General Information on Track Circuits - RGS Online

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Railway Group Approved Code of Practice GK/RC0752 Issue Two Date December 1998 Page J4 of 5 5 Wrong Side Failures Withdrawn Document Uncontrolled When Printed <strong>General</strong> <strong>Information</strong> on Track Circuits 4.3.3 Use of Track Circuit Fault Detector The track circuit fault detector comprises a test signal transmitter and a receiver, both units being self contained with their own battery power supply. The detector is designed to be used on a track circuit whose feed has been disconnected and replaced by the test transmitter. However, with audio frequency track circuits, the transmitter may not be required, as the receiver will detect the steady tone of the feed frequency. A full description and details of operation are given in Part F. 4.3.4 Subdivision of Track Circuit This technique is particularly useful for track circuits in S & C where the sections of the track circuit are pieced together with jumper cables. It can be applied in other situations by removal of fishplates and associated bonds in conjunction with the Permanent Way Engineer. Note: This technique must not be applied to a traction return rail or jumper unless the work is under the direct control of the Electric Traction Engineer. Where the feed end test indicates a short circuit and a jumper part of the way through the track circuit is subsequently disconnected, the effect on the feed end will provide clues as to the location of the short circuit. If the short circuit lies between the feed and the disconnected jumper, the feed current and rail voltage will be largely unaffected. However, if the short circuit is between the disconnected jumper and the relay end, the feed end test will now indicate the symptoms of a disconnection. 4.3.5 Faulty Concrete Sleeper Insulations Rails on concrete sleepers are usually insulated from the chair fastenings; the rail sits on a pad whilst clips (eg. Pandrol clips) bear on a plastic insulation piece against the foot of the rail. It is unusual for individual faulty rail insulations to fail a track circuit. Rather, a number of such failures may contribute to a general deterioration of ballast resistance. For the specific investigation of faulty rail insulations, a special test unit; the Rail Clip Insulation Tester, is available. For the applicable description and operating instructions see Part G. 4.3.6 Failure of Insulated Rail Joints Care must be taken when attempting to check the insulation resistance of IRJs in situ due to the parallel path provided by the ballast on either side of the joint. Methods of testing IRJs are given in Part G. 5.1 Rail Surface Permanent or intermittent wrong side failures involving loss of train shunt can occur because of a poor rail surface due to rust, leaf debris, oil film, or crushed coal/sand/ballast. The surface condition should be visually checked throughout the track circuit and suitably cleared if possible. At locations where oil film or rust is excessive and speeds are less than 5 mph (eg. locomotive depots, terminal stations), a stainless steel “zig–zag” strip can be applied to the surface of the running rail by the Permanent Way Engineer. J4 R A I L T R A C K
Withdrawn Document Uncontrolled When Printed <strong>General</strong> <strong>Information</strong> on Track Circuits Railway Group Approved Code of Practice GK/RC0752 Issue Two Date December 1998 Page J5 of 5 5.2 Faulty Track Relay It is possible that a track relay may be mechanically damaged in some way which prevents it properly de–energising. A check should be made to see that the relay operates correctly when a shunt is applied. 5.3 Extraneous Interference It is possible that the track circuit is receiving energy from other than its own feed unit. Disconnect the feed and confirm that the relay voltage is less than 30% of its drop–away value. 5.4 Gaps In Track Circuits This is a problem arising particularly on electric traction railways due to the need to provide parallel alternative paths for traction return current in the rails, but can arise in any situation where the bonding is not in series. It can be seen from Figure J2 that defective bonding in the traction return rail can lead to a wrong side failure; a train between the two disconnected bonds would not shunt the track circuit current. Yellow Bonding is now provided to prevent such occurrences. Where parallel bonding exists, it must be inspected and short circuits applied to confirm correct detection. Figure J2 Two Disconnections R A I L T R A C K J5
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