VRIOGS 010.7 RevA - Public Transport Victoria

22 VRIOGS 010.7 Revision A4. Similar values shall be calculated for individual track circuits and used toverify that the measures provided to protect the relay and / or feed units aresufficient.5. Where the length of track circuit is excessive, the levels of DC beingsuperimposed may result in failure of the relay-protecting fuse. The designshall provide sufficient series resistance in the relay circuit to limit DCtraction current to a level that will ensure continuous operation of the trackcircuit equipment. A minimum DC loop resistance of 1 ohm is required in therelay circuit.6.6.5 Audio Frequency Track Circuits1. Jointless track circuits are normally separated by means other than IRJs.2. Jointless track circuits are suitable for use in traction areas as there are notraction sensitive components.3. Traction current unbalances between rails are normalised at tying-in points,and by air-cored inductors in some CSEE jointless track circuits.4. The maximum length of audio frequency jointless track circuits is not limitedby traction current but by the net effect of shunt resistance across the track,including the effects of any impedance bonds used for tying in or connectionto substations and sectioning huts.5. In some circumstances, audio frequency track circuits may be installed asconventional track circuits commonly separated by IRJs and withimpedance bonds to provide traction return continuity usually where a sharpcut off is required or when interfacing with another type of track circuit.Traction return and bonding requirements for this arrangement are the sameas for conventional double rail track circuits.6.6.6 Impulse Track CircuitsSingle rail impulse track circuits develop a higher voltage impulse than their doublerail counterpart and are therefore slightly more effective in obtaining a shunt underpoor conditions. The traction return rail of a single rail impulse track circuit may beconnected to the neutral point of any type approved impedance bond in an adjacenttrack.High voltage impulse track circuits shall be used particularly over points andcrossings, and infrequently used tracks where it is most important to guarantee asafe and effective shunting of the track circuit.6.7 Electrolysis Bonds6.7.1 GeneralThe traction current return system shall include the connection of electrolysis bondsas required.1. The Infrastructure Manager in consultation with the Electrolysis Committee ofVictoria (ECV) shall determine the actual location at which electrolysisbonding facilities are required. The type of bonds to be used together with theNOTE: 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.