US3731244A - Transposition of insulating core windings - Google Patents

Abstract

A device for reducing the incidence of circulating currents within the coil structure of multiple-conductor windings of transformer/reactors of the insulating magnetic core type, by a transposition of the electrical connections between the several conductors of the multiple-conductor winding at the outer part of the winding after the core and coil assembly is completed. When effecting the necessary electrical connections between adjacent outer layers of winding, connections between analogous conductors of the multiple-conductor bundle are interchanged, the outermost conductor of one bundle being connected to the innermost conductor of the other bundle, second-outermost conductor of the one bundle being connected to the second-innermost conductor of the other bundle, and so forth.

Description

United States Patent [191 Johnson 1 51 May 1, 1973 [54] TRANSPOSITION OF INSULATING [73] Assignee: High Voltage Power Corporation,

Westboro, Mass.

22 Filed: July 3,1972 21 Appl. Na; 268,761

[52] US. Cl. ..336/l87, 336/212, 336/219 [51] Int. Cl. ..H01f 27/28 [58] Field of Search ..336/69, 70, 180,

[56] References Cited UNITED STATES PATENTS Primary Examiner-Thomas J. Kozma Att0rneyHenry C. Nields [57] ABSTRACT A device for reducing the incidence of circulating currents within the coil structure of multiple-conductor windings of transformer/reactors of the insulating magnetic core type, by a transposition of the electrical connections between the several conductors of the multiple-conductor winding at the outer part of the winding after the core and coil assembly is completed. When effecting the necessary electrical connections between adjacent outer layers of winding, connections between analogous conductors of the multiple-conductor bundle are interchanged, the outermost conductor of one bundle being connected to the innermost conductor of the other bundle, second-outermost conductor of the one bundle being connected to the second-innermost conductor of the other bundle, and so forth.

PATENTEDHAY 1 1915 SHEET 1 OF 2 TRANSPOSITION OF INSULATING CORE WINDINGS BACKGROUND OF THE INVENTION This invention relates to high-voltage insulating core type electrical induction apparatus and more particularly to a device for reducing power loss in such apparatus by employing multiple conductor bundle windings but avoiding difficult internal transpositions.

Today, the pressing requirement for more and cheaper electrical power faces growing technical and esthetic problems including the national desire to maintain the attractiveness of populated areas. To meet this continuing need for more electric power without adding more generating and transmission systems within cities and surburban areas, electric utilities are now building power plants in remote regions close to the source of either large amounts of hydropower or large coal deposits. This power can be transmitted to load centers most economically by overhead transmission lines. However, because of increased population density and pressure to preserve the esthetic and economic values of the countryside, transmission rights-of-way are increasingly difficult to obtain. The utilities are thus compelled to increase several-fold the power transmitting capacity of their existing right of ways, and to plan on still further increases in power in the future. Forthese and other reasons, the electric power industry is rapidly converting to extra high voltage (El-IV) for the transmission of electric power having line-toline voltages in excess of 345 KV. Already 500 KV systems are in service, and more recently 765 KV systems have been energized. Such high voltages permit the transfer of larger blocks of power over extensive geographic areas. EHV interconnections are also used to even out demands over large regions and to improve the reliability of the total system. Indeed, the trend toward higher voltages is fundamental to meeting the predictable power needs of the next decade.

As electrical devices have developed, different techniques have evolved depending upon the magnitude of the various parameters involved. For example, high voltage d.c. equipment entails strong electric fields and high power a-c equipment has come to entail strong magnetic fields. Specialized techniques have been worked out for handling these strong electric fields in high voltage d.c. equipment: for example, megavolt accelerator apparatus employ hollow, rounded high voltage terminals and equipotential planes for controlling the electric field and shaping it uniformly. On the other hand, different specialized techniques have been worked out for handling the strong magnetic fields of high power a.c. equipment: for example, ferromagnetic material is used to form magnetic circuits in which elaborate steps are taken to minimize reluctance and eddy currents. However, the need for these specialized techniques exists only for certain ranges of certain parameters. For example, conventional household appliances do not require special techniques for shaping electric fields, and high-voltage electrostatic accelerators do not require ferromagnetic material.

