US3617966A

US3617966A - Core and coil assembly

Info

Publication number: US3617966A
Application number: US814733A
Authority: US
Inventors: Anthony B Trench; Vaughan I C Marks
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-04-11
Filing date: 1969-04-09
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: CA898921A

Abstract

A shell core transformer having a core and coil assembly located in a casing with each coil being a separate element having a plurality of windings of conductor encapsulated in a potting compound. The coils are assembled in side-by-side relation and embraced by a magnetizable material preferably in the form of ribbon bands spirally wound around two or all four legs of the rectangularly shaped coils. Posts are formed integral with the encapsulant which serve as terminals and mounting members supporting the core and coil assembly within the casing. Each coil has a semiconductive film on the surface of the encapsulant. To facilitate dissipating heat, heat sinks are provided consisting of flat plates or fins having a portion disposed between adjacent faces of the coils and a further portion projecting radially outward therefrom and in contact with the casing. The casing also is provided, in some instances, with fins. There is also a method of forming a coil which includes winding a plurality of turns onto a disc having a groove in one face thereof for receiving the conductor and subsequently assembling further members to enclose the wound coil in a chamber for receiving an encapsulant.

Description

United States Patent [72] Inventors Anthony B. Trench 25 Elizabeth St., Thornhill;

Vaughan 1. C. Marks, 56 Blakemanor Blvd., Scarborough, both of Canada [21] Appl. No. 814,733 [22] Filed Apr. 9, 1969 [45] Patented Nov. 2, 1971 [32] Priority Apr. 11, 1968 [33] Canada [31] 017327 [54] CORE AND COIL ASSEMBLY 7 Claims, 14 Drawing Figs.

[52] U.S. C1 336/61, 336/84, 336/92, 336/96, 336/107, 336/205 [51] Int. Cl. 11011 27/06 [50] Field of Search 336/61,9 2, 84,96, 205, 105, 107

[56] References Cited UNITED STATES PATENTS 2,997,527 8/1961 Kessel et al. 336/96 X 3,246,272 4/1966 Wiley 336/96 X 3,354,417 11/1967 Davis 336/96X 1,367,957 2/1921 Garretson 336/92 1,659,548 2/1928 Johannesen... 336/92 2,185,831 1/1940 Camilli 336/96 2,613,238 10/1952 Wiesemam. 336/84 X 2,652,521 9/1953 Westphal 336/84 Primary Examiner-Thomas J. Kozma Attorney-Shanley and O'Neil ABSTRACT: A shell core transformer having a core and coil assembly located in a casing with each coil being a separate element having a plurality of windings of conductor encapsulated in a potting compound. The coils are assembled in sideby-side relation and embraced by a ma'gnetizable material preferably in the form of ribbon bands spirally wound around two or all four legs of the rectangularly shaped coils. Posts are formed integral with the encapsulant which serve as terminals and mounting members supporting the core and coil assembly within the casing. Each coil has a semiconductive film on the surface of the encapsulant. To facilitate dissipating heat, heat sinks are provided consisting of flat plates or fins having a portion disposed between adjacent faces of the coils and a further portion projecting radially outward therefrom and in contact with the casing. The casing also is provided, in some instances, with fins. There is also a method of forming a coil which includes winding a plurality of turns onto a disc having a groove in one face thereof for receiving the conductor and subsequently assembling further members to enclose the wound coil in a chamber for receiving an encapsulant.

PATENTED nuvz I971 SHEET 1 BF 4 PATENTEU NUV2 1911 SHEET 3 BF 4 CGRE AND COIL ASSEMBLY The present invention relates to an insulated coil encapsulated in a potting compound, to an encapsulated coil having a metallized coating on the surface thereof, to a transformer consisting of a plurality of individual coils disposed side-byside and each of which consists of 'a plurality of turns of con ductor encapsulated in a potting compound, and to a transfonner wherein at least one of the coils is covered by a metallized coating on the surface thereof.

It is an object of the present invention to provide a coil which may be used along with one or more similar coils to form an induction device.

A further object of the present invention is to provide a transformer of individual discrete coil elements which may be readily removed and replaced.

A still further object of the present invention is to provide a method of making a transformer whereby transformers of various capacities may be manufactured from appropriate selection of standard coil assemblies.

In accordance with one aspect of the present invention, there is provided a coil for use in an induction device comprising a plurality of turns of conductor encapsulated in a potting compound and a metallized film coating on the external surface of the encapsulant.

