1. Intelligent Infrastructure Track Circuit Monitoring A guide from LNW(N)
John Walsh (v1.0)
Date /02/2012
v1.0

2. Typical DC Track Circuit Installation
Track relay
Current Sensor
Data Logger
Central Server
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3. Typical AC Quick Release Track Circuit Installation~
Data Logger
Central Server
Transformer - Rectifier
Current Sensor
Track relay
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4. Typical AC 50Hz Vane Track Circuit Installation
VT1 Vane-type
Track relay
Data Logger
Central Server ~
Local Current
Control Current
VT1 Integrator
Current Sensor
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5. Typical Digital TI21 (aka EBI Track 200) Track Circuit Installation
TI21 Digital
Receiver
Data Logger
Central Server
Serial Link
Transmitter
Track relay
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6. Dividing the current level into bands
Relay coil current (mA)
Time
These 4 levels are set by the Delivery Unit and therefore define the 5 bands.
No Alarm or Alert events so long as current level sits in either ‘Occupied’ or ‘Clear’ bands (‘deadband’ timings allows transit from one level to another without event).
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7. Moving out of Clear / Occupied bands
Relay coil current (mA)
Time
Current moving into the following bands:
Excess
Low Clear
High Occupied
Generates an ‘event’, but it normally II is set take more than 1 event to produce an Alarm or Alert (how many is again set by the Delivery Unit)
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8. Setting the Count levels
Count before Hi (Alert) generated
Actual event count
Count before Hi Hi (Alarm) generated
However all counts reset at midnight!
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9. Moving out of the ‘Clear’ band
There are 3 cases:
Excess Current
If Excess Current threshold is exceeded
Low Clear Current
Current falls below Low Clear Current threshold greater than set time
Unstable Clear Current
If current falls into the Low Clear threshold for a short duration (less than set time)
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10. Excess current
Here the current is higher than the Excess Current Limit ( shown by red line)
No count made on this event – Alert generated (Recorded as priority 3)
Possible causes – track circuit set for what was poor ballast resistance which has since improved, adjacent (un-staggered) track feed assisting this track etc.
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11. Low Clear Current
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12. Low Clear Current Low Clear Deadband set to 2 seconds
Low Clear Level is set to 230mA
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13. Low Clear Current Low Clear Level count Midnight count reset
This event is only generated when transition is made from known good level in Clear band.
Track circuit current remains in Low Clear band for a duration greater than Low Current-Clear deadband (here it is set to 2s)
Track circuit current is above Occupied Level but below Low Clear Level.
Possible causes: deteriorating rail insulation pads (pads and nylons), high resistance tail cables or connections or IBJ failure, salt in level crossing etc
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14. Unstable Clear Current Count
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15. Unstable Clear Current Count
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16. Unstable Clear Current Count
Falling below Low Clear Current threshold
Unstable Clear Current count
This event is only generated when transition is made from known good level in Clear band but returns back within deadband time
Track circuit current falls below the Low Clear Current threshold
Causes could be due to intermittent connection (loose track circuit pin, damaged tail cable, loose back nut etc)
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17. Unstable Clear Current Count
Low Clear Current threshold
Occupied Level
Another example, a genuine track circuit occupation is not counted.
Also it is normal (at the moment!) for the count to sometimes lag the event (for all events)
Count increases for each incursion into Low Clear band for duration < Low Current – Clear deadband (s) AND recovers in this time
This clearly shows the current is unstable - moving rapidly and erratically.
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18. Moving out of the ‘Occupied’ band
There are 2 cases of moving out of this band
High Occupied Current
Exceeds High Occupied Current for a set time
Poor Shunt
Exceeds High Occupied Current level for a less than set time (also known as ‘unstable occupied’)
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19. High Occupied Current
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20. High Occupied Current
High Occupied Level is set so that it is no higher than 50% of minimum drop away value (OCC Level)
High Current – Occupied Deadband set to 2 seconds
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21. High Occupied Current Occupied Current
Greater than 2 seconds duration in High Occupied band
High Occupied Current count
High Occupied Current limit
Track circuit current rises above the High Occupied Current Limit (termed WSF level in II) for duration greater than High Current - Occupied deadband time – i.e. it has stayed in the High Occupied band for too long.
Possible causes are: wheel or rail contamination, failure of an un-staggered block joint (adjacent track feeding the relay).
In this case it was staff working – possibly with trolley or RRV that shunted the track sufficiently for it not to be classed as a Poor Shunt (next)
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22. Track Occupied Current
Poor Shunt
High Occupied Limit (WSF Level)
Track Occupied Current
Greater than 2 seconds High Occupied Current event
Less than 2 seconds Poor Shunt event
Poor Shunt count
High Occupied Current count
IF current rises above High Occupied Current for duration less than High Current – Occupied deadband time AND returns back into Occupied band.
Wheel or rail contamination briefly preventing the train from properly shunting the track circuit.
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23. Track circuit flicks 2 cases: Track flick: Clear-Occupied-Clear
Track flick: Occupied-Clear-Occupied
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24. Flick: Clear-Occupied-Clear
Clear Occupied Clear Flick count
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25. Flick: Clear-Occupied-Clear
Clear-Occupied-Clear Flicks, to register the duration must be:
greater than Lower Limit (s) but less than Upper Limit (s)
Duration
Count of Clear-Occupied-Clear
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26. Flicks
Flicks are basically genuine track clear and occupy events but the duration doesn’t tally with normal operation
For example if a track circuit occupies for a time less than the fastest and shortest train (with a sensible tolerance) what has caused it? This is counted as a “Clear – Occupied – Clear Flick”.
Conversely if the track circuit clears whilst is it occupied (“Occupied – Clear – Occupied Flick”) you would certainly want to know about that as it could potentially be a WSF, but there could more subtle reasons especially at the instant the train rolls on and off the track circuit.
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27. Processes
This presentation has focussed on the analysis of track circuits only.
Success of RCM also depends heavily on our judgment, knowledge, experience and good communication between all parties.
Be careful not to make the system redundant or insensitive by masking Alarms out or setting wide tolerances.
Relevant procedures:
NR/L3/MTC/II0219 [Issue 1] Management of Alerts and Alarms from Remote Condition Monitoring (9 pages)
NR/L3/OCS/043/3.11 [Issue 2] Response to Remote Condition Monitoring Alarms (3 pages)
NR/L2/SIG/19811 [ Issue: 3 ] FMS For Network Rail Fault Management (Formerly NR/SP/SIG/19811)
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28. Questions
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