Forth Bridge: how would you electrify it?

[gingertom]

Possible? Yes. Easy? No.

Expensive? Absolutely!

 

[furnessvale]

Possible? Yes. Easy? No.

No-one is talking easy. As a former resident engineer supervising the construction of new bridges and the rebuilding of old ones for BR in the 1970s, I have some idea of the difficulties involved.

 

[NotATrainspott]

It introduces additional weight and technology that is likely to fail when needed. Keep it simple with just tried and tested 25kv.

No. Small batteries involve the least amount of additional technology and complexity of any of the suggested options. Second pantographs or 3kV capability or third rail shoes would be entirely useless away from the small sections of track which necessitated them in the first place. Batteries would be useful everywhere, enabling electric trains to do limited self-powered operation anywhere on the network where overhead lines were not active. OHLE will sometimes fail and batteries are the way you can make electric trains able to crawl to the next station, or a level crossing, to simplify evacuation if things can't be put right.

It's not about fitting enough batteries to be able to do DMU diagrams. Instead, it's just enough to get through any common obstacle, like a bridge or tunnel or sensitive track section. That means batteries will become the norm for all electric vehicles. Replacing traditional lead-acid batteries (as are fitted to all passenger rolling stock) with Li-ion cells would get you most of the way there without incurring any extra weight penalty.

 

[snowball]

No. Small batteries involve the least amount of additional technology and complexity of any of the suggested options.

We can't conduct proper discussions about this until we have more information on the problem(s) that need to be solved.

I suggest that the least amount of additional technology is a bit of plastic such as I suggested in #169. But we don't have enough certain information to know whether that or any other proposed solution is necessary or sufficient. Therefore we have people suggesting moving girders that are part of the bridge structure.

 

[najaB]

Small batteries involve the least amount of additional technology and complexity of any of the suggested options.

Sorry, gotta disagree there. 3kV just requires an additional tap off of the transformer and a basic A/B switch. Batteries require a whole lot of charging circuitry and DC/DC voltage changing.

 

[deltic08]

No. Small batteries involve the least amount of additional technology and complexity of any of the suggested options. Second pantographs or 3kV capability or third rail shoes would be entirely useless away from the small sections of track which necessitated them in the first place. Batteries would be useful everywhere, enabling electric trains to do limited self-powered operation anywhere on the network where overhead lines were not active. OHLE will sometimes fail and batteries are the way you can make electric trains able to crawl to the next station, or a level crossing, to simplify evacuation if things can't be put right.

It's not about fitting enough batteries to be able to do DMU diagrams. Instead, it's just enough to get through any common obstacle, like a bridge or tunnel or sensitive track section. That means batteries will become the norm for all electric vehicles. Replacing traditional lead-acid batteries (as are fitted to all passenger rolling stock) with Li-ion cells would get you most of the way there without incurring any extra weight penalty.

How small? Batteries in an electric car are not small to propel only a ton.
How big must batteries be to propel an electric freight loco across the bridge on the few times it would be needed?

 

[najaB]

How big must batteries be to propel an electric freight loco across the bridge on the few times it would be needed?

I'm going to guess that they'd weigh more than a genset and small fuel tank.

 

[AndrewE]

How big must batteries be to propel an electric freight loco across the bridge on the few times it would be needed?

For electric freight maybe you could have a battery loco banker for the bridge which would recharge under the wires either side - but I guess you'd stick with a diesel unless the drive to decarbonise was extreme.

I'm going to guess that they'd weigh more than a genset and small fuel tank.

How would that compare with the weight of a limited clearance pantograph? Presumably each pan has an isolator, but apart from the wire to take the power to the main one, there wouldn't be much extra weight. Certainly no need to maintain a totally different system, although I agree there are wider benefits from having a supply of self-power available. No reason why electric and any other locos can't have a secondary baby pan though.

 

[alangla]

There’s practically no freight over the bridge since SAK opened and of the stuff that does go over like the cement, most goes north via Stirling to avoid the weight limits on this & the Tay bridge. In short, don’t worry about freight

 

[najaB]

How would that compare with the weight of a limited clearance pantograph? Presumably each pan has an isolator, but apart from the wire to take the power to the main one, there wouldn't be much extra weight.

Yes, a second pan would be lighter, but I still think that standard pantos with dead sections of wire in the tightest clearance sections or reduced voltage is more likely for a pure electric solution - due to the consequence of getting it wrong (failing to swap pantographs).

