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Railway Group Approved Code of Practice GK/RC0752 Issue Two Date December 1998 Page H2 of 2 4 Full Test Withdrawn Document Uncontrolled When Printed <strong>General</strong> <strong>Information</strong> on Track Circuits shunt box may be connected across the track circuit relay links in the lineside apparatus housing. The value of drop shunt obtained at the lineside apparatus housing will usually be higher than that obtained at the rails, the resistance of the relay end track leads being the most significant factor. It is only permissible to undertake drop shunt tests at the track circuit relay links in the lineside apparatus housing. where comparative shunts have previously been carried out both at the rails and at the lineside apparatus housing, and the two values are endorsed on the record card. It is then possible to judge any value obtained at the lineside apparatus housing relative to its theoretical railequivalent. Where such a theoretical value can be seen to approach the minimum acceptable, the test should be verified at the rails. The procedure for carrying out a drop shunt test is detailed in Part F 3.2. A variation in the drop shunt value may be caused by variations in equipment performance, or by expected variations in environmental conditions, with the drop shunt reaching the upper end of its range in wet weather and the lower end in dry weather. If the drop shunt exceeds the maximum value for the track circuit (see the relevant Code of Practice ), it is likely that the track circuit is being shunted by poor ballast or debris. The track circuit should be examined for these faults. If it appears to be in good physical condition, the track circuit equipment should be regarded as failed and the cause of the failure investigated through the fault finding procedure (see the relevant Code of Practice). If the drop shunt is lower than the minimum value for the track circuit (see the relevant Code of Practice), there has been an unexpected equipment failure. The Engineering Supervisor is to be informed, and immediate investigations undertaken to ascertain the cause of the low drop shunt value. The full test must be applied whenever alterations are made (eg. relaying, lead/jumper renewal, equipment replacement, adjustment, etc). The full test comprises the following: a) Carry out a Routine Examination. b) At the feed end, measure and record the voltages, currents and other parameters as required on the front of the record card. Any adjustments required must be in accordance with the relevant section of this handbook for the type of track circuit under test. c) At the relay end, with the track circuit clear, measure and record the voltages, currents and other parameters required and enter on the front of the record card. d) Perform a drop shunt test with the shunt box across the rails at the relay end and enter details on the record card. Where the track circuit is of a type able to be routine shunted at the relay links in the lineside apparatus housing, perform a second drop shunt test at this position and endorse the record card with that value. e) Set the shunt box to the minimum for that track circuit and connect across the rails at all extremities of the track circuit, confirming that the track circuit occupies on each occasion. This test must obtain simultaneous track circuit occupation where an overlapping section exists. H2 R A I L T R A C K
<strong>General</strong> <strong>Information</strong> on Track Circuits 1 Introduction 2 Categories of Failure 3 Intermittent Failures Withdrawn Document Uncontrolled When Printed Part J Fault Finding Railway Group Approved Code of Practice GK/RC0752 Issue Two Date December 1998 Page J1 of 5 This Part gives a general outline to faults common to all types of track circuits; faults caused by electric traction systems or peculiar to a particular track circuit design are given in the appropriate Code of Practice of the Track Circuit Handbook. When clearing a fault, details of all readings and results should be noted, to establish a logical pattern of testing and adjustment. The track circuit record card(s) should always be investigated, as deteriorating readings during maintenance can show the impending failure of a component. When a fault has been located, the relevant tests carried out up to that point should be repeated, as, in the case of multiple simultaneous faults, one fault can mask another. Once a fault has been cleared, the track circuit must be fully tested prior to restoration. Track circuit failures fall into the following categories: Right Side: Indication shows occupied with no train in the section. Protected Wrong Side: Indication shows clear when a train is in the section, but is caused by a failure of the indication system only; the train is still protected by the interlocking. Unprotected Wrong Side: Track circuit or repeat relay fails to de–energise when a train is in the section; the train is no longer protected by the interlocking. The nature of the failure can be further categorised: Permanent: Failure remains static. Intermittent: Failure is only apparent for short periods. Intermittent faults are often the most difficult to solve, as the failure does not usually remain static long enough to take all necessary readings and observations. The following are possible causes dependent on circumstances: Vibration Vibration caused by the passage of trains can create intermittent high resistance in bonding or intermittent short circuits between the rails (ie. the failure may remain after one train but be cleared by a subsequent one). Trains, or operation of other equipment such as point machines, should be observed on site or on the signalman’s diagram; If the failure always occurs with a train at a particular point or coincides with operation of other equipment, that geographic site should be fully investigated. R A I L T R A C K J1
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