US1396825A - Railway signaling system - Google Patents

Description

c. VLEG. FORTESCUE.

RAILWAY SIGNALING SYSTEM. APPLICATION mso AUG.28, 1915. RENEWED NOV. 5, I920.

1,396,825. Patented Nov. 15, 1921. v

WITNESSES v INVENTOR I Y [/mr/es Z96. fZr/esme BY UNITED STATES PATENT OFFICE.

CHARLES LE G. 'FORT'ESCUE, CF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WEST- INGHOUSE ELECTRIC AN'D MANUFACTURING COMPANY, A CORPORATION OF .rmmsnvama Specification of Letters Patent.

Patented Nov. 15, 1921.

Application filed August 28, 1915, Serial No. 47,884. Renewed November 5, 1920. Serial No. 422,078.

To all whom it may con/0mm:

Be it known that I, CHARLES LE G. Fonrnsoos, a subject of the King of Great Britain, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Railway Signaling Systems, of which the following is a specification.

My invention relates to systems of electrical distribution, and it has special reference to alternating-current railway systems embodying means for minimizing inductive disturbances in adjacent electrical circuits and, at the same time, offering paths for the unimpeded flow in the track circuits of the alternating currents adapted to operate the signalingdevices that afford protection to the railway systems.

In electrical-railway systems operated by alternating currents, means are usually provided for minimizing the inductive disturbances arising from the flow of the propulsion currents. At the same time, the signaling currents must be confined to their re- SPBCtlVGblOCk sections or track circuits in order to properly operate the signaling devices aifording protection to the traffic accommodated by the railway. One of the most effective means for minimizing the inductive disturbances arising from the propulsion currents contemplates the insertion of a number of series transformers at spaced intervals in the railway system, the primary windings of the transformers being connected in series circuit relationship with the trolley or third rail conductor, and the secondary windings thereof being connected, preferably through impedance bonds, to the track rails and in shunt to the insulating joints. This system for minimizing inductive interferences is fully described in United States PatentNo. 1,196,300 issued to Chas. F. Scott, Aug. 29, 1916, for means for minimizing inductive interference. By inductively interlinking the track circuit and the trolley conductor, as mentioned above, electromotive forces are impressed at intervals in the rails which serve to confine the flow of the propulsion currents to them. In conjunction with the above system, means must be provided for permitting the unimpeded flow of the signaling currents in each of the block sections or track circuits.

An object of my invention, therefore, is

to provide a novel means for dividing the track into block sections or track circuits for signaling purposes without breaking the electrical conductivity of the rails for the return flow of the propulsion currents. In conjunction therewith, means are incorpo rated for inductively interlinking the trolley and the rails with each other in order to confine the return flow of the trolley currents to the latter so as to minimize the inductive interferences that may be impressed upon an adjacent electrical circuit, such as an intelligence transmission circuit.

In addition to accomplishing the aforementioned object, my present invention permits series transformers such as are shown in the aforementioned United States Patent No. 1,196,300, and employed for impressing compensating electromotive forces at intervals in the track rails to more perfectly interlink the same with the trolley or supply conductor, to be inserted in circuit at oints intermediate the ends of the signaling locksections or track circuits without impeding the flow of the signaling currents in the separate block-sections of the track. Ordinarily, the signaling currents would be impeded since the insulating joints in the rails necessary for connecting these series transformers in circuit would offer high impedance to the flow of thesignaling currents. By means of my invention, however, the series transformers may be connected in circuit at frequent intervals and intermediate the ends of the signaling block sections and other insulated track sections without impairing the electrical conductivity of the rails as regards the flow of the propulsion currents and the flow of the signaling currents in the block-sections.

My invention is particularly adapted to be employed in connection with a railway sys tem comprising a plurality of tracks each of which has an associated trolley or power supply conductor, and in which the blocksections of one track are staggered and maintained electrically independent with respect to the block-sections of another parallel track. To provide suitable paths for the power currents, the several tracks are electrically interconnected in parallel relationship so as to constitute a conductor of low impedance for the return flow of the power currents. The series transformers, therefore, are common to all of the adjacent tracks, the secondary windings of said transformers'being required to conductthe power currents flowing in the several tracks. the same time, the signaling block-sections are maintained electricallv independent of one another, although portions of the transformer windings are common paths for both the powercurrents and the signaling currents. By means of my present invention, the aforementioned results may be obtained, andthe series transformers adapted for accomplishing them may be economically constructed by providing a plurality of paths through the transformer windings for the high value power currents flowing therethrough. V

Other advantages accruing from the use ofmy invention will be hereinafter described and pointed out with particularity in the appended claims.

