TECHNICAL FIELD OF THE INVENTION

This invention relates to the control of stray currents associated with railways. BACKGROUND ART

In an electrified railway at least one of the rails of a track is employed for traction return currents. In direct current traction systems these rails are deliberately insulated from the support structure in an attempt to eliminate or at least reduce traction current flow in the earth. In a practical system there is however always some current leakage from the rail into the earth and this is defined as stray current.

In a direct current electrified railway traction system the substation, electric locomotive and the electrical traction system forms a complete system. In this system the substation connection to the rail exhibits the most negative potential to which traction current including stray current will return. It thus follows that an electric field (potential gradient) exists along the return conductors in the traction system.

These earth or stray currents will follow a path of least resistance in the earth and therefore will find their way into buried metallic structures such as pipe lines. These currents contribute to electrolytic corrosion of utility infrastructure which shortens the lifespan and increases maintenance and replacement costs.

In addition to this stray currents can enter electric cable armouring causing heating and eventual failure. The presence of stray currents can also affect older railway signalling installations with undetected earth faults and cause right-side and/or wrong-side failures with probable catastrophic consequences.

Many attempts have been suggested for the control of stray currents emanating from the return currents in the rails of a railway.

In EP1914346 rails fixed to sleepers by metal bolt-spring assemblies are provided with a shielding element made from a non-conductive material between the spring and the rail A differential transformer is provided by Russian Patent 20041049232. The transformer has three circuits, the first having a filtering capacitor, the second has an electronic two-sided switch and first reactor; and the third has a similar switch with second reactor. Both positive and negative potentials can be taken from the rails

In US Patent 6588677 an insulating rail boot encases a rail embedded in concrete, asphalt or paver construction. The rail and the rail boot are secured in place by retaining clips. The rail boot has two exposed top surfaces which are sloped away from the rail. An outside edge of each top rail boot surface is positioned flush with a surface of the road material. This cooperation between the top surfaces of the rail boot and the road surface facilitates flow of water and debris away from the rail, and thus uphold a low rail to earth conductivity.

These solutions to the problem require additional equipment or material and it is an object of the present invention to provide a simple arrangement based on an existing railway arrangement.

Such an existing arrangement has been described in South African Patent Numbers 97/11696 and 2003/8452.

In the earlier patent , the concept of which has been used extensively and is known as TUBULAR TRACK trenches are dug longitudinally to correspond with the rails that are to be laid. Elongated plastic tubes are laid in the trenches and are filled under pressure with concrete to fill the trenches and contact the bottoms of the rails. Transverse sleepers and ballast are, therefore, unnecessary and there is continuous contact of the rails with the tubular structure, the latter setting around the bottoms of the rails. In the later patent the tubular track is preformed into short lengths for transport to the site.

DISCLOSURE OF THE INVENTION

According to the invention the longitudinal track support includes one or more electrically connected conductors embedded into the support and are adapted to convey the return current to a chosen location of lower potential in the electrical traction system. This will set up an electric field between the conductors and the rail, constituting the conditions for stray current collection.

In a preferred form of the invention the conductors are lengths of reinforcing steel or the like. In the case of the short lengths of the track support, conductive wires are attached between reinforcing in adjacent lengths, for example by welding, crimping or soldering. The electrical access provided to the embedded conductors make it compatible with existing traction return systems and in addition allows integration of conventional traction conductors, to form an integrated traction return and stray current reduction system.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is described below by way of example only and with reference to the following drawings, in which;

Figure 1 is a representation of a railway track including the track support structure;

Figure 2 is a cross section of the railway track support structure;

Figure 3 is a photographic depiction of a track support module;

Figure 4 is a schematic representation of the stray current collection elements;

Figure 5 is a further schematic representation of the stray current collection elements;

Figure 6 is a representation of the railway track and support.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention is described below with reference to the accompanying figures in which like features are indicated by like numbers. The track support structure 10 consists of longitudinal tubular concrete modules 12 with embedded reinforcement 14 (rebar), as shown in Figure 1. The rebar components are physically and electrically connected by binding wire 16. Standard railway tracks 18 are supported on the support structure 10 and retained in place with proprietary clips 20. Railway gauge bars 22 connect the parallel railway tracks 18 and support structures 10

In addition steel wire connections 24 are attached at the ends of each track support module 12 as shown in the photograph of Figure 3. This allows electrical connection between modules 12 and allows electrical separation of the modules where continuity is not required.

The inter-module connections 24 are accessible to facilitate electrical connection to external conductors in the traction return system 25 or to stray current return conductors in the cable cavities 26.

The connection configuration of the embedded stray current collection elements are shown schematically in Figure 4 and Figure 5. Figure 4 shows the connection configuration with an external traction return conductor 25 such as the earth return, while Figure 5 show the connection configuration with an internal stray current return conductor within the cable cavity 26. In the invention the track is configured into sections of N modules connected together. Referring to figure 6, the Nth Module 30 is not connected to the N + 1 module 32, as is evidenced by the lack of a steel wire connection 24. Furthermore the rebar pigtail 14 of the Nth module is connected to the railway track 18.