US3268843A

US3268843A - Electric induction apparatus for use in railway signal systems

Info

Publication number: US3268843A
Application number: US382551A
Authority: US
Inventors: Popp Ralph
Original assignee: Westinghouse Air Brake Co
Current assignee: Westinghouse Air Brake Co
Priority date: 1964-07-14
Filing date: 1964-07-14
Publication date: 1966-08-23
Anticipated expiration: 1983-08-23
Also published as: ES315316A1

Description

Aug. 23, 1966 R. POPP 3,268,843

ELECTRIC INDUCTION APPARATUS FOR USE IN RAILWAY SIGNAL SYSTEMS Filed July 14, 1964 2 Sheets-Sheet 1 INVENTOR.

Pop 0. BY d-LQ af R. POPP Aug. 23, 1966 ELECTRIC INDUCTION APPARATUS FOR USE IN RAILWAY SIGNAL SYSTEMS Filed July 14, 1964 2 Sheets-Sheet 2 ll/d United States Patent O 3,268,843 ELECTRIC INDUCTIDN APPARATUS FOR USE IN RAILWAY SIGNAL SYSTEMS Ralph Popp, Millvale, Pa., assignor to Westinghouse Air Brake Company, Swissvale, Pa., a corporation of Pennsylvania Filed July 14, 1964, Ser. No. 382,551 10 Claims. (Cl. 336-223) This invention relates to electric induction apparatus, and more particularly to a combination impedance bond and signaling device for use in railway signaling systems in electric propulsion territory provided with electrically continuous welded track rails which are supplied with alternating signaling current as well as serving as a doublerail return circuit for the propulsion current.

This apparatus can be used, for example, in the system described in the copending application for Letters Patent of the United States, Serial No. 382,620, filed July 14, 1964, by Crawford E. Staples, for Rapid Transit Speed Control System, and which is assigned to the 'assignee of the instant application.

It is an object of this invention to provide a new and improved electric induction apparatus to be used in track signaling systems having electrically continuous welded double-rail return circuits for the propulsion current.

It is another object of this invention to provide a new and improved combination impedance bond and signaling device.

It is a further object of this invention to provide a new and improved combination impedance bond and signaling device of simple, compact and inexpensive construction.

Further objects, features, and advantages will be pointed out in particularity in the following detailed description of a specific embodiment thereof when read in conjunction with the appended drawings wherein:

FIG. 1 is a perspective view of the combination impedance bond and signaling device with portions thereof broken away to show construction details.

FIG. 2 shows a partially diagrammatic and partially schematic view of the core and windings and the method of connection to the track rails.

FIG. 3 shows a sectional view of the primary conductor spacer assembly taken along line IIIIII of FIG. 1.

FIG. 4 is a perspective view of the combination impedance bond and signaling device with a mounting bracket to show a method of fastening to a railroad tie.

FIG. 5 is a perspective view of a broken-away portion of the device of FIGQ3 after its encapsulation.

FIG. 6 is an exploded view of the signal lead terminal assembly.

Referring now to the drawings, more particularly to FIG. 1, the combination impedance bond and signaling device consists essentially of core members generally designated as 10 and 12, the

primary windings

14 and 16, and two secondary windings 18 (only one of which is fully shown). The

primary windings

14 and 16 are strap conductors of large current carrying cross section formed flatwise into a generally U-shaped configuration. The strap conductor of the primary winding 16 is positioned in aligned mating relationship within the primary winding 14 and suitable insulating material 20 is interposed therebetween to electrically isolate the two windings of the primary. One leg 15 of the primary winding 16 is longer than the other and is bent outwardly and perpendicularly to form a flange terminal 22. The flange terminal 22 has suitable holes 24 drilled therein to provide means for connection to an external conductor. Similarly, the primary winding 14 has a short leg 17 adjacent the long leg 15 of the primary winding 16, and the long leg 19 of the winding 14 is perpendicularly and outwardly turned to form a flange terminal 26 generally coplanar with the flange terminal 22. Holes 28 are drilled in flange terminal 26 to provide means for electrical connection.

Terminal lugs

30 and 32 are made of right angularly shaped strap conductor material of large current carrying capacity and are brazed to the

short legs

17 and 13, respectively, of the primary windings with the bent portions thereof extending outwardly and generallycoplanar. In actual usage, the

terminal lugs

30 and 32 are electrically connected to provide a center tap for the two-winding primary (see FIG. 4).