For a better'understanding of the nature and scope of my invention, reference may be had to the following description and to the accompanying drawing, the single figure of which is a diagrammatic representation of a railway system embodying a form of my invention.

A source of. power or propulsion current (not shown) is connected to trolley conductors 1 and 2, and to their associated tracks 3 and 4, respectively, in the usual manner. The tracks comprise paths for the return flow of these propulsion currents. Spaced insulating joints 5 are inserted at intervals in the trolley conductors 1 and 2, and, similarly, spaced insulating joints 6 and 7 are inserted in the tracks 3 and 4. In certain instances, additional insulating joints 8 and 9 are inserted in the tracks in order to divide them into a series of insulated block sections or track circuits each of which is protected by means of a signaling device 10. For the purpose of illustration only, one signaling device 10 is shown associated with each of the tracks 3 and 4, but it will be understood that these signaling devices are disposed at convenient intervals along the railroad, depending upon the character of the protection to be afforded.

Adjacent to each other and on each side of the insulating joints 8 and 9 are inserted impedancebonds 11, and adjacent to the insulating joints 6 and 7 are inserted other impedance bonds 12, each of said impedance bonds comprising current-carrying windings provided with taps at their mid-points. An intelligence transmission conductor 8 shown as a telephone conductor, is disposed adjacent to the trolley conductors 1 and 2 and the tracks 3 and t and is, therefore, under the inductive influences arising from thecurrents flowing over the aforementioned railway circuits. It is important,

therefore, to minimize the inductive disturbances impressed upon the telephone conductor S in order to insure the satisfactory transmission of intelligence. At the same time, means must be provided for the effect ive operation of the signaling devices 10 in order that the traiiic accommodated upon the several tracks may be amply protected. To this end, transformers 13 and it have been provided each of which comprises a plurality of windings that are connected in circuit with the tracks, as will be hereinafter described.

Since the two railway systems are substantially similar, my description will be confined to that one comprising the trolley conductor 2 and the track 1 it being understood that the operation of the other railway system is identical therewith. It will be noted that a block section or track circuit 15 is formed in the track at by means of the spaced insulating joints 8* and 9 which are inserted in the rails of the track. The several block sections comprising the railway system are connected together through impedance bonds 11, in order to constitute a continuous path for the flow of the propulsion currents as hcreinbefore described. Intermediate the insulating joints 8 and 9 which form the block section 15, I

have disposed the insulating joints 6 and 7 which are spaced from one another, as will be hereinafter described, in order that the insulating joint 5 in the trolley 2 may be disposed substantially midway between them. On the sides of the insulating joints 6 and 7 adjacent to the insulating joints 8 and 9, I have disposed the impedance bonds 12, the mid-points of which are connected through conductors 16 and 17 to corresponding mid-points of the impedance bonds 12 inserted in the track At the same time, the conductors 16 and 17 are connected to the terminals of secondary windings 18 and 19 of the transformer 13. ings 20 and'21, which are connected across the insulating joints 5 in the trolley conductors 1 and 2, respectively, serve to inductively interlink the several trolley conductors with their associated tracks. In this manner, the return flow of the trolley currents is confined to the tracks, the relative flow over the tracks 3 and 4 being adjustable by means of taps 22 provided on the secondary windings 18 and 19. Consequently, in the illustrated system, the propulsion currents are substantially equal ized in all four of the rails, by reason of the provision of the four equal-impedance paths including the respective halves of the impedance bonds 12. Since the return flow of the propulsion currents is confined to the tracks 3 and 4, the inductive disturbances that may be impressed upon the transmission conductor 8 are substantially Primary windnegligible. This condition of operation and result are in accordance with the systems shown and described in the aforementioned United States Patent, No. 1,196,300.