Conventional electric power techniques have evolved in a similar manner. Initial efforts involved d.c. and the requirements of average household equipment, such as lighting, led to voltages of the order of volts.

With the development of a.c. and transmission of electric power over greater distances at higher voltages to reduce losses in transmission, apparatus capable of handling voltages of the order of 10 volts were developed, and related insulating and magnetic circuit techniques were devised. Such techniques were limited to their own range, however, and the more recent interest in even higher voltages for power transmission has triggered a need for fundamentally new approaches and has generated new generic names: EHV (which stands for extra high voltage and includes the range 345-765 kilovolts in overhead systems and 230 kilovolts and up in underground systems) and UHV (which stands for ultra-high voltage and includes the voltages above 765 kilovolts now contemplated for overhead transmission). At the extra-high voltage range, problems not before faced must be solved: the Ferranti effect becomes a problem in transmission lines, the strong magnetic fields required by transformers must overlap the strong electric fields which must be controlled at these high voltages, and other new problems arise.

The basic approach to the design of apparatus for coping with strong electric and magnetic fields is disclosed in the insulating-core patents of Van de Graaff, and more recently of Trump, et al. US. Pat. No. 3,684,991. The present invention is an improvement and refinement of these approaches in which insulating-core principles are applied to electromagnetic induction apparatus for use with EHV and UI-IV transmission lines for the absorption and storage of large quantities of electric charge associated with the capacitance of long transmission lines, or in the transfer of power from one voltage level to another in such large megavoltampere amounts.

Due in part to the insulating gapsin the magnetic core of such devices, a significant magnetic field frequently exists in the coil structure, beyond the physical boundaries of the core. Changes in the magnetic field may thus induce eddy currents in the coil conductors resulting in inefficiencies from losses in the form of heat and of attendant deterioration of insulation and reduction of life of the device.

Since eddy current loss decreases relatively quickly when conductor thickness is decreased in the dimension transverse to that of the magnetic field, it is possible, subject to practical limitations, to reduce eddy current incidence by subdividing the conductor in the dimension extending radially from the axis of the magnetic field, so that the conductor thickness in this radial dimension is relatively small. In order to preserve current-handling capability of the winding in high-power apparatus, one must preserve or even increase the dimension of the conductor in the dimension parallel to that of the magnetic field. Accordingly, reducing eddy currents in high-power apparatus may result in a winding which has a plurality of lengths of conductive tape. In insulating-core apparatus of this type, the inner extremity of each tape is connected to a ferromagnetic core element, and the tape is spirally wound in a layer about said core element. Depending upon the extent of subdivision of the conductor to reduce eddy currents, two or more such tapes in each spiral layer are connected in parallel.

Because the insulating core construction requires the connection of each tape to the core at the tapes inner extremity, the conductor-subdivision required for eddy current reduction results in parallel paths between such connections. I have discovered that circulating currents resulting in substantial power loss occur in the closed paths formed by such parallel paths unless special precautions are taken, in accordance with the invention, to insure that the electromotive force generated about each such closed path is minimized.

In accordance with the invention, the outer extremities of such tapes are not connected to each other, and in making the necessary connections between adjacent spiral layers, the outer extremity of each tape is connected only to the outer extremity of that adjacent tape which will minimize the electromotive force around the loops formed by the parallel paths between the inner extremities of the two tapes thus connected at their outer extremities. In other words, the electromotive force generated between the inner extremities of each thus-connected pair of tapes in a pair of adjacent spiral layers is substantially the same for all such tape-pairs.

