Forth Bridge: how would you electrify it?

[K.o.R]

Apologies in advance if there was a thread, I have almost certainly missed it.

Disclaimer: The following may not have the slightest basis in reality, but I was thinking to myself (dangerous) and wondered what others might think

I've seen several times the absolute headache that the Forth Bridge presents regarding electrification and such (clearances, earthing, leakage, etc.). Some of those things I don't understand because I'm not familiar with OHLE beyond "wires on gantries with big ol' insulators between them".

So, a couple of possibilities I mused upon:

• A non-energised OHLE wire extending the length of the bridge, or at least the impinging support structures, with a neutral section at each end, so that lowering pantographs is not necessary.

• Could a 225, travelling at appropriate speed on the approach, successfully coast the full distance? Similarly, a Class 80x (though even the electric one could limp over if it ran out of speed)?

• Could an EMU, for example a 387, that was stopped at either North Queensferry or Dalmeny, accelerate away from the station to sufficient speed to coast the full distance?

• Alternatively: 750V third rail the length of the bridge. Obviously doable; my thinking here was on a different line: could you "power" a 750V (or, indeed, any lower voltage) section from the 25kV section? Like, literally have a 750V feeder station whose "supply side" is the OLE itself?
• And on a similar note to the above, the same but the 750V section is OLE as well.

 

[snowball]

There have been discussions on this before (though not a specific thread as far as I know) but it's very difficult to answer without knowing what the problems are. We would need to see all the dimensions of parts of the bridge near the upper part of the loading gauge.

I read on here some years ago, and have since mentioned in various threads, a claim that the main problem is clearance between diagonal girders and the ends of a passing pantograph. I am no electrical engineer, but I have often thought that the solution might be to apply a layer of insulating material to sections of those girders closest to where the pantograph might be. I have recently seen it stated that the underside of a bridge at Cardiff has been covered with insulating material to avoid having to raise the bridge. I have no idea why this technique has not been used in the past.

 

[K.o.R]

and the ends of a passing pantograph

I hadn't even thought of the pantograph itself. Those must be tight clearances then. Presumably that's already with the wire as low as possible over the roof of the train?

 

[Aictos]

Coasting is possible however I'm not sure if a EMU could reach enough speed from a standing start to get enough speed to coast without getting stuck in the middle of the section.

As to the non stop services, they shouldn't have a issue as long as they are are travelling at a appropriate speed.

With coasting unless there has been changes in the industry, the driver sees the board advising him of where to drop the pantograph just before the start of the coasting section then there's another sign to advise him he's out of the coasting section where he's meant to come to a stop and raise the pantograph.

I know a few years ago, there was a coasting section though Hitchin and it was weird seeing the 365s coast though with their pantographs lowered.

As to the Forth Bridge, I'm no engineer but maybe a solid overhead bar as used in the Thameslink Core amongst other places instead of having wires?

 

[K.o.R]

Why would you drop the pantograph?

 

[jfowkes]

As I understand it, pantographs are held against the wire by compressed air or springs. In the absence of a wire they'd travel to their further extent. They might foul the bridge structure and I imagine it would cause issues meeting a new section of OLE at the other end.

(Disclaimer: I know very little about almost everything)

 

[gazthomas]

I do find it ironic that such a gigantic structure would have issues accommodating OHLE, but there you are

 

[K.o.R]

As I understand it, pantographs are held against the wire by compressed air or springs. In the absence of a wire they'd travel to their further extent. They might foul the bridge structure and I imagine it would cause issues meeting a new section of OLE at the other end.

(Disclaimer: I know very little about almost everything)

Right, it makes sense if there was a section with no wires, hence why I suggest having a wire even if it isn't energised.

 

[Darandio]

I'd go along with the energised rigid bar as mentioned above. I believe it's what has recently been installed in the Severn Tunnel to overcome some of the issues mentioned in the first post.

 

[snowball]

I'd go along with the energised rigid bar as mentioned above. I believe it's what has recently been installed in the Severn Tunnel to overcome some of the issues mentioned in the first post.

Except that it might not address the actual problem with the Forth Bridge, if what I said in post #2 is true (I don't claim to know but it's plausible).

