US2135527A - Railway track circuit - Google Patents

Description

NOV. 8, 1938. I w PQWELL I 2,135,527

RAILWAY TRACK CIRCUIT Original Filed July 28, 1934 Compensafin Line BY ATTORNEY Mum Patented Nov. 8, 1938 PATENT OFFICE RAILWAY TRACK CIRCUIT Winfred T. Powell, Brighton, N. Y., assignor to General Railway Signal Company, Rochester,

Original application July 28, 1934, Serial No. 737,433, now Patent No. 2,083,920, dated June 15, 1937. Divided and this application December 3, 1936, Serial No. 114,089

12 Claims.

This invention relates in general to track circuits such as used in railway signalling practice and it has more particular reference to means for maintaining current through a track relay associated with a stretch of railway track substantially constant, regardless of changes in ballast leakage between the rails of the track due to Weather conditions.

The invention also relates to means for automatically discriminating between current changes in the track circuit due to the occupied condition of the track and due to leakage currents resulting from poor ballast conditions.

This application is a division of my prior application Ser. No. 737,433 filed July 28, 1934, now

U. S. Letters Patent 2,083,920 dated June 15,

In railway operation it is quite essential that the usual track relay connected across the track section at one end of a signalling block be sufficiently energized when the block is unoccupied to pick up and hold up with certainty. It is likewise essential that the occupancy of the track section will so effectively shunt or condition the relay that it will be positively released. For example, in the usual track circuits if the normal holding current is too high shunting may not be effective to drop the relay and if the normal holding current is so low that shunting is made more positive then it is possible that at times the holding current will be insuflicient.

Taking the above into consideration it will be apparent that the usual variation in ballast resistance encountered in practice, due primarily to vchanges in weather conditions, may interfere with the proper operation of the track relay unless some means are provided to compensate for the current ordinarily shunted away from the track relay by extreme ballast leakage, or for discriminating between changes due to ballast resistance and track occupancy. The present arrangement is proposed as a means for regu lating the potential applied to the holding winding or windings of a track relay under various ballast conditions and also for discriminating between slow changes in the shunting of the relay due to ballast changes and rapid changes in the shunting of the relay due to track occupancy.

It will be obvious that an increase in ballast resistance results .in a decrease in the leakage current between the rails so that the voltage across the terminals of a track relay connected across these rails increases. Conversely, as the ballast resistance-decreases the leakage current between the rails increases and the terminal voltage at the usual track relay decreases. The relay current will vary over a considerable range and cover a range at times which may prevent proper response of the relay under occupied or unoccupied conditions of the track section.

It is therefore proposed in accordance with this invention to provide means automatically operable to permit a change in current in the track relay eifected by the entrance of a train into the associated track section, but to automatically maintain a substantially constant current in the track relay regardless of changes in Values of leakage current through the ballast from one rail to the other.

It is further proposed to improve the shunting eificiency of the track circuit and for this purpose a discriminating arrangement is included in the circuit of the track relay which discriminates between a slow change in track shunt due to track ballast and a rapid change in track shunt due to train occupancy.

Further objects, purposes and characteristic features of the invention will appear as the description progresses, reference being made to the accompanying drawing which shows by way of example one form which the invention may assume.

The single figure illustrates one form of the present invention in a diagrammatic and conventional manner.

Apparatus.---Referring to the single figure, a section of railway track including rails I is shown separated from the adjacent track sections by insulated joints 2. A track battery BT and a track relay T are shown connected to the track rails at opposite ends of the illustrated section.

As typical of the control exercised by the track relay, a semaphore signal SG is illustrated at the left end of the track section and in the present description it will be assumed that traflic moves from left to right over this section as indicated by the arrow appearing above the track rails.

The track relay and the track rails are connected to the track battery through the medium of an electrical network comprising various resistors, relays and impedance coils laid out in the form of a Wheatstone bridge.

Normal conditions.-Referring to the drawing it will be assumed that the ballast is in a dry condition so that there is approximately no leakage current flowing between the rails l of the track section. Under this condition relay T is energized over a circuit extending from the terminal of battery BT, compensating line conductor l5, through the bridge network in the direction of the arrows, lower winding of relay T and resistor H in multiple, compensating line wire i6, upper track rail, upper winding of relay T and lower track rail to the terminal of battery ET.

