VRIOGS 010.7 RevA - Public Transport Victoria

VRIOGS 010.7 Revision A 216.6.2 50Hz AC Track CircuitsIt has been established that this type of track circuit is sensitive to interference bystray mains frequency currents, resulting in potentially unsafe situations. Specialmaintenance precautions are required to ensure safe operation of existinginstallations, and no new tracks of this type shall be installed except in the case ofminor changes in the midst of an existing installation.6.6.3 Double Rail1. In a double rail AC track circuit impedance bonds permit the DC tractionreturn current to flow in both rails whilst preventing the actual track circuitfeed from flowing from rail to rail. Impedance bonds rely for their properoperation on traction currents remaining balanced between the rails of thetrack circuit. It is the responsibility of the Signal Engineer to ensure that thetraction return path is properly balanced.2. The impedance of these bonds on double rail AC track circuits becomes alimiting factor in setting the length of the track circuit and the maximumshunt value at which the relay will drop.3. Older style bonds have an impedance of 0.3 to 0.4 ohms at 50 Hz that limitsthe maximum shunt characteristic to 0.15 - 0.2 ohms.4. A resonated bond may have an impedance approaching 2.5 ohms at 50 Hz.6.6.4 Single Rail1. The design of single rail 50 Hz track circuits shall include arrangements tolimit the maximum level of DC traction current which may be applied to thetrack relay.2. The design of single rail 50 Hz track circuits shall include arrangements tolimit the maximum level of DC traction current which may be applied to thetrack relay.3. Track circuit length shall be limited such that the longitudinal DC voltagedrop under maximum traction conditions does not exceed 20 V. Typicalmaximum single rail AC track circuit lengths are 200 m. However this lengthmay need to be reduced in certain cases. Typical values for DC voltagedrop are set out in Table 6.Traction Current (A)1700 3400 5200 6800Track Circuit Length (m) Voltage Drop (volts) (For 60kg rail)50 2.81 5.61 8.58 11.2275 4.21 8.42 12.87 16.83150 8.42 16.83 25.74 33.66200 11.22 22.44 34.32 44.88250 14.03 23.05 42.90 56.10300 16.83 33.66 51.48 67.32Shaded values exceed permitted maximum of 20 volts.Table 6 D.C. Voltage drop across Track Relay on Single Rail TrackNOTE: This document is controlled only when viewed on the DOT Engineering Standards website.Any other copy of this document is uncontrolled, and the content may not be current.