US3368174A - Spacer for pancake coils - Google Patents

Description

Feb. 6, 1968 HG JHSWIEFQ 3,368,174

SPACER FOR PANCAKE COILS I Originl Filed May 21; 1962 I 3 Sheets-Sheet 1 F ig. IA

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1? TL B INVENTOR Heinz G. Fischer ATTORNEY H. G. FISCHER SPACER FOR PANCAKE COILS Feb, 6, 1968 5 Sheets-Sheet 3 Original Filed May 21 1962 .Fig. 68

United States Patent 3,368,174 SPACER FOR PANCAKE COILS Heinz G. Fischer, Muncie, Ind., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Original application May 21, 1962, Ser. No. 196,089, now Patent No. 3,252,117, dated May 17, 1966. Divided and this application Oct. 11, 1965, Ser. No. 494,506

3 Claims. (Cl. 336-60) ABSTRACT OF THE DISCLOSURE An insulating and spacer member for axially separating pancake type coils in an electrical transformer. The insulating and spacer member is formed of a sheet of electrical insulating material having spaced ridges and furrows, which form first and second wavy opposed surfaces, the extremities of which lie on spaced parallel planes and define the axial dimension of the member. The insulating and spacer member has a plurality of transverse openings therein which extend completely through the member, and which co-operate with the ridges and furrows to direct cooling fluid in the transformer both longitudinally and transversely to said member.

This is a division of application Serial No. 196,089, filed May 21, 1962, now US. Patent 3,252,117, issued May 17, 1966.

This invention relates to windings for electrical inductive apparatus, such as transformers, and more particularly to an arrangement of insulation and conductors in the windings of such apparatus.

A method commonly used to construct windings for inductive apparatus is to form a flat disc or pancake type coil from a main conductor comprising a plurality of strands or conducting elements. When the current requirement of the apparatus is high, a sufficient number of these thin pancake coils are connected in a parallel circuit relationship to provide the necessary quantity of conducting material, or the number of strands per conductor has to be increased and the coils are connected in a series circuit relationship. In both cases a multiplicity of brazed joints are necessary to connect the individual coils. The plurality of parallel or series connected coils are separated by thin spacers or Washers which give support to the coils and still provide channels or paths which allow a cooling medium to flow in thermal communication with the coils.

When the current requirement of an inductive electrical apparatus is high, it would result in lower manufacturing costs if the winding could be constructed of coils having a larger quantity of conducting material, making it unnecessary to have a multiplicity of brazed joints. However, other problems must be solved if a coil having a large quantity of conducting material is to be as eflicient as a plurality of conventional coils connected in a parallel or series circuit relationship.

One such problem is the fact that eddy current losses in a copper conductor of an inductive apparatus, such as a transformer winding, vary with the square of the dimension of the conductor at right angles to the direction of the leakage flux, which in the case of the interleaved type of winding, is approximately at right angles to the axis of the winding or in the plane of the winding coils. To improve efiiciency of the electrical inductive apparatus, these eddy current losses are reduced in magnitude by subdividing the required conductor area into a plurality of parallel connected conducting elements or strands, which thereby reduces the dimension of the conductor at right angles with the direction of the leakage flux. The conducting strands or subdivided conductor elements are insulated from each other with paper, enamel, or other ice suitable insulation, and the several strands are wrapped or taped together to form a single conductor structure from which a coil is wound. Although the method just described reduces the eddy current losses in the windings of a transformer, there is an offsetting increase in losses due to circulating currents between the parallel connected strands or subdivided conducting elements. Losses due to circulating current in a winding whose coils are formed from parallel connected strands can be reduced by transposing the relative position of the strands with respect to the direction of the leakage flux. This transposing of the strands prevents some strands from being longer than others When they are wound concentrically, and averages out the fact that the self inductance caused by leakage flux is different in the individual strands.

