Alternating current track circuit apparatus

Abstract

Alternating current track circuit apparatus is provided for obtaining optimum shunting sensitivity throughout a stretch of track divided by insulated joints into adjoining double rail track circuits and having impedance bonds at respective transmitting and receiving ends. An alternating current track feed is connected to the track rails at the transmitting end of each of the track circuits through a circuit tuned to resonance by a capacitor connected in series with a winding of the impedance bond at that end for energization of the associated track circuit from a source of alternating current. An alternating current receiver is provided for connection to the track rails at the receiving end of each of the track circuits through a circuit tuned to resonance by a capacitor in series with a winding of another of the impedance bonds and a track winding of a receiving relay for sensing the presence of a vehicle in the associated track section. The receiver comprises a local source of energy derived from the same source as the transmitting apparatus and connected to a local winding of the relay in series with a variable capacitor for adjusting of the phase difference between energization of the track and local windings for providing optimum sensitivity of the relay.

Description

BACKGROUND OF THE INVENTION

This invention relates to alternating current track circuits for railroads, and while the invention is subject to a wide range of applications, it will be particularly described as being of the double rail type for application to a stretch of railway track divided into track sections by insulated joints.

The present invention is particularly useful in the use of alternating current track circuits for electrified railroads having D.C. power propulsion. A system of this character is disclosed in the Estwick U.S. Pat. No. 1,822,572, issued Sept. 8, 1931, and assigned to the same assignee (by change of name) as the present invention. This patent is incorporated by reference in the present application. This patent discloses in FIG. 1 a conventional alternating current track circuit for frequencies of 25-60 HZ using a track and local phase detecting relay for sensing occupancy of the associated track section. The track feed energy and the energy for the local winding are obtained from the same source, and the track winding current lags the input voltage in accordance with inductive reactance of the track rails and of an adjustable reactance in series with the track rails at the feed end of the track circuit. It is the adjusted phase difference between the currents in the track and local windings that makes the track relay, which can be of a vane type, operable. Optimum operating conditions are obtained when there is a 90.degree. difference in the phase relationship of the track and local windings of the track relay.

It is pointed out in this patent that for long track circuits it is difficult to obtain the optimum phase difference in the track relay, and thus various remedies are proposed including shifting the phase of the local winding of the track relay. With the improvements according to this patent, there are still shunting sensitivity problems and phase shift problems involved for long track sections of electrified railroads, where impedance bonds must be used, and particularly where protection for broken down rail joints is provided by staggering the instantaneous polarities of adjoining track sections.

An object of the present invention is to provide an alternating current double rail track circuit which substantially obviates one or more of the limitations and disadvantages of the described prior arrangements.

Another object of the present invention is to provide an alternating current track circuit having improved shunting sensitivity for long track circuits.

SUMMARY OF THE INVENTION

Alternating current track circuit apparatus is provided for a stretch of railway track divided by insulated joints into adjoining double rail track circuits and having impedance bonds at respective transmitting and receiving ends of the track circuits permitting power propulsion direct current to bypass the joints. An alternating current track feed is connected across the track rails at the transmitting end of each of the track circuits through a circuit tuned to resonance by a variable capacitor connected in series with a winding of the impedance bond at that end of the track section for energization of the associated track circuit from a source of alternating current. An alternating current receiver is provided for the receiving end of each of the track circuits for connection across the track rails through a circuit tuned to resonance by a variable capacitor in series with a winding of another of the impedance bonds and a track winding of a receiving relay for sensing the presence of a vehicle in the associated track section. The receiver comprises a local source of energy derived from the same source as the track feed and connected to a local winding of the relay in series with a variable capacitor for adjustment of the phase difference between energization of the track and local windings for providing optimum sensitivity of the relay.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the accompanying description, taken in connection with the accompanying drawings, while its scope will be pointed out in the appending claims.

IN THE DRAWINGS

FIG. 1 illustrates schematically a typical alternating current double rail track circuit according to a preferred embodiment of the present invention;

FIG. 2 illustrates by vector diagrams typical prior art phase displacements of currents in a track winding as compared to applied voltage for different lengths of track circuits;

FIG. 3 illustrates by vector diagram typical phase displacements of current in a track winding as compared to applied voltage for different lengths of track circuits according to the preferred embodiment of the present invention as illustrated in FIG. 1; and

FIG. 4 illustrates the affect of variable capacitance in series with the local phase relay winding when the transmitting and receiving ends of the preferred embodiment of the present invention as illustrated in FIG. 1 are tuned to resonance.

With reference to FIG. 1, alternating current track circuit apparatus is provided for a stretch of railway track 10 divided by insulated joints 11 into adjoining double rail track circuits 12, 13 and 14 respectively. These track circuits have impedance bonds at respective transmitting and receiving ends permitting power propulsion direct current to bypass the joints.

An alternating current track feed 16 is provided at the transmitting end of each of the track circuits and is connected to the track rails through a circuit tuned to resonance by a variable capacitor C1 connected in series with a winding 18 of bond 15 for energization of the associated track circuit from a source of alternating current 19.

An alternating current receiver 20 is connected across the rails at the right-hand end of each of the track sections through a circuit tuned to resonance by a variable capacitor C2 in series with a winding 22 of another of the impedance bonds 15. Also included in series in the receiving circuit is a track winding 23 of a track relay TR. The receiver 20 also comprises a local source of energy 24 derived from the source 19 and connected to a local winding 25 of the relay TR in series with a variable capacitor C3. The variable capacitor C3 is for adjustment of the phase difference between energization of the track and local windings of the track relay TR for providing optimum sensitivity of this relay. A center tap of the primary winding 17 of each of the bonds 15 is connected to a corresponding center tap of the next adjoining bond 15 so that the D.C. propulsion return bypasses the insulated joints 11.

