Scottish Electrification updates & discussion

[MadMac]

Much talk about the Forth Bridge and wires, but how would the traction return path work? It’s axle counters because track circuits won’t work on the metal deck, so how will it get a return?

 

[alangla]

If you look at Street View images you can see that the OHLE was able to be naturally fit in on the lighting structures. https://goo.gl/maps/PEet8bErPWV7gJu2A

Unfortunately, the designers of the Tay Bridge didn't think to include any.

The bridge has the OHLE on the lighting structures now, but it used to be the other way around.

picture of the bridge in 1932, taken from https://en.m.wikipedia.org/wiki/Sydney_Harbour_Bridge

Given both the Forth & Tay bridges are metal girder structures, I’m sure modern 25kV OHLE can be fitted and made to look a natural part of the structure.

 

[Geeves]

As has been said the Sydney Harbour bridge was designed from the start to carry the railway (and the trams on the other side) and its OHLE. The lights being attached to the stanchions is just out of convenience. You cannot really compare the two. Also one is 1500V DC and the other 25KV with all the different restrictions that come with it

 

[edwin_m]

Much talk about the Forth Bridge and wires, but how would the traction return path work? It’s axle counters because track circuits won’t work on the metal deck, so how will it get a return?

With AC there's no corrosion from stray current, so as far as I can see they can probably just let it find its way through the rails or structure.

 

[najaB]

Slight nuance.. but weren't those gantry structures actually designed for DC OHLE right from the start? There used to be two pairs of lines when the bridge opened, one either side of the bridge and both sets of gantries remain today as per the photo.

Thanks for the correction, and that even more makes the point that they weren't changing the esthetics of the bride by stringing up OHLE as would be the case with the Forth and Tay bridges.

I'm not saying that it can't be done, just that they need to take the time to make sure that the design complements rather that detracts from either structure.

 

[Philip Phlopp]

Much talk about the Forth Bridge and wires, but how would the traction return path work? It’s axle counters because track circuits won’t work on the metal deck, so how will it get a return?

You bond the bridge to the traction return through a 'structure bond' - this is necessary because there's always going to be some risk that due to a mechanical failure of the electrification system, the bridge itself becomes electrified at 25kV. That needs to be detected and will in turn automatically trip the supply to the electrical section covering the bridge.

Corrosion isn't (really) an issue with AC and any issues, which will be particularly minor in any case, will be detected for structures such as the Forth and Tay Bridges through their already extensive corrosion detection, remediation and prevention processes, and which in any case will be updated to account for electrification components which will need periodic inspection for corrosion (purely as a result of the environment both these bridges are situated in).

 

[GRALISTAIR]

Both bridges in an estuarine environment salt laden exposed to elements which accelerate corrosion hence regular painting and inspection. DC is very bad for corrosion AC not so.

 

[najaB]

Both bridges in an estuarine environment salt laden exposed to elements which accelerate corrosion hence regular painting and inspection. DC is very bad for corrosion AC not so.

Doesn't an AC trickle actually provide some protection against corrosion?

 

[PaulLothian]

Oh electrification o’er the silvr’y Tay
Wi fiendish storm and tempest blast a’ the way
How the wires would tremble and sway
If the Series 1 components they did give way

We need a 'like' button!

 

[gsnedders]

The Forth Road Bridge can't (easily or cheaply) take train tracks - suspension bridges have significant issues with train tracks and I don't really know if the Forth Road Bridge is structurally designed or capable of withstanding the specific loads imparted by trains.

There was some study done involving an option of putting trams on the Forth Road Bridge; https://www.transport.gov.scot/media/24880/j10568b.pdf appears to be it looking quickly. The rough conclusion was, IIRC, a single-track tram line is viable.

 

[Philip Phlopp]

There was some study done involving an option of putting trams on the Forth Road Bridge; https://www.transport.gov.scot/media/24880/j10568b.pdf appears to be it looking quickly. The rough conclusion was, IIRC, a single-track tram line is viable.

Oh yes, I'd forgotten about that, and is it really that old. I think there's something more recent or more detailed from Arup/others which settled on two tracks situated tight to the central reservation to balance out load and/or to protect the trams a bit more from high winds.

Heavens, it only seems like yesterday we were all laughing about the planning application SNAFU for the toll plaza for the Forth Road Bridge...

 

[gsnedders]

Oh yes, I'd forgotten about that, and is it really that old. I think there's something more recent or more detailed from Arup/others which settled on two tracks situated tight to the central reservation to balance out load and/or to protect the trams a bit more from high winds.

Heavens, it only seems like yesterday we were all laughing about the planning application SNAFU for the toll plaza for the Forth Road Bridge...

Yeah, I have a similar memory of something along those lines, but that was the only thing I could find looking quickly! I do remember both conclusions, but I have no memory about relative recency.

That all said, I still don't really see the appeal versus increasing capacity and performance on the Fife Circle, though clearly congestion at Waverley is likely an issue.

 

[InOban]

https://twitter.com/NetworkRailSCOT/status/1305782975037046785?s=19

The original Levenmouth thread has been locked, but feel free to move this to a better thread.

Veg clearance and soil investigations along the route to Levenmouth have begun.