Where the number of strands is small, as in the commonly used pancake type coil, the transposition of the strands can be easily accomplished. However, where high currents must be carried by the winding, several strands must be used and the transposition ofthe strands presents a greater problem. Cables with a multiplicity of transposed strands which are currently available have many disadvantages in that the conducting structure or cable dimensions increase at the transposition points and the strands spring apart and rub the edges of adjacent strands when the conducting structure or cable is bent with a small radius. It is, therefore, desirable to provide a winding for electrical inductive apparatus having a high current capacity and a plurality of conducting strands. The winding should have a new and improved transposition method to reduce losses due to eddy currents and circulating currents, and at the same time present a high degree of safety from short circuits between adjacent strands in the conducting structure or cable.

Further, since the coil having a large quantity of conducting material is thicker than the conventional pancake coils, cooling the coils becomes a major problem. The method commonly used to insulate adjacent pancake type coils involves cutting diamond or rectangular blocks from a fibrous material and gluing them in a definite predetermined pattern on a thin board formed of a fibrous material. This insulating board or washer insulates and supports adjacent coils and still allows a path for flow of the cooling medium between the coils. This process of constructing the insulating washer, however, is slow and expensive. It is, therefore, desirable to provide a winding for electrical inductive apparatus having a high current capacity and a plurality of conducting strands that has a new and improved cooling method and a new and improved insulating washer to separate the adjacent .coils in the winding.

Accordingly, it is an object of the invention to provide a winding for electrical apparatus having an improved insulation arrangement and more efficient path for the flow of the cooling medium.

Briefly, the present invention accomplishes the above cited object by providing a Winding for electrical apparatus which is suitable for high currents without brazing a multiplicity of coil sections in parallel or series.

The coil is comprised of a large number of conducting strands per conducting structure and is provided with an improved method for transposing the conducting strands. It is also provided with a new and improved method for cooling the coil turns and a new insulating washer for insulating adjacent coils and provide an improved path for flow of a cooling medium.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1A is a plan view of a coil of the type in which this invention may be employed;

FIG. 1B is a cross-sectional view, taken on line lB-IB of FIG. 1A, showing the relative locations of the conductors and insulating members, and the cooling method employed in this invention;

FIGS. 2A and 2B are cross-sectional views showing construction of main conductors that may be used to form the coil of FIGS. 1A and 113;

FIG. 3A is a plan view of a coil showing a coil turn formed of a plurality of conductors;

FIG. 3B shows the cross point between two coils;

FIGS. 4A and 4B show how the starting length of a coil is brought out and how the strands are bent to form the starting length;

FIGS. SAand 5B are right and left-hand isometric views showing the transposition method used in the coil of FIGS. lA'and 1B;

FIG. 5C shows the transposition sequence of the subdivided conductors within the coil of FIG. 1;

FIGS. 6A, 6B and 6C show the side elevation, top plan view and end elevation respectively of an insulating member which is used to insulate adjacent coils;

FIGS. 7A, 7B and 7C show another embodiment of the invention; and,

FIG. 8 shows how the insulating member used to in sulate adjacent coils may be cut from one sheet of in sulating material.

