Discontinuous electrification schemes should be replaced by continuous electrification

[D365]

Because it is heavy rail they aren't converting it to light rail.

Oh god the pedantry continues.
Alright, light rail VEHICLES then.

It's not really pedantry from tomuk as light rail and heavy rail are built to different standards and the core valley lines are built to heavy rail standards.

Don’t think there’s any point in having a speculative discussion if the OP is going to snap at anyone who makes a valid comment. The whole point of a tram-train is that ’heavy’ trains can continue to use the route, hence why the infrastructure is engineered to mainline standard.

 

[John R]

I have already given evidence.

So I've dug out my paper version (March 22). IW (who's views I respect) has a lot of bad things to say about the concept of discontinuous electrification (DE).

But the article doesn't once mention the Cardiff Valleys project (which is interesting, given his close association with the area). So I don't think there's any evidence in it that DE is the cause of any of the project's over-run to date, more a critique of why it may not be the better long term solution.

 

[Trainbike46]

Having read the article, I think it makes a lot of valid criticism of discontinous electrification as a concept in general. There is a reason TDNS concluded full electrification was best for the vast majority of lines.

However, it also makes a lot (informed) guesses on costs, which is fair enough when real data isn't availabe, but doesn't provide any evidence that for the specific case of the valleys it would have been cheaper to do full electrification - and I assume the welsh government or keolisamey have in fact done an assesment of the advantages and disadvantages of different options, which would be a much better source for any statements about the specific case of the valleys. If you really want to know, you could try getting it through a FOI request

 

[Bald Rick]

The Walmsley article is a perfectly valid source and simply saying you disagree isn't a valid criticism.

it is a valid source, but equally, saying I disagree is equally valid.

I never said that battery electrics were heavier than DMUs

No, you said:

Battery electrics are not lighter than diesels

This might be hair splitting, but it’s much the same thing, no?

I disagree that the maintenance saving issue is minimal when it has historically been one of the main reasons to electrify.

Historically, the reasons to electrify were:
faster & better accelerating trains
cheaper trains (to buy, maintain and in energy costs)
environmental considerations, principally about the local effects of emissions of burning coal and diesel on air quality, but more recently in CO2 terms.

Reduced track maintenance cost barely comes into it, not least because in many electric trains run more quickly and with longer formations than their diesel predecessors, more than offsetting any reduction due to weight. Then there’s the cost of operating and maintains the OLE / power system…

 

[Lawner]

Surely infrastructure maintenance will cost more post-electricification, especially overhead? The savings are in traction maintenance.

RIA say that infrastructure maintenance costs go down, the following can be found in their free to download report at https://www.riagb.org.uk/ria/newsroom/stories/electrification_cost_challenge_report.aspx which says the following:

They are lighter and so do less damage to the track. Although there are additional costs involved in maintaining electrification infrastructure, these are significantly outweighed by the train operating cost savings.

it is a valid source, but equally, saying I disagree is equally valid.

Simply saying you disagree without saying why or giving any evidence to support your disagreement isn't a valid criticism and doesn't mean or add anything.

This might be hair splitting, but it’s much the same thing, no?

You yourself showed that there isn't any meaningful difference in the weight of a DMU and similar BEMU proving my point. BEMU's are also more expensive than EMUs.

Historically, the reasons to electrify were:
faster & better accelerating trains
cheaper trains (to buy, maintain and in energy costs)
environmental considerations, principally about the local effects of emissions of burning coal and diesel on air quality, but more recently in CO2 terms.

Reduced track maintenance cost barely comes into it, not least because in many electric trains run more quickly and with longer formations than their diesel predecessors, more than offsetting any reduction due to weight. Then there’s the cost of operating and maintains the OLE / power system…

Those reasons were also used to justify electrification along side the benefit in track maintenance. The RIA report I linked to above shows that OLE maintenance costs are outweighed by the reduced operating costs of an electric railway.
It is included within this 2009 NR article https://www.networkrailmediacentre.co.uk/news/electrification-plans-a-good-start Which says " Passengers will soon reap the benefits that electrified lines bring – quieter and smoother rides on trains that cause less wear and tear to the track, trains that are more reliable and often faster." Older documents are obviously hard to find online.