The core members, generally designated as 10 and 12, are made of grain oriented electrical steel and, as better illustrated in FIG. 2, comprise two pairs of generally C-shaped cores of substantially similar size and shape, each pair having its respective core legs aligned with but spaced from the legs of the opposite core to form

air gaps

36 and 38, each pair of cores defining a window. The length of the air gaps is so adjusted to prevent saturation of the core means by direct current flux levels normally encountered during operation of the device. As can be seen, the

core members

10 and 12 form essentially a three-legged core means with an air gap in each of the three legs. It is to be understood, however, that one or more air gaps may be utilized and positioned in such a manner to give a generally symmetrical magnetic circuit. The

primary windings

14 and 16 pass through the respec tive openings or windowsin the

core members

10 and 12 to encircle the adjacent inner legs of the core members. The secondary winding 18 is composed of many turns of .wire of relatively small cross section positioned upon the outer legs of the

respective core members

10 and 12, and are connected in series with their fluxes aiding.

As shown in FIG. 2, the primary windings 14 and 16 v are connected to

track rails

40 and 42, respectively, and a center tap 44 of the primary windings serves as a neutral conductor for cross-bonding and at certain points it is tied to a neutral from the substation as better described in the aforementioned Staples application. The secondary windings 18 are provided with suitable terminals 46 for connection to a signal transmitting or signal receiving device.

The construction of the combination impedance bond and signaling device is relatively simple as can be seen from FIG. 1. The

primary windings

14 and 16 are formed from strap conductors bent flatwise on forming jigs and are positioned one within the other with insulation 20 interposed therebetween. The

flange terminals

22 and 26 are positioned so that they are outwardly extending in opposite directions. The connecting

holes

24 and 28 can be drilled prior to forming. The

terminal lugs

30 and 32, brazed to the respective

short legs

17 and 13 of

primary windings

14 and 16, have the bent portions thereof extending in a plane perpendicular to the plane of the

flange terminals

22 and 26 so as not to interfere therewith. It is to be understood that the

flange terminals

22 and 26 and the

terminal lugs

30 and 32 may take any shape or configuration suitable for the intended purposes and such other shapes are within the contemplated scope of the invention.

The legs of the primary windings are held in aligned spaced relationship by means of a spacer assembly 48 which includes a plurality of relatively noncompressible washers 50 of suitable insulating characteristics positioned on either side of an adjoined pair of legs with washers 51 inserted until the desired width is attained. A bolt 52 is inserted through the washer 50 and through aligned pre-drilled holes in the respective primary legs and terminal lugs. The spacer assembly 48 insures against torsional stresses in the primary windingvdue to undue stresses placed upon the

flange terminals

22 and 26, or the

terminal lugs

30 and 32 and protect against rupture of the brazed joints. The spacer assembly 48 additionally provides close coupling between the core members and 12 and the secondary windings 18.

The spacer assembly 48 is better illustrated in the sectional view of FIG. 3. An insulating cylinder 49 extends through the

legs

17 and 19 of the outer primary conductor 14, the

legs

13 and 15 of the inner primary conductor 16 and the terminal lugs and 32, thereby insulating the bolt 52 inserted therein from the primary windings. Insulating washers are disposed on either side of each pair of adjoined primary legs, while additional spacer washers 51 are positioned between the pairs of legs to maintain the desired width between the legs of the primary conductor 16. The washers 51 are made of metal but need not be, so long as they are relatively noncompressible. The nut 53 and the bolt 52 maintain the primary conductors in properly aligned and spaced relationship by means of the spacer assembly 48 so that the adjoined pairs of legs are generally parallel.

The secondary windings 18 (see FIGS. 1 and 2) are prewound and preformed to facilitate assembly. The core member 12 is composed of the two C-

core members

54 and 56 which are disposed in facing relationship so as to encompass the

legs

19 and 13 of the

primary windings

14 and 16, respectively. The prewound secondary winding 18 and an insulating sleeve 60 are positioned prior to the assembly of the core member 12 so that the core legs I of C-

oore members

54 and 56 pass through the openings thereof. As can be seen in the cutaway portion of FIG. 1, suitable insulating material 58 is provided between the abutting faces of the core legs of C-

core members

54 and 56 to provide the desired air gap. Similarly, insulating material is positioned between the abutting faces of the core legs which are not shown. The C-

core members

54 and 56 are then bound together by a nonmagnetic strap 62 to form core member 12. Core member 10 is constructed in the same manner and bound together 'by a suitable strap 64 which likewise is nonmagnetic. Then, the entire core assembly is tied together by suitable nonmagnetic straps 66 encircling both

core members

10 and 12.

