US2123965A - Track circuit - Google Patents

Description

Jul 19, 1938. F, X; REES 2,123,965

TRACK CIRCUIT Filed Aug. 2]., 1935 FIG. 1.

ATTORNEY Patented July 19, 1938 oFFice TRACK CIRCUIT Frank X. Rees, Albany, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application August 21, 1936, Serial No. 97,204

3 Claims.

This invention relates to improvements in the well-known track circuits for railroads, and more particularly to'alternating current track circuits. .The primary object .of the presentinvention is to improve the shunting operation of the usual track re lay .of alternating current track circuits under varying conditions of rail surface and ballast resistance.

This invention is in the nature of a variation or modification for carrying out the principles and mode of operation characteristic. of the track circuit organization disclosed and claimed in my prior application Ser. No. 24,074, filed May 29, 1935, and no claim is made herein to the invention disclosed in said prior application.

The reliable operation .of the usual track circult depends upon establishing a conducting path of low resistance through the axles and wheels of a car or train; and the weight of the equipment and condition of the rail surface are important factors affecting theresistance of a wheel shunt. For example, where the track rails of ,sidings, crossovers, and the like areinfrequently used, a coating of rust, usually an .iron oxide, accumulates on the rail surface, and makes any wheel shunt of high resistance for the relatively small inter-rail voltages commonly employed; and even where train movement. is 30, frequent and the rail surface appears clean, a coating or film in the form of .an oxide of silicon, or some other stable. compound, is present on the rail surface, and offers a relatively high effective resistance for low voltages. It is found that :5 these various coatings or films on the rail surface, apparently because they are in the nature of .a stable chemical compound or composition, will break down and become a low resistance conducting path upon the. application of suffii0= cient voltage, which may be termed an ionization voltage.

Generally speaking, and Without attempting to define the exact nature and scope of the invention, it is proposed to provide a transformer of special construction, conveniently termed a peaker voltage transformer for supplying current to the ordinary alternating current track circuit, so that relatively high peak voltages of short duration are obtained,'as compared with the usual sine wave shape of voltage required for the average orefiective relay energizing current, thereby serving to break down or ionize the film or coating on the rail surface and render more effective the shunting action of the wheels and 55. axles of a train or trains.

Various characteristic features, attributes, and advantages of the invention will be in part apparent, and in part pointed out, as the description progresses.

The accompanying drawing illustrates in a simplified and diagrammatic 'manner certain specific embodiments of the invention, the parts and circuits being shown more with the view of facilitating an explanation and understanding of the invention, than for the purpose of showing in detail the structural organizations to be employed in practice.

In the drawing, Fig. 1 shows one track circuit section equipped with an alternating current track circuit in accordance with this invention; Fig. 2 is a fragmentary View illustrating a modified arrangement including a single element relay with the usual impedance bond; and Fig. 3 is an explanatory diagram of a theoretical relation of the primary and secondary fluxes and secondary voltage of a peaker voltage transformer characteristic of the invention.

Referring to Fig. 1, it is assumed that the track rails l of the track section shown will be bonded together in the usual way, with insulated. joints 2 in both track rails to define the ends of the track section. At one end of the track section, preferably the entering end, an .alternating current track relay T of the .usual type and construction is connected across the track rails I. As illustrated, this track relay T is of the usual two-element or polyphase type, having a track phase winding 3 connected across the track rails and a local winding 4 connected to the usual transformer 5 energized from an alternating current line 6, which in turn is energized from a generator G, or equivalent source, usually of a commercial frequency, such as 60 cycles. The track relay '1 may be a single element relay of the vane or rotor type, or in fact a relay of any one of the various types well known in the art and used for alternating current track circuits as for instance shown in Fig. 2.

In accordance with this invention, alternating current is supplied .to the other end of the track section from a peaker voltage transformer PT of special construction. This transformer PT is shown diagrammatically, and comprises a primary 1 connected to the A. C. line circuit 6, and a secondary winding .8 connected across the track rails I in series with the usual limiting resistance or reactance 9. In the type of peaker voltage transformer PT contemplated, the core for the secondary 8 has a small magnetic section as compared with the core for the primary 1, and is also provided with a magnetic shunting core l0 of appropriate section with a reluctance gap.

The purpose of this peaker voltage transformer PT is to provide high peaked secondary voltage waves of short duration. Referring to Fig. 3, if the primary flux is represented by the sign curve A, the parts are so proportioned that the secondary flux corresponds approximately with that indicated by the dot-and-dash curve B, and the secondary voltages are those illustrated by the curve C. These curves of Fig. 3 are merely illustrative of the principles and operation, and are not intended to show quantitative values or relations. These characteristics are obtained by proportioning the cross section of the core for the secondary winding 8 so that it becomes substantially saturated with a low flux density, the primary flux also passing in part through the shunting cores I0 and reluctance air-gap.

With such a peaker voltage transformer PT producing secondary voltages as indicated by the curve C in Fig. 3, it is apparent that the maximum or peak Voltage which may be applied across the track rails to produce an average or efi'ective relay energizing current, is much greater than with the ordinary sine wave of voltage commonly employed with alternating current track circuits. According to the principles of this invention, it is contemplated that these maximum or peak voltages will serve to break down or ionize the rail film and render the wheel shunt effective to conduct current at a lower inter-rail potential. These peak voltages for breaking down rail film are repeatedly applied so as to be effective as the wheels move to different spots on the track rails.