 

[NSEFAN]

I read on here some years ago, and have since mentioned in various threads, a claim that the main problem is clearance between diagonal girders and the ends of a passing pantograph. I am no electrical engineer, but I have often thought that the solution might be to apply a layer of insulating material to sections of those girders closest to where the pantograph might be. I have recently seen it stated that the underside of a bridge at Cardiff has been covered with insulating material to avoid having to raise the bridge. I have no idea why this technique has not been used in the past.

Could it be to do with line speed? At high speed there may be more risk of the OHLE wires moving around and making contact, hence you need to raise bridges rather than just insulate them?

 

[najaB]

Could an EMU, for example a 387, that was stopped at either North Queensferry or Dalmeny, accelerate away from the station to sufficient speed to coast the full distance?

I very much doubt that it could. At least not reliably. And it would b*****r up the timetable in the process.

 

[vinnym70]

Surely any ideas of coasting are limited by speed restrictions on the bridge itself? My observations (as a sightseer only) suggest that trains tend to go relatively slowly across the bridge - 40 mph?

It seems like insulating areas of the bridge close to any OHLE (either by insulating the bridge or coming up with a specific OHLE design) would be the way to go.

 

[Warwick]

Get the French in to do it. They'd have wires up and trains running whilst Network Rail were still dithering.

 

[gsnedders]

Surely any ideas of coasting are limited by speed restrictions on the bridge itself? My observations (as a sightseer only) suggest that trains tend to go relatively slowly across the bridge - 40 mph?

It seems like insulating areas of the bridge close to any OHLE (either by insulating the bridge or coming up with a specific OHLE design) would be the way to go.

Yeah, 40mph line speed over the bridge.

 

[markindurham]

There have been discussions on this before (though not a specific thread as far as I know) but it's very difficult to answer without knowing what the problems are. We would need to see all the dimensions of parts of the bridge near the upper part of the loading gauge.

It does look a little tight under those diagonal braces where the ends of a pantograph would be, looking at these clips

A proper drawing is needed, I think, though

 

[twpsaesneg]

I've never had cause to look at the Forth Bridge before now, i'm sure my colleagues in Scotland would be all over it though. From the video posted it appears that the diagonal bracing is the greatest constraint which would need sufficient clearance to passing pantograph horns (the side bits).

Normally 230mm allowance is given for sway which could probably be cut down for a 40mph linespeed. Conductor beam would effectively stop uplift which would buy some clearance, but may be regarded as more visually intrusive and requires frequent support compared to a catenary system if one could fit.

Insulating paint rated for 25kV was only approved for use on Network Rail about 3-4 years ago after a trial installation at the York Station footbridge - this would help to mitigate flashover possibility but couldn't be used as the primary means of insulation, which is air gap, without a standards change / derogation.

Track lower not easily possible without someone on the P-Way side coming up with something really creative.

Without seeing dimensions this is all speculation, but this is kind of the way it would be approached... if someone can send me some as-fitted drawings and money I'll happily give them a design

Anything is possible given enough money and time.

 

[AndrewE]

We could have a combination of some of the ideas suggested so far: There are not many through services over the bridge to the rest of the UK, and new ones are likely to use new trainsets or traction, plus the line speed is 40mph and unlikely to be increased.
So how about dealing with the pantograph horn problem by having special narrow pantographs for use on something minimal like a trolley-wire just installed over the bridge? Maybe even a trolley wheel running on a conductor in a downward-facing channel? Lots of locos and trainsets have multiple pantographs - and abroad they even use different ones on different OLE systems - so I would think that we could have new or adapted electric traction specially for the bridge. It needn't be all Scottish electrics, just the stuff for working north.

 

[K.o.R]

Use a Pendolino and tell its tilt system to shift the pantograph towards the appropriate side of the roof

Jokes aside, that video is amazing. It's like a tunnel of steel girders. I wonder if the fact that the main portion of the bridge is absolutely straight would give more options?

The Forth Bridge is an extraordinary structure, so it clearly needs an extraordinary method, and that's probably third rail. You could make it super-insulated third rail, in like a trough to keep the H&S bods happy; the benefits must surely outweigh the issues.