The inner faces of the legs of the primary winding 16 are spaced so as to be just slightly larger than the width of the core legs inserted therebetween. Similarly, the Width of each core window is generally the minimum size necessary to permit insertion of the

primary windings

14 and 16, and the secondary winding 18. This permits a compact structure with close coupling electromagnetically to provide maximum energy transfer efficiency. This construction further provides the balancing action of an ordinary impedance bond, while providing efiicient transformer action not previously obtainable in conventional bonds. The leakage inductance is extremely low, and similarly the capacitance coupling between primary and secondary is very low. Due to these factors and the close coupling, higher signaling frequencies can be employed at reasonable power levels with accurate tuning.

Upon completion of the assembly the combination impedance bond and signaling device can be encapsulated so that only the

flange terminals

22 and 26, the bent portions of the

terminal lugs

30 and 32, and the winding leads 46 are exposed. Such encapsulation will hermetically seal the core members and secondary winding, and further provide for a fixed electromagnetic circuit. It is to be understood that encapsulation is not absolutely necessary and other appropriate housing methods may be employed.

A preferred mounting arrangement for the combination impedance bond and signaling device of FIG. 1 is shown in FIG. 4 for installing the device between the railroad ties of a trackway. A mounting bracket 68 is formed into a generally C-shaped configuration and has an upper arm 70 longer than and generally parallel to the lower arm 72. The terminal lugs 30 and 32 of the combination impedance bond and signaling device are bent outwardly at right angles and are generally coplanar. A coupling member 74 of suitable strap conductor material of large current carrying capacity is secured to the terminal lugs 38 and 32 in any well-known manner, as by brazing, for example, to electrically connect the terminal lugs 38 and 32 to provide a center tap. The combination impedance bond and signaling device is then oriented in the space between the upper arm 70 of the mounting bracket 68 and the lower arm 72 thereof in such a manner that the coupling member 74 abuts with the under surface of the upper arm 70 with the secondary windings 18 positioned rearwardly toward the bight portion of the mounting bracket 68. The device is then secured to the upper arm 70 of the mounting bracket 68 by suitable fastening means such as screws 76 inserted through aligned holes in the upper arm 70, the coupling member 74, and the respective terminal lugs 30 and 32. The screws 76 are positioned generally flush with the top surface of the upper arm 70 by means of countersinking. This tends to minimize the possibility of damage to the impedance bond and signaling device by equipment dragging from a train. In order to avoid the possibility of destructive electrolytic action between the coupling member 74 and the inner surface of the upper arm 70, a sheet of suitable insulating material 82 is interposed therebetween (as shown in FIG. 5). The width of the mounting bracket 68 is such that the terminal lugs 30 and 32 and the

terminal flanges

22 and 26 protrude outwardly therefrom a distance sufiicient to attach a cable connector 78 (only one of which is shown) by fastening means such as nuts and bolts 80. The cable connector 78 for the center tap or coupling member 74 can be attached to the terminal lug 30 or the terminal lugs 32 and can be oriented perpendicular or parallelto the mounting bracket 68. The mounting bracket 68 is secured to the railroad tie 84 by means of lag bolts 82 extending through the holes in the upper arm 70 of the mounting bracket 68. In this position the lower arm 72 abuts against the side of the railroad tie 84 (partially cut away). Thus it can be seen that this construction permits a low profile device, the maximum height of which is generally flush with the maximum height'of the railroad tie 84. The plane of the

flange terminals

22 and 26 of the

primary conductors

16 and 14, respectively, is generally parallel to the side of the railroad tie 84. This permits a cable conductor to be run from each

flange terminal

22 and 26 to its associated track rail alongside of the railroad tie 84. The plane of the bent portions of the terminal lugs 30 and 32 is generally perpendicular to the plane of the

flange terminals

22 and 26 so as not to interfere therewith.

