US3644859A - Electrical winding of sheet conductor - Google Patents

Abstract

A high-current capacity winding of sheet conductor for stationary induction apparatus which substantially reduces eddy current and circulating current losses has a plurality of coaxial coils each of which is spirally wound from a plurality of conductor sheets in parallel that extend the entire coil height with insulation between paralleled sheets and between spiral turns. Crossover connector strips extending parallel to the winding axis connect paralleled conductor sheets in the plurality of coils in series relation and so that the innermost and outermost of the paralleled conductor sheets of different coils are transposed and the net flux linkages of the plurality of flux paths are approximately equal.

Description

United States Patent Waterman Feb. 22, 1972 [54] ELECTRICAL WINDING OF SHEET 3,464,043 8/1969 Benko et a1 ..336/185 X CONDUCTOR 3,466,582 9/1969 Sealey et al. ..336/60 1,672,702 6/1928 Weed ..336/186 X [72] Inventor: Michael W. Waterman, Milwaukee, Wis.

Auk ha! M M and C Primary Examiner'l'homas .l. Kozma [73] Ass'gnee Milwfukemfiis' a g mummy Attorney-Lee H. Kaiser, Thomas F. Kirby and Robert B. Benson [22] Filed: Aug. 17, 1970 21 Appl. No.:- 64,472 [57] ABSTRACT A high-current capacity winding of sheet conductor for sta- [52] U S Cl 336/187 336/60 336/223 tionary induction apparatus which substantially reduces eddy [51] 6 27/28 current and circulating current losses has a plurality of coaxial [58] Fieid 60 185 coils each of which is spirally wound from a plurality of con- 6 ductor sheets in parallel that extend the entire coil height with insulation between paralleled sheets and between spiral turns. Crossover connector strips extending parallel to the winding [56] References cued axis connect paralleled conductor sheets in the plurality of UNITED STATES PATENTS coils in series relation and so that the innermost and outermost of the paralleled conductor sheets of different coils are trans- 3,l95,088 7/1965 Sandoz ..336/187 X posed and the net fl linkages f the plurality f fl paths 2,436,207 2/1948 DEntremont.. .....336/186 x are approximately equal, 2,998,583 8/1961 Worcester .336/223 X 3,546,644 12/1970 Wilbum et al. ..336/187 2 Claims, 10 Drawing Figures PAIENIEBrsazz I972 3. e44. 859

SHEET 2 BF 3 PATENTEUFEBZZ m2 3. 644, 859

saw 3 or a BACKGROUND OF THE INVENTION Shunt reactors may be used in high voltage, alternating current power transmission and distribution lines to compensate for line charging current and to allow the charge remaining in the line to bleed to ground when the line is opened. A reactor is often immersed in oil within a tank, and the reactor may be constructed without any magnetic material for a core so that it will have high-magnetizing current. Such an air-core reactor sets up a large magnetic field, and a problem with large size high voltage reactors is that the magnetic flux near the ends of the reactor winding deviates from the axial direction and has a cross direction relative to the winding axis. This cross flux interacts with the current in the conductor turns of the windings to cause high eddy current losses and to produce high axial compressive forces on the winding. Cross flux and its disadvantages are substantially eliminated in the extra high-voltage (EHV) shunt reactor disclosed in US. Pat. No. 3,362,000, in which I am a joint inventor with William C. Sealey, wherein a closed magnetic yoke having laminations in planes parallel to the axis of the reactor winding surrounds the winding to reduce the reluctance of the magnetic circuit external to the winding to reduce the reluctance of the magnetic circuit external to the winding and has portions closely adjacent the axial ends of the winding to straighten the lines of magnetic flux within the winding. The reactor winding is short in an axial direction and preferably has a high ratio of winding radius to winding axial height which further increases the inductance. The reactor winding disclosed in said patent comprises a plurality of axially aligned pancake coils disposed in a stack and arranged in two similar groups of series connected coils wound in opposite directions, and the patent discloses that the pancake coils may be wound from rectangular conductor having a substantially wider dimension in the axial direction than in the radial direction to improve the space factor. Reactors are also known wherein the reactor winding is wound from a board ribbon of conductive material which extends the entire axial height of the winding such as disclosed in U.S. Pat. No. 3,014,189 to McKinnon et a]. However, it has heretofore been impracticable to use such wide conductor ribbon in large kv./a. shunt reactor windings requiring conductor of large cross section because of the high eddy current losses which vary with the square of the dimension of the conductor at right angles to the direction of the magnetic flux.

