The present invention relates to an electrical device for providing the necessary high electrical impedance between the return current rail and the overhead electrical mast and is capable of eliminating the signal leakage path of the electrically sensitive equipment like audio frequency track circuits, which are deployed along the railway tracks.
The current system, being adopted in the railways, that of connecting the return rail current path and the overhead electrical mast is offering very low impedance that can potentially cause electrical interferences to the equipment on the track side.
To overcome the limitation of the current system in vogue, the new device with novel characteristics is designed as per the present invention described in detail below.
Accordingly, the present invention consists of A high impedance safety bond capable of improving the performance of audio frequency track circuit comprising of a metallic strip with a predetermined shape, selected from a plurality of coils of varying sizes and connected between the return current carrying rail and the overhead electric mast.
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 arrangement
FIG 2 " Audio Frequency Track Circuit - General arrangements in electrified section
FIG 3 - Audio Frequency Track Circuit - General arrangement in electrified section
(safety bond, electrical equivalent)
FIG 4 - Audio Frequency Track Circuit - General arrangement in electrified section
(with present invention)
FIG 5 - Safety Bond


As shown in Figl, Railway traction uses a traction voltage, 25KV AC (kilo volts alternating current) single-phase 50 HZ mainly to cater to the needs of electric locomotives. The railway 25 KV over head system is a single-phase distribution network with the neutral at the feeder station (1) and rail return (2) solidly earthed. 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 (3) are connected to the return rail (safety bond) (6). The return rail (2) 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 2, a 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. The shape of these bonds could be from a wide variety of geometrical shapes such as helical, parabolic or spherical.
Electric traction equipment, by virtue of high power consumption potentially can interfere with signaling equipment (harmonic interference). The most susceptible signaling equipment (8) on the issue of interference is the track circuit, as the rails (9) & (10) are the common conductors to both traction systems and the track 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 (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 (19). It is sufficient to use one rail per track for these purposes. Unfortunately this produces possible "un balance" of track circuit which maximizes the interference on the audio frequency track circuit (20). It can potentially effect length reduction of the audio frequency track circuit.
For example the simplest form of safety bonding (19) for line side structures (required on high voltage systems) requires their connection to one rail (17). This unbalance operation of audio frequency track circuits (20) imposes uneconomic length restrictions.
As shown in the Fig 4 the proposed device (21) is to be restoring the "balance" to a large extent.
As shown in Fig 5, the safety bond consists of metallic strip with predefined length, width and shape and based on the contextual requirements the number of loops in the coil shall vary.
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 high impedance safety bond capabie of improving the performance of audio frequency track circuit comprising of a metallic strip with a predetermined shape, selected from a plurality of coils of varying sizes and connected between the return current carrying rail and the overhead electric mast.
2) The device as claimed in claim 1 the said metallic strip is a mild steel strip with anti corrosion protection.
3) The device as claimed in claim (1) wherein the shape is, selected from a wide variety of geometric shapes such as helical, parabolic and spherical.
4) The device as claimed in claim 1 and deployed as an electric conductor
between the overhead electric masts is capable of providing the required
high Impedance value.
5) The device as claimed in claim 1 is capable of attenuating the possible
leakage current paths operating at frequencies equal to or above 3 Kilo
Hertz.
6) The device as claimed in claim (1) is capable of restoring the "balance" in currents between the Overhead electrical mast and the return current carrying rail
7) The device as claimed in claim (1), is capable of achieving higher and effective track circuit length by providing "electrical interference free" operations.


8) The device as claimed in claim (1) is adaptable effectively to both AC and DC types of traction areas.
9) 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 5 of the accompanying drawings.