'For encapsulation purposes it is necessary to maintain a spaced aligned relationship between the upper arm 70 and the lower arm 72 of the mounting bracket 68 to prevent a rupture between the potting compound and the mounting bracket 68. A metal support member 86 is welded to the inner surface of the lower arm 72 in a generally central location. A hole (not shown) is drilled therein and threaded. A pipe spacing member 88 of sufficient length is positioned between the surface of the support member 86 and the inner surface of the upper arm 70 and a bolt 90 is inserted through an aligned hole in the upper arm 70 through the pipe spacing member 88 and into the threaded aperture of the support member 86. The pipe spacing member 88 is located between the adjoined pairs of legs of the primary conductors. The coupling member 74 is notched in the vicinity of the pipe spacing member 88 to prevent interference therewith.

FIG. 5 shows a broken-away portion of the device of FIG. 4 after it has been encapsulated. Only the

terminal flanges

22 and 26 and the bent portions of the terminal lugs 30 and 32 with the coupling member 74 are exposed. The

primary windings

16 and 14, the secondary windings 18, and the

core members

10 and 12 are completely hermetically sealed with a nonconductive encapsulating or potting compound extending between the lower arm 72 and the upper arm 70 of the mounting bracket 68. The upper arm 70 of .themounting bracket 68 has been cut back to show the details of the pipe spacing member 88 with the notched-out portion of the coupling member 74, and the sheet of insulation 92 interposed between the coupling member 74 and the inner surface of the upper arm 7 0 of the mounting bracket 68. A signal lead terminal assembly 94 is provided for the circuit connections to the secondary winding, and is shown in its assembled position in FIG. 5.

An exploded view of the signal lead terminal assembly 94 is illustrated in FIG. 6. The secondary windings 18 are tied together in series aiding relationship and the signal lead terminals 46 are brazed or soldered to the ends of terminal studs 96 which are embedded in a trapezoidally shaped recess 98 formed in the potting compound adjacent one of the

flange terminals

22 or 26. A rectangular gasket 100 with a centrally located aperture 102 encloses the recess 98 and a rectangular metallic terminal cover 104 is secured to the potting compound adjacent the recess with the gasket 100 interposed therebetween by means of bolts 108 inserted through apertures in the terminal cover 104 and the gasket 100 into nuts '1-10 embedded in the potting compound. The terminal cover 104 is provided with a centrally located weathertight bushing 106 through which is inserted a two-conductor cable 112, each lead of which is secured to one of the terminal studs 96 by means of screws 114.

Thus it can be seen that this particular mounting construction provides a hermetically sealed unit of high structural strength and a compact low profile.

In the foregoing description, the strap conductors 14 and '16 have been designated the primary winding and the multi-turn coil 18 has been designated the secondary winding. It is to be understood, however, that this has been done for the convenience of description rather than to be limiting. By referring to the aforementioned Staples 3. A combination impedance bond and signaling device for a two-rail return track circuit, said device comprising, a first generally U-shaped strap conductor having a long leg and a short leg, the long leg having an end portion thereof forming a flange terminal for connecting to one of the track rails, a second generally U-shaped strap conductor having a long leg and a short leg and positioned in adjoining relationship within and being insulated from said first strap conductor with the long leg thereof adjacent the short leg of said first strap conductor, the long leg of said second strap conductor having an end portion thereof forming a flange terminal for connecting to the other one of said track rails, terminal means on the short leg of each of said strap conductors for connecting them together to form a two-turn winding, generally three-legged core means having two windows therein, an

application it will be seen that the strap conductors are utilized as both a primary or secondary winding with the multi-turn coil 18 acting as the secondary or primary, respectively, depending on whether the device is located at the entrance end or exit end of the particular section.

Having described a preferred embodiment of my invention, it is desired that the invention be not limited to that specific construction inasmuch as it is apparent that many additional modifications may be made without departing from the broad spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Electric induction apparatus comprising, a first generally U-shaped strap conductor, a second generally U- shaped strap conductor positioned, in adjoining relationship within and being insulated from said first strap conductor, terminal means on one end of each of said first and said second strap conductors for connecting them together to form a two-turn winding, terminal means on the other end of each of said strap conductors for connection to an external circuit, generally three-legged magnetic core means having two windows therein, an adjoined pair of legs of said strap conductors extending through each of said windows, and other winding means on the outer legs of said core means.

2. A combination impedance bond and signaling device for a two-rail return track circuit, said device comprising, a first generally U-shaped strap conductor, a second generally U-shaped strap conductor positioned in adjoining relationship within and being insulated from said first strap conductor, terminal means on one end of each of said first and said second strap conductors for connecting them together to form a two-turn winding, terminal means on the other end of each of said strap conductors for connection to the track rails, generally three-legged core means having two windows therein and at least one air gap, an adjoined pair of legs of said strap conductors extending through each of said windows, and a winding positioned on each outer leg of said core means.

adjoined pair of legs of said strap conductors extending through each of said windows, and other winding means on each outer leg of said core means for connecting to other circuit means.