Referring to FIG. 1A of the drawings, a coil 10 of the type shown may be formed from a main conductor 12 comprising a plurality of parallel connected strands or subdivided elements 14. FIG. 2A shows a cross section of the main conductor 12 shown in FIG. 1A, illustrating in greater detail the plurality of parallel connected strands 14 and the strand insulating material 15. If desired, a subdivided strand 11, as shown in FIG. 2B may be used instead of the single wire strand 14. The subdivided strand 11 may be used to increase the current capabilities of the coil 10 shown in FIG. 1A without increasing eddy current losses or interfering with the winding procedure. The subdivided strand 11 is handled in the same manner as the single wire strand 14. The strands 14 are insulated from each other by enamel, paper, or other suitable insulation material 15 and the strands 14 are then taped or wrapped together, usually in two layers, to form a solid conducting structure or main conductor 12. Referring again to FIG. 1A, the main conductor 12 is then wound into a coil 10, with each turn 16 of the coil 10 insulated from the adjacent turn 16 by an insulating member 18. When very large currents are to be carried by the coil 10, or for other considerations, it may be desirable to connect a plurality of conductors 12 in parallel. FIG. 3A illustrates a coil 80 with two conductors 82 and 84 connected in a parallel circuit arrangement. The conductors 82 and 84 are crossed at the start 86 and finish 88 connections if more than one coil 80 per winding is used. An insulating material, such as pressboard is used to fill the space 90. FIG. 3B shows the crossing point between two coils viewed from point 3B in FIG. 3A. Connecting a plurality of conductors in parallel also improves the balance in a transformer as it allows a plurality of coils 80 to be connected in a series circuit relation instead of the parallel circuit relation that would be used for coils using a single conductor. An insulating member 18 may be used between the parallel connected conductors 82 and 84. Referring again to FIG. 1A, the insulating member 18 not only serves to insulate adjacent turns 16, but it spaces the turns and provides a path for a cooling medium only. This transverse or cross-flow of cooling medium through the coil makes possible the use of a coil having a multiplicity of conducting elements, because each conducting element in the main conductor is cfficiently and adequately cooled.

The insulating member 18 used to insulate adjacent turns must not only have good insulating qualities, but it must also have the strength to support the turns and still provide an adequate path for flow of a cooling medium. A fibrous material, shaped into continuous -'cor-' rugations, has been found to provide these necessary qualities and is very easy and economical to manufacture. FIG. 1A also shows quarter sections of a new insulation member 30 and 31) used to support and insulate adjacent coils. This insulating spacer washer 30 and 30' will be described in detail hereinafter.

Where one, or an odd number of these cross flow type coils are used per winding group, the start conductor-is brought out, as illustrated by conductor 12 in FIG. 1A. The standard type coil in use today commonly uses a prepared conductor, consisting of a plurality of insulated and transposed strands, brazed to the coil start 17. The transpositions are necessary in this prepared conductor because when the prepared conductor crosses the coil 10 adjacent to the turns 16, the prepared conductor is subjected to a very strong stray field, and because of the relatively short distance between the brazed joint of the prepared conductor to the coil start and the brazed joint to a bushing cable or similarconnection.

The design characteristics of the cross flow type coil, however, make the use of a separate prepared conductor and the accompanying brazed joint unnecessary. The cross flow type coil has a very long strand length per coil and the resistance of the strand loop is, therefore, relatively high. This higher resistance makes it practical to use the strands from the conductor that forms the coil to take the place of the prepared conductor, and transposition of the strands is unnecessary during this starting length. FIG. 4A shows in detail how the strands 14 are brought out to form the starting length of the conductor 12 for the coil 10. The strands 14 are bent so the two layers of strands 14 that form conductor 12, form one layer of wires while crossing the turns 16 of the coil 10. FIG. 4B shows the bending of the strands 14 of the conductor 12 to form one layer, viewed from point 4B-4B in FIG. 4A.

FIG. 1B is a cross-section, taken on line 113-113 of FIG. 1A, with the relative location of adjacent coils 31, insulating spacer washers 30, and flat pressboard washers 29 shown to illustrate the cooling medium flow path in detail. The coolant enters the coil at arrow 26 and leaves at arrow 28. To insure that the coolant traverses the coil through passageways 19 formed by the insulating members 18, the upper end of longitudinal passage 20 is blocked with a suitable member 22. The other longitudinal passageway 21 is blocked at the lower end with a member 24. With this arrangement of passageways, the cooling medium is forced to flow into the coil longitudinally at arrow 26 and along passage 20 formed by insulating spacer washer 30. Adjacent coils 31 are separated by a flat washer 29 formed of a pressboard or other suitable material. Since passage 20 is blocked by member 22, the coolant can only flow through the openings 19 between the turns 16 provided by the insulating spacers 18. When the coolant reaches passage 21, it cannot flow downward because of blocking member 24. Therefore, the coolant must flow through insulating spacer washer 30- and from the coil at arrow 28. It can readily be seen from FIG. 1B