However, provision must be made for the operation of the signaling devices 10 and, to this end, the insulating joints 6 and 7 are respectively shunted by windings 23' and 24 of the transformer 13. When the rails comprising the block section 15 are not bridged by a train, the signaling currents which are supplied from a power supply circuit 25 through a transformer 26 flow over a circuit comprising a rail-section 27, a conductor 27, the inductive current carrying winding 23 of the transformer 13, a conductor 27", a lead 28, a signaling relay 29, a lead 30, a rail section 31, a conductor 31, the current-carrying inductive winding 24: of the transformer 13, a conductor 31". and the secondary of the transformer 26. As the current flows through the signaling relay 29, the signal 10 controlled thereby operates to indicate safety. It will be noted that the signaling currents traverse the current-carrying windings 23 and 2 .1 simultaneously and in opposite directions and, consequently, the inductive effects arising therefrom are substantially neutralized, thereby providing a path of negligible impedance for the flow of the signaling currents.

When a railway train indicated at 32 bridges the rail sections 27 and 31, the signaling currents are shunted through the trucks of the railway train, thereby shortcircuiting the sign ttl relay 29 which operates the signals to indicate danger. It will be noted that the impedance bonds 11 confine the signaling currents to the insulated block section 15 and that these currents are also shunted across the insulating joints 6 and 7 by the inductively related windings 23 and 24 of the transformer 13.

It will be observed that the two tracks 3 and 4: are electrically interconnected through the impedance bonds 1.2 and the common conductors 16 and 17 leading to the secondary windings 18 and 19 of the transformer 13. Because of the inductive relation between these secondary windings and the secondary windings 23 and 24 with their associated primary windings 20 and 21, the propulsion currents of both railway systems are confined to the paths afforded by the aforesaid secondary windings. As a consequence thereof, the windings 23 and 2a of the transformer 1.3 are so designed as to carry both the signaling currents and a portion of the return propulsion currents, sin e the pro ulsion currents, which are of relatively high values, are divided between the windings 23 and 2-1. connected in shunt to the insulating joints 6 and 7 respectively, and used as paths for the flowof the signaling currents, and the secondary windings l8 and 19.

The current-carrying windings of the transformer 13 serving to interlink the trolley conductors and the tracks with one anotherare wound upon a single iron core, thereby closely inductively interlinking the several windings with one another. The whole is then inclosed in a single casing to comprise one transformer, such as shown at To provide for the adjustment of the currents flowing through the respective (-urrent-carrying windings, taps are provided as is usual for regulating purposes.

In actual installations, it has been found that, under certain conditions of separation of the rail insulating joints and their position in the track with respect to the insulating joints in the trolley conductor, a large portion of the propulsion currents may be forced through the signaling relay, sometimes in sufficient quantity to burn it out. The solution of this trouble is dependent upon the dimensions of the locomotive and may be solved by setting a limitation of a certain number of feet, namely, 5 feet. be tween the insulating joints 6 and 7 in the two rail sections 27 and 31, respectively, and having the insulating joint 5 in the trolley conductor 2 disposed substantially midway between the said insulating joints in the track. This requirement is based on the dimensions of the locomotive 32 to insure that both. of the track joints 6 and 7 are bridged. by the locomotive before the insu- I lating joint 5 in the trolley conductor 2 is crossed by the pantograph shoe 33 of the locomotive.

While the foregoing description has been confined to the operation of the track ft, by referring to the signaling block-section of the track 3,it will be noticed that the windings of the transformer 14 are connected to the track 3 in a manner similar to the connection of corresponding windings of the transformer 13 to the track 4.

It will be apparent that each of the transformers interlink both tracks 3 and 4t and the trolley conductors 5 with one another. Again, the block sections are continuous to the flow of the signaling currents, although the rail sections are broken. by insulating joints that are employed in connection with the series-transformers 13 and 14-. By employing the secondary windings 18., 19, 23 and 24, the propulsion currents are divided therebetween, thereby eliminating the necessity of furnishing a single winding which would, of necessity, comprise a conductor of very large cross-sectional area in order to permit the propulsion currents of the several railway systems to flow therethrough. At the same time, two of the secondary windings, namely, 23 and 24, are employed to conduct signaling currents around the insulating joints 6 and 7 inserted intermediate the ends of the block sections.

By employing my invention, a single transformer suffices to inductively interlink both the tracks and their associated power conductors. In addition, means are employed for rendering the separate block sections electrically continuous for the signaling currents, although said block sections are interrupted by insulating joints. By providing a plurality of secondary windings, such as herein described, as a substitute for a single winding comprising a conductor of large cross-sectional area, an economical construction of the transformers may be effected.

While I have shown one embodiment of my invention, it will be understood by those skilled in the art that many modifications may be madetherein without departing from the spirit and scope of the appended claims.