The Wheatstone bridge is made up of two resistors comprising arms a and b and two impedances comprising arms 0 and d, all having direct current resistance values such that the product of arms ab equals the productof arms cd. Under this condition,'points A and B'of the bridge circuit are at equal potential so that no current flows through the upper winding of detector relay P.

Therefore track relay T' is energized by way of its potential winding which is connected across the track rails and also by way of its current winding which is connected in series with thebridge across the trackrails. It will be understood that contact 33- of relay T is. used to control the signals in any manner required by practical conditions.

Under these conditions relays P, G and AX are normally de-energized.

Track occupancy.-It will be assumed that a train enters the track section at the left end under the conditions above outlined, that is; normal dry ballast conditionsr The shunt provided across the track rails by the train, short circuits the upper winding of relay T. The lower winding of relay T is of such a value in ampere turns that the relay will not hold up with current through the lower winding alone. Therefore the shunting of the upper winding ordinarily drops the relay'for signalling purposes.

In addition to this operation of relay T, a check is provided by the sudden shunting of the track by the train causing a sudden rushof current from the terminal of battery BT, line I5, arm a of the bridge, upper winding of relay P, armb of the bridge,-resistor H, line l6, upper track rail, through the shunt provided by the train and thelower track rail to the terminal of battery ET. This sudden increase of current flows in the above described circuit in the direction of the arrows. The reason that the current flows throughthe winding of relay P is because the bridge is out of balance under this condition due to arms 0 and d being inductive so that the sudden rush of current is choked out of these arms of thebridge; Therefore relay P will operate its'polar contacts to the left. It will be understood that resistor H is provided in shunt-of the lower winding of relay T to provide a non-inductive path for thesudden rush of current which would ordinarily be choked back if ithad to go through the inductive winding of relay T.

The operation of relay P tothe left closes. a'

stick circuit for this relay and a pick-up circuit for therelay AX extending from contact 28 of relay P in its left hand dotted position, lower winding of relay P, contact 2| of relay P in its left hand dotted position, back contact 22 of relay G- and" winding of relay AX, to RelayAX short circuits resistor H and the lower winding of relay T at its front contact 23-. Since both windings of relay T are now effectively short ci'rcuited it will be positively released.

It will thus be seen that in the event of the failure of relay T to release when shunted by a train an additional shunt is provided for posi tively releasing this relay in response to an impulse of current set up by the entrance of a train into the track section. In the event that relay T is dropped by the shunting of its upper winding alone then a circuit is closed for picking up relay AX extending from back contact 24 of relay T, back contact 22 of relay G, and winding of relay AX, to Under either of the above described conditions the dropping of back contact 24 short circuits the lower winding of relay P which allows this relay to restore its contacts to neutral after a check has been made that relay T has dropped. Relay P is not energiz'ed through its; upper winding after the sudden rushof current because the bridge reaches a stable condition, due to the direct current resistances of the arms of the bridge being so proportioned that no current flows between points A and B'. 7

Track 1 .noccupancy.-When the train leaves the illustrated track section, a sudden decrease of current flow across the track rails is effected. The removal ofthe shunt across the upper winding of relay T is-eiiective to permit sufficient current toflow through this winding to pick up re' lay T. Also this sudden decrease of current flow through the bridge causes a momentary rush of current in the opposite direction to that indicated by the arrows which is efiective to operate relay P'to the right. This rush of current is due tothe self-inductance of inductances c and d which tends to maintain the original current flow afterthe current flow from battery BT has been decreased; The decreased current flow from the battery establishes an immediate value through arms a and b but there are momentary added currents in arms d and c in the original direction (due to the self-inductance of these arms), which currents are in aiding relation for causing a resultant current to flow through the upper winding. ofrelay? in'a' direction opposite to the arrow. This closes a circuit for sticking relay P and for picking up'relayG extending from contact 21' of relay P in its right hand dotted position, lower winding of relay P, contact 20' of relay Pinits right hand dotted position, front contact 25" of relay AX, to

The picking up of-relay G opens the circuit of relay AX at back contact 22, allowing relay AX to drop its front contact 23 for removing the assumed that a high leakage current, due to an,

abnormally wet ballast condition, flows from the terminal: of battery BT, line conductor i5, through the bridge, lower winding of relay T, line conductor l6; upper track rail, upper winding of relay T and the lower track rail to the terminal of battery BT. Due to the low resistance ballast shunt, a substantial portion of v the current is" shunted from'the' upper winding of relay T. A'lsodue to this leakage current an increase in current flow is effective through the' lower winding of relay T sothat the increased shunting eiTect of the upper winding of the relay (due to' the leakage) will be compensated for by the increased current flow through the lower winding of the relay due to this leakage. It will be noted that any leakage current which flows must go through the lower winding of relay T.

