General Information on Track Circuits - RGS Online

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<strong>General</strong> <strong>Information</strong> on Track Circuits
Figure D11
AA
13.10 IRJs at Electrified/Non–electrified Boundary
Railway Group Approved Code of Practice
GK/RC0752
Issue Two
Date December 1998
Page D15 of 20
13.10.1 Running Lines
At the boundary between electrified and non–electrified lines, initial isolation IRJs
must be provided in both running rails at a sufficient distance beyond the end of
the catenary/conductor rail to prevent an overrunning train from injecting traction
current into the rails on the non–electrified side of the joints. The collector
shoes on d.c. multiple units are interconnected within each multiple unit set.
Therefore, it is the length of the longest multiple unit which will dictate the
position of the initial isolation IRJs in d.c. traction areas.
All track circuits within 800m of the initial isolation IRJs on the non–electrified side
must be immune to the traction system and provided with double rail IRJs.
Where there are no track circuits on the non–electrified side of the initial isolation
IRJs, a second set of isolation IRJs must be provided in each rail 800m beyond
the initial isolation IRJs.
If any siding occurs within the above 800m areas, a second set of isolation IRJs
must be provided in each rail of the siding immediately clear of the running line.
13.10.2 Sidings Off Electrified Lines
In electrified traction areas, two sets of IRJs are to be provided in both rails at
least 27m apart. These are to be provided beyond the last track circuit in private
sidings leading to stores or depots containing flammable or explosive
substances, and in other sidings where isolation from electric traction is required.
In d.c. electrified areas, the traction return bonding must be extended by the
Electric Traction Engineer onto track circuited non–electrified lines and sidings
for at least 120m beyond the conductor rail or the tips of the points. Track
circuits beyond this distance must be fully isolated with double rail IRJ’s or the
traction return bonding must be continued for at least another 335m. This
ensures that an electric traction unit inadvertently entering a non–electrified area
will not lose its negative return whilst any shoe is still in contact with a conductor
rail.
On lines where Eurostar operations are authorised, the above distances will
need to be extended accordingly.
If the line concerned connects with a d.c. electrified line at more than one point,
it must have continuous traction bonding throughout in order to prevent traction
return current passing through the couplings of a train which is bridging two
traction portions of a siding.
13.11 A.C. and D.C. Electric Traction Areas Abutting
Where there is a requirement for inter–running with trains operating on differing
electrification systems, IRJ separation between the differing traction systems
cannot generally be achieved. In these areas, a suitable “buffer” zone of dual
immunisation must be provided.
As a general guide, for track circuit applications, immunisation against 50Hz
electrification should be maintained for a distance of 3km beyond the extremity
RAILTRACK D15