WEEK 2 Flashcards
What does fail safe mean?
In the event of a failure, the entire system will fail in a safe state, causing a self-announcing, right-side failure. This will put the associated signal at danger.
What is an example of a wrong-side failure?
2 Earth faults bypassing safety critical equipment.
Why is the NX100 busbar connected to Earth in the 7 way fuse bay?
- In the event of an Earth fault, the fuse will blow, causing a self-announcing right-side failure.
- If we did not do this, one Earth fault would go undetected.
- If 2 Earth faults occurred, it could bypass safety critical equipment, causing a wrong-side failure.
What are some pre-installation checks for a changing a relay?
- Like-for-like: type (DEV), contact arrangements, frequency (33 1/3Hz = red, 125Hz = silver).
- Overhauled within 3 years.
- Visual checks for damage: broken glass, spindle is straight, vane is not touching coils, damage to frame.
- Impact detector has not been dislodged.
- Continuity across armatures.
What must be done when installing a new relay?
- Line up lid and tighten thumbscrew.
- Ensure relay energisation level is correct and front contacts break.
- Lift Q2 and observe relay de-energise immediately, and front contacts break with smooth movements.
- 1Ω shunt track and observe relay de-energise and front contacts break.
- If there is TR-TR, lift R coil of one relay and ensure the other relay de-energises. If there is TR-GR, lift the R coil of the GR and ensure the TR de-energises.
What is track circuit opposition?
Track circuit opposition is employed to ensure each track circuit is 180° out of phase. This is so that in the event of a block-joint failing, at least one track will fail, causing a self-announcing, right-side failure.
If we did not, the current would all flow in the same direction, and could make 2 track circuits into 1. This could cause a full speed SPAD where we have trainstops.
Where do we have anti-opposition tracks and why do we have them?
- Where the positive traction rail has been transposed - to ensure the continuous rail is next to the positive traction rail, to dissipate any fault current.
- Substation boundaries - To mitigate phase drift, where substations have not been phase locked.
- Platforms - maintainer’s break.
What are the characteristics of an anti-opposition track?
- It has no phase relationship with its’ adjacent tracks.
- It has 2 IBJs (one on continuous and one on section).
- It has continuous rail jumper cables.
List the Tracks to Standard:
- Continuity across IBJs (all 3 tracks isolated).
- Adjacent fuses replaced for Ballast Leakage Tests: extraneous voltage (R3-R1 < 0.5V) and induced loop (0Ω shunt, R3-R1 < 0.2V).
- All fuses replaced. Opposition (V1 + V2 = V3).
- Capacitor in section - output of capacitor—> Earth = track volts.
- Relay energisation check.
- Top link at section rail potential for both TDBs. Top link —> Earth = track volts.
- Q1 at BX potential. Q1 —> Earth = 100V.
- Q2 break test to observe relay fully de-energise and front contacts break.
- If TR-GR, break R coil on GR to ensure TR fully de-energises.
- Gauge any equipment.
- 1Ω shunt track.
How do you test for track swaps and what are the cable types:
- Opposition?
- Capacitor in section?
- Relay energisation?
- Output of transformer / input of capacitor changes opposition and relay drive - pirelli cable.
- Output of capacitor / input of T.TDB changes ALL - concentric cable.
- Swap R3 and R1 changes relay drive - pirelli cable.
How do you test different IBJs after a re-rail?
Benkler Mark 2: There is a test terminal on both sides. One probe must be placed in there, whilst the other is testing on all bolts and both rails.
Triple 6: One probe stays on one side of the rail, whilst the other tests on all bolts, and the same is done on the other side.
There should be no continuity. If there is, there is a block-joint failure and it must be replaced.