- that this cross-flow cooling arrangement causes the coolto flow across the coil and in thermal communication 1 with each coil turn transversely. The thin pancake coils in common use provide for coolant to flow longitudinally ing medium to come into thermal communication with every conducting strand, and, therefore, making possible the use of a large number of conducting strands and hence the design of a very high current coil. To accomplish this cross-fiow cooling design, an insulating spacer or washer 30 and 30' was developed to insulate and space adjacent coils and at the same time provide the passageways and 21, shown in FIG. 1B. It is not only desirable that this insulating washer adequately insulate adjacent coils but it must provide the shortest free copper length, or distance between adjacent supports, to give support to the coil turns under normal and short circuit conditions. However, the obtaining of the shortest possible free copper length should not be accomplished at the expense of covering a large percentage of the coil surface with the insulating washer, as this would unduly hinder the flow of cooling medium.

A method commonly used to form these insulating washers consists of cutting specially shaped blocks from a fibrous material and gluing them to a fiber board in a predetermined pattern. This process is laborious and results in a spacer washer that produces a free copper length of two and three-quarter inches and covers approximately twenty percent of the coil surface.

FIGS. 6A, 6B and 60 show a new spacer washer developed for use in the cross-flow coil. This new spacer washer 30 completely eliminates the cutting and gluing of blocks. The washer consists of a heavy insulating board 30, corrugated or folded and shaped into parallel ridges and furrows so as to form a wavy surface. Points 32 on the spacer washer 30 contact and support adjacent coils and the cooling medium flows in the channels 34. To allow the cooling medium to flow transversely to the insulating spacer, as well as longitudinally, and hence allow all the cooling medium to traverse the coil, the washer 30 must have a suitable number of openings 36, as shown in FIGS. 6A and 6B. The openings 36 in the spacer washer 30 may be milled, punched, sawed or performed in some other suitable manner. If the openings 36 in the v spacer 30 are formed by a saw cut, the openings 36 will be in line across the washer 30, as shown in FIGS. 6A and 613. If the openings 36 are formed by punching, or by some other suitable method, the openings 36 may be placed in any desirable pattern, as shown in FIGS. 7A, 7B and 7C.

The spacer washer 30 not only provides an insulator between adjacent coils that is inexpensive and easy to manufacture, but it presents greater support to the coil turns with less hindrance to the flow of coolant than the conventional spacer washer. Using the new design spacer washer 30, the free copper length is reduced as opposed to the conventional washer. Also, the coil surface has less area covered when using the corrugated spacer washer 30than when using the conventional washer.

FIG. 8 shows an additional advantage of the new corrugated washer 30 as quarter sections 30 and 30" of the washer 30 may be cut from one large sheet of material 41. FIG. 8 shows how the cut should be made if a radius 42 is desired on the washer. The strips are the only excess material. FIG. 1A shows the quarter sections 30 and 30' and how they are placed relative to the coil 10.

FIG. 1B shows the individual conducting strands 14, which, as pointed out previously are necessary to reduce eddy current losses. The large number of strands 14 and the efiicient cross-flow method of cooling the conducting strands allows the construction of a single high current coil 10. However, to reduce circulating currents caused by the large number of parallel connected conducting strands 14, the strands 14 must be transposed, or continuously shifted about the main conductor 12 or cable axis without twisting the strands 14, and so that each strand 14 successively occupies the same position as is occupied by all the other strands 14.

One type of transposition, commonly used with a multiplicity of strands, is called the complete transposition. It involves two layers of conductors, with all conductors moving at a common transposition point to the opposite layer and in the mirror image of its original location. In other words, the strand in the upper left corner of one layer of strands would move to the lower right corner of the adjacent layer of strands and the strand in the upper right corner would move to the lower left corner.