It is an object of the invention to provide an improved high current capacity electrical winding for stationary induction apparatus which, in comparison to known structures, has reduced eddy current and circulating current losses, has a high space factor and increased short strength, and is simpler and less costly to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS This and other objects and advantages of the invention will be more readily apparent from the following detailed description when considered in conjunction with the accompanying drawing wherein:

FIG. 1 is a partial elevation view of a polyphase shunt reactor yoke and winding assembly incorporating a preferred embodiment of the invention;

FIGS. 2 and 3 are views taken along lines II-II and III-III respectively of FIG. 1;

FIGS. 4 and 5 are enlarged partial views. of FIGS. 2 and 3 respectively showing the crossover connectors;

FIG. 6 is a view taken along lines Vl-VI of FIG. 2;

' FIG. 7 and 8 are views similar to FIGS. 4 and 5 schematically illustrating alternative embodiments of the invention wherein a greater number of conductor sheets are wound in parallel than in the FIG. 1 embodiment;

' FIG. 9 is an enlarged sectional view taken along line IX-IX of FIG. 2 adjacent the abutting surfaces of the upper and lower coils; and

FIG. 10 is an enlarges sectional view taken along line X-X of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawing, apolyphase shunt reactor yoke and winding assembly incorporating a preferred embodiment of the invention has a plurality of cylindrical phase windings A, B and C (of which only windings A and B are shown) arranged with their axes vertical and aligned in a common vertical plane. The phase windings A, B and C are surrounded by a closed magnetic yoke 10 which provides a low reluctance magnetic circuit external to the windings. Yoke 10 has magnetic steel laminations 11 disposed in vertical planes with upper and lower horizontal yoke portions 14 and 15 respectively closely adjacent the axial ends of all phase windings A, B and C and connected by vertical end portions 16. The laminations llY of the upper and lower yoke portions 14 and 15 may have overlap miter joints 17 with the laminations 11E of the end portions 16, and the number of laminations may vary in a horizontal direction in the manner disclosed in US. Pat. No. 3,466,582, in which I am a joint inventor with William C. Sealey, so that the magnetic flux density is approximately uniform in any cross section through yoke 10.

The three phase windings A, B and C are identical, and only winding A will be described. Winding A comprises an upper coil 20 wound from sheet, or strip conductor such as aluminum as wide as the axial length thereof and a lower coil 21 also wound from sheet, or strip conductor such as aluminum as wide as the axial length thereof. The upper and lower coils 20 and 21 are coaxial and connected in electrical series relation and both are wound on the same insulating support tube 24 with an annular horizontal insulating washer 25 disposed therebetween. Washer 25 may have apertures 30 therethrough (see FIG. 9) and radial insulating spacers 31 art'- fixed to the upper surface thereof.

Upper coil 20 comprises inner and outer conductor sheets, or strips 22 and 23 having a width substantially equal to the axial height of upper coil 20 spirally wound counterclockwise in parallel. The large number of spiral turns of strips 22 and 23 cannot be shown in FIGS. 2 and 3, and only the inner turn and a portion of the outer turn are illustrated with a dotted line representation of the spiral convolutions connecting the inner and outer turns. Conductor sheets 22 and 23 may be covered with an insulating film (not shown) such as epoxy resin or, alternatively, layer insulation (not shown) of suitable material such as kraft paper sheet may be wound between conductor sheets 22 and 23. Layer insulation 26 (see FIG. 4) of suitable material such as sheet kraft paper is wound between the spiral multilayer turns of paralleled sheet conductors 22 and 23.