More specifically, in insulating core type transformer/reactors it may be desirable to utilize a winding of n individual conductors. An individual conductor may be a conductive tape or band, and a conductor bundle may be n such tapes juxtaposed in front-to-back insulated relation and spirally wound about a core element to form substantially a disc-shaped coil section. At the inside of each coil section, all the conductors of the coil are electrically connected to the associated core element. To minimize circulating currents, it is important that the electromotive force in all conductors between adjacent core connection loci be substantially identical. However, in any turn of the spiral coil, the n conductors of a bundle each follow different paths with respect to the magnetic flux surrounding the core. As the spatial relation of the conductors to each other remains constant from turn to turn of the spiral section, this path-flux discrepancy between the various conductors of the bundle is augmented with every turn of the coil.

At any point along the length of the wound conductor bundle, the individual conductors may be related by their distances from that point to the core element (measured along a line through and perpendicular to the longitudinal core axis). One conductor will be closest to the core, one farthest, and others intermediate distances. If this measurement is performed at another location along the length of a wound bundle, the same conductor will be found to be closest (farthest) to the core as was determined in the first measurement, and,in general, the i'" closest conductor of the bundle at one location is the i" closest conductor at any location. This ordering relation of course cor" responds to the order in which the conductors are juxtaposed in front-to-back relationship when being spirally wound. Therefore, the conductors of the bundle may unambiguously be designated by terminology such as innermost, outermost, second-innermost, etc.

It will readily be recognized in such an arrangement that, at any location along the spirally wound conductor bundle, any two individual conductors are related also in the following ways:

1. The inner conductor has a greater instantaneous curvature than the outer conductor,

2. The length of the inner conductor from the core to the selected bundle location is less than the corresponding length of the outer conductor,

3. The inner conductor couples fewer lines of magnetic flux than does the outer conductor. Therefore, the flux-induced electromotive force will differ between these two conductors, thereby contributing to an EMF discrepancy between parallel conductive pathways between adjacent core connection loci.

The present invention provides a construction and transposition which will tend to reduce the flux-induced EMF discrepancies among the individual conductors of the multiple conductor winding, minimize eddy and circulating current incidence and resultant power loss and thermal deterioration of insulation. While the efficiency of the invention will vary depending on the symmetries of the conductor-coil arrangements and the magnetic field outside the core in the vicinity of the coils, excellent results are achieved with the spirally wound disc-like coil sections suggested above and described more fully below in connection with the preferred embodiments.

It is an important feature of the present invention that the transposition involves only the outer edge of the winding. This permits transposition after the assembly of the core and coil structure and allows the transposition to occur where magnetic flux is minimal or near-zero. Due to the nature of insulating core type induction devices, internal transpositions are effected only with great difficulty. Additionally, the transposition of the present invention does not add significantlv to theexpense or size of the coil or winding structure, and there is no interference with the surge and distribution method of the transformer/reactor. The invention works effectively with two, three, four, or a larger number of individual conductors within the bundle.

SUMMARY OFTHE INVENTION Briefly, the present invention accomplishes the above objectives by interchanging the electrical con-.

nections between individual conductors in windings of the aforementioned type. Suchinterchange occurs at the points, on the outer layer of winding, where windings associated with adjacent core elements are to be electrically connected. In particular, where a conductor bundle contains n individual conductors, ordered in the above-described sense, the i"'-outermost conductor of the bundle associated with one core element is connected to the i"-innermost conductor of the bundle associated with the adjacent core element, for values ofi=l ,2, n.

BRIEF DESCRWTION OF THE DRAWINGS FIG. 1 shows a diagrammatic view of a reactor of the insulating core type.

FIG. 2 shows the manner in which coil sections are wound.

FIG. 3 shows an alternate manner of winding adjacent coil sections associated with the same core element.

FIGS. 4, 5, 6 indicate possible coil configurations and the scheme of electrical connections between adjacent coil sections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention may be seen in connection with FIG. 1, which shows an insulating core type reactor useful in handling high voltages.