In accordance with a further aspect of the present invention, thereis provided a coil for a transformer comprising at least two coil elements disposed side-by-side adjacent one another and each coil element comprising a plurality of turns of conductor encapsulated in a potting compound and having a metallized film on the external surface thereof.

In accordance with a further aspect of the present invention, there is provided a transformer comprising a plurality of individual discrete coils disposed side by-side in close adjacent relation and at least one body of magnetizable material embracing a selected portion of the assembled coils, said coils each consisting of a plurality of turns of conductor encapsulated in a potting compound.

The invention is illustrated, by way of example, in the accompanying drawings wherein:

FIG. I is a partial sectional, top plan view of a transformer constructed in accordance with the present invention;

FIG. 2 is a cross-sectional view taken substantially along the line 2-2 ofFIG. I;

FIG. 3 is a partial section, oblique view of a portion of a transformer illustrating a modified casing;

FIG. 4 is a cross-sectional view of the casing illustrated in FIG. 3, taken substantially along line 44;

FIG. 5 is an elevational view of a portion of a core and coil assembly for an induction device;

FIG. 6 is a section taken along section 6-6 of FIG. 5; FIG. 7 is a sectional view taken along section 7-7 of FIG.

FIG. 8 is a side elevational view of the assembly illustrated in FIG. 5;

FIG. 9 is a section similar to FIG. 6;

FIG. I0 is a top plan view of a portion of one terminal and bushing for the coil assembly;

FIG. 11 is a partial cross-sectional view of one terminal and bushing for the coil assembly;

FIG. 12 is an oblique view, in partial section, of a form for use in making a coil and encapsulating the same;

FIG. 13 is a diagrammatic illustration of one method of making a coil; and

FIG. 14 is a diagrammatic illustration of apparatus for encapsulating a coil.

Referring now in detail to the drawings. there is illustrated in FIGS. 1 and 2 a transformer consisting of a casing enclosing a core and coil assembly 50 and a plurality of heat sinks 70 which engage the core and coil assembly and the casmg.

The casing 20 consists of respective front and

rear panels

21 and 22 each appropriately formed to provide a side wall and a portion of an end wall. Each panel includes, at opposed marginal edges, an outwardly directed flange 23 substantially parallel to and offset from the main portion of the panel. A pair of flanges 23 on panel 21 are attached to the correspondingly oriented flanges 23 on the panel 22 by means of bolts,- welding or the like and thereby provide a space between the side faces to receive the core and coil assembly. A cover member 24 overlies the

panel members

21 and 22 except for the outwardly directed flanges 23 and, if desired, a downwardly turned lip may overlap a selected upper portion of the side walls. The core and coil assembly 50 may be suspended from the cover 24. Alternatively, the core and coil assembly may be supported upon a bottom wall 25 secured to the

casing panel members

21 and 22 as, for example, by welding, riveting, or the like. The cover member 24 and the bottom wall 25 have respective high-voltage bushings 26 and low-volt age bushings 27 projecting therethrough and arranged in a manner to be described in more detail hereinafter.

In FIGS. 3 and 4, there is illustrated a transformer 10A consisting of a modified casing 30 and a core and coil assembly 50. The casing 30 includes a generally oblong-shaped tank portion which is closed at opposed ends by respective walls 32 and 33. The end wall 33 is preferably detachably secured to the sidewalls (provided by the tank and identifiedby reference numeral 34) and projects laterally beyond such walls for the purpose which will become apparent hereinafter. A plurality of cooling fins project outwardly from the casing sidewall 34 and consist of a plurality of channel members each having a plurality of tins 36 projecting outwardly from a web member 37. The members, each consisting of a web 37 and fins 36, may be extruded or rolled and are from a highly heat-conductive material. The webs 37 are disposed in spaced relation with respect tothe casing sidewall 34 (see FIG. 4) and adjacent elements are also disposed in spaced relation. The elements are secured to the casing as, for example, by welding the upper and lower ends to the side walls of the casing. Since the end wall 33 projects laterally beyond the side wall 34 of the casing, the cooling fins may also be secured thereto. Alternatively, the end wall 33 may terminate flush with the sidewall of the casing in which event spacer elements may be utilized to interconnect the webs 37 and the sidewall 34.