I claim as my invention:

1; In a railway system, the combination with a source of propulsion current supply, a trolley conductor connected thereto, a source of signaling current, a track comprising a plurality of insulated sections, said track forming a portion of a signaling circuit, and additional insulating joints inserted in the rails comprising each of said sections, of means for inductively interlinking the track andthe trolley conductor in order to confine the return flow of the propulsion current to the track and to permit unimpeded flow of a signaling current in each insulated section.

2. In a railway system, the combination with a source of propulsion current supply, a trolley conductor connected thereto, a source of signaling current, a track comprising a plurality of insulated sections, and additional insulating joints inserted in the rails comprising each of said sections, of means for inductively interlinking the trolley conductor and the track in. order to confine the return flow of the propulsion current to the track and means for inductively interlinking the rails of each section in order to provide a substantially unimpeded flow for the signaling current in each of said sections.

3. In a railway system, the combination with a source of propulsion current supply, a trolley conductor connected thereto, a source of signaling current, a track comprising a plurality of insulated sections, and additional insulating joints inserted in the rails comprising each of said sections, of primary windings connected in series with the trolley conductor, secondary windings inductively related therewith connected in shunt to said insulating joints in order that the propulsion-current flow may be confined to the track, and current-carrying windings also connected in shunt to said insulating joints, said last named windings being inductively related with each othe' and with said primary windings to provide unimpeded paths for the flow of signaling currents in the block sections and paths for the flow of the propulsion currents.

4. The combination with two railway tems each having a track and a trolley Con ductor, a source of propulsion current supply therefor, a source of signaling current, insulating joints inserted in the rails of the tracks, and impedance bonds adjacent to said insulating joints for connecting together the rails of each track, of spaced transformers having primary windings connected in series circuit with the trolley conductors and a secondary winding connected in common to the impedance bonds inserted in both tracks, and windings inductively related to each other and to said primary windings, said inductively related windings being connected in shunt to said insulating joints of one track to provide an unimpeded path for the simultaneous flow therethrough of signaling currents and portions of the propulsion current.

5. The combination with a plurality of railway systems each having a track and a trolley conductor, a source of propulsion current supply therefor, a source of signaling current, and insulating joints inserted in the trolley conductors and the rails of the tracks, of transformers having primary windings connected in shunt to the insulating joints of the trolley conductors, and secondary windings connected in shunt to the insulating joints in the rails for interconnecting all the tracks together, and other secondary windings so inductively interlinking the rails of one track that substantially unimpeded paths for the flow of signaling currents are provided.

6. In an electric railway system employing alternating current both for propulsion and signaling, the combination of a track consisting of two rails, a third conductor paralleling said track, means whereby said third conductor may be made to serve as one side, and the two rails in parallel as the other side of said propulsion circuit, means whereby said track may be made to serve as the circuit of said signaling current, a series transformer having one winding in series with said third conductor and the other winding in series with the other side of said propulsion circuit, and means whereby said series transformer may be effectively connected to Said propulsion circuit at any point in a signal section without rendering said signal section discontinuous for signaling currents.

7. In an electrical transmission system for the simultaneous transmission of two separate component alternating currents, the combination of three parallel conductors, two of which serially constitute the circuit ing alternating current of one of said component currents and in parallel one side of the circuit of the other of said component currents; an insulating joint in each of said two conductors; means associated with said two conductors whereby said first named component current is transmitted across said insulating joints,

and a second means connected in series with the third conductor and mutually inductively related with said first-mentioned means, whereby the current in said third conductor and the sum of the currents in said two conductors in parallel may be substantially equalized. l a

8. In an electric railway system employing alternating current for both propulsion and signaling, the combination of a track consisting of two condurting rails; means whereby said rails serially constitute the circuit of said signaling current and in parallel one side of the circuit of said propul sion current; a third conductor paralleling said track; an insulating joint in each of a said two rails of said track; means whereb said si nalin current ma be transb l i mitted across said insulating joints; and a second means connected in series with said third conductor and mutually inductively related with said first named means, whereby said propulsion current in returning to its source may be confined entirely to the rails associated with said third conductor.