The track circuit organization of this inven tion may be advantageously employed with double rail track circuits for electric propulsion roads, where impedance bonds are used, as illustrated in Fig. 2. With such an arrangement, the impedance of the bond is materially increased by the use of the time-spaced peaked voltages obtained from the peaker voltage transformer PT, as compared with the impedance of an equivalent core section and number of turns excited with alternating current of the sine wave form. Consequently, the desired impedance across the bond to provide proper excitation of the track relay T may be obtained by use of this invention by fewer turns, thereby reducing the cost of the bond and lowering its resistance to the propulsion current.

One important characteristic of this invention is that it assures reliable shunting of the ordinary track circuit under unfavorable conditions of rail surface, weight of equipment, and ballast conditions. This desirable characteristic is due to the application of high peaked voltages to break down the film or coating on the track rails, thereby assuring a shunting effect of the wheels and axles of a car or train under conditions where a lower voltage would be insufiicient.

The resistance of the wheel contact is found to vary greatly with the conditions of the rail surface and the weight of the equipment; and it appears that in many cases voltages much higher than the relatively small voltages, of about 2 volts normally employed for track circuits are necessary to break down the resistance of the wheel contact to a point where ionization and actual shunting of the track relay takes place. The peak voltages provided by this invention, which are many times those commonly used in track circuits, apparently break down the resistance at the wheel contact by an ionization effect, and enable effective shunting with dirty or rusty track rails and light-weight equipment in a manner not obtainable with the ordinary track circuit arrangement.

In this connection, it will be noted that the peak voltages are periodically applied at frequent intervals and are available to break down the resistance of the wheel contact, as the car or train moves along the track and its wheels contact with successive points on the rails, and with the resistance once broken down it will remain of low value until the train has left and an opportunity for soiling and oxidization of the rail surface has been presented.

The particular embodiments of the invention shown and described are merely illustrative; and various adaptations, modifications, and additions may be employed, without departing from the principles and mode of operation of the invention.

What I claim is:-

1. In an alternating current track circuit for railroads, the combination with a section of railway track, a polyphase alternating current relay having two windings one connected across the track rails at one end of said section and the' other connected to a source of substantially sinewave alternating current, a peaker voltage transformer for changing a substantially sinewave alternating current voltage to a very peaked alternating current voltage comprising a core structure for very loosely inductively coupling a primary winding and a secondary winding wound thereon, said core structure also including a leakage magnetic path for passing magnetic flux linking only said primary Winding, and means for connecting said primary winding to said source and connecting said secondary winding across the track rails at the other end of said section, whereby the winding of said relay connected across the track rails is energized by a voltage which has a high ratio of'maximum to average value so that the voltage peaks of the alternating current voltage may act to break down the film resistance existing between wheels and rails to cause more effective wheel shunting without supplying suflicient effective current to maintain said relay energized during the presence of a train.

2. In a track circuit for railway signalling systems, the combination with a section of railway track isolated from adjacent track sections by insulating joints, an alternating current track relay connected across the track rails at one end of said section and of a construction to assume an energized condition when an alternating current of a certain effective value derived from a source of substantially sinewave form and of a certain voltage is connected across the rails at the opposite end of said section but assumes a deenergized condition upon entrance of a train into said section, and a peaker voltage transformer for transforming sinewave form alternating voltage into a peaked alternating voltage connected between a source of alternating current of substantially sinewave form and said opposite end of said section to supply alternating voltage of peaked wave form to said opposite end having a maximum value which is much greater than the maximum voltage of said certain alternating voltage but supplies a current of only said certain effective value to said relay, whereby a high ratio of maximum to effective track circuit voltage is established in the track circuit so that the high voltage peaks of the alternating voltage may act to break down the film resistance existing between wheels and rails to cause more effective wheel shunting without supplying sufficient efiective current to maintain said relay energized during the presence of a train.

3. A track circuit for railway tracks in which due to atmospheric conditions a high resistance film forms on the track rails, the combination with a section of railway track isolated from adjacent track sections by insulating joints, a twoelement alternating current track relay having its track circuit element connected across the track rails at one end of said section and having its local element connected to a source of substantially sinewave form alternating current, a series impedance, and a peaker transformer energized from said source and supplying peaked wave form alternating voltage to the other end of said section through said series impedance to supply peaked alternating current to the track element of said relay, said peaker transformer transforming said alternating voltage of substantially sinewave form into a peaked Wave form voltage which has a very high maximum voltage for each unit of efiective voltage as compared with the maximum voltage of sinewave form of unity effective value, whereby a high ratio of maximum to effective track circuit voltage is established in the track circuit so that the high voltage peaks of the alternating voltage may act to ionize the film and break down the resistance existing between wheels and rails to cause more efiective wheel shunting without supplying suflicient effective current in the track element of said relay to maintain said relay energized during the presence of a train.

FRANK X. REES.

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