The casings 20 and 30 each preferably consist of an aluminum or an aluminum alloy or any other material of highly heat-conductive characteristics. Cooling fins may be provided on either of the casings 20 or 30 and they may consist of separate elements, as previously described, or alternatively be formed integral with the side walls. A pair of bushing members 26 are secured to the top wall and a pair of bushings 27 are secured to the bottom wall in each of the transformers illustrated and provide connections to the coils located within the casing.

The core and coil assembly 50 consists of a coil portion 51 and a core portion 52. The core portion 52 consists of a ribbon of highly magnetizable material spirally wound flatwise around each of the legs of the generally rectangular-shaped coil 51. The magnetizable material is preferably a silicon steel with grain orientation parallel to the length of the ribbon well known and commonly used in transfonners. The coil portion 51 of the core and coil assembly 50 consists of a primary winding 53 sandwiched between a pair of secondary windings 54. Each of the primary and secondary coils consists of a plurality of turns of conductor 55 encapsulated in a potting compound 56 of preferably a high-temperature resistant epoxy resin or some other potting compound, for example, phenolic resins. Y

The potting compound may be a resin such as an epoxy, polyester or silicone type either filled or unfilled, or any other well-known types selected to provide suitable characteristics such as temperature of operation and thereby class the transformer as to operation. A high-temperature potting compound minimizes heat sinking and an epoxy found suitable in No. 2258 Epoxy of Union Carbide with CIBAs No. 972 hardener. Anhydride epoxy systems are deemed suitable. Numerous proposals have been made concerning various suitable encapsulants and in this regard, attention is directed to Canadian Pat. Nos. 76l,60l and 734,998 issued, respectively, June 20, 1967 and May 24, 1966.

The encapsulant 56 has a smooth external surface 57 covered with a thin semiconductive coating 58 of, for example, metal. The coating 58, for example, may be a resin filled with carbon black and/or metal powder, or it may be a metal surface. The resin-filled material may be applied by painting, spraying or the like, or the metal may be applied as, for example, by metal flame spray. It is most important that the surface 57 be. extremely smooth and the conductivity low enough so as not to provide a short circuit turn for the coils.

The primary and secondary coils may be rectangular in cross section, as illustrated in FIG. 6, or alternatively, only the primary winding 53 may be rectangular in cross section, as illustrated in FIG. 9, having a pair of opposed flat faces 59 and 60 disposed adjacent a flat face 61 of respective ones of the pair of secondary coils 54. The remaining external surfaces of the

coils

53 and 54 are such that the assembled coils define a substantially circular outline. The coil portion 51 may consist of two or more coils assembled in side-by-side relation although only three coils have been illustrated in the drawings.

Each coil element, that is, the primary 53 and secondaries 54 are physically in the form of closed loops as illustrated in FIG. 5. Each coil element further includes a pair of posts 62 projecting outwardly therefrom and in selected spaced relationship with respect to one another. The posts 62 are formed from the encapsulant and include a ferrule 63 (see FIG. ll) embedded therein. The ferrule 63 serves to connect a terminal 64 to the terminal end of the conductor 55. The ferrule 63 has a bore 65 extending inwardly from one end thereof receiving an end portion of the conductor 55 and may be crimped or otherwise deformed to clampingly engage the conductor. Alternatively or additionally, a set screw may be used which is threaded into the ferrule and projects into the bore 65 for engagement with the conductor. The opposite end of the ferrule has a threaded bore 66 threadingly to receive a terminal post 64. The ferrule 63 and conductor 55 may be the same material or alternatively, dissimilar materials. For example, conductor 55 may be aluminum and the ferrule 63 may be aluminum or copper or brass. The ferrule and conductor are embedded in the encapsulant 56 and, accordingly, interaction of dissimilar metals is minimized because of being unexposed to the atmosphere.

The posts 62 each have a tapered conical recess 67 in the end thereof for receiving a correspondingly shaped portion of a bushing 26 (see FIG. 2 where there are illustrated bushings 26 and 27). Each of the

bushings

26 and 27 have a tapered end portion 68 which projects into the conical recess 67 and has an enlarged outer end portion 69 which overlies the remaining portion of the post 62. The

bushings

26 and 27 may be ceramic, epoxy resins, phenolic resins or the like and have a central bore for receiving the terminal post 64. The bushing 26 is held in assembled relation by a lock nut N1 threaded onto the terminal 64 and a further nut N2 may be provided for connecting conductors to the terminal. When assembled, the

bushings

26 and 27 have the sloped tapered ends 68 thereof in pressural engagement with the sloped sidewalls of the recess 67 preventing entry of foreign matter into the connection of the terminal post to the ferrule. The connectors accordingly are projected from the elements and, if desired, suitable sealing materials may be utilized between the bushing 26 and the terminal post to completely separate the connection of terminal 64 to the ferrule 63 from air and thus avoid deterioration which might otherwise be caused.