9. In an electrical transmission system for the simultaneous transmission of two separate component alternating currents, the combination of three parallel conductors, two of which serially constitute the circuit of one of said component currents and in parallel one side of the circuit of the other of said component current an insulating joint in each of said two conductors and the third conductor; and a transformer having a primary winding bridgingthe insulating joint in said third conductor and a pair of secondary windings bridging the insulating joints of said two conductors, respectively,

so as to offer a substantially unimpeded path across said insulating joints for the ffow of u the first-mentioried component current. i l l 10. In an electric railway system cmployfor both propulsion and signaling, the combination of a track consisting ottwo conducting rails; means whereby saidrails serially constitute the oil.- cuit of said signaling current and in parallel one side of the circuit of said propelsion current, a third conductor paralleling said track; an insulating joint in each of said rails and in said third conductor; and a transformer having a primarywinding bridging the insulating joint in said third conductorand a pair of secondary windin bridging theinsulating joints of said rail s respectivelymoas to 0 er a substantially unimpeded path across said insulating joints for the flow of signaling current in opposite directions in said rails.

11. in an electrical transmission system, the combination of two pairs of conductors adapted for the simultaneous transmission of two; separate component alternating cur rents, the two conductors of each pair serially constituting the circuit of one of said coi'nponcnt currents and in parallel one side of the circuit of the other of said component currents, an insulating joint inserted in each of said. conductors, a pair of mutually inductive windings associated with the conductors oi one of said pairs so as to offer a substantially unimpeded path across said insu lating joints for the flow of the first of said cinnponent currents in opposite directions in the two conductors, and means for equal.- izing the flow of the second of said component currents in the same direction across said insulating joints in all four conductors.

12. A system as specified in claim 11, said mutually inductive windings bridging the insulating means of their associated'conduetors. j

13, In an alternating-current railway signaling system of the type wherein thetwo rails of? each track serve as parallel paths for the return flow of propulsion currents and also as the two sides of the signaling current circuits, the combination of a pair of tracks, each comprising a pair of rails, insulating joints inserted at corresponding points in each of said tracks, a pair of mutually inductive windings, associated with the rails of one track so as to offer a substantially unimpeded path across said insulating joints tor the flow of signaling currents in opposite directions in the two rails, and means for equalizing the flow of propulsion currents in the same direction across said in sulating-joints in all four rails, and for preventing harmful ground currents.

14:. A system as specified in claim 13, said mutually inductive windings bridging the insulating joints of their associated rails.

15. 111 an electrical transmission system employing two separate component alternating currents, the combination of a plurality of groups of conductors, each group com the conductors of all of said groups; a transformerhaving primary windings connected across the joints of thethird conductors of the respective groups, and a pair of secondary windings bridging the insulating by rendering said conductors joints of said two conductors of one of said groups so as to offer a substantially unimpeded path across. said insulating joints for the flow of the first of said component currents in opposite directions in said two conductors; and means for equalizing the flow of the second of said component currents in the same direction across said insulating joints in said two conductors of all of said groups.

16. In an electric railway system employing alternating current for both propulsion and signaling, the combination of a plurality of tracks, each comprising a pair of rails; means whereby the two rails of each track serially constitute the circuit of the respective signaling currents and in parallel one side of the circuit of the propulsion current; a trolley conductor for each track; insulating joints-inserted at corresponding points in each ofsaid rails and trolley conductors; a transformer having primary windings connected across the joints of the respective trolley conductors, and a pair of secondary windings bridging the rail joints of one of said tracks so as to offer a substantially unimpeded path across said insulating joints for the flow of signaling currents in opposite directions in said rails, and means for equalizing the flow of propulsion currents in the same direction across said insulating joints in all of the rails, and for preventing harmful ground currents.

17. In an electrical transmission system, the combination of a plurality of groups of conductors, each group comprising three parallel conductors, adapted for the simultaneous transmission of two separate component alternating currents, two of which conductors serially constitute'the circuit of one of said component currents and in parallel one side of the circuit of the other of said, component currents, insulating means inserted in each of said two conductors at corresponding points in each group, therediscontinuous means associated with said two conductors in one of said groups whereby the first of said component currents may be transmitted across said point of discontinuity, and transforming means associated with said thirdconductors and said two oonductorsin parallelin each group, whereby the sum of the currents in said third conductors and the sum of the currents in said two conductors in both groups in parallel may be substantia 11y. equalized.