 

[Bald Rick]

RIA say that infrastructure maintenance costs go down

No, it doesn’t. Read it again. It says that the savings to Train Operators outweigh the increased cost of maintaining the electrification system, which is very different than saying infrastructure maintenance costs go down.

You yourself showed that there isn't any meaningful difference in the weight of a DMU and similar BEMU proving my point.

I showed that BEMUs are lighter than DMUs. You said they were heavier. Please don’t try to deflect from the point that you were incorrect.

BEMU's are also more expensive than EMUs.

Indeed they are. But compared to the extra cost of electrification, they will make sense in many applications.

I will freely admit that I don’t know exactly how much a typical BEMU costs compared to a straight EMU. But given battery prices in automotive use, and trebling the cost per kWh (rail is always more expensive), a 500kWh battery pack - which could power a 4 car EMU for an hour / 50 miles on a typical cycle, and would weigh about 5 tonnes - would cost around £200k. Double that to allow for extra software etc, and call it £400k

Or put another way, the extra cost of equipping 10 trains with batteries (when designed in from new) is the same as the price of 1 single track km of electrification. Or 100 trains for 10km. You get the picture. Given that battery trains have other benefits too (not least when the power is off in an emergency), you can expect batteries to appear on most new electric trains from now on.

Now these are my calcs, but based on real world data out there (and also based on talking to two of my friends who has actually bought / are buying batteries for rail traction use).

 

[SouthEastBuses]

And what with the many gaps in between the wires, requiring said tram-trains to switch to battery mode temporarily, with those batteries then recharged by the wires when the tram-train returns under them, regular heavy rail electric trains wouldn't be able to run the line even if TfW wanted them to.

On this part I fully agree. This is why I'm always against the idea of discontinuous electrification. If you electrify, you electrify the whole thing, otherwise what's the point? Not to mention that battery electric trains aren't fully sustainable, think about the cost and emissions of producing batteries in the first place!

 

[TT-ONR-NRN]

The whole point of a tram-train is that ’heavy’ trains can continue to use the route, hence why the infrastructure is engineered to mainline standard.

The infrastructure we’re talking about is the overhead wires. What heavy train uses overhead wires with many, many gaps? A bi-mode freight train that’ll go back and forth to and from diesel ten times between Cardiff and the Valleys?

 

[MarkyT]

It's worth pointing out that traction battery and diesel maintenance costs are in totally different leagues. A battery and solid state management system has precisely ZERO moving parts compared to the hundreds of precision mechanical components in a powerful internal combustion engine, so the additional operating costs for having a battery onboard over an electric-only version of the same train can be very small. There is a periodic replacement cost clearly, but careful choice of battery chemistry and attention to how charging is managed can increase the interval dramatically. Slower opportunity charging on discontinuous OHLE should be far less damaging than frequent fast charging in layovers at termini and other stops en route, although some diagrams may need a combination of both. Note diesel engines don't last forever either and need replacing from time to time.

 

[John R]

The infrastructure we’re talking about is the overhead wires. What heavy train uses overhead wires with many, many gaps? A bi-mode freight train that’ll go back and forth to and from diesel ten times between Cardiff and the Valleys?

Not much (= 0) freight up the valleys through Pontypridd these days. Scotland is planning on having bi-mode heavy rail trains on several routes as electrification is rolled out over the next few years, so discontinuous electrification and heavy rail is in no way incompatible.

 

[Lawner]

No, it doesn’t. Read it again. It says that the savings to Train Operators outweigh the increased cost of maintaining the electrification system, which is very different than saying infrastructure maintenance costs go down.

This is clearly inclusive of maintenance costs. This line is also from the report:

• Is lighter, meaning less wear to the track and therefore less maintenance;

The RIA report isn't the only document I've linked to which says this.

I showed that BEMUs are lighter than DMUs. You said they were heavier. Please don’t try to deflect from the point that you were incorrect.

You haven't shown this at all. You gave numbers for a bimode and DMU and failed to give a number for the 777 none of which have you given sources for. The only number I can find for the 777 is 99t for the EMU variant which is unsourced from the wikipedia page.