There’s practically no freight over the bridge since SAK opened and of the stuff that does go over like the cement, most goes north via Stirling to avoid the weight limits on this & the Tay bridge. In short, don’t worry about freight

Practically none and none aren't the same thing. The cement empties go back via the bridges, for example. Just realised you were saying the same thing!

 

[snowball]

quite so. If the clearance at the diagonal girders can't be achieved then short earthed sections in the 25kv is the way.

The diagonal girders are at frequent intervals, as the videos in #16 show. What's the minimum practicable distance in which you can go from live to earthed to live? Is a neutral section required between live and earthed to avoid shorting out?

 

[najaB]

The diagonal girders are at frequent intervals, as the videos in #16 show. What's the minimum practicable distance in which you can go from live to earthed to live? Is a neutral section required between live and earthed to avoid shorting out?

I imagine that were this the chosen solution, drivers would be instructed to coast as much as possible and only take power if absolutely necessary. So it should be possible to have the necessary non-conductive (as opposed to earthed) sections as required.

 

[deltic08]

How small? Batteries in an electric car are not small to propel only a ton.
How big must batteries be to propel an electric freight loco across the bridge on the few times it would be needed?

Still no reply from NotATrainspottto my question. I assumed he would have an answer.

 

[AndrewE]

Still no reply from NotATrainspottto my question. I assumed he would have an answer.

[edit: 2 of] the Helsingor - Helsingborg ferries are now battery powered. I believe the original Diesel engines are still in situ for emergencies, surprisingly http://sailwiththecurrent.com/ says

640 batteries of 6.5 kWh are installed on top of each ferry along with two deckhouses for transformers, converters and cooling of the batteries. Cables run from the deckhouses to connecting points at each end of the ship, so that the batteries can be quick-charged – to provide the power of 70 electric cars.

when I would have thought that weight high up was not a good idea. Apparently Li-ion batteries are quite light...

 

[Highlandspring]

I would have thought that weight high up was not a good idea.

Do you seriously think the shipyard naval architects, classification society, flag state safety authority and insurers won’t have given a thought to the affect on stability and seaworthiness? A poster on a speculative thread about the Forth Bridge on a railway forum is pointing out something that hasn’t been considered before? Seriously?

 

[AndrewE]

Do you seriously think the shipyard naval architects, classification society, flag state safety authority and insurers won’t have given a thought to the affect on stability and seaworthiness? A poster on a speculative thread about the Forth Bridge on a railway forum is pointing out something that hasn’t been considered before? Seriously?

The point I was making was that enough batteries to run an 8400T ferry for a crossing are not as heavy as one might expect. I agree that if they were heavy they wouldn't have been allowed to be installed up there.
We were talking about whether a diesel power-pack would be heavier than a battery equivalent and I thought it might illustrate the point (as well as being interesting.)

 

[najaB]

We were talking about whether a diesel power-pack would be heavier than a battery equivalent and I though it might illustrate the point (as well as being interesting.)

It does, and it is.

 

[RichardN]

Looking at the video. Singling the track over the central part of the bridge would increase the distance to the diagonal members. No idea how much of an operational constraint that would be though. (AKA the Hastings line solution, but with a bridge as opposed to narrow tunnels)

EDIT: Just looked at RTT, and it looks far too busy for single track.

 

[Wst71Pa2]

Looking at the video. Singling the track over the central part of the bridge would increase the distance to the diagonal members. No idea how much of an operational constraint that would be though. (AKA the Hastings line solution, but with a bridge as opposed to narrow tunnels)

EDIT: Just looked at RTT, and it looks far too busy for single track.

Yup considering I can sometimes see the taillights of the service in front

 

[AndrewE]

The singling comment reminds me that this thread is another one that is going round in circles, but I don't think that is necessarily a problem. It's only 4 months and 225 posts old but newcomers can't really be expected to go back over it all and, who knows, a fresh mind might even suggest a novel solution!
I agree with Snowball that we have probably said all that we can until proper new info becomes available (and if we're bored with it then just stop watching it.)

 

[najaB]

EDIT: Just looked at RTT, and it looks far too busy for single track.

It's barely got enough capacity as a dual line.

 

[gingertom]

The singling comment reminds me that this thread is another one that is going round in circles, but I don't think that is necessarily a problem. It's only 4 months and 225 posts old but newcomers can't really be expected to go back over it all and, who knows, a fresh mind might even suggest a novel solution!
I agree with Snowball that we have probably said all that we can until proper new info becomes available (and if we're bored with it then just stop watching it.)