"=18. In-an electric railway system employing alternating current for both propulsion and signaling, the combination of a plurality of'itracks, each of said tracks consisting of two conducting rails; means whereby the two rails of'each track serially constitute the circuit-of the respective signaling currents 'andin parallel Jone side'of the circuit 01" said propulsion current; a plurality of third conductors paralleling sald plurality of tracks: an insulating joint in each rail of said plurality of tracks; means associated with one of said plurality of tracks whereby the naling current associated with said track may be transmitted across said insulating joints; and a second means associated with said third conductors and said rails in each track whereby said propulsion current associated with said plurality of tracks in returning to its source may be confined entirely to said plurality of tracks.

19.,In an electrical transmission system. the combination of two pairs of parallel conductors; insulating joints inserted at corresponding points in each of said conductors, whereby said conductors are di vided into parallel sections, the parallel sections of each pair being adapted for the simultaneous transmission of two separate component alternating currents, the two sections of each pair serially constituting' the circuit of one of said component currents and in parallel one side of the circuit of the other of said component currents: an inductance device disposed at each side of the insulating joints of one of said pairs of conductors and having its terminals connected to the respective sections of said pair, each of said inductance devices being provided with a mid-tap; a transformer having three windings, one of said windings bridging said mid-taps, the other two windings bridging the insulating joints in the respective conductors of the other pair; and means connected to said transformer for equalizing the second component currents in the conductors ofsaid other pair and for equalizing also the second component currents in the two pairs, whereby all four conductors are used to carry the second component currents required by a load on either pair of con-- ductors.

20. In an alternating-current railway signaling system of the type wherein the two rails of each track serve as parallel paths for the return flow of propulsion currents and alsoas the two sides of the signaling current circuits, the combination of a pair oi tracks. each comprising a pair of rails; an insulating joint in each of said rails; a source of alternating currents for signaling, a signal controlling device, and an inductance device all connected across the rails of one of said tracks on each side of said insulating joints, each of said inductance devices being provided with a mid-tap; a transformer having three windings, one of said windings bridging said mid-taps, the other two 7 bridging the insulating joints in the respective rails of the other track; and means connected to said transformer for equalizing the propulsion currents in the rails of said other track and for equalizing-also the propulsion windings currents in the two tracks, whereby all four rails are used to carry the propulsion currents for vehicles on either track.

21. The system as specified in claim 19, including two additional windings on the transformer, a. third conductor for each of said pairs of conductors, and insulating joints in each of said third conductors,said additional transformer windings being connected across the insulating joints of the respective third conductors.

22. A system as specified in claim 20, including two additional windings on the transformer, a trolley conductor for each track, and an insulating joint in each of said trolley conductors, said additional trans former windings being connected across the insulating joints of the respective trolley conductors.

23. In an electrical transmission system, the combination of two pairs of conductors adapted for the simultaneous transmission of two separate component alternating currents, the two conductors of each pair serially constituting the circuit of one of said component currents and in parallel one side of the circuit of the other of said component currents, an insulating joint inserted in each of said conductors, an inductance device connecting the conductors of each pair on each side of said insulating joints, each of said inductance devices beingqprovided with a mid-tap, a pair of connecting devices, one of said connecting devices connecting the mid-taps of the two inductance devices which are connected to the respective pairs of conductors on each side of said insulating joints, and a transformer having three windings, two of said windings being connected respectively across the insulating joints oi.

the conductors of one of said pairs, and the remaining winding having its respective terminals connected to said connecting means. i U H 24'. an alternatingmurrent railway s1g-,

naling system, the combination of a pair of tracks, each comprising a pair of rails, an insulating joint in each of said rails, an in ductance device connecting the rails of each track on each side of said insulating joints, each of said inductance devices, being provided with a mid-tap, a pair of connecting conductors, one of said connecting conductors connecting the mid-taps of the two inductance devices which are connected to the respective track-rails on each side of said insulating joints, and a transformer having three windings, two of said windings being connected respectively across the insulating joints of the'rails of one of said tracks, and. the remaining winding having its respective terminals: connected to said connecting conductors.

25. The system as specified in claim 23, including two additional windings on th tcm for preventing the flow of earth-currents and for providing the use of an alternatingcurrent block signaling system, the combination of a pair of tracks, each comprising a pair of rails; a trolley conductor for each of said tracks; means whereby said trolley conductors may be made to serve as one side and the four rails in parallel as the other side of the circuit for propulsion currents; means whereby the two rails of each track may be made to serve as the two sides of the circuit for signaling currents; and means for inductively interlinking said tracks and trolley conductors in such a manner as to confine the return flow of the propulsion current to the track, to permit substantially unimpeded flow ofsignaling currents in one section of said tracks, and to impede the flow of signaling currents in the adjacent sections of track.