4. A combination impedance bond and signaling device for a two rail return track circuit, said device comprising, a first generally U-shaped strap conductor having a long leg and a short leg, the long leg having a portion thereof extending outwardly and generally perpendicular to form a flange terminal for connecting to one of the track rails, a second generally U-shaped strap conductor having a long leg and a short leg and positioned in adjoining relationship within and being insulated from said first strap conductor with the long leg thereof adjacent the short leg of said first strap conductor, the long leg of said second strap conductor having a portion thereof extending outwardly and generally perpendicular to form a flange terminal for connecting to the other one of said track rails, terminal means on the short leg of each of said strap conductors for connecting them together to form a twoturn winding, generally three-legged core means having two windows therein, an adjoined pair of legs of said strap conductors extending through each of said windows, and other winding means on the outer legs of said core means for connecting to an external circuit.

5. Electric induction apparatus comprising, a first generally U-shaped strap conductor, a second generally U- shaped strap conductor positioned in adjoining relationship within and being insulated from said first strap conductor, terminal means on one end of each of said first and said second strap conductors for connecting them together to form a two-turn winding, terminal means on the other end of each of said strap conductors for connection to an external circuit, two pairs of generally C- shaped core members, each pair of C-s'haped core members positioned in facing aligned relationship to form a window therein, an adjoined pair of legs of said strap conductors extending through each of said windows, and winding means on each pair of said core members for connecting to other circuit means.

6. A combination impedance bond and signaling device for a two-rail return track circuit, said device comprising, a first generally U-shaped strap conductor, a second generally U-shaped strap conductor positioned in adjoining relationship within and being insulated from said first strap conductor, terminal means on one end of each of said first and said second strap conductors for connecting them together to form a two-turn winding,

' terminal means on the other end of each of said strap conductors for connection to the track rails, spacing means between the adjoined pairs of legs of said strap conductors adjacent the ends of said strap conductors, fastening means cooperating with said spacing means to secure the legs of said strap conductors in aligned spaced relationship, generally three-legged core means having two windows therein, an adjoined pair of legs of said strap conductors extending through each of said windows, and a winding positioned on each outer leg of said core means.

7. A combination impedance bond and signaling device, said device comprising, a first generally U-shaped strap conductor, a second generally U-shaped strap conductor positioned in adjoining relationship within and being insulated from said first strap conductor, terminal means on one end of each of said first and said second strap conductors for connecting them together to form a two-turn winding, terminal means on the other end of each of said strap conductors for connection to an external circuit, generally three-legged magnetic core means having a center leg and an outer leg disposed on either side thereof to form two windows therein, an adjoined pair of legs of said strap conductors extending through each of said windows in close abutting relationship with and being insulated from the center leg of said core means, and a multi-turn coil encircling each outer leg of said core means in close proximity to its adjoined pair of legs of said strap conductors to provide close coupling electromagnetically, said coils being connected in series aiding relationship to form a second winding for said device.

8. A combination impedance bond and signaling device for a two-rail return track circuit, said device comprising, a first generally U-shaped strap conductor having a long leg and a short leg, the long leg having a portion thereof extending outwardly and generally perpendicular to form a flange terminal for connecting to one of the track rails, a second generally U-shaped strap conductor having a long leg and a short leg and positioned in adjoining relationship within and being insulated from said first strap conductor with the long leg thereof adjacent the short leg of said first strap conductor, the long 'leg of said second strap conductor having a portion thereof extending outwardly and generally perpendicular to form a flange terminal for connecting to the other one of said track rails, a pair of terminal lugs of strap conductor material having a right angularly bent portion, each of said terminal lugs abutted against and secured to the short leg of one of each of said strap conductors with the bent portions extending outwardly and being generally coplanar, a coupling member of strap conductor material secured to the bent portions of said terminal lugs for electrically joining said terminal lugs to provide a center tap for a two-turn winding, the plane of said terminal lugs being generally perpendicular to the plane of said flange terminals, generally three-legged core means having two windows therein, an adjoined pair of legs of said strap conductors extending through each of said Windows, and other winding means on the outer legs of said core means for connecting to an external circuit means.

