US3705371A

US3705371A - Electrical winding

Info

Publication number: US3705371A
Application number: US228076A
Authority: US
Inventors: Robert I Van Nice
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1972-02-22
Filing date: 1972-02-22
Publication date: 1972-12-05
Anticipated expiration: 1989-12-05
Also published as: JPS5242329Y2; FR2173188B1; CS171279B2; JPS48111807U; FR2173188A1

Abstract

Winding structures having two or more interconnected winding groups. The winding groups have different levels of surge voltage strength, with the group having the highest level being electrically located nearest to a line end of the winding structure. In a first embodiment, the winding group nearest the line end is a single disc winding with the disc spacing adjusted to provide a uniform series capacitance throughout the winding structure. In a second embodiment, an interleaved turn winding group is connected between the winding groups of the first embodiment and the line end of the winding.

Description

United States Patent Van Nice [451 Dec. 5, 1972 [54] ELECTRICAL WINDING [72] Robert 1. Van Nice, Sharon, Pa.

[73] Westinghouse Electric Corporation,

Pittsburgh, Pa. I

Feb. 22, 1912- 228,076

Inventor:

Assignees Filed:

App]. No.:

us. (:1 .Q. ..336/70, 336/187 1m. c1 .1m1r 15/14 References Cited UNITED STATES'PATENTS 3,479,629 11/1969 Brosm.... ..336/70 FieldoiSearch; ..336/6 9,7() ,l86,187"

Primary Examiner-Thomas J. Kozma Attorney-A. T. Stratton et a1.

[57] ABSTRACT winding structure. In a second embodiment, an inter-' leaved turn winding group is connected between the winding groups of the first embodiment and the line end of the winding.

7 Claims, 7 Drawing Figures H H HF 1 Q sl -L lTB 1 WA 1813] 18A I ISBI 19A [2015 [20A PATENTEDnEc 5l972 3,705 371 V saw u or a FIG? -1 ELECTRICAL WINDI G BACKGROUND OF THE INVENTION which apply a fast rise voltagepulse to the transformer winding. The high frequency characteristics of the surge voltage cause it. to distribute across the winding initially according to the' capacitive structure of the winding rather than to its inductive structure.

From a studyof the well-known equivalent capacitivecircuit for this type of transformer winding, it has been found advantageous to make the ratio of the series capacitance to the groundcapacitance high. In general, the higher this ratio, the more evenly the surge voltage is distributed along the winding. When the ratio is relatively low, the line end portion of the transformer winding is stressed morethan theother portions of the winding. Hence, the winding insulation structure must often be strengthened ;at the line end of such windings to prevent failure from surge voltages.

' Various arrangements have been proposed and used in the prior art toenhance the surge strength of a trans- I former winding. Some have been economically feasible, but others have provided the desired characteristics with arrangements that are costly to construct. One basic method for improving the surgestren gth is to increase the insulation near the lineend or ends of the winding, that is, where the stressiis the greatest. This method has the disadvantage .of increasing the surge stresses also, because the series capacitance is reduced and the inductance per unit length is'reduced. Another basic method known in the prior art involves special winding techniques, such as theinterleaving of turns to make the series capacitance as high as practical. The first of these methods reduces the space factor of the transformer, and'both of these methods adversely affect the cost. I 1

Hybrid windings consisting of high series capacitance coils at line ends and conventional and lower cost coils, for the remainder of the winding have also been proposed. Some of these have been useful; however, the series capacitance discontinuity which exists between the difi'erent forms of winding coils is conducive to voltage oscillations in the winding. Several arrangements have been used to reduce this series I capacitance discontinuity, such as the arrangement-disclosed in U.S. Case No. 41 ,930, filedDec. 8, 1970, Ser.

An'ideal power transformer winding would have high series capacitance, high voltage break-down particularly at the line end, and relatively low manufacturing costs. Unfortunately, the arrangements known in the nected by start-start and finish-finish connections.-

Although the double-disc winding involves a minimal amount of hand labor to construct, the potential between discs is greater than with a single-disc winding. In a single-disc winding, adjacent coil discs are interconnected by start-finish connections. Although the potential distribution with single-disc coils is better, the labor involved in winding and interconnecting'the single coil discs is greater than in double-disc windings.

' It is desirable, and it is an object of this invention, to provide adisc-type winding which has excellent surge voltage characteristics without significantly increasing the manufacturing costs of the winding.

It is also desirable, and it is another object of this invention, to provide a transformer winding structure which exhibits a substantially constant. series capacitance and inductance throughout the axial length of the winding.

