrical winding assembly into the first compartment of said other section.

2. The electrical transformer of claim 1 wherein said electrical winding assembly has at least first and second oppositely disposed substantially flat side portions, which are disposed against the solid insulation adjacent the top and bottom portions of said casing, respectively.

3. The electrical transformer of claim 1 wherein said electrical winding assembly has concentrically disposed high and low voltage coils, and a substantially rectangular opening for receiving the leg portion of said magnetic core.

4. The electrical transformer of claim 1 including heat exchanger means connected to the first compartment of the upper and lower sections of said casing, said pumping means forcing said fluid dielectric to flow through said heat exchanger means.

5. The electrical transformer of claim 1 wherein said fluid dielectric is a liquid which completely fills said casing, and including an expansion tank disposed in com munication with said casing which contains liquid dielectric to insure that said casing will be completely filled with said liquid dielectric over the operating temperature range of the transformer.

'6. The electrical transformer of claim 1 wherein said sidewall portions include first and second sidewall members disposed opposite the first and second ends of said electrical winding assembly, respectively, and third and fourth sidewall members, and wherein said electrical winding assembly includes concentrically disposed high and low voltage coils, and including high and low voltage bushing assemblies disposed through the first and second sidewall members, which are electrically connected to said high and low voltage coils.

7. The electrical transformer of claim 6 wherein said third and fourth sidewall members, and their associated solid insulating means, closely conform to the shape of the adjacent winding assembly and magnetic core, to insure that the only communicating spaces between the first and second compartments of both the upper and lower sections of said casing are through the openings in said winding.

8. The electrical transformer of claim 1 wherein said electrical winding assembly includes concentrically disposed high and low voltage coils, each having a plurality of superposed turns of electrically conductive strip material, to reduce the axial unbalance in the forces between the high and low voltage coils during short circuit conditions.

9. The electrical transformer of claim 8 including corrugated duct former means disposed between certain of the turns of said winding assembly, with the winding direction of the turns being at an angle of substantially 45 to the direction of the corrugations, the corrugations of said corrugated duct former means having a plurality F of narrow openings disposed therein to a predetermined depth, at an angle of substantially 90 with respect to the direction of the corrugations.

10. The electrical transformer of claim 1 wherein said magnetic core has two outer and one inner leg portions, with said at least one electrical winding assembly being disposed on said inner leg portion.

11. The electrical transformer of claim 1 wherein said magnetic core has a plurality of spaced, parallel leg portions, and including an electrical winding assembly disposed on each of said leg portions.

12. The electrical transformer of claim 11 wherein certain of said sidewall portions are disposed against the electrical winding assemblies disposed on the outer leg portions of said magnetic core, to aid in restraining the winding assemblies against deformation during short circuit stresses.

References Cited UNITED STATES PATENTS 2,388,565 11/1945 Paluev 33657 3,151,304 9/1964 Miller 336-60 XR 3,368,174 2/1968 Fischer 336-60 LEWIS H. MYERS, Primary Examiner.

10 T. I. KOZMA, Assistant Examiner.

US. Cl. X.R. 336197, 210, 60

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