I have been sent the Fault Tree attachment to comment upon.
1. It is good that right side and wrong side failures have been separately considered
2. Need to be careful to distinguish between AND and OR; all seem to have been drawn as ANDs, whereas most at least should have been ORs
3. Conventionally the failures are drawn at the top of the sheet of paper and the various faults in a heirarchy below; this presentation reads left to right- it isn't wrong but probably best to do conventionally.
4. I liked the portion of the tree which leads to NO POWER (although where it said "head transformer" it presumably means "feedset transformer")
5. Other elements should have been broken down in this manner rather than simply all summating all at one node. For example it would have been easy to have separated the faults:
a) leading to high resistance between feed and relay,
and
b) leading to excessive leakage diverting current from track relay
and
c) opposing voltage from neighbouring track imposed due to failed Insulated Rail Joint
any one of which would cause insufficient pick up current.
6. Then for example item 5b could then have been further broken down into the various causes of poor ballast resistance (flooding, contamination, failed rail insulations / pads, point stretcher insulations),
7. Could have considered also the TR failing to pick because it had become open circuit, mechanically jammed. Also it could have high resistance contact or line circuit to TPR in interlocking itself having a fault wheres the actual track circuit on site was working fine.
8. In summary I think that you had a reasonable number of failures of different types, but you should have presented with groupings and sub-groupings to get a more heirarchical structure. The idea is that you can "drill down" from the top event and get more and more levels of detail, with a range of different types of faults then at the next level down a range of different ways in which that particular type of fault can occur from different lower level causes.
Also it would have been good to have demonstrated some combinational faults.
e.g. track set up in wet conditions with too low a drop shunt
AND
ballast resistance gets very high during hot weather
GIVES
train shunts insufficient current to cause TR to drop.
Similarly you could have assumed duplicated rail leads from location to rails. Cable can fail and track carries on working ok, but if this situation is not revealed by routine testing or chance inspectiion and then the other lead fails, then the track will fail.
I note you had as a fault "pipeline crossing railay line"; by itself this is not a FAULT. It is a relevant factor so you need to combine it with some act or omission that turns the result into a fault.
9. Would have been good to have demonstrated that you knew the role of a Fault Tree is to be able to feed in numerical estimates of probabilities of the various fault events at the roots of the tree, to be able to do some probabilistic number crunching to give estimates of probabilities for the various branches of the tree.
10. Overall it would probably have been aound a Pass- certainly have the general idea both of Fault Trees and Track Circuits but not quite there; presents a picture but it is a little "out of focus"
==========================================================================
I assume that you have found the previous discussion of track circuit fault tree but did you download
a) the attachment for the signal lamp out (to look at the presentation) and
b) read the IRSE News article?
These should help
1. It is good that right side and wrong side failures have been separately considered
2. Need to be careful to distinguish between AND and OR; all seem to have been drawn as ANDs, whereas most at least should have been ORs
3. Conventionally the failures are drawn at the top of the sheet of paper and the various faults in a heirarchy below; this presentation reads left to right- it isn't wrong but probably best to do conventionally.
4. I liked the portion of the tree which leads to NO POWER (although where it said "head transformer" it presumably means "feedset transformer")
5. Other elements should have been broken down in this manner rather than simply all summating all at one node. For example it would have been easy to have separated the faults:
a) leading to high resistance between feed and relay,
and
b) leading to excessive leakage diverting current from track relay
and
c) opposing voltage from neighbouring track imposed due to failed Insulated Rail Joint
any one of which would cause insufficient pick up current.
6. Then for example item 5b could then have been further broken down into the various causes of poor ballast resistance (flooding, contamination, failed rail insulations / pads, point stretcher insulations),
7. Could have considered also the TR failing to pick because it had become open circuit, mechanically jammed. Also it could have high resistance contact or line circuit to TPR in interlocking itself having a fault wheres the actual track circuit on site was working fine.
8. In summary I think that you had a reasonable number of failures of different types, but you should have presented with groupings and sub-groupings to get a more heirarchical structure. The idea is that you can "drill down" from the top event and get more and more levels of detail, with a range of different types of faults then at the next level down a range of different ways in which that particular type of fault can occur from different lower level causes.
Also it would have been good to have demonstrated some combinational faults.
e.g. track set up in wet conditions with too low a drop shunt
AND
ballast resistance gets very high during hot weather
GIVES
train shunts insufficient current to cause TR to drop.
Similarly you could have assumed duplicated rail leads from location to rails. Cable can fail and track carries on working ok, but if this situation is not revealed by routine testing or chance inspectiion and then the other lead fails, then the track will fail.
I note you had as a fault "pipeline crossing railay line"; by itself this is not a FAULT. It is a relevant factor so you need to combine it with some act or omission that turns the result into a fault.
9. Would have been good to have demonstrated that you knew the role of a Fault Tree is to be able to feed in numerical estimates of probabilities of the various fault events at the roots of the tree, to be able to do some probabilistic number crunching to give estimates of probabilities for the various branches of the tree.
10. Overall it would probably have been aound a Pass- certainly have the general idea both of Fault Trees and Track Circuits but not quite there; presents a picture but it is a little "out of focus"
==========================================================================
I assume that you have found the previous discussion of track circuit fault tree but did you download
a) the attachment for the signal lamp out (to look at the presentation) and
b) read the IRSE News article?
These should help
PJW