General Information on Track Circuits - RGS Online

More documents

Recommendations

Info

Railway Group Approved Code of Practice GK/RC0752 Issue Two Date December 1998 Page B22 of 25 Withdrawn Document Uncontrolled When Printed <strong>General</strong> <strong>Information</strong> on Track Circuits 15.5 Double Rail Track Circuits Where both running rails are used for traction current return, the electrification arrangements, using impedance bonds, are designed to keep the currents flowing in each rail balanced. Under such conditions, any interference content within the traction current should similarly be balanced and little or no interference applied to the receiver. However, due to a number of reasons, interference currents flowing through the track circuit may be, or become, imbalanced: • presence of check rails; • track curves; • earthing of one rail; • bonding differences; • asymmetric position of conductor rail / catenary; • broken rails; • disconnected impedance bond sideleads When the track circuit becomes unbalanced any interference in the traction return current due either to disturbances in the supply, or generated by traction units, will result in interference being presented to the receiver. The magnitude of this interference is largely independent of the length of the track circuit, but is proportional to the imbalance of currents flowing through the receiver end of the track circuit (either an impedance bond or tuned zone). Therefore, with a train occupying the track circuit, interference can be applied to the track receiver, which if of sufficient magnitude, form and duration, will cause a wrong side failure of the track circuit. 15.6 Rolling Stock Compatibility Means of providing compatibility between rolling stock and track circuits, without the use of ICMUs, is preferable and modern traction units may be acceptable for use with the existing track circuits, if it can be demonstrated that the predictable level of interference which may be generated, is insufficient to interfere with correct track circuit operation. Such an assessment will need to make reasonable assumptions as to the proportion of traction current that can flow through an individual track circuit, the resulting magnitude of interference which will be presented to the track receiver and the minimum response time of the receiver and interlocking. Therefore the validity of such assessments relies upon the following: • cross bonding between parallel tracks; • track circuit length limitations; • prevention and detection of imbalance; • integrity of rails and bonds; • operating times. CAUTION: Although general precautions and limits that provide compatibility between rolling stock and track circuits, have been included in the Train Detection Handbook Codes of Practice, these are not comprehensive and special conditions may apply to certain routes to permit the operation of rolling stock. Where new types of rolling stock are to be introduced, existing constraints will require reassessment, as to their adequacy. B22 RAILTRACK
<strong>General</strong> <strong>Information</strong> on Track Circuits 16 Impedance Bonds Withdrawn Document Uncontrolled When Printed Railway Group Approved Code of Practice GK/RC0752 Issue Two Date December 1998 Page B23 of 25 16.1 Operation Impedance bonds are devices which allow traction current (d.c. or a.c.) to pass through, whilst limiting the track circuit current. They are necessary wherever double rail traction return and IRJ dependent track circuits coexist. An impedance bond is configured to provide a very low impedance path to double rail a.c. or d.c. traction return currents (typically less than 0.4mΩ per coil) whilst presenting a high enough a.c. impedance between the rails (typically greater than 15Ω) to allow the operation of track circuits. It also provides a centre connection for cross bonding, which minimises the passage of track circuit current between circuit currents. The winding connected between the rails is comprised of heavy gauge copper, fitted with a centre tap connection and wound on a heavy iron core. Provided that each running rail carries equal amounts of traction return current, the current from each rail passes in opposite directions through the coil from the rail to the centre tap connection. The net flux in the iron circuit will be zero and the impedance to traction current (d.c. or a.c.) will be very small, as shown in Figure B16. Figure B16 IRJ IRJ 1/2 Traction Current 1/2 Traction Current Cross Bond Cross Bond Track Transmitter Track Receiver The a.c. track circuit current attempts to flow between the two rails and is therefore in the same direction through the two halves of the winding, resulting in the track circuit current seeing a larger, albeit still relatively small, impedance. Track–to–track cross bonding on double rail track circuits must be provided via the centre taps of impedance bonds on electrified lines, as shown in Figure B17. Figure B17 Cross Bonds RAILTRACK B23
Page 1 and 2: Approved by Keith Turner Standards
Page 3 and 4: General In
Page 9 and 10: Withdrawn Document Uncontrolled Whe
Page 27: Withdrawn Document Uncontrolled Whe
Page 79 and 80:
Withdrawn Document Uncontrolled Whe
Page 81 and 82:
General In
Page 83 and 84:
General In
Page 85 and 86:
General In
Page 87 and 88:
General In
Page 89 and 90:
General In
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
General In
Page 97 and 98:
General In
Page 99 and 100:
Page 101 and 102:
General In
Page 103 and 104:
General In
Page 105 and 106:
Page 107 and 108:
General In
Page 109 and 110:
Page 111 and 112:
General In
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
General In
Page 119 and 120:
Page 121 and 122:
General In
Page 123 and 124:
General In
Page 125 and 126:
Page 127 and 128:
General In
Page 129 and 130:
General In
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
General In
show all

General Information on Track Circuits - RGS Online

Create successful ePaper yourself

Delete template?

Save as template?