Here the magnetic circuit comprises a pair of end yokes 11 and 12 which couple a pair of segmented legs 13 and 14, each formed of a plurality of similar, coaxially aligned core elements such as 15 and 15', with insulating layers 18 separating the core elements.

Surrounding each core segment 15 is a coil winding comprising at least two coil sections 16 and 17. All conductors of each sections are electrically connected to their associated core segment, thereby establishing the electric potential level of the core segment at substantially that of the coil. Taken in totality, the coils of each leg 13, 14 provide multiple electric paths encircling the length of each leg. The manner in which the coil sections are arranged and electrically connected to each other and to the leg segments is described in more particularity in connection with succeeding figures.

Here the high voltage lead 19 is located at the center of the legs. Other leads (not shown) are located near the ends of the legs or at the yokes.

FIG. 2 shows a portion of core element 15 from FIG. 1 and a portion of its associated coil sections 16, 17. The coil section 16 is composed of a spiral winding of a conductor bundle containing n individual conductors 16,, 16 16,, labelled in ascending subscript order from the innermost (closest to the core) to the outermost (farthest from the core).

Each conductor 16, through 16, is of the form of a tape or flexible band. While the invention is not limited to conductors of this nature, it has been found that such conductors have convenient electrical and mechanical properties. A conductor bundle comprises the n individual conductors aligned in a front-to-back relation, adjacent conductors being electrically separated by suitable insulating material.

FIG. 3 shows two coil sections 36 and 37, associated with the same core element 35, wound simultaneously as a single unit 31. Coil section 36 consists of n conductors here labelled 36,, 36,, from innermost to outermost in the manner described on connection with FIG. 2, above. Similarly, coil section 37 consists of n conductors 37,, 37,. The adjacent coil sections 36 and 37 are electrically connected in parallel, as described below in connection with FIG. 6. Multiple coil section units such as 31 may aid in enabling the electromagnetic apparatus to handle high current requirements. In addition, where the magnetic flux external to the core deviates from parallel to the core axis, a desirable electromotive force equalization may be achieved by subdividing each tape conductor, such as 16,, l6, of FIG. 2, into a plurality of conductors each of which may be narrow in the dimension of the core axis as well as in the radial dimension. Such a subdivision into two parts is shown embodied in the twocoil section unit 31. The narrowing effect is suggested in the drawings in that the conductors of coils 36 and 37 of FIG. 3 are all narrower in the direction of the core axis than are the analogous conductors of coil 16 of FIG. 2. In practice, where the flux geometry makes such subdivision desirable,-greater subdivision, hence multiple coil section units with greater numbers of coils, may be useful. Electrical connections may be made in a fashion analogous to that indicated in FIG. 6. It is to be understood herein that multiple coil sections units may be employed in place of two (or more) single coil sections where appropriate and convenient.

FIG. 4 is a representation of a portion of the reactor of FIG. 1, illustrating details of a preferred coil configuration and electrical connections of the present invention. Each coil section 16, 17, and 17' is formed from a spiral winding of a two-conductor (20 and 21) bundle similar to that of FIG. 2.

Coil sections 16 and 17, associated with the same core element 15, have all conductors connected 22 at the inside of the coil sections, to each other and to the core element.

Adjacent coil sections 16 and 17, associated with adjacent core elements 15 and 15', respectively, are connected to each other at the outer part of the winding. In effecting the connection 23, the two conductors of each winding are transposed, the outer conductor of the winding of each of coil sections 16 and 17' being connected to the inner conductor of the winding of the other coil section. An important feature of the present invention is that due to the convenient location of the transposition, the connections may be carried out after otherwise completing assembly of the core and coil structure.

Coil section 17, adjacent to high voltage lead 19, has both conductors of its winding connected to the high voltage lead at the outer part of the coil section.

FIG. 5 illustrates the transposition connection 24 where the coil sections 26 and 27 consist of an n conductor winding. As shown, the i" innermost conductor of the winding of one coil section is connected to the (n+li),, innermost conductor of the winding of the other coil section, for values of i=1 ,2,3, n.