The price comparison of a battery to STK isn't very useful as discontinuous electrification isn't cheaper than full electrification so the cost of the battery is purely additional cost. Batteries also need to be replaced roughly every seven years, so you're looking at another several hundred thousand added cost over the the lifetime of the train. Using battery trains also adds cost to the project as battery performance has to be modelled to make sure that the battery trains will reliably have enough power over the dead sections of railway.

It's worth pointing out that traction battery and diesel maintenance costs are in totally different leagues. A battery and solid state management system has precisely ZERO moving parts compared to the hundreds of precision mechanical components in a powerful internal combustion engine, so the additional operating costs for having a battery onboard over an electric-only version of the same train can be very small. There is a periodic replacement cost clearly, but careful choice of battery chemistry and attention to how charging is managed can increase the interval dramatically. Slower opportunity charging on discontinuous OHLE should be far less damaging than frequent fast charging in layovers at termini and other stops en route, although some diagrams may need a combination of both. Note diesel engines don't last forever either and need replacing from time to time.

The metro does plan to use fast chargers and I understand that there are concerns over how much they will shorten the useful life of the battery.

The infrastructure we’re talking about is the overhead wires. What heavy train uses overhead wires with many, many gaps? A bi-mode freight train that’ll go back and forth to and from diesel ten times between Cardiff and the Valleys?

The class 756. Electric freight isn't compatible with discontinuous electrification, batteries aren't adequate to provide power to freight trains outside of slow speed movements into and out of their origin/destination.

 

[Class 317]

Discontinuous electrification if very likely for a lot of secondary routes with no freight.

Stadler do a Flirt AKKU operating and on order in Germany which is a battery AC overhead bi mode. Range 100 to 150km on battery, top speed 160kmh and a charge time of 15 mins from overheads.

Batteries have lifetimes of 10 plus years in first use and then retain at least half thier value for reuse in a less demanding secondary roles for at least another 10 years.

Also when batteries are replaced the technology will be better offering likely greater range, lower costs, lower weight etc.

Capital costs will be much lower as economies of scale lower battery train costs.

 

[Bald Rick]

The price comparison of a battery to STK isn't very useful as discontinuous electrification isn't cheaper than full electrification

Id be interested to see how you have reached that conclusion. Are you suggesting that discontinuous electrification is more expensive than full electrification? Ie installing less kit costs more?

Re battery life - it’s looking increasingly likely that Lithium titanate batteries won’t ever need replacing in the lifecycle of an EMU. Source: a friend who is buying them…

== Doublepost prevention - post automatically merged: 11 Apr 2023 ==

You haven't shown this at all. You gave numbers for a bimode and DMU and failed to give a number for the 777 none of which have you given sources for. The only number I can find for the 777 is 99t for the EMU variant which is unsourced from the wikipedia page.

I’ll leave it for others to judge. But I’m certain that BEMUs are / will be lighter than DMUs.

This is clearly inclusive of maintenance costs.

Yes, rolling stock maintenance costs.

Having been responsible and a budget holder for track maintenance in the past, I can confirm that the changes to track maintenance costs from electrification are there on paper…. But not on steel, ballast and concrete. It doesn’t reduce inspection frequencies, nor tamping frequencies or the rate of track faults. The cost changes are essentially negligible in the whole scheme of things, and an electrification business case (Which I have also been responsible for writing). Again I will leave to for others to judge whether they believe me or not.

 

[Halish Railway]

I'd put forward the Harrogate Loop as a suitable candidate for discontinuous electrification. Its traffic is almost entirely self-contained with no freight, the exception being the already bi-mode Azuma services from London and there is a need for fast-accelerating EMUs on parts of the route with steep gradients and frequent stops.

However, there are many challenges to full electrification - Long and wet tunnels and a lot of viaducts, the one of which being the very scenic Knaresborough, with a discontinuous electrification approach not impacting the spectacle of the viaduct and the station. That being said this is counteracted by areas that ought to be very simple to electrify, such as the section between Knaresborough Tunnel and York. With that being said I could see it being difficult to justify complete electrification of the route given the likely high costs involved, but fairly easy to justify a discontinuous approach.

(I'm sure a lot of people remember the idea to use old Tube trains on the Harrogate loop with complete third rail electrification).