SUMMARY OF THE INVENTION There are disclosed herein new and useful winding structure arrangements which economically enhance the surge voltage strength of the winding structure. The

winding structure comprises at least two winding groups. A first group consists of double-disc continuous for by making the disc-to-disc spacing in the second winding group less than in the first winding group. In

anotherembodiment of this invention, a third or interleaved turn disc coil winding group is positioned-at the line end." This third winding group is specially constructed to have a moderate value of series capacitance to prevent a large discontinuity in series capacitance between the-winding groups.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawings, in which:

prior art for increasing the series capacitance and-the FIG. 1 is a partial view of a transformer constructed according to one embodiment of this invention with the groups of the windings shown in phantom;

FIGS. 2, 3 and 4 are schematic diagrams of winding structures constructed according to embodiments of this invention; I

FIG. 5 is a table listing typical spacing distances, in inches, for the winding structures shown in FIGS. 2, 3 and.

FIG. 6 is a partial view of a transformer constructed I according to an embodiment of this invention having three winding groups; and

FIG. 7 is a schematic diagram of a winding structure constructed with three winding groups.

DESCRIPTION OF THE PREFERRED I EMBODIMENTS prises a plurality of coil discs which are wound, connectedand spaced such thatthe surge voltage strength of the winding group 14 is greater than that of the winding group 16. The winding group 16 comprises a plurality of coil discs which are less expensive to construct than the discs of the winding group 14. By constructing the winding 12 from separate winding groups possessing different qualities, the overall surge voltage strength of the winding 12 is better than it would be if constructed entirely of the winding group 16. This is achieved without substantially increasing the cost of constructing the winding 12.

The portion of the winding 12 which is shownis connected only to the line lead 22. The other end of the winding 12, although not illustrated,would be connected to another lead.This other lead may or may not be'connected to line potential and subjected to high surge voltages. In general, when the winding is delta finish-finish connection 40 and the coil disc 36 is interconnected to the coil disc 34 by the transposed startstart connection 42.

By connecting adjacent coil discs with start-finish connections in the winding group 14, the maximum voltage developed between the discs is less than that which would be obtained with start-start or finish-finish connections as shown in the winding group 16. The maximum voltage between discs having start-finish connections is about one-half that of discs having startstart or finish-finish connections. Consequently, the surge voltage strength of the winding group 14 is greater than that of the winding group 16 and this is desirable since higher surge voltage strength is needed near the line end of the winding 12. By thisarrangement of the coil disc interconnections, the winding group 16 may be constructed of the less expensive start-start and finish-finish connected coil discs and the winding group 14 may be constructed of start-finish connected coil discs which have a lower disc-to-disc connected, both leads would be connected to line potential. When wye connected, one lead would be connected to a neutral point which may be grounded. When both leads are connected to line potential, a

winding group having a high surge voltage strength should be adjacent both ends of the winding 12. For simplicity reasons, only one end of the winding 12 will be shown and described in detail. The other end may or may not have a high surge strength'winding group located thereat.

} FIG. 2 illustrates a physical and electrical schematic of a winding 12 constructed according to one embodiment of this invention. A. laminated magnetic core 10 is surrounded by a low-voltage winding 24 which has an insulation structure 26 disposed thereabout. The highvoltage winding 12 comprises the winding

groups

14 and 16. The winding group 14 comprises a plurality of coil discs, each axially positioned at a different location in the winding group 14. Each coil disc involves four conductor-turns, such as lA-lB, 2A-2B, 3A- 3B and 4A-4B in the coil disc 28. The numbers represent the turns and the letters represent the conductor strands.

Thus, the coil disc 28 is wound with four turns of two This nomenclature applies to other coil discs in this and other figures;

The coil disc 30 is interconnected to the coil disc 28 by the start-finish connection 31 in which the A and B strands are suitably transposed. The start-finish convoltage.

It is desirable in voltage stress calculations to have a uniform series capacitance between the coil discs of the winding groups. From an operation standpoint, this reduces oscillations in the winding and prevents the shifting of surge voltage stresses from the line end 'coil discs to the coil discs in other portions of the winding. It can be calculated and measured that the capacitance between coil discs which are interconnected by starttinish connections is about 75 percent of that which exists between coil discs with the same spacing but which are interconnected by start-start or finish-finish connections.

To make the series capacitance uniform in the winding 12 of FIG. 1, it is necessary to make the separation distances S1, S2 and S3 between the

coil discs

28, 30, 32 and 34 approximately 75% of the separation distances S4 and S5 between the

coil discs

34, 36 and 38. Typical spacings, in inches, are tabulated in FIG. 5. With this arrangement of disc spacings, the series capacitance throughout the winding 12 is substantially constant. Without the decrease in separation distances S1, S2 and S3, more surge voltage would be developed between the

coil discs

28, 30, 32 and 34 because of the capacitive structure of the winding 12.

