13

The present invention relates to an electrical device to eliminate false energization of audio frequency track circuits. This device is capable of, providing the passage, for necessary track circuit signal current and achieves necessary balance between the two rails under a specific condition of train occupying the track In the track circuit area and one of the rails is in broken condition.
The current system being adopted in the railways that of connecting the two rails with flat mild steel strip and the return current rails of the adjacent tracks, which can create a potential difference between the two rails, thereby causing electrical interference to the equipment residing on the track side.
To overcome the above described limitation, in the current practice followed by railways, we have come out with a device and a method of connecting as explained in the subsequent paragraphs.
Accordingly, a device consisting of a metallic steel strip with predefined shape and size placed between the two rails of a track, along with a metallic strip, connectable between the centre, of the device to the return rail of the adjacent track and is capable of providing the desired electrical impedance.
The tuning bond is then connected from its centre point to the adjacent track return current carrying rail.
Now the invention will be described in more detail with reference to the accompanying drawings, bringing out a number of embodiments of the arrangement according to the invention
FIG 1 - General Track and Overhead electrical mast arrangement
FIG 2 - Audio Frequency track circuit - general arrangement in electrified track
sections
FIG 3 - Audio Frequency track circuit - general arrangement in electrified track
sections (Multi tracks)


FIG 4 - Audio Frequency track circuit - general arrangement in electrified tracl<
sections (Broken rail at the Tx end)
FIG 5 - Audio Frequency track circuit - general arrangement in electrified track
sections (Broken rail and broken rail and Audio frequency signal path with new type
of arrangement)
FIG 6 - Cross bond connection to the centre tap of special shaped bonds
FIG 7 - Audio Frequency track circuit - general arrangement in electrified track
sections (Broken rail at Rx end and receiver signal path)
As shown in Fig 1 Railway traction uses a traction voltage, 25KV AC (kilo volts alternating current) single phase 50 HZ mainly to cater to the needs of electric propulsions. The railway 25 KV over head system is a single-phase distribution network with the neutral at the feeder station (1) and rail return solidly earthed (2). Overhead electrification (OHE) masts (3) are installed at interval of 70-80m, all along the track. Locos collect propulsion current from the overhead catenary system (4) using pantographs and return the current back to the sub station (1) via running rails (2) & (5). Currently in railway OHE system, the masts are connected to the return rail (safety bond) (6). The return rail in turn is solidly earthed at traction sub station (1) (located at interval of 40-50 Kms) and also intervals of 10 Kms (7). As shown in Fig 3 the adjoining return rails In a multi track system are connected together (cross bonding) (16) with mild steel strip at regular intervals forming a grid.
As shown in Fig 2 device known as track circuit (8) is used to detect the absence of vehicle on a section of track and is the basis for all forms of signaling in railways. This device normally uses both the running rails (9) & (10) as transmission medium. In electrified territories to avoid interference from the 50 HZ traction return current, a concept of joint less track-circuiting, audio frequency is used. The Audio frequency track circuit equipments (8) typically consist of transmitter and receiver modules. The transmitter transmits signal at one end of rails (11) & (12) and receives the signal at other end of track (13) & (14) in the specified area. Custom made bonds (15) which are galvanized steel connected across the rails to either terminate or isolate adjacent track circuits.


Electric traction equipment, by virtue of high power consumption potentially can interfere with signaling equipment (8) (harmonic interference). The most susceptible signaling equipment on the issue of interference is the track circuit, as the rails are the common conductors to both traction systems and the tracl< circuit. When audio frequency track circuit signals are transmitted over the electrified railway tracks, they are subject to special interferences. A non-electrified railway permits complete electrical isolation of track circuit. The electrified railway infrastructure bonds (6) & (16) the rails into a conducting mesh, which makes it impossible to fully isolate the rail section.
As shown in Fig 3 Electrified railways use the running rails (17) & (18) for traction return current and implementation of safety bonding (16). It is sufficient to use just one rail (18) per track for these purposes. Unfortunately this produces an "un balanced" track circuit which maximizes the interference to the signaling equipment (19) (track circuit). It also reduces the effective length of the track circuit. For example the simplest form of safety bonding (16) for line side structures (required on high voltage systems) requires their connection to one rail (18). This "unbalances" the operation of audio frequency track circuits (19) and imposes uneconomic length restrictions.
Typical deployment scenario (multi track system) is depicted In Fig 3, The audio frequency track circuit (19) operating over the grid of traction return conductors (in a multi track system) transmit the operating signal along the "signal" rail (17) and return it along the network of traction return rails (18). The vehicle shunt is only applied between the "signal" rail (17) and the other running rail (18) of the track circuit. A proportion of the operating current passes along other traction return rails and is not shunted. This can cause false energization of the track circuit.
As shown in Fig 4 the "worst case" situation occurs when there is a broken rail (20) in the traction return rail (21) near one end of the track circuit and the vehicle (23) is standing on the interior of the track circuit close to it. In the broken rail (20), the audio frequency current from transmitter (24) takes the path ABCDFGH (since path CH is broken). At audio frequency the path CD has considerable rail impedance and


hence voltages drop across CD. This voltage can drive a current through the receiver via path BED, Which may falsely energize the receiver (24) with train on the track circuit. This is a wrong side failure and can be dangerous.
As shown in Fig 5, the proposal is to reduce the potential across the receiver to zero (theoretically) under such broken rail (26) condition. The scheme is to connect point 'D' to mid point of high impedance choke (27). In this case the current I flowing in the portion of rail AB will divide into two equal parts, 1/2 in BE and 1/2 in CK. This is because the impedance of rail BE will be the same as that of CK. These two equal currents will be forced to flow into the choke (27) in opposite directions in the path KD and ED. Hence the voltage across EK that is across the receiver will be zero and as a result no current will flow through the receiver (28).
As shown in Fig 6 (29) (30) & (31) instead of separate choke we propose to use the center tap in the tuning strip (25) (which acts like a high impedance choke).
As shown in Fig 7, a similar argument will apply to a situation, where rail breakage (32) is nearer the receiver end and the wheel (33) is standing on the interior side of the track circuit side. In this case, using the center tap of the tuning strip (34) of transmitter will mitigate the current unbalance problems and prevent a possible false energization of receiver (35) with train on being present on the track circuit.
Although the invention has been described in considerable detail with particular reference to certain preferred embodiments, thereof, variations and modifications can be effected within the spirit and scope of the invention as described herein above and as defined in the appended claims.

We claim:
1) A device consisting of a metallic steel strip with predefined shape and size placed
between the two rails of a track, along with a metallic strip connectable between
the center of the device to the return rail of the adjacent track and is capable of
providing the desired electrical impedance.
2) The device as claimed in claim 1 the said metallic strip, is galvanized steel, anti
corrosion coated strip.
3) The device as claimed in claim 1 wherein the said metallic strip, is capable of
eliminating the possibility of false energization and consequent misinterpretation
of the context by the audio frequency track circuits, leading to a system failure.
4) The device as claimed in claim 1 is capable of giving necessary impedance to the
track circuit equipment and to enable balancing of the current on the two rails of
a track*
5) The device as claimed In claim 1 wherein the means for initiating a passage of
flow of continuous traction current return path under a return rail broken
condition.
6) The device as claimed in claim 1 is adaptable effectively for both the AC and DC
traction areas.
7) The device as claimed in claim 1 is adaptable for any electrical equipment on
track side and operating with frequencies equal to or above 3 Kilo Hertz.
8) The device according to any one of the claims 1 to 7 substantially as herein
described with reference to and as shown in FIG 1 to 7 of the accompanying
drawings.