Forth Bridge: how would you electrify it?

[najaB]

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.

Thing is, you really want to avoid adding something 'special' to the trains that'll be used for a mile or so out of a 300 mile route.

 

[AndrewE]

Thing is, you really want to avoid adding something 'special' to the trains that'll be used for a mile or so out of a 300 mile route.

It's better than no electrification because "it can't be done" though... It's only an extra pantograph, and most stock has the space for one, including the 11-car pendolinos.

 

[snowball]

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 ).

I seem to recall that when it was first designated as a world heritage site the principle of future electrification was cleared with Unesco. I think any chosen method will be accepted provided NR demonstrates that all reasonable alternative methods have been considered and mitigations applied.

 

[najaB]

It's better than no electrification because "it can't be done" though... It's only an extra pantograph, and most stock has the space for one, including the 11-car pendolinos.

I agree, but it really should be a last resort after all other options have been deemed impractical.

 

[matacaster]

Not sure about best method of electrifying Forth Bridge, but I am certain finding a suitable earthing point will be very easy!

 

[NotATrainspott]

Non-powered conductor bar and batteries. The South Wales Metro project is going to demonstrate use of batteries to get through Caerphilly Tunnel, which is a comparable length to the problematic part of the bridge. Batteries capable of getting a train over the bridge would be small enough to be easily retrofitted to existing electric rolling stock, and would have enough utility across the network (e.g. self-rescue, other restricted clearance sections) to be worth fitting as a standard part of any EMU. An Edinburgh to Dundee wiring project would need to handle both Forth and Tay bridges but they could share the same solution, and there would be plenty of 25kV AC available to charge up the battery in between.

 

[Warwick]

The answer is simple.Do a Hastings line tunnels across it. Sin

It's better than no electrification because "it can't be done" though... It's only an extra pantograph, and most stock has the space for one, including the 11-car pendolinos.

"It's only an extra pantograph..."
Yep, something else that can and will go wrong. Warwick's inverse law. Make it complicated and it'll take longer to fix when it goes wrong - which it will.

 

[Tio Terry]

Carefully!

It's not beyond the wit of man to do it. Just look at some of the clearance issues that have been resolved at Paddington for example. At least there's no reason to consider passengers on platforms carrying helium balloons and selfie sticks!

 

[gsnedders]

Carefully!

It's not beyond the wit of man to do it. Just look at some of the clearance issues that have been resolved at Paddington for example. At least there's no reason to consider passengers on platforms carrying helium balloons and selfie sticks!

Ultimately there's gradient limits on the wire, and with Dalmeny and North Queensferry stations are more or less at each end of the bridge.

 

[furnessvale]

surely a dead section of OHL would be nicked?

Would it need to be made of "nickworthy" material?

 

[bavvo]

If you dropped the voltage, say to 3KV, could you allow lower clearances? You'd still need a dual voltage train of course but doesn't that happen on the continent in some places?

 

[AndrewE]

If you dropped the voltage, say to 3KV, could you allow lower clearances? You'd still need a dual voltage train of course but doesn't that happen on the continent in some places?

Surely that has got to be a lot more expensive than a low narrow 25kV pantograph for use across the bridge? And as for Warwick's

The answer is simple. Do a Hastings line tunnels across it. Sin

I hate to think what damage singling one of the main line rail approaches to the Scottish capital would do for reliability! Care to suggest which of the lines approaching London might also benefit from this proposal? You could make lots of money selling land (to be invested in the whole UK rail network) if we halved the track area by singling various stretches of line on all the routes into and around London...

 

[najaB]

Surely that has got to be a lot more expensive than a low narrow 25kV pantograph for use across the bridge?

It wouldn't be. It just means a transformer with two tapoff points rather than one. Everything else about it would be the same. No second pantograph, second wiring run, etc.

 

[AndrewE]

It wouldn't be. It just means a transformer with two tapoff points rather than one. Everything else about it would be the same. No second pantograph, second wiring run, etc.

So that's a new transformer for every bit of existing traction then, rather than an extra pantograph bolted on the top - generally in existing pantograph wells. I don't think that the "spares" on locos with two get used very often: if the wires get pulled down then you're not going anywhere! Most of the first generation BR electric locos had them removed anyway, and a second wiring run is simply strung along the roof, not a big deal and a lot easier than rebuilding a transformer!

 

[najaB]

So that's a new transformer for every bit of existing traction then, rather than an extra pantograph bolted on the top - generally in existing pantograph wells.

And two VCBs, two pantograph up/down controls. What happens when someone forgets to lower the wide pantograph? What's more likely to fail and cause services to be cancelled: a set of solid-state electronics or something with moving parts? And I suspect that a lot transformers already have the 3kV tap-off anyway since it's easier to just build one part that can be used on dual voltage or single voltage systems.

 

[gsnedders]

I hate to think what damage singling one of the main line rail approaches to the Scottish capital would do for reliability! Care to suggest which of the lines approaching London might also benefit from this proposal? You could make lots of money selling land (to be invested in the whole UK rail network) if we halved the track area by singling various stretches of line on all the routes into and around London...

Not just reliability, but also capacity. The bridge is already a capacity bottleneck, and this would just be making it worse.