9. A combination impedance bond and signaling device for a two-rail return track circuit, said device comprising, a first generally 'U-shaped strap conductor having a long leg and a short leg, the long leg having a portion thereof extending outwardly and generally perpendicular to form a flange terminal for connecting to one of the track rails, a second generally U-shaped strap conductor having a long leg and a short leg and positioned in adjoining relationship within and being insulated from said first strap conductor with the long leg thereof adjacent the short leg of said first strap conductor, the long leg of said second strap conductor having a portion thereof extending outwardly and generally perpendicular to form a flange terminal for connecting to the other one of said track rails, a pair of terminal lugs of strap conductor material having a right angularly bent portion, each of said terminal lugs abutted against and secured to the short leg of one of each of said strap conductors with the bent portions extending outwardly and being generally coplanar, a coupling member of strap conductor material secured to the bent portions of said terminal lugs for electrically joining said terminal lugs to provide a center tap for a two-turn winding, the plane of said terminal lugs being generally perpendicular to the plane of said flange terminals, generally three-legged magnetic core means having a center leg and an outer leg disposed on either side thereof to form two windows therein, an adjoined pair of legs of said strap conductors extending through each of said windows in close abutting relationship with and being insulated from the center leg of said core means, and a multi-turn coil encircling each outer leg of said core means in close proximity to its adjoined pair of legs of said strap conductors to provide close coupling electromagnetically, said coils being connected in series aiding relationship to form a secondary winding for said device.

10. A combination impedance bond and signaling device for a two-rail return track circuit, said device comprising, a first generally U-shaped strap conductor having a long leg and a short leg, the long leg having a portion there-of extending outwardly and generally perpendicular to form a flange terminal for connecting to one of the track rails, a second generally U-shaped strap conductor having a long leg and a short leg and positioned in adjoining relationship Within and being insulated from said first strap conductor with the long leg thereof adjacent the short leg of said first strap conductor, the long leg of said second strap conductor having a portion thereof extending outwardly and generally perpendicular to form a flange terminal for connecting to the other one of said track rails, a pair of terminal lugs of strap conductor material having a right angularly bent portion, each of said terminal lugs abutted against and secured to the short leg of one of each of said strap conductors with the bent portions extending outwardly and being generally coplanar, a coupling member of strap conductor material secured to the bent portions of said terminal lugs for electrically joining said terminal lugs to provide a center tap for a two-turn winding, the plane of said terminal lugs being generally perpendicular to the plane of said flange terminals, generally three-legged core means having two windows therein, an adjoined pair of legs of said strap conductors extending through each of said windows, other winding means on the outer legs of said core means for connecting to external circuit means, a generally C-shaped mounting bracket having an upper arm longer than and generally parallel to a lower arm, said coupling member being secured to and insulated from the upper-arm of said mounting bracket between the upper and lower arms thereof with the bight portion of said strap conductors being located adjacent the bight portion of said mounting bracket and the terminal lugs extending transverse to and beyond the width of said upper arm, encapsulating means between the upper and lower arms of said mounting bracket with the flange ter minals and terminal lugs being at least partially exposed for electrical connection thereto, and terminal means for said other winding means on said encapsulating means.

No references cited.

LEWIS H. MYERS, Primary Examiner. D. J. BADER, Assistant Examiner.

Claims

1. ELECTRIC INDUCTION APPARATUS COMPRISING, A FIRST GENERALLY U-SHAPED STRAP CONDUCTOR, A SECOND GENERALLY USHAPED STRAP CONDUCTOR POSITIONED IN ADJOINING RELATIONSHIP WITHIN AND BEING INSULATED FROM SAID FIRST STRAP CONDUCTOR, TERMINAL MEANS ON ONE END OF EACH OF SAID FIRST AND SAID SECOND STRAP CONDUCTORS FOR CONNECTING THE TOGETHER TO FORM A TWO-TURN WINDING, TERMINAL MEANS ON THE OTHER END OF EACH STRAP CONDUCTORS FOR CONNECTION TO AN EXTERNAL CIRCUIT, GENERALLY THREE-LEGGED MAGNETIC CORE MEANS HAVING TWO WINDOWS THEREIN, AN ADJOINED PAIR OF LEGS OF SAID STRAP CONDUCTORS EXTENDING THROUGH EACH OF SAID WINDOWS, AND OTHER WINDING MEANS ON THE OUTER LEGS OF SAID CORE MEANS.