Lower coil 21 similarly comprises inner and outer conductor sheets 28 and 29 covered with an insulating film (not shown) and having a width substantially equal to the axial height of lower coil 21 spirally wound clockwise in parallel with sheet layer insulation 26 between spiral multilayer turns so that the direction of magnetic flux generated in the upper and lower coils 20 and 21 is the same. The conductor strips 22, 23, 28 and 29 may be slightly narrower in an axial direction than the layer insulation 26, and keepback insulation 35 may be disposed between washer 25 and the edges of the strips 22 23, 28 and 29 to increase the dielectric breakdown strength between upper and lower coils 20 and 21. Elongated wooden spacer sticks 32 (see FIG. 9) extending parallel to the winding axis are inserted at circumferentially spaced positions between the spiral multilayer turns of the paralleled conductor sheets 22-23 of the upper coil 20 and also between spiral turns of paralleled conductor sheets 28-29 of lower coil 21 and form vertical ducts 33 for cooling fluid which extend through both the upper coil 20 and the lower coil 21 and communicate with the horizontal ducts formed by the radial spacers 31 and also with the apertures 30 in insulating washer 25.

The insulation film is removed from conductor sheets 22 and 23 at the outward end thereof so that the outer ends of the sheet conductors 22 and 23 are electrically connected together, and a START terminal 36 (see FIGS. 1, 2 and 6) for winding A is provided on upper coil 20 and may comprise a plurality of superimposed elongated strips 34 of conductive material such as aluminum welded to the outer ends of the conductor sheets 22 and 23 where they engage and are electrically connected together. As shown in FIGS. 2 and 6, two elongated aluminum strips 34A and 34B are disposed radially inward from the ends of the radially outer turn of the conductor sheets 22 and 23 and two elongated aluminum sheets 34C and 34D are disposed radially outward from the conductor sheets 22 and 23 adjacent the ends of the outer turn thereof, and the six layers of conductor 34A, 34B, 22, 23, 34C and 34D are welded together. The superimposed elongated conductors 34A, 34B, 34C and 34D are bent outwardly and upwardly adjacent the upper edge of the conductor sheets 22 and 23 to form START terminal 36 for phase winding A of the shunt reactor. A horizontal phase bus bar 37 may be welded to the START terminal 36.

A FINISH terminal 38 for phase winding A of the shunt reactor is provided adjacent the upper edge of lower coil 21 and is similar to START terminal 36. FINISH terminal 38 may be affixed to a horizontal bus bar 40 which is electrically connected to similar FINISH terminals on the other shunt reactor phase coils B and C to electrically connect phase coils A, B and C in wye. The insulation film is removed between sheet conductors 28 and 29 at the ends of the outer turn thereof to electrically connect these conductor sheets together at their outer ends, and FINISH terminal 38 may comprise four elongated aluminum strips (not shown) welded to the outer ends of conductor sheets 28 and 29 where said sheets abut in a manner similar to START terminal 36.

An annular insulating washer 44U having a plurality of apertures 46 therethrough (see FIG. and elongated radial spacer members 45 affixed to both surfaces thereof is positioned between the upper end of upper coil 20 and the upper yoke portion 14 to form radial ducts in communication with the vertical ducts 33 and also with ducts 55 described hereinafter in coil 20, and a similar insulating washer 44L having apertures 46 therein is positioned between the lower end of lower coil 21 and the lower horizontal yoke portion to form radial ducts communicating with the vertical ducts 33 and 55 in lower coil 21.

Two elongated, straight, vertical aluminum crossover strip connectors 50 and 51 electrically connect the inner and outer sheets 22 and 23 of the top coil to the outer and inner sheets 29 and 28 respectively of the lower coil21, while keeping the two conducting paths insulated from each other, to obtain the same netflex linkage for each conductor. Crossover connector 50 is disposed against outer sheet 23 of the upper coil 20 along its entire vertical height and adjacent the inner end thereof (see FIGS. 4 to 10) and is also disposed against the radially inner sheet 28 of lower coil 21 along the entire vertical height thereof. Sheet insulation 53 is folded in U- shape around the abutting crossover connector 50 and the end of outer conductor sheet 23 in upper coil 20, and the radially inner end 22i of inner conductor sheet 22 is bent around such U-shaped insulation 53 and abuts against crossover connector 51 along the entire vertical height of inner sheet 22.