In the transformer illustrated in FIG. 2, the enlarged portion 69 of the bushing 26 engages the outer face of the casing top wall 24 and the opposite side of the wall 24 engages the pair of posts 62. Similarly, the downwardly directed posts 62 of the coil assembly engage the casing bottom wall 25 supporting the core and coil assembly in the casing and the bushings 27 engage the lower face of the bottom wall. The

bushings

26 and 27 accordingly retain the core and coil assembly in assembled relation with respect to the casing which surrounds the core and coil assembly. In the arrangement illustrated in FIG. 2, bushings 26 with the terminals thereon project upwardly above the casing and it will be noted that the casingrsidewalls project downwardly below the bottom bushings 27 and the terminals associated therewith. The lower terminals, accordingly, are protected'from atmosphere and a further cover plate may be secured to the casing providing an enclosed area for the lower terminals.

The coil portion of the transformer is illustrated in FIGS. 6 to 9 inclusive and, as previously mentioned, there is a primary coil located intermediate a pair of secondary coils. Each of the primary and secondary coils are discrete separate elements consisting of conductors encapsulated in a potting compound having a smooth outer surface which preferably is covered with a semiconductive coating. The secondaries need not be coated but it is preferable that at least the primary or high voltage winding be coated. The

coils

53 and 54 are disposed in side-by-side relation as illustrated in close abutting relation, and the core for the transformer consists of a ribbon of magnetizable material wound flatwise around each of the four legs of the rectangularly shaped coils. The ribbon may be wound tightly to hold the primary and secondary coils in an assembled relation. Alternatively, the spirally wound ribbon material may be replaced by flat sheet stock consisting of arranged pairs of oppositely directed U-shaped elements suitably joined as is commonly known in the transfonner art (see, for example, Canadian Pat. No. 52!,487 issued Feb. 7, 1956). In a transformer of this type arranged with discrete coil elements, one coil may be readily replaced when burned out merely by removing the core material and substituting an operative coil for the unserviceable one.

In order to facilitate dissipating heat from the transformer illustrated in FIGS. 1 and 2, heat sinks 70 are provided and consist of highly heat-conductive metal fins directly engageable with the transformer casing 20. The fins 70 may be welded to the casing or clampingly engaged between the casing flanges 23, as illustrated in FIG. 1. There is a pair of heat sinks 70 located at each of the four corners of the rectangular core and coil assembly in the transformer illustrated in FIG. 2. Each heat sink 70 includes a flat portion 71 disposed intermediate

adjacent coils

53 and 54 with a portion 72 projecting inwardly of a core 52 wound on one leg and a further portion 73 projecting inwardly of the core 52 located on a leg adjacent thereto. The portions 72 and 73 of the heat sinks are effectively, arms extending at right angles to one another and are clampingly engaged between the adjacently disposed coils. Each heat sink 70 includes an angular portion 74 merging into an outer end portion 75 located between the casing flanges 23. The heat sinks 70 are preferably aluminum or an aluminum alloy or some other highly heat-conductive material and serve to dissipate heat from the core and coil assembly. The heat sinks further serve the purpose of retaining the core and coil assembly in a selected location relative to the casing.

Each of the

coils

53 and 54 may be formed in a manner as illustrated in FIGS. 12 to 14 inclusive. It is important to have the external surface of the encapsulant of each coil free from depressions, i.e. a relatively smooth surface and in order to accomplish this, the coil unit is preferably formed in a mold. Referring to FIG. 12, there is illustrated a coil 54 in a fonning mold 80. The mold consists of a two-part backing member 81 and a cover member 82 held in assembled relation by a plurality of U-shaped clips or clamp members 83. The member 81 may be a unitary member but in the preferred form, consists of a pair of

members

84 and 85 which may be readily assembled and disassembled. The member 84 is generally T-shaped in cross section having a peripheral concave groove 86 in one face thereof surrounding a generally flat planar portion 87. The member 81 terminates in an outer peripheral edge 88 tapered inwardly in a direction outwardly from the mold. The purpose of this will become apparent hereinafter.

