WEEK 3 Flashcards
What would you do if you found a wire off?
- Take a picture of the wire (wire off and context) and prints.
- Update and inform my DSIM. Enact ‘Wire Off Procedure’. Request AWC and ask for a 2nd competent person.
- Prove the wire and host terminal: can the wire go anywhere else? hand trace, check for label, type of wire and colour, electrically prove - read 100V then 0V with each side isolated, one at a time.
- Pre-wire count for independent verification.
- Confirm with DSIM that AWC is in place and has been granted. Request AWC number.
- Isolate.
- Re-terminate wire and label with my name and date. Take a picture.
- Post-wire count. Ask 2nd competent person to check the security of termination.
- Reinstate fuse and observe TR energise.
How do you perform a wire count?
- Get wire schedule.
- Ask competent person to confirm where they are (what kiosk, TDB etc).
- Ask them to wire count the desired place and if it has a label.
- Ask them to re-confirm discrepancy.
Where will we find a train-stop TQ proving circuit?
At a replacing track, with a following move.
What provides our ATP?
Trainstops and Tripcocks - in the event of a train-stop being stuck in the ‘OFF’ position, the track will stay de-energised. This is Automatic Train Protection.
How do I prove there is a train-stop failure?
- R coils = track volts
- Q coils = 0V
- Perform a missing potential test: Q1 and Q2 —> Earth = 0V = missing BX. Q1 and Q2 —> Earth = 100V = missing NX.
- 1F —> Earth = 100V = fuse is good. 1A —> Earth = 0V = train stop failure.
What is a pick path, and what is a stick path?
Pick: the conditions expected to initially energise a load.
Stick: the ‘memory’ that the conditions have been met, but expected to change.
Where would we find a T.C.I and why are they installed on the railway?
Track circuit interrupters are found at sidings and terminal stations. When a train enters an illegal area, it will break the T.C.I. and leave the track de-energised.
At the end of lines, there is a risk of de-railment. A train could run past end of line equipment, which means it would no longer be shunting the track. The danger with this is that the route can clear into a section where a train has de-railed, resulting in collision. To mitigate this, we have TCIs.
In the event of a driver breaking it, it will create an open circuit and the track relay will de-energise. Even if that train left the area, the track will remain de-energised, as there may be broken end of line equipment. This means the signal will not be able to clear into this section.
What are some types of end of line equipment?
- T.C.I
- Fixed train stop
- Fixed red lights
- Sand drag
- Position detector
- Stopping diamond
What are 2 types of T.C.I’s and how do they vary?
Non-insulated:
Insulated:
Why are fan tracks bonded in series?
We find fan tracks at depots and sidings. They are bonded in series to ensure that if a bond breaks, the track relay will de-energise, causing a right-side failure.
If the fan track was bonded in parallel and a bond broke, the track relay would still be able to energise. This would cause a latent failure (undetected). This means that a train could be on a track, with the TR still energised. This would allow for a route to be cleared into the occupied section, and another train would be able to go on the same track. This could cause a collision and possibly de-rail a train. This is why it’s important that we have self-announcing failures, to prevent them from stacking up.
What is the effect of an earth fault developing anywhere on the BX leg of a train stop proving TQ circuit?
The current would bypass the contacts, creating an overcurrent, which would blow the fuse. This would create an open circuit, keeping the track de-energised, and the signal it’s replacing is at danger, as well as the signal in the rear. This is because the NX leg is at Earth potential. This ensures we keep at least 1 working train stop between trains and 2 signals at danger.
If we did not do this, 1 earth fault would be latent, and another could bypass safety critical equipment. This would make the circuit unable to prove the train stop is ON.
Where are 3 places a check rail may be used?
- Points and crossings
- Tight bends
- Adjacent to tripcock
What would be the possible outcome if the T.C.I was installed in the incorrect position after a re-rail?
If it was installed too close (within 3 metres of FRL) the train may strike end of line equipment, without breaking the T.C.I. This would mean the track is still energised even if the fixed red lights are damaged. When another train approaches, the driver may not see other end of line equipment, and could have an end of line de-railment.
If the T.C.I was installed too far away (before stopping diamond), it would break when the train stops at its usual position.
What effect could rusty or contaminated rails have on a track circuit?
This could prevent a train from de-energising the track relay, as it may not detect. This could cause a wrong-side failure, as a train could be on a track, but the relay may still be ‘UP’.
What is the purpose of a Trainstop Proving TQ Circuit?
We find this circuitry at every replacing track with a following move, providing our ATP.
This circuit has a pick path (the trainstops 1 and 1:1 contacts), and a stick path (TR 1F and 1A contacts). This ensures that the track relay will only energise when the trainstop is in the fully ‘ON’ position.
This also ensures that in the event of a trainstop being stuck in the ‘OFF’ position, the TR will have no pick path, and therefore cannot energise: this track will stay de-energised and the signal in the rear will stay at danger. We therefore have at least one working trainstop in the rear, providing our ATP.