 

[NotATrainspott]

For NR the first question is whether it's practical to install just standard 25kV AC. That might require special treatment on the bridge with custom kit, but if that can provide a consistent 25kV AC for trains to use in the standard loading gauge, then there's no need for special trains at all.

If that isn't practically possible, then NR has to come up with a system which isn't only applicable to the Forth Bridge, as there are huge numbers of other places on the network with limitations on OHLE install. Consider all of the tunnels, low bridges, sensitive areas, depots, level crossings, dual electrification zones and the like across the network. Come up with a solution for all of them and you make it more worthwhile and affordable to fit it to trains, and make it possible to deliver the benefits of electrification at a lower cost on more lines across the country. Would 3kV DC/AC help? Not really - there are still plenty of situations where the existence of an electrified overhead line at all is a problem regardless of voltage. Would narrower pantographs help? Again, not really. It'd be marginally helpful in a few low-clearance situations with rounded corners but it won't do much elsewhere.

Small batteries are the only technology which would be useful and applicable across the entire network. It'd be massively helpful for NR if electric trains were able to rescue themselves to the next station or off the mainline when power supplies fail. For DC trains it would help capture regenerative braking energy when it'd otherwise go to resistor grids at the substations. It would allow DC and AC supplies to be separated when there's a switchover. At stations it would massively reduce the cost of electrification as the platform area could be made a neutral section, meaning that nearby bridges which were acceptable under previous standards will no longer need raised or replaced.

 

[edwin_m]

Ultimately there's gradient limits on the wire, and with Dalmeny and North Queensferry stations are more or less at each end of the bridge.

There are approach viaducts each end of the main spans, which have nothing above the track, so should be enough length to ramp the wire down to the correct height. The OLE would be more visually obtrusive here than on the main spans where with careful design it would just be lost amongst all the metalwork.

I think I would agree that we ought to be considering a battery on all future EMUs, capable of moving the train a few miles in the event of loss of OLE power. Most of the time trains could coast across the Forth Bridge, as it's only a mile or so and level. Even trains calling at the stations either end could probably coast through if necessary provided the approach viaducts were wired. But the battery would give extra insurance, especially as evacuating passengers from a stranded train half way across the bridge on a dark and stormy night could be tricky.

 

[Lucan]

Is it really impossible to lower the tracks?

 

[twpsaesneg]

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).

Yes, you can, but it falls off if (when) not maintained correctly - it's been used as "secondary insulation" on the GE/LTS lines for years and it isn't ideal. Really nowadays most things want to be "fit and forget".

 

[HSTEd]

Given that there are really very low risks associated with tresspassers on the bridge..... why is a third rail solution verboten here?

Do people really get caught wandering around on the bridge?

 

[Journeyman]

Given that there are really very low risks associated with tresspassers on the bridge..... why is a third rail solution verboten here?

Do people really get caught wandering around on the bridge?

Apparently further third rail electrification is not permitted, unless it's an extension of an existing installation.

 

[HSTEd]

Apparently further third rail electrification is not permitted, unless it's an extension of an existing installation.

The justification given by ORR (which I don't agree with but there we go) is that the risk to personnel and tresspassers is too high for the risk to be as low as reasonably practicable.

This does not really apply in this specific scenario because the bridge is likely to be far better secured than the average piece of railway line, and there are far fewer people around to wander on.

 

[TwistedMentat]

More different stuff to maintain if nothing else. Honestly I think a smallish battery pack would be ideal here. Tie it into a system that automatically towers and raises the pantograph and boom. You've got a relatively simple system that also provides benefits outside of the one application.

Like other gauge restricted areas as mentioned upthread, limp home capability, etc. Hell, you could even use it in areas to close overheads for work but still operate some level of service.

The more I think about it the more it makes sense as something to do right now, Forth bridge or not.

 

[D365]

If you're only using the battery function for one unelectrified section you don't want to have to change the batteries every five years, which means you need a normal sized battery pack in order to maintain a low (e.g. 30%) depth of discharge.

 

[DarloRich]

build a new bridge...................

 

[HSTEd]

In all honesty an immersed tube tunnel crossing is probably the best option.

 

[GRALISTAIR]

The justification given by ORR (which I don't agree with but there we go) is that the risk to personnel and tresspassers is too high for the risk to be as low as reasonably practicable.

This does not really apply in this specific scenario because the bridge is likely to be far better secured than the average piece of railway line, and there are far fewer people around to wander on.

Absolutely

 

[edwin_m]

In all honesty an immersed tube tunnel crossing is probably the best option.

The banks of the Forth rise quite steeply on both sides so an immersed tube would need long lengths of bored tunnel each end, or to be located somewhere the ground is less sloping but the crossing itself is much longer.

 

[DackandBlecker]

The justification given by ORR (which I don't agree with but there we go) is that the risk to personnel and tresspassers is too high for the risk to be as low as reasonably practicable.

This does not really apply in this specific scenario because the bridge is likely to be far better secured than the average piece of railway line, and there are far fewer people around to wander on.

There's been a few trespass incidents in recent times.

Forth Rail Bridge trespasser 28/01 - could more be done to improve security?