The member 85 is elTectively annular in shape, having a substantially flat bearing surface 89 engageable with an adjacent flat face of the cover member 82. The member 85 has a peripheral grooved or recessed portion 90 contiguous with the groove 86 in the member 84. The grooved portion 90 merges into a further portion 91 which is complementary to the shape of the peripheral surface or edge 88 of the member 81. The remaining portion of the member 85 may be of any configuration and, for example, may include a peripheral flange 92 for the purpose of facilitating interconnecting the members 81 and 82. The

members

84 and 85 may be readily assembled and disassembled merely by fitting the member 84 into the member 85, positioning being facilitated by complementary shaped abutting

surfaces

88 and 91 on the respective members. In assembled relation, the surface of the groove 86 is contiguous, as previously mentioned, with the surface of the groove 90 so as to provide a smooth molding surface for the coil 54 located in the molding chamber. The clips 83 may be substantially U-shaped, in cross section, members retained by frictional engagement on the cover 82 and flange 92thereby retaining the members 81 and 82 in assembled relation. Adjustable clips may be utilized or, if desired, the cover 82 may be fastened by means of studs or the like to the member 85 and/or 84.

The member 84, as previously mentioned, is readily removable from the annular outer member 85 and the purpose of such arrangement is so that the member 84 may be utilized as a winding form or mandril. In this regard, the coil consists of a plurality of turns of conductor 55 wound into a closed loop. Referring to FIG. 13, the conductor 55 may consist of a conductor 700 drawn off a spool 701 pivotally mounted on a shaft 702 by a winding unit 703. The conductor may be either a bare wire or an insulated wire and in either event, an adhesive material 705 is applied to at least selected portions for holding a spacer on the conductor, the purpose of which will become apparent hereinafter. The adhesive is preferably a silicone type and may be applied by rollers, brushes or the like applicators, and either as a continuous film or alternatively, in strips in which case they would normally extend longitudinally along the conductor. In FIG. 13, the conductor 700 is illustrated as being drawn through a bath of adhesive material 705 contained within a tank 706. Alternatively, the conductor may be insulated by a coating which may be suitably treated as, for example, by the application of heat, solvents or the like to provide a tacky surface in which case the insulation of the conductor performs the dual function of being an, insulator and selectively an adhesive surface. The tacky surface or adhesive is for the purpose of retaining a spacer element on the conductor.

Downstream from the adhesive-applying station, the conductor with the adhesive thereon is indicated generally by the reference numeral 715. Filament glass 710 in rope form is drawn off a bobbin 711 mounted on a shaft 712 to rotate about a substantially horizontal axis. The rope form of filament glass is drawn off the bobbin 711 by a winding arm 713 mounted to rotate about the longitudinal axis of the conductor. The winding arm consists of a member directed outwardly from the axis of the conductor and has at least one arm adjacent the free end thereof extending parallel to the length of the conductor. The filament glass is drawn off the bobbin through a combing element 714 to form the strands into a flat ribbon and such flat ribbon is spirally wound around the conductor by the winding arm as the wire is moved horizontally to the right as viewed in FIG. 13. The adhesive-covered conductor 715, with the filament glass thereon, is wound onto a winding mandril, preferably under tension so as to place the adjacent windings of the coil in tight intimate contact. The wind ing mandril rotates about the axis of a driven shaft 720 to which is secured a plate 721. The plate 721 includes a plurality of apertures 722 through which studs may pass and be threaded into the member 84 (FIG. 12) with the face 87 thereof in abutting relation with the plate 721. The latter plate may extend laterally beyond the member 84 a selected amount and together provide effectively a reel for winding a plurality of turns of the conductor into a closed loop coil. After the conductor has been wound onto the member 84,

which effectively is a winding mandrel, the latter is removed from the plate 721 and inserted into the member 85 whereafter the cover 82 is attached by the clips 83. The entire assembly, generally designated in FIG. 12 by reference numeral 80, is then placed in a vacuum chamber 1200 and the space confining the coil 54 is connected by a conduit 1101 to a supply of potting compound 1103. The potting compound, or encapsulant as it may be referred to, may be a resin such as an epoxy, silicone, polyesters, e.g. Vibrin or Permasil or the like, either filled or unfilled, or any type selected to provide suitable range of temperature operation and thereby class the transformer as to operation.