ScotGov needs to commit to wiring the Fife circle. Once committed they will appoint engineering consultants to assess the bridge and work out what needs doing and cost the work. I reckon they have shyed away from Fife because the costs of electrifying the bridge are perceived to be high. We won't know the costs until that engineering assessment is done.

 

[Pigeon]

[edit: 2 of] the Helsingor - Helsingborg ferries are now battery powered. I believe the original Diesel engines are still in situ for emergencies, surprisingly http://sailwiththecurrent.com/ says when I would have thought that weight high up was not a good idea. Apparently Li-ion batteries are quite light...

Look at the way they pile containers up and up and up on container ships, to cross actual oceans. It looks unspeakably precarious, but they get away with it most of the time. Thing is just looking at it doesn't give a very good idea of where the weight (and the buoyancy) actually is.

Those batteries are probably a tiny weight in comparison with any decent size ferry, so that isn't much of a problem, but they are a fire hazard which goes up like a rocket and can't be put out. Which you really don't want happening down in the bowels of a ship, and sticking them on the roof is the best place to avoid setting fire to everything else.

 

[NotATrainspott]

How small? Batteries in an electric car are not small to propel only a ton.
How big must batteries be to propel an electric freight loco across the bridge on the few times it would be needed?

Batteries work on multiple units since you can spread the batteries across the entire train. Unlike most other train components, batteries would consist of a very large number of identical small parts, so spreading them around is easy. Therefore I don't see major battery freight operation happening until we see freight vehicles act more like multiple units. Freight is quite a different world than passenger services though, so they won't need to electrify as much as passenger services will. It'll be perfectly possible to fit batteries as standard fit to the standard EMUs ScotRail will use for the majority of passenger services now and in the future.

 

[snookertam]

ScotGov needs to commit to wiring the Fife circle. Once committed they will appoint engineering consultants to assess the bridge and work out what needs doing and cost the work. I reckon they have shyed away from Fife because the costs of electrifying the bridge are perceived to be high. We won't know the costs until that engineering assessment is done.

They just built a new bridge a few miles to the west. Could've taken the opportunity to at least put capacity on it for a double track railway which could have been developed in the future if necessary.

 

[Indigo Soup]

They just built a new bridge a few miles to the west. Could've taken the opportunity to at least put capacity on it for a double track railway which could have been developed in the future if necessary.

They refused to make it big enough for all the motor vehicles that need to go across it. Trains as well would have been right out!

 

[deltic08]

Batteries work on multiple units since you can spread the batteries across the entire train. Unlike most other train components, batteries would consist of a very large number of identical small parts, so spreading them around is easy. Therefore I don't see major battery freight operation happening until we see freight vehicles act more like multiple units. Freight is quite a different world than passenger services though, so they won't need to electrify as much as passenger services will. It'll be perfectly possible to fit batteries as standard fit to the standard EMUs ScotRail will use for the majority of passenger services now and in the future.

The title of this thread is Forth Bridge, how would you electrify it not how you would avoid electrifying it.

 

[najaB]

The title of this thread is Forth Bridge, how would you electrify it not how you would avoid electrifying it.

I suppose that "I wouldn't" is a valid answer to "How would you..?" (though not nearly as much fun!)

 

[Aictos]

Sorry, gotta disagree there. 3kV just requires an additional tap off of the transformer and a basic A/B switch. Batteries require a whole lot of charging circuitry and DC/DC voltage changing.

Umm why 3kV? Is there any particular reason why that system should be used to electrify the Forth Bridge?

I ask this because back in 1955 the British Railways Modernisation Plan actually called for all OHL systems to use the 25 kV AC standard BUT on the Great Eastern for example, parts of the route was instead electrified at 6.25 kV AC due to low clearances under bridges until they found out that it wasn't a issue after all!

So why not use the 6.25 kV AC standard again to electrify routes where 25 kV AC is going to be rather difficult, note I said difficult not impossible.

OR even go one further and look at our Germanic friends and use the 15 kV AC to electrify these routes which as above will be difficult to electrify at 25 kV AC but again not impossible.

 

[najaB]

Umm why 3kV? Is there any particular reason why that system should be used to electrify the Forth Bridge?

No specific reason why 3kV other than that it's in use on the Continent so it should be easier to find ready-to-go equipment. Any voltage reduction reduces the clearance required, and 3kV seems like a happy medium before conductor thickness starts becoming and issue.