Signalling/power issues in the Streatham area 4/7-5/7

[Tio Terry]

Why does the signalling power supply in the area not have UPS?

Can't comment specifically about Stretham but with two entirely separate grid supplies and a traction derived supply there is little chance of a total supply failure. If there is no traction derived supply then there is normally no traction supply for trains, so trains won't be running anyway. UPS for signalling supplies require large batteries - for the East London line some years ago the calculations indicated that a UPS to provide 12 hours standby would weigh around 13 tons and would require a room with reinforced floor to house it.

I don't have any details for the design of the supplies at Streatham but a switching system failure and a cable fire, as mentioned in another post, makes me wonder about diversity of cable routes within the compound between the incoming supplies transformers and the switching system.

 

[RichardAsh1981]

I don't have any details for the design of the supplies at Streatham but a switching system failure and a cable fire, as mentioned in another post, makes me wonder about diversity of cable routes within the compound between the incoming supplies transformers and the switching system.

Very much. This seems to be a system design blind spot - if you look into the major outages on the DNO networks (the ones so bad that they get OFGEM to let them off the penalties, and so incident reports become public) then they almost always involve loss of two independent supply circuits (N-1 redundant at 33kV and up). They also nearly always involve both of those "redundant" circuits being routed side by side for a considerable distance, or through a vulnerable location like over the same bridge. Yet the industry design codes (as far as I know) place no restrictions on doing this.
At 11kV level the only significant power cut I have had at home in the last 10 years was when a joint in one of the 11kV circuits to the local substation faulted, and the force caused the adjacent joint in the other circuit to go out in sympathy. Cue several days on a generator, but credit that they got said generator running within a couple of hours (something to be said for standardisation!). They then put the circuits back, with two pairs of adjacent joints, about 10m between the pairs ...

Back with signalling supply, I'm surprised to find an apparently radial distribution system to mean their could be a single point of failure - equivalent DNO network design switches over to a ring / mesh topology where reliability is important, so that adjacent areas can be called on to "backfeed" (prop up) the network in the event of a fault at an single point of supply. I would have expected signalling to be set up similarly, so that power (maybe at reduced capacity, but some) could be fed in from the "wrong end" of the distribution cables by manually closing switches which are normally open to define the supply areas.

 

[Tio Terry]

Very much. This seems to be a system design blind spot - if you look into the major outages on the DNO networks (the ones so bad that they get OFGEM to let them off the penalties, and so incident reports become public) then they almost always involve loss of two independent supply circuits (N-1 redundant at 33kV and up). They also nearly always involve both of those "redundant" circuits being routed side by side for a considerable distance, or through a vulnerable location like over the same bridge. Yet the industry design codes (as far as I know) place no restrictions on doing this.
At 11kV level the only significant power cut I have had at home in the last 10 years was when a joint in one of the 11kV circuits to the local substation faulted, and the force caused the adjacent joint in the other circuit to go out in sympathy. Cue several days on a generator, but credit that they got said generator running within a couple of hours (something to be said for standardisation!). They then put the circuits back, with two pairs of adjacent joints, about 10m between the pairs ...

Back with signalling supply, I'm surprised to find an apparently radial distribution system to mean their could be a single point of failure - equivalent DNO network design switches over to a ring / mesh topology where reliability is important, so that adjacent areas can be called on to "backfeed" (prop up) the network in the event of a fault at an single point of supply. I would have expected signalling to be set up similarly, so that power (maybe at reduced capacity, but some) could be fed in from the "wrong end" of the distribution cables by manually closing switches which are normally open to define the supply areas.

Agree.

As I understand it - and I may be wrong - Victoria reksignalling is an Interlocking renewal scheme primarily. It does not include a re-engineering of the power supply arrangements. Other recent schemes - including those associated with the GWR electrification - include a re-engineering of the power supplies to include a dual ended feeding arrangement that improves reliability. But there is a cost associated with that and the power feeding arrangements for Stretham had been very reliable over the past 15 years, so the cost of re-engineering them could not be justified.

The design remains questionable however, diversity seems to have been lacking. I doubt we will ever get to know the truth.

 

[tsr]

I would have expected signalling to be set up similarly, so that power (maybe at reduced capacity, but some) could be fed in from the "wrong end" of the distribution cables by manually closing switches which are normally open to define the supply areas.

I believe a workaround like that also happened during the incident in question but was aborted when a previously-mentioned cable started to catch fire. So far as I know, power was drawn at two points from the DNO.

It did sound really quite complex.