 

[snowball]

Insulating paint rated for 25kV was only approved for use on Network Rail about 3-4 years ago after a trial installation at the York Station footbridge - this would help to mitigate flashover possibility but couldn't be used as the primary means of insulation, which is air gap, without a standards change / derogation.

Why does it have to be stuff you paint on? I was imagining sheets of solid plastic or other insulating material to be attached to the metal, maybe 10 or 20 mm thick (or more if there's room).

 

[gordonthemoron]

surely a dead section of OHL would be nicked?

 

[edwin_m]

I've never had cause to look at the Forth Bridge before now, i'm sure my colleagues in Scotland would be all over it though. From the video posted it appears that the diagonal bracing is the greatest constraint which would need sufficient clearance to passing pantograph horns (the side bits).

Normally 230mm allowance is given for sway which could probably be cut down for a 40mph linespeed. Conductor beam would effectively stop uplift which would buy some clearance, but may be regarded as more visually intrusive and requires frequent support compared to a catenary system if one could fit.

Insulating paint rated for 25kV was only approved for use on Network Rail about 3-4 years ago after a trial installation at the York Station footbridge - this would help to mitigate flashover possibility but couldn't be used as the primary means of insulation, which is air gap, without a standards change / derogation.

Track lower not easily possible without someone on the P-Way side coming up with something really creative.

Without seeing dimensions this is all speculation, but this is kind of the way it would be approached... if someone can send me some as-fitted drawings and money I'll happily give them a design

Anything is possible given enough money and time.

The uplift is only an issue where you pass one of the diagonal bracings, so if it is supported at each of these by a support that allows little or no uplift then that particular problem goes away. Then it doesn't matter whether it's a single ("trolley") wire or a bar - a trolley wire would be good enough for 40mph and less visible than a bar as well as having more clearance to whatever is above it for the same contact height.

 

[ainsworth74]

It is also worth recalling that the bridge is a UNESCO World Heritage Site and also has a Category A listing by Historic Environment Scotland. Whilst that doesn't mean that it would be impossible to alter for electrification it is worth bearing in mind that its unlikely that permission would be granted for installing great big plastic sheets of insulation or other very intrusive methods.

 

[najaB]

Whilst that doesn't mean that it would be impossible to alter for electrification it is worth bearing in mind that its unlikely that permission would be granted for installing great big plastic sheets of insulation or other very intrusive methods.

Even if they're red and sympathetically designed?

 

[ainsworth74]

Even if they're red and sympathetically designed?

I am by no means an expert on such matters but I'd have thought that that might be permissible. I just wanted to make the wider point that this isn't just your common garden variety rail bridge. There will be a lot of outside scrutiny (with legal powers behind them) of any proposed scheme to electrify the bridge (well, the railway on the bridge anyway, I think electrifying the bridge itself would definitely run into a few hurdles ).

 

[The Ham]

Just plug the whole bridge into the mains and hope that the power jumps the gap to the trains.

 

[Aictos]

Seeing as the lines to and from Oxley CS are electrified between there and Wolverhampton using trolley wire OHL as it's designed for low speed movements, could not the same be applied for the Forth Bridge seeing as it has a low speed restriction of 40mph.

You could then electrify to Stirling and get the Fife Circle electrified as well.

 

[TwistedMentat]

With the improvement of battery technology would it be a crazy idea to add a smallish battery to a trainset and use that for such a gapped point? Couple with some sort of auto lowering and raising system for the pantograph like you have on the 800s. A battery could also help be a limp to next station feature for odd situations.

 

[najaB]

With the improvement of battery technology would it be a crazy idea to add a smallish battery to a trainset and use that for such a gapped point?

No. Not the least bit crazy. There have been several BEMU trials over the years.

 

[AndrewE]

Seeing as the lines to and from Oxley CS are electrified between there and Wolverhampton using trolley wire OHL as it's designed for low speed movements, could not the same be applied for the Forth Bridge seeing as it has a low speed restriction of 40mph.

You could then electrify to Stirling and get the Fife Circle electrified as well.

Agreed, but the concern seemed to be about whether there was even clearance for standard pantograph horns... which is why I wondered whether a special narrow low-speed pantograph could be a goer, just for the line across the bridge.