In bottom coil 21 crossover connectors 50 and 51 abut against the radial outer surface of inner and outer sheets 28 and 29 respectively adjacent the ends thereof. Sheet insulation 54, is folded in U-shape around the abutting portions of crossover connector 50 and inner sheet 28 in the lower coil 21 to isolate the two electrical paths. The inner conductor sheet 22 of top coil 20 is thus transposed so that it becomes the outer conductor sheet 29 of the lower coil 21, and also the outer conductor sheet 23 of top coil 20 is thus transposed so that it becomes the outer conductor sheet 28 of the lower coil 21. As described hereinbefore, the sheets 22 and 23 are electrically connected at their radial outer ends in upper coil 20, and the sheets 28 and 29 are electrically connected at their radial outer ends in lower coil 21. The disclosed structure thus provides a conductor having the same cross section but only one half the thickness of the conductor sheet of a reactor such as US. Pat. No. 3,014,189 wherein the sheet conductor extends over the entire height of the reactor coil. It will be appreciated that such reduction in conductor thickness reduces to onefourth the eddy current losses (which are proportional to the square of the conductor dimension perpendicular to the direction of magnetic flux). Further, inasmuch as the inner and outer conductor sheets are transposed so that they occur in different radial positions in the upper and lower coils, the disclosed structure averages out the fact that the self-inductance caused by the magnetic flux is different in the inner and outer conductor sheets. Consequently, the circulating current generated by voltage inducted in the inner conductor sheet in one coil is canceled by the circulating current generated by the voltage induced in the outer conductor sheet in the other coil.

As shown in FIGS. 4 and 5, cooling ducts 55 for an insulating fluid may be provided between the support tube 24 and the first spiral multilayer turn of the paralleled conductor sheets, and the vertical elongated wooden spacers 56 which form such ducts 55 and are in alignment with the crossover connectors 50 and 51 are thinner in a radial direction than the vertical wooden spacers 57 which form such ducts 55 in the other parts of the coil to prevent the crossover connectors 50 and 51 from causing a bulge in the coil. It will be appreciated that the radial thickness of such spacers 56 and 57 must be exaggerated in the drawing. Further, an elongated insulation pad 59 may be provided between the crossover connector 51 and the first spiral turn of paralleled conductor sheets in both coils 20 and 21 to electrically isolate the two current paths.

FIG. 7 schematically illustrates an embodiment of the invention wherein three conductor sheets 60, 61 and 62 are spirally wound in parallel in the upper coil 20, similarly three conductor sheets 65, 66 and 67 are spirally wound in parallel in the lower coil 21, and three straight vertical crossover strip connectors 70, 71 and 72 electrically connect and transpose the sheet conductors so that the outermost sheet of the top coil 20 is connected to the innermost sheet of the bottom coil by crossover connector 70; the innermost sheet 62 of the top coil 20 is connected to the outermost sheet 67 of the bottom coil 21 by crossover connector 72; and the center sheet 61 of top coil 20 is connected to the center sheet 66 of bottom coil 21 by crossover connector 71. Such transposition of the inner and outer sheets in the upper and lower coils results in substantially equal flux linkages for all three conductors and in nearly total cancellation of circulating currents due to the magnetic flux. U-shaped insulating members schematically shown in dotted lines electrically isolate the three current paths at the positions where the crossover connectors 70, 71, and 72 connect coils 20 and 21 in series. The folded portions at the inner ends of sheet conductors 61 and 62 permit use of simple straight crossover connectors 70, 71 and 72 which are easy to fabricate and connect to the conductor sheets and without causing bulges in the coils.