Assuming that a train enters the track section and winding of relay G,

under this condition, the upper winding of relay T is short circuited and the sudden shunting of the track by the train causes relay P to actuate its contacts to the left as before. This closes a circuit for picking up relay AX and for sticking relay P'in its left hand position. This is assuming that relay T did not drop when the train shunted its upper winding.

The picking up of relay AX short circuits the lower winding of relay T and since its upper winding is shunted by the train, it will be positively released. The dropping of relay T closes the above described circuit for relay AX which also short circuits the lower winding of relay P for restoring this relay to neutral.

When the train leaves the track section it will be assumed that, due to the extremely high leakage current, relay T does not pick up because its upper winding is eifectively shunted. Relay P, however, will actuate its contacts to the right as previously described and a circuit closed for pickingup relay G extending from contact 2! of relay P in its right hand dotted position, lower winding of relay P, contact of relay P in its right hand dotted position, front contact of relay AX and winding of relay G, to It will be understood that relay AX is picked up because it is assumed that relay T is not picked up. It will be noticed that this operation of relay P sticks the relay in its right hand position by means of current flowing through its lower winding in opposition to the full line arrow, which corresponds to the current which operated relay P to the right which was opposite to the full line arrow in the upper winding of relay P.

The picking up of relay G drops relay AX which inserts the lower winding of relay T in the track circuit and since the leakage current is high, suflicient current flows through this lower winding to positively pick up relay T. To prevent relay AX being again picked up before relay T picks up its back contact 24, relay G is made slightly slow acting.

The above rather specific description of one form of the present invention has been given solely by way of illustration and is not intended in any manner whatsoever in a limiting sense. It will be obvious that the general principles therein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention defined in the following claims.

What I claim is:

1. Ina track circuit, a track relay, a source of current connected to the railroad track, a potential winding and a current winding of said relay connected to said track, said potential winding being shunted by a train on said track cir-' cuit, an electrical network connected to said source of current, means including said potential and said current windings for maintaining said relay eflectively energized under various track leakage conditions, and means including said network responsive to said train shunt for shunting said current winding.

2. In a track circuit, a track relay, a source of current connected to the railroad track, a potential winding and a current winding of said relay connected to said track, said potential winding being shunted by a train on said track circuit, an electrical network connected to said source of current, means including said potential and said current windings for maintaining said relay 'efiectively energized under various track leakage conditions, means including said network responsive to said train shunt for shunting said current winding, and means including said network responsive to the removal of said train shunt for removing the shunt from said current winding.

3. In a track circuit, an insulated section of track, a source of current connected to said track, a track relay including windings connected to said track and maintained picked up during the slowly changing current values in its windings due to variations in ballast resistances, a Wheatstone bridge connected in series with said relay, means responsive to the entrance of a train into said section for producing a rapid change in current in the circuit of said relay and said Wheatstone bridge whereby said bridge is unbalanced, and means controlled in response to the unbalanced condition of said bridge and said train shunt for shunting one of said windings.

4. In a track circuit, an insulated section of track, a source of current connected to said track, a double wound track relay connected to said track and maintained picked up by an increase of current in one winding when the current in the other winding decreases due to an increase in ballast leakage current, the current in one of said windings being decreased by the presence of a train on said track circuit, and means responsive to the entrance of a train into said section for decreasing the current in the other winding whereby said relay is released.

5. In a track circuit; in combination with an insulated stretch of track; a source of current connected to one end and a track relay connected to the other end of said track; and regulating means controlled over said track by current from said source for automatically shunting at least a portion of said relay whereby the shunting efiect of a train in said stretch of track is augmented, said regulating means including a balanced detector which selectively detects current changes in said track due to its occupancy by a train and changes due to ballast leakage.

6. In a track circuit; in combination with an insulated stretch of track; a source of current connected to one end and a track relay connected to the other end of said track; and regulating means controlled over said track by current from said source for automatically shunting part of the winding of said relay whereby the shunting effect of a train in said stretch of track is augmented, said regulating means including a balanced detector which selectively detects current changes of distinctive character in said track due to its occupancy and unoccupancy by a train and changes due to ballast leakage.