FIG. 6 shows another possible coil arrangement which can be used in connection with the present invention. Here each of the single coil sections 17, 17, 18 of FIG. 5 has been replaced by two similar coil sections 17a and 17b, 17'a and 17'b, 18a and 18b, respectively, connected in parallel. The transposition connection 25 is effected as illustrated by joining the outer conductors of coil sections 17 'a and 17 'b to the inner conductors of coil sections 16a and 16b, and joining the outer conductors of coil sections 16a and 16b to the inner conductors of coil sections 17'a and 17'b.

It is to be understood that the foregoing discussion of the principles and embodiments of the present invention is presented for descriptive and illustrative purposes and not by way of limitation. The invention is not limited to transformers or reactors, but also includes generators which make use of insulating-core-type windings, such as the generators disclosed and claimed in U. S. Pat. No. 3,239,702 to Van de Graaff.

Iclaim:

1. High voltage high power apparatus comprising a magnetic circuit including a series of alternating thick layers of ferromagnetic, electrically conducting material and thin layers of electrically insulating material,

a winding about said magnetic circuit having a plurality of spiral layers,

each spiral layer comprising a plurality of lengths of means connecting the outer extremity of each tape to the outer extremity of a tape in an adjacent spiral layer,

said outer-extremity connecting means being such that the electromotive force generated between the inner extremities of each thus-connected pair of tapes in a pair of adjacent spiral layers is substantially the same for all such tape pairs.

2. Apparatus of claim 1 wherein each spiral layer comprises n conductive tapes, n 2, juxtaposed in front-to-back insulated relation and spirally wound to form substantially a disc about said one ferromagnetic layer.

3. Apparatus of claim 2 wherein said connections of outer extremities of tapes of adjacent spiral layers are such that the i"'-innermost tape of one spiral layer is connected to the (n+1-i -innermost tape of the other spiral layer, i-l,2, n.

4. Apparatus of claim 3 wherein 2 5 n 5 4.

5. Apparatus of claim 1 wherein about each said ferromagnetic layer are wound two units of spirallayers, each said unit comprising a plurality of spiral spiral layers connected in parallel.

6. Apparatus of claim 1 wherein each said conductive tape is subdivided along its width into a plurality of conductive parts connected in parallel.

Claims (6)

1. High voltage high power apparatus comprising a magnetic circuit including a series of alternating thick layers of ferromagnetic, electrically conducting material and thin layers of electrically insulating material, a winding about said magnetic circuit having a plurality of spiral layers, each spiral layer comprising a plurality of lengths of conductive tape spirally wound about one of said ferromagnetic layers, each such length of tape being electrically connected at its inner extremity to said one ferromagnetic layer, a plurality of such lengths thus being electrically connected in parallel in order to handle high currents while preserving a small radial dimension so as to reduce eddy currents, means connecting the outer extremity of each tape to the outer extremity of a tape in an adjacent spiral layer, said outer-extremity connecting means being such that the electromotive force generated between the inner extremities of each thus-connected pair of tapes in a pair of adjacent spiral layers is substantially the same for all such tape pairs.

2. Apparatus of claim 1 wherein each spiral layer comprises n conductive tapes, n > or = 2, juxtaposed in front-to-back insulated relation and spirally wound to form substantially a disc about said one ferromagnetic layer.

3. Apparatus of claim 2 wherein said connections of outer extremities of tapes of adjacent spiral layers are such that the ith-innermost tape of one spiral layer is connected to the (n+1-i)th-innermost tape of the other spiral layer, i 1,2, . . . , n.

4. Apparatus of claim 3 wherein 2 < or = n < or = 4.

5. Apparatus of claim 1 wherein about each said ferromagnetic layer are wound two units of spiral layers, each said unit comprising a plurality of spiral spiral layers connected in parallel.

6. Apparatus of claim 1 wherein each said conductive tape is subdivided along its width into a plurality of conductive parts connected in parallel.

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