 

[Class 317]

I'd put forward the Harrogate Loop as a suitable candidate for discontinuous electrification. Its traffic is almost entirely self-contained with no freight, the exception being the already bi-mode Azuma services from London and there is a need for fast-accelerating EMUs on parts of the route with steep gradients and frequent stops.

However, there are many challenges to full electrification - Long and wet tunnels and a lot of viaducts, the one of which being the very scenic Knaresborough, with a discontinuous electrification approach not impacting the spectacle of the viaduct and the station. That being said this is counteracted by areas that ought to be very simple to electrify, such as the section between Knaresborough Tunnel and York. With that being said I could see it being difficult to justify complete electrification of the route given the likely high costs involved, but fairly easy to justify a discontinuous approach.

(I'm sure a lot of people remember the idea to use old Tube trains on the Harrogate loop with complete third rail electrification).

Or just use Stadler Flirt AKKU battery overhead bi modes or similar with enough range to operate via charging at York and Leeds only.

Maybe electrify Harrogate station for trains turning around their.

Far lower cost overall.

 

[Trainbike46]

Discontinuous electrification if very likely for a lot of secondary routes with no freight.

Stadler do a Flirt AKKU operating and on order in Germany which is a battery AC overhead bi mode. Range 100 to 150km on battery, top speed 160kmh and a charge time of 15 mins from overheads.

Batteries have lifetimes of 10 plus years in first use and then retain at least half thier value for reuse in a less demanding secondary roles for at least another 10 years.

Also when batteries are replaced the technology will be better offering likely greater range, lower costs, lower weight etc.

Capital costs will be much lower as economies of scale lower battery train costs.

the 756 is effectively a UK version of the FLIRT AKKU (albeit with a single diesel engine as well)

As the FLIRT is a modular concept, it can be adapted to meet different needs. The same will apply to the flirt akku

 

[Lawner]

Id be interested to see how you have reached that conclusion. Are you suggesting that discontinuous electrification is more expensive than full electrification? Ie installing less kit costs more?

Re battery life - it’s looking increasingly likely that Lithium titanate batteries won’t ever need replacing in the lifecycle of an EMU. Source: a friend who is buying them…

== Doublepost prevention - post automatically merged: 11 Apr 2023 ==



I’ll leave it for others to judge. But I’m certain that BEMUs are / will be lighter than DMUs.



Yes, rolling stock maintenance costs.

Having been responsible and a budget holder for track maintenance in the past, I can confirm that the changes to track maintenance costs from electrification are there on paper…. But not on steel, ballast and concrete. It doesn’t reduce inspection frequencies, nor tamping frequencies or the rate of track faults. The cost changes are essentially negligible in the whole scheme of things, and an electrification business case (Which I have also been responsible for writing). Again I will leave to for others to judge whether they believe me or not.

I'm not aware of any rolling stock being fitted with lithium titanate batteries, they're also less energy dense than the current batteries so again add weight and need more space.

The passage specifically mentions track maintenance, your simply wanting it to say something it doesn't.

Installing discontinuous requires the installation of expensive power supply feeder cables to continue the power supply to the OLE on the other side of the gap. Walmsley puts the cost of this at 10 times the cost of continuous OLE. The preferred solution in discontinuous electrification is to use permanently earthed OLE, so all the equipment is installed but isn't energised. This was done so that only mechanical clearances need to be achieved without need to consider electrical clearances. The problem with this is that since the electrification of Cardiff intersection bridge it's unnecessary. Deployment of insulating coating and surge arrestors allows bridges with tight clearances to be electrified without significant works to the bridge.

There's no reason to believe what you say, non of its backed up and multiple industry sources contradict you, you've repeatedly only tried to argue pointless pedantry which does nothing to argue against the issue you originally took exception to.

 

[Halish Railway]

Installing discontinuous requires the installation of expensive power supply feeder cables to continue the power supply to the OLE on the other side of the gap. Walmsley puts the cost of this at 10 times the cost of continuous OLE.

Could you say the same about regular electrification as evidenced by the 'Great Extension Lead' from Heyrod to Manchester Victoria East (Which is about to be replaced by electrification that will be powered from the Heyrod feeder station, as well as the feeder cables that will be