7. In a track circuit for railroads, the combination with a section of track insulated from the adjacent track by insulating joints, a source of track circuit current connected across the track rails at one end of said section through the medium of a Wheatstone bridge consisting of two multiple conductors each having an intermediate tap, said Wheatstone bridge having the four elements so formed constituting impedances having electrical constants so that said bridge is balanced and has no voltage between its taps for direct current flowing to said bridge but has voltage of one polarity impressed between said taps when the direct current through the bridge is increased and has voltage of opposite polarity impressed between said taps when said direct current is decreased, a polar relay connected between said taps, a second relay, a circuit for picking up said second relay when said polar relay is energized to one polarity position, and a holding circuit for said second relay which is broken when said polar relay is operated to the other polarity position.

8. In combination, a railway track divided into blocks by insulating joints, a signal at the entrance to each block, a track circuit for each block including a track battery and a Wheatstone bridge connected in series, said Wheatstone bridge having four elements connected end to end to form a closed link of which two oppositely located elements are more highly inductive than are the other two elements which bridge is so included in the track circuit that the track circuit current divides a portion flowing through two elements in series and the rest flowing through the other two elements in series said elements having ohmic resistances so that the bridge is balanced and no voltage exists between the two points each joining two elements in series when direct current flows therethrough but whereby voltage of one polarity exists between said two points when the direct current is increased and Voltage of the opposite polarity exists between two points when the direct current is decreased, a signal control relay for controlling the signal at the entrance to said block, and means including said Wheatstone bridge for picking up said relay when voltage of one polarity exists between said points and for dropping said relay when voltage of the opposite polarity exists between said points.

9. In combination, a railway track divided into blocks by insulating joints, a signal at the entrance to each block, a track circuit for each block including a track battery and a Wheatstone bridge connected in series, said Wheatstone bridge having four elements connected end to end to form a closed link of which two oppositely located elements are more highly inductive than are the other two elements and which bridge is so included in the track circuit that the track circuit current divides in flowing through said bridge a portion of the current flowing through two elements in series and the rest of the current flowing through the other two elements in series said elements have ohmic resistances so that the bridge is balanced and no voltage exists between the two points each joining two elements in series when direct current flows therethrough but whereby voltage of one polarity exists between said points when the direct currentrsupplied by said battery is increased and voltage of the opposite polarity between said points exists when the direct current supplied by. said battery is decreasecl, a normally energized signal control relay for controlling said signal which signal control relay is caused to assume its deenergized position when said track circuit is interrupted, means for causing said signal relay to assume its deenergized position when voltage of one polarity between said points exists and for causing said relay to assume its energized position when voltage of the opposite polarity exists between said points.

10. In a track circuit of the normally closed type, a section of track insulated from the rest of the track by insulating joints, a track relay normally assuming an attracted condition and having two windings arranged on the same core and having one winding connected across the track rails at one end of said section, a source of direct current connected across the track rails at the other end of said section, and means controlling the fiow of current in the other winding of said track relay to cause said track relay to assume its retracted condition upon sudden increase in the flow of current from said source to said track circuit and to assume its attracted condition in response to a sudden decrease in the flow of current from said source to said track circuit.

11. In a track circuit of the normally closed type, a section of track insulated from the rest of the track by insulating joints, a track relay normally assuming an attracted condition and having two windings arranged on the same core and having one winding connected across the track rails at one end of said section, a source of direct current connected across the track rails at the other end of said section, a two-position relay controlling the flow of current in theother winding of said track relay to cause said track relay to assume its retracted'condition when said to cause it to be actuated to one position in response to a sudden increase in the flow of current from said source to said track circuit and to cause it to be actuated to its other positionin response to a sudden decrease in the flow of current from said source to said track circuit.

12. In a track circuit of the normally closed type, a section of track insulatedfrom the rest of the track by insulating joints, a track relay normally assuming an attracted condition and having two windings arranged on the same core and having one winding connected across the track rails at one end of said section, a source of direct current connected across the track rails at the other end of said section, and means con: trolling the flow of current in the other winding of said track relay including a neutral relay which is picked up in response to a sudden increase in the current supplied by said source to said track circuit and may be held up'through a holding circuit including a' back contact of said track relay and including means for breaking said holding circuit in response to a sudden decrease in the current supplied to said track circuit by said source,

WINFRED T. POWELL,

Images