28. A system as specified in claim 10. characterized, by the fact that the joints in the runs. are disposed at points not exactly opiosite to each other, but close enough togethcr so that both rail joints will be bridged by the wheels of a passing vehicle before the third-conductor joint is bridged by the current-collecting device of the vehicle, whereby the signalingcircuit is protected against abnorn'lal voltages.

29. In an alternating-current railway sys tem 'for preventing the flow of earth currents and for providing for the use of an alternating-current block signaling system, the combination of a plurality of tracks comprising two pairs of rails; a trolley conductor; means whereby said trolley conductor may be made to serve as one side and the four rails parallel as the other side of the circuit for propulsion currents; an insulating joint in each of said rails and in said trolley conductor; a source of alternating currents for signaling, a signal controlling device, and an inductance device all connected from one rail to the other on each side of said insulating joints, each of said inductance devices being provided with a mid-tap; a transformer having one winding connected across the insulating joint of said trolley conductor, and another winding having its terininals connected to said mid-taps, the joints in the rails being disposed at points not exactly opposite to each other but close enough together so that both rail joints will be bridged bythe wheels of a passing vehicle before the trolley-conductor joint is bridged by the currentcollecting device of the vehicle, whereby the signaling circuit isprotected against abnormal voltages.

' 30. In an 'electric'railway system employing alternating current for both propulsion and signaling-the combination of a track consisting of two conducting rails; means whereby said rails serially constitute the circuit of said signaling current and in parallel one side of the circuit of said propulsion current a third conductor paralleling said track; an insulating joint'in each of said two rails of said track and in said third conductor; transforming means bridging said insulating joint in said conductor and said insulating joints in said rails in such a manner as not to short circuit said signaling current, whereby said propulsion current in returning to its source may be confined entirely to the rails associated with said third conductor, the joints in the rails being disposed at points not exactly opposite to each other, but close enough together so that both rail joints will be bridged by the wheels of a passing vehicle before the third-conductor joint is bridged by the current-collecting device of the vehicle, whereby the signaling circuit is protected against abnormal volt- -e 31. In an alternating-current railway signaling system, the combination of a pair of tracks, each comprising a pair of rails, an insulating joint in each of said rails, an inductance device connecting the rails of each track oneach side ofsaid insulating joints, each of said inductance devices being provided with a mid-tap, connecting means connected with said mid-taps for equalizing the propulsion currentsin all four of said rails,'a trolley conductor for each of said tracks, means'in series with said trolley conductors and mutually inductively related to said connecting means whereby the sum of the currents in said trolley conductors and the sum of the currents in said rails may be substantially equalized, means whereby the rails of the respective tracks may serve as the circuits for alternating signaling currents, characterized by the fact that the joints in the rails of each track are disposed at points not exactly opposite to each other but close enough together so that both rail joints will be bridged by the wheels of a passing vehicle before the corresponding trolley conductor joint is bridged by the currentcollecting device of the vehicle, whereby the signaling circuits are protected against abnormal voltages.

A system as specified in claim 16, characterized by the fact that the joints in the rails of each track are disposed at points not exactly opposite to each other but close enough together so that both rail joints will be bridged by the wheels of a passing vehicle before the corresponding trolley conductor joint is bridged by the current-collecting device of the vehicle, whereby the signaling circuits are protected against abnormal voltages.

33. A system as specified in'claim 22, characterized by the fact that the joints in the rails of each track are disposed at points not Xactly opposite to each other but close enough together so that both rail joints will be bridged by the wheels of a passing vehicle before the corresponding trolley conductor joint is bridged by the current-collecting device of the vehicle, whereby the signaling circuits are protected against abnormal voltages.

34-. A system as specified in claim 27, characterized by the fact that the joints in the rails of each track are disposed at points not exactly opposite to each other but close enough together so that both rail joints will be bridged by the wheels of a passing vehicle before the corresponding trolley conductor joint is bridged by the current-collecting device of the vehicle, whereby the signaling circuits are protected against abnormal voltages.

In testimony whereof, I have hereunto subscribed my name this 19th day of Aug, 1915.

CHARLES LE Gr. FORTESCUE.

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