This process is followed for all the strands. The complete transposition, however, causes a bulging of the main conductor at the transposition point and causes ed-ge-to-edge contact of the strands, making necessary the placement of additional insulation of these points. Also, it is diflicult to bend the main conductor in a small radius and impractical to perform the transposition automatically by a bending machine, as the bending angles differ for each strand, depending upon the number of strands used.

Another transposition, commonly called the full transposition, involves two layers of conducting strands, with several transposition points required to complete one full transposition. With this method, each strand moves to the space occupied previously by the adjacent strands. This process is repeated at successive intervals until each strand has occupied the same position as is occupied by all the other strands. Cable presently available using the full transposition has disadvantages in that there is a bulging of the cable at each transposition point and there is an edge-to-edge contact between some of the strands. Edge-to-edge contact of the strands should be avoided if a high degree of safety from short circuits is desirable. When the cable is bent into a coil, the pressure is increased at these edge-to-edge contacts and when the coils are pressed during assembly or stressed due to short circuits while in operation it is highly probably that the protective insulation will eventually become ineffective. This cable is also difiicult to bend flat in a small radius because of a tendency of the strands to spring apart and distort the cable.

The transposition method developed for use in the cross-flow coil previously described eliminates the disadvantages of the methods just discussed. FIGS. 5A and 5B show right and left-hand isometric views of a main conductor 50 with'the strands transposed according to the principles of the new method. FIG. 5C shows the sequence that may be followed to accomplish the transposition. In particular, a horizontal bend is made changing conducting strand 1 from one layer or row of strands to the other layer or row. Strand 1 is moved into a blank space 63 available in the adjacent layer because an odd number of strands is used to form the main conducting structure. This movement of conductor 1 can be seen in cross-sectional views 62 and 64 of FIG. 5C. Then, the conductive strands 2, 3,4 and 5, remaining in the layer vacated by strand 1, are simultaneously bent one conductor space in a vertical direction. Strand 2 takes the place formerly occupied by strand 1, strand 3 occupies the place previously occupied by strand 2, strand 4 occupies the place previously occupied by strand 3, and strand 5 occupies the place previously occupied by strand 4. This process leaves a blank space 65 as shown in crosssection 64 of FIG. 5C. At the next transition point, the blank space 65 is filled by strand 6, which is bent horizontally, and the strands 1, 9, 8 and 7 remaining inthe layer formerly occupied by strand 6 are bent in a vertical direction, leaving a blank space 67 as shown in crosssection 66 of FIG. 5C. This process is repeated until one full transposition has been completed, as shown in crosssection 74. As many full transpositions of this type may be used per cross-flow coil as may be found desirable.

Although, the above description outlines a transposition where the individual strands move about the main conductor axis in a clockwise direction, as shown in FIG. 50, it is not meant to be so limited. For instance, the first step in the transposition could be a vertical bend by conductors 9, 8, 7 and 6, as shown in crosssection 62 of FIG. 5C, thus filling the vacancy 63. The next step would then be a horizontal bend by conductor 5 into the next layer and the space previously occupied by strand 6. With this method, the strands would rotate counterclockwise about the main conductor axis.

To maintain dimensions 51 and 53 uniform throughout the length of the main conductor or cable 50, an odd number of conducting strands 52 are used, with the blank space between transposition points occupied with afiller .piece 54 or strip, such as pressboard. Using a filler 54, the cable 50 can maintain auniform shape throughout its length, whether or not there is a transposition, ;and the dimensions of the cable will not change. In summary, an odd number of conductors are used so that the first bend always moves a strand into the vacant space, leaving a vacant space for other conductors, and therefore, allowing all the bends to be made without creating a bulge in the conducting structure.

From FIG. C, it can be seen that at each transposition point, only one conducting-strand 52 changes from one layer to another, with the other bends being made within one of the layers. As pointed out previously, this conducting strand always moves into a vacant space which is present because of the odd number of conducting strands. Then the remaining conducting strands, in the layer just vacated by the strands moving to the other layer, all simultaneously move one space, thus filling the newly vacated space and creating a space at the other end of the layer. This process is successively repeated until each conducting strand has occupied the space occupied by every other strand, and has made a complete circuit around the axis of the main conductor or cable.