Decreasing the separation distances S1, S2 and S3 increases the voltage gradient between the

discs

28, 30, 32 and 34 somewhat. However, because of the nonlinearity of the breakdown voltage with respect to the separation distance, the breakdown voltage remains at a substantially safe value for the small distance changes taught by this invention. Typically, a 25 percent reduction in spacing reduces the breakdown voltage by only about 20 percent. Since the voltage stress has decreased by about percent to percent with the start-finish connection, the overall voltage stress has increased on the order of 45 percent greater than the surge voltage strength between the coil discs of the winding group 16. The stress has decreased much more than the strength. The spacing arrangements for the t windinggroup 16 which are taught bythis invention are contrary to ordinary prior art practices. Previously, disc spacings have been increased near the line end in attempts to achieve better surge voltage strength.

The. reduction of disc spacing in the winding group 14 increases the inductance per unit length of the winding group 14 over the winding group-16. In order to maintain a constant inductance per unit length .throughout the winding 12, the coil discs of the winding group 14 may be wound with fewer turns than the discs in the winding group 16. Normally, about a 5 percent reduction in turns is required to make the inductance per unit length uniform. The small variation in inductance per unit length caused .by the different spacings is not particularly critical, and it is within the contemplation of this invention that the number of coil disc turns may or may not be changed to provide a substantially uniform inductance per unit length.

Manufacturing costs in constructing a disc-type winding depend largely upon the type of the winding. Normally, the double-disc winding, such as the winding group 16 of FIG. 1, may be wound less expensively than thesingle-disc winding, such as the winding group 14 of FIG. 1. With a double-disc winding, only every other disc must bewound and manually rebuilt to make the turn spiral inwardly. In a single-disc winding which is be rebuilt. Additionally, and also costly, in single disc windings the start-finish connections are manually made and, especially if they require metal joining operations at the start and finish turns, and less economical thanstart-start or finish-finish connections which are. simply formed by bending. Thus, from an economical standpoint, manufacturing costs will usually be reduced by windingthe coil discs in a manner which will require, the least amount of rebuild- FIG. 3 illustrates a winding 12 which comprises a winding group 14 constructed of coildiscs 44. 46 and 48 which have conductors that spiral outwardly. The line lead 22 is connected to the start conductor turn lA-lB. The discs are interconnected by the start-finish *Reducing the spacings between the coil discs which are connected by start-finish connections may impose a clearance restriction between the discs for the physical placement of the start-finish connection. FIG. 4 illustrates an arrangement which may be used to provide a windinggroup having higher surge strength than a dollhie-disc winding group. In this embodiment, the winding group 14 comprisescoil discs which are interconnected by start-finish connections and by a start-start connection. A similar arrangement would be obtained with a finish-finish connection in place of the start-start connection, in which case discs 66 and 68 would be replaced by a pair of discs similar to the discs 60 and 62 The coil discs 60 and 62 are interconnected by the start-finish connection 64 which is physically located between the coil discs 62 and 66. The coil discs 62 and started at the finish end of the first disc, every disc must a 6 66 have a greater spacing than the coil discs and 62 to provide substantially uniform disc-to-disc capacitance throughout the winding 12. The extra spacing is adequate for placement of the connection 64. Typical spacings are tabulated, in inches, in FIG. 5. Additional discs interconnected by start-finish-connections, such as the connection 68, may be included in the winding group 14. As with the other embodiments of this invention, the number of discs, or repeating disc patterns, per winding group is determined by'the type and rating of the winding and may be changed without departing from the scope of the invention. a

The teachings of this invention may be combined with other winding arrangements to provide a winging having suitable surge voltage strength. FIG. 6 illustrates the winding

groups

14,16 and17f which are interconnected by the leads 18and 19. The winding

groups

14 and 16 may be similar to the winding groups taught in the other embodiments of this invention. The winding group 17 may comprise a plurality of interleaved-turn coil discs which provide a suitable series capacitance in relation to the series capacitance of the winding groups- 14 and 16. I

FIG. 7 illustrates an embodiment of the invention which is shown generally in FIG. 6. The winding group 17 is described in detail in US. Case No. 41 ,930, filed Dec. 8, I970, Ser. No. 96,0l0, and may be constructed in any of the arrangements taught by that patent.

In general, the

coil discs

70, 72, 74 and 76 are spirally wound to form a plurality of conductor-turns. Following the nomenclature used inthe referenced patent, the conductor-turns are numbered according to their electrical distance from the line lead 22. For example, conductor-turn 2 has two turns electrically connected between it and the line lead 22. Although a single conductor is illustrated, multipleconductors may be used in any of the winding groups and such is within the contemplation of this invention.

Turn insulation, such as the insulation 78, is shown thicker in the winding group 17 than in the other winding groups. This is one means by which the series capacitance of the winding group 17 may be kept ata satisfactory level for suitable matching to the series capacitance of the other winding groups. In order to prevent an extreme discontinuity in the series capacitance of the winding

groups

14 and 17, the series capacitance of the interleaved-turn winding group 17 is purposely maintained at a value equal to lessthan approximately four times the series capacitance of the other winding groups. A value of two is satisfactory. The series capacitance of the interleaved-turn winding group 17 is due largely to the capacitance between the conductor turns. The series capacitance of the continuous winding groups is due largely to the disc-to-disc capacitance in transformers having medium power ratings. Thus, the series capacitance per disc in the winding group 17 would be in the order of two times the series capacitance per disc in the winding

groups

14 and 16. The ease of matching the winding group 17 to the winding

groups

14 and 16 is a further advantage of this arrangement. Since the combination of the winding

groups

14 and 16 permits a high series capacitance, the desired ratio of the winding group 17 capacitance to the capacitance of the winding

groups

14 and 16 is more easily obtained. In some applications, the turn intions areshown to conform to the description in the referenced patent, there are physically only eight conductor'turns per disc in the winding group 1 7. Exaggerated radial build is also the result of the exaggerated turn insulation thickness in the coil discs of the winding group 17. The winding

groups

14 and 16 use a single conductorto conform to the single conductor winding group 17. As hasalready been stated, this invention also applies to coil discs havingmore than one conductorpercoilturn.

The winding arrangements disclosed herein provide economical solutions to the problem of high surge voltage stresses 'at the line end or ends of a transformer winding. Since numerous changes may be made in the above-described apparatus and different embodiments of this invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in theforegoing description, or shown in the accompanying drawings, shall be interpreted as illustrative rather than limiting.

I claim as my invention:

1. A winding structure for electrical inductive apparatus comprising a line lead, first and second winding groups, said first winding group having a plurality of axially spaced coil discs each having start and finish conductor-turns, said second winding group having a plurality of axially spaced coil discs each having start and finish conductor-turns, said first winding group being disposed electrically closer to said line lead than said second winding group, start-finish connections which interconnect adjacent coil discs in said first winding group, start-start and finish-finish connections which interconnect the coil discs in said second winding group.

2. The winding structure of claim 1 wherein adjacent coil discs in the first winding group are spaced to provide substantially the same capacitance per disc in the first winding group as exists in the second winding group.

3. The winding structure of claim 1 wherein adjacent coil discs in the first winding group are spaced approximately three-fourths of the spacing between adjacent coil discs in the second winding group.

4. The winding structure of claim 1 wherein the first winding group comprises first, second and third coil discs, said second coil disc being axially disposed between said first and third coil discs, said first and second coil discs being interconnected by a start-finish connection, said second and third coil discs being interconnected by a start-start connection when said second and third coil discs are interconnected to adjacent coil discs by their finish conductor-tums' and being interconnected by a finish-finish connection when said second and third coil discs are connected to adjacent coil discs by their start conductor-turns, said first and second coil discs being spaced to provide substantially the same capacitance between said first and second coil discs as'exists between said second and third coil discs.

5. The winding structure of claim 4 wherein the first and second coil discs are spaced approximately threefourths of the distance et ween the second and third coil discs, and the startmish connection between the first and second coil discs is physically positioned between said second and third coil discs.

6. The winding structure of claim 1 including a third winding group, said third winding group being located electrically closer to the line lead than the first winding group, said third winding group comprising a plurality of axially spaced coil discs each having start and finish conductor-turns, means interconnecting predetermined ends of adjacent coil discs of said third winding group in series circuit relationship, the coil discs of said third winding group being of the interleaved turn type wherein electrically connected turns are physically separated by turns from an electrically distant portion of the coil disc, the axial spacing of adjacent coil discs in said third winding group exceeding the axial spacing of adjacent coil discs in the first and second winding groups.

7. The winding structure of claim 6 wherein the coil discs of the third winding section have a degree of interleaving and spacing between turns which provides a series capacitance per disc approximately equal to four times the series capacitance of the discs in the first and second winding groups.

Claims

4. The winding structure of claim 1 wherein the first winding group comprises first, second and third coil discs, said second coil disc being axially disposed between said first and third coil discs, said first and second coil discs being interconnected by a start-finish connection, said second and third coil discs being interconnected by a start-start connection when said second and third coil discs are interconnected to adjacent coil discs by their finish conductor-turns and being interconnected by a finish-finish connection when said second and third coil discs are connected to adjacent coil discs by their start conductor-turns, said first and second coil discs being spaced to provide substantially the same capacitance between said first and second coil discs as exists between said second and third coil discs.

5. The winding structure of claiM 4 wherein the first and second coil discs are spaced approximately three-fourths of the distance between the second and third coil discs, and the start-finish connection between the first and second coil discs is physically positioned between said second and third coil discs.