FIG. 8 schematically illustrates an embodiment similar to FIG. 7 wherein three conductor sheets are spirally wound in parallel in both top coil 20 and lower coil 21 but only one con ductor is transposed. Inner sheet conductor 62 of top coil 20 is bent in U-shape at its inner end so that it abuts and is electrically connected to the upper end of crossover strip connector 72 which, at its lower end, abuts and is electrically connected to the outer sheet conductor 67 of lower coil 21. This construction results in substantial, but not perfect, cancellation of the circulating currents in the two coils 20 and 21 due to the magnetic flux. The structure shown in FIG. 8 would result in equal net flux linkages for the three conductors and the total cancellation of circulating current if it were used to connect three coils in series each of which is spirally wound with three conductor sheets in parallel.

Although the invention has been illustrated and described as embodied in a shunt reactor winding, it will be appreciated that the invention is also applicable to electrical windings for other stationary induction apparatus such as power transformers.

It should thus be understood that I do not intend to be limited to the particular embodiments shown and described, for many modifications and variations will be obvious to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A shunt reactor winding having high-current capacity comprising, in combination,

a plurality of superimposed coaxial coils each of which is spirally wound from a plurality of conductor sheets in parallel terminating together at their radially outer ends and which terminate at their radially inner ends in a common radial plane and which sheets extend substantially the entire axial height of said coil, insulation between paralleled conductor sheets in each coil and between the spiral turns of paralleled sheets,

a START terminal on one of said coils electrically connecting said radially outer ends of the paralleled sheets of said one coil together and a FINISH tenninal on another of said coils electrically connecting said radially outer ends of the paralleled sheets of said another of said coils together,

said plurality of coils being wound so that the direction of magnetic flux is the same in all of said coils, and

means including a plurality of elongated flat crossover connector strips disposed in a common radial plane extending between adjacent coils at the radially inner coil periphery in a direction parallel to the coil axis and joining oppositely disposed radially inner conductor sheet ends in said adjacent coils for electrically connecting said paralleled sheets in said plurality of coils in series relation,

the radially inner ends of certain of said conductor sheets in one of said adjacent coils being offset in a radial direction and joined to crossover connector strips affixed to conductor sheets occupying different radial positions in said adjacent coil so that the net flux linkages of the plurality of conductor paths formed by said series connected conductor sheets are approximately equal.

2. An electrical winding in accordance with claim 1 wherein the radially inner end of the radially inner conductor sheet in said one coil is bent in U-shape to a different radial position so that it is joined to a conductor strip afiixed to the radially inner end of the radially outer conductor sheet of said adjacent coil.

Claims (2)

1. A shunt reactor winding having high-current capacity comprising, in combination, a plurality of superimposed coaxial coils each of which is spirally wound from a plurality of conductor sheets in parallel terminating together at their radially outer ends and which terminate at their radially inner ends in a common radial plane and which sheets extend substantially the entire axial height of said coil, insulation between paralleled conductor sheets in each coil and between the spiral turns of paralleled sheets, a START terminal on one of said coils electrically connecting said radially outer ends of the paralleled sheets of said one coil together and a FINISH terminal on another of said coils electrically connecting said radially outer ends of the paralleled sheets of said another of said coils together, said plurality of coils being wound so that the direction of magnetic flux is the same in all of said coils, and means including a plurality of elongated flat crossover connector strips disposed in a common radial plane extending betWeen adjacent coils at the radially inner coil periphery in a direction parallel to the coil axis and joining oppositely disposed radially inner conductor sheet ends in said adjacent coils for electrically connecting said paralleled sheets in said plurality of coils in series relation, the radially inner ends of certain of said conductor sheets in one of said adjacent coils being offset in a radial direction and joined to crossover connector strips affixed to conductor sheets occupying different radial positions in said adjacent coil so that the net flux linkages of the plurality of conductor paths formed by said series connected conductor sheets are approximately equal.

2. An electrical winding in accordance with claim 1 wherein the radially inner end of the radially inner conductor sheet in said one coil is bent in U-shape to a different radial position so that it is joined to a conductor strip affixed to the radially inner end of the radially outer conductor sheet of said adjacent coil.

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