It is a well known practice in alternating current track circuits to guard against a possible failure due to breaking down of the insulated joints by staggering the instantaneous polarities of the track circuits as is illustrated in FIG. 1. Two position A.C. vane relays such as is disclosed in the Maenpaa, U.S. Pat. No. 2,559,448 are generally used for track relays TR which are operable only when the phase difference between the track winding and local winding of the relay is within a predetermined range. If the track circuit is so long that the rail impedance plus the impedance of the bonds shifts the phase difference beyond this range, it is necessary to reverse the polarity of the local winding in order to make the relay responsive; but to do this, would make the relay also responsive to the adjoining track circuit in case the rail joints are broken down. Thus, where the normal A.C. track circuit is used for a long track circuit wherein only the bond at the relay end is tuned to resonance, broken down joint protection cannot be provided.

FIG. 2 illustrates the phase shift of the track phase of a track relay TR relative to the supply voltage for different lengths of track circuits, assuming that only the relay end of the track circuit is tuned to resonance. It will be readily understood from this diagram that there is considerable difficulty in providing proper control for A.C. track circuits of varying length, particularly where long and short track sections are adjoining, and still provide broken down joint protection.

In the system according to the present invention, however, it is possible to obtain much improved results as is illustrated in FIG. 3 by tuning both the transmitting and receiving ends of each track section to resonance to effectively cancel the inductance of the impedance bonds, and to obtain optimum phase difference between the local winding and the track winding of each track relay by adjustment of capacitor C3 in series with the local winding. This reduces the phase shift spread for different length track circuits from 119.degree. according to a test of the prior art system as illustrated in FIG. 2, to only 44.degree. according to a test of the preferred embodiment of the present invention as illustrated in FIG. 3.

To obtain the optimum operating characteristics for the track circuit according to the preferred embodiment of the present invention, the capacitor C3 in series with the local winding 25 of relay TR is adjusted, after first tuning both ends of the track circuit to resonance. This adjustment is to a value providing close to 90.degree. phase displacement between the track and local windings of the relay and to obtain a shunting resistance within the track circuit requirement calling for the track relay to be responsive to at least a 0.3 ohm resistance rail shunt.

In FIG. 4, for a typical set of values in a 6,000 foot track circuit, shunt resistance and local-track phase difference curves 26 and 27 are obtained respespectively. The optimum adjustment of the capacitor C3 is to a value corresponding to the point 26a of curve 26 corresponding to a 0.31 ohm shunting resistance. This adjustment obtains a phase difference between the track and local windings 23 and 25 corresponding to point 27a on curve 27. The curves 26 and 27 are for a 6,000 foot 75HZ track circuit having a ballast resistance of 5 ohms per thousand feet, and having the feed and relay ends of the track circuit tuned to resonance wherein capacitor C1 is adjusted to 2.24 mfd and capacitor C2 is adjusted to 2.3 mfd. Shunting resistance at point 26a of curve 26 is 0.31 ohms, the variable capacitor C3 is adjusted to 2.3 mfd, and the phase difference between the local and track phases as represented by the point 27a is 90.degree..

The track circuit thus provided according to the preferred embodiment of FIG. 1 can be adjusted for obtaining high track voltage and good shunting sensitivity, and the local phase of the relay TR can be adjusted independently for the required operating characteristics, such adjustments all resulting in being able to provide full broken down joint protection for different lengths of adjoining track circuits. It is to be understood that the frequency of 75HZ has been chosen only for example and that frequencies from 25HZ to 100HZ could be used.

While there is disclosed what at present is considered to be the preferred embodiment of the present invention, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention and it is therefore aimed in the appending claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

What is claimed is:

1. Alternating current track circuit apparatus for a stretch of railway track divided by insulated joints into adjoining double rail track circuits and having impedance bonds at respective transmitting and receiving ends permitting power propulsion direct current to bypass the joints, wherein the improvement comprises:

a. an alternating current track feed for connection across the track rails at the transmitting end of each of the track circuits through a circuit tuned to resonance by a capacitor connected in series with a winding of the impedance bond at that end for energization of the associated track circuit from a source of alternating current, and

b. an alternating current receiver for connection across the track rails at the receiving end of each of the track circuits through a circuit tuned to resonance by a capacitor in series with a winding of another of the impedance bonds and a track winding of a receiving relay for sensing the presence of a vehicle in the associated track section,

c. the receiver comprising a local source of energy derived from said source and connected to a local winding of the relay in series with a variable capacitor for adjustment of the phase difference between energization of the track and local windings for providing optimum sensitivity of the relay,

d. whereby improved shunting sensitivity and broken joint protection is obtained over a wide range of lengths of alternating current track circuits.

2. Alternating current track circuit apparatus according to claim 1 wherein the impedance bond for the track feed end of each of the track circuits has a primary winding connected across the track rails and has a center tap connected to a return conductor for propulsion current, the primary winding being inductively coupled to the bond winding in series in the track feed.

3. Alternating current track circuit apparatus according to claim 2 wherein the impedance bond for the receiver end of each of the track circuits has a primary winding connected across the track rails and has a center tap connected to a return conductor for propulsion current, the primary winding being inductively coupled to the bond winding in series with the track winding of a receiving relay.

4. Alternating current track circuit apparatus according to claim 3 wherein the track feed and the local winding of each track circuit are energized through respective transformers from a common source of energy.