A bleeder conduit 1102 is connected to the chamber containing the coil 54 and a control valve 1104 located in the bleeder line 1102 may be selectively opened and closed to control filling the chamber containing the coil 54 with the potting compound 1103. The vacuum chamber 1200 is evacu ated to selected negative pressures by a vacuum pump generally designated 1300. After the chamber containing the coil has been completely filled with the potting compound, the the potting compound is then cured and when using a thermal setting resin as the potting compound, the coil may be energized to provide the necessary heat to accomplish the curing. The coil assembly 54 in the mold is then removed from the vacuum chamber and the coil 54 removed from themold.The encapsulated coil is then completely covered with a metallized surface or semiconductor. The coating, for example, may consist of a resin filled with carbon black and may be applied by spraying or, alternatively, it may consistof a resin filled with a metal powder and likewise applied by spraying. The coating alternatively may be metal applied by flame spraying so as to deposit discrete particles of metal in a continuous layer.

The cross-sectional shape of the encapsulant is determined by the shape of the chamber in the mold 80. The coils are ap propriately shaped as, for example, that illustrated in FIG. 9 where three coil assemblies, arranged side-by-side in close abutting relation, present a substantially circular outline or alternatively, substantially square as shown in FIG. 7. Coils assembled side-by-side are then embraced at selected areas by core material 52 which, as previously mentioned, is a ribbon of silicon steel or the like spirally wound flatwise around the assembled coils to embrace the same.

With regards to disposing the coil assembly side-by-side, discrete coil elements, that is, individual primaries and secondaries as illustrated in FIG. 8, permit stacking a series of coil elements to vary the size of the transformer. For example, two primary coils may be located intermediate two secondaries, or alternatively, primary and secondary coils may be arranged in alternate relation and the entire assembly embraced by core material. In stacking, it is preferable to maintain all of the coils physically symmetrical and when stacked, the coils may be suitably interconnected electrically, for example, all of the primary coils may be connected in parallel and likewise all of the secondary coils may be connected in parallel.

From the foregoing, it is seen that the metallized film which completely covers each coil segment separates one winding from the other. The metallized surface provides a transformer which is substantially free from corona and helps to increase the basic insulation level of the core and coil assembly. The use of an encapsulant which is molded to a relatively smooth outer surface cuts down or eliminates spiking, that is, surfaces which project inwardly toward the coil and thereby reduces flash inducing edges or points.

We claim: 1. Inductive device including a core and coil assembly comprising at least two closed loop coil elements disposed with exterior closed-loop surfaces in side-by-side contiguous relationship, each of such coil elements comprising a plurality of electrically insulated turns in an integral encapsulation and at least one body of magnetizable material embracing in common a selected portion of the side-by-side coils and, casing means enclosing the core and coil assembly,

the coil encapsulation including integral projection means extending from the coil elements to the casing means so as to support the coil elements within the casing means.

2. The structure of claim 1 further including a semiconductive film covering the external surface of at least one of the integral encapsulations.

3. The structure of claim 1 including at least one heat conductive member having a portion interposed between the contiguous coils.

4. The structure of claim 3 wherein the heat conductive member is extended to engage the casing.

5. The inductive device of claim 1 in which the plurality of electrical turns of an electrifircoil terminate in a bushing which is unitary with the encapsulation.

6. A coil assembly for use in an encased inductive device comprising a casing and a plurality of electrical turns in an integral encapsulant including post means integrally formed of such encapsulant and supporting the integral encapsulant in the casing.

7. The structure of claim 6 in which the post means include bushings secured thereto and which project outwardly from the casing.

II I I I

Claims

1. Inductive device including a core and coil assembly comprising at least two closed loop coil elements disposed with exterior closed-loop surfaces in side-by-side contiguous relationship, each of such coil elements comprising a plurality of electrically insulated turns in an integral encapsulation and at least one body of magnetizable material embracing in common a selected portion of the side-by-side coils and, casing means enclosing the core and coil assembly, the coil encapsulation including integral projection means extending from the coil elements to the casing means so as to support the coil elements within the casing means.

5. The inductive device of claim 1 in which the plurality of electrical turns of an electrical coil terminate in a bushing which is unitary with the encapsulation.