It is. veryimportant that all bends 62 performed in the same layer and all bends 60 moving a strand from one layer to the next be made over a very short distance and not gradually. The distance 58, between the point 62 where all strands are simultaneously bent in one layer, to the point 62 where all strands are simultaneously bent in the other layer, depends upon the number of transpositions required in one coil. However, this distance should not be too small. For example, in one coil design it was found that a minimum distance 58 of three inches was required. The distance between the bend where one strand 52 changes layers or the horizontal bend 60, and the bend where all conductors in one layer are bent or the vertical bend 62, is very critical, and should allow enough space for the strand which changes layers to move back and forth. For one coil design this distance was found to be a minimum of three-quarter inch. During distance 56, all strands 52 have flat surface to fiat surface contact and the horizontal transposition or bend 60 can slide back and forth when the main conductor 50 is bent flat, even over a radius as small as 2 inches, without an edge-to-edge contact and resultant insulation scraping.

\ With this transposition method, all horizontal bends 60 are identical and all vertical bends 62 are identical. Therefore, the angle of the bends is dependent only on the size of the conducting strand 52 and not on the number of conducting strands used. This makes it practical to accomplish the bends in a transposing machine. Also, by accurately bending each strand over a short distance with the sameangle, the strands have no tendency to spring out of the main conductor or cable 50 and there is no bulging or change in cable dimension, even when bent flat over a small radius.

It will, therefore, be apparent that there has been disclosed a new and improved winding for electrical apparatus. It is a winding that is capable of carrying high current and yet is efficiently cooled and with low losses due to eddy currents and circulating currents. Also, it is a winding that has an improved insulating arrangement and more efiicient path for the flow of cooling medium.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereof. will-readily occur,

to those skilled in the art. For example, the coil. described applicable to the high voltage side of inductive apparatus. Further, the dimensions given arefor illustrative purposes only and are not to limit in any way the subjectm'att'er of this invention.

Since numerous changes may be made in 'the abovje described apparatus and different embodiments" or the" invention may be made without departing from the spirit thereof, it is intended that all the matter contained -in' the foregoing description or shown in'the accompanying drawings shall be interpreted as illustrative, and not in a limiting sense. 1 I claim as my invention: v

1. An insulating and spacer member for axiallysep arating, contacting, and mechanically restraining adjacent pancake type coils in an electrical transformer containing a cooling medium, comprising: a substantially flat washershaped insulating structure having a predetermined outer configuration and a central opening therein; said washer shaped insulating structure being formed of at least one sheet of electrical insulating material, said at least one sheet of electrical insulating mtaerial having a plurality of spaced ridges and furrows which form first and second wavy opposed surfaces, the extremities of which lie on first and second spaced parallel planes and define the effective axial dimension of the insulating structure; said sheet member having a plurality of transverse openings therein which extend completely through said sheet member, and which are defined, at least in part, by certain of the extremities of its wavy surfaces; said ridges and furrows and said plurality of transverse openings in said sheet member cooperating to direct a cooling fluid both longitudinally and transversely to said sheet mem-, her, when it is disposed between axially adjacent coils of the electrical transformer. 2. The insulating and spacer member of claim 1 where; in said substantially fiat washer shaped insulating structure includes a plurality of said sheet members disposed in substantially the same plane and arranged incontacting relation, to each define a portion of the predetermined outer configuration, and a portion of the central open: ing of said washer shaped insulating structure. 7 i

3, The insulating and spacer member of claim2wherein the relative direction of the ridges and furrows is differ: ent in at least certain of said plurality of sheet members.

References Cited LEWIS'H. MEYERS, Primary Examiner. E. GOLDBERG, Assistarzt Examiner.

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