NR NR/L3/SIG/11767/B030 ISSUE 3 PDF

GENERAL

The EBI Track 400 Single Rail track circuit is of the jointed type and is designed for AC or DC electrified areas where high levels of interference may be present.

Two types of track interface can be used:

• End Termination Units (ETU). EBI Track 400 frequencies are used in four pairs – A/B, C/D, E/F, G/H. One pair is used per track and the frequencies are alternated, e.g. 'frequency A' track circuit, then 'frequency B' track circuit, then 'frequency A' track circuit, and so on. Further details of frequency allocation are given in section 4.2.4.

• Surge Protected ETU (SPETU). The SPETU is functionally identical to the ETU except that it contains a surge protection device to ensure that high voltage transients do not damage the internal circuitry of the unit. SPETUs are normally used on DC 3rd rail traction installations where the risk of traction voltages appearing on the running rails is relatively high.

‘Single Rail’ jointed track circuits are commonly found in three areas:

• Areas using single rail traction return, e.g. 25kV traction systems and where the traction currents are generally low enough such that a single rail return system does not degrade traction efficiency.

Note: When used in areas of 25KV AC traction only frequencies A,B,C &D are permitted.

• Points and crossings where it is difficult to achieve full double rail traction return because of the physical arrangement of the rails or there is insufficient space to accommodate 20m tuned areas.

• In areas where the track layout is complicated and adjacent tracks are in close proximity, and it is not physically possible to position TUs or ETUs at the trackside because of the limited space available.

In jointed single rail mode, the tuned area is replaced by an insulated block joint in one running rail and uses ETUs or SPETUs in place of Tuning Units.

The track circuit functions like the conventional AC track Circuit. Since the traction bonding is done through transverse bonding, the traction return current flows through only one rail and removes the need for Impedance Bonds. The effect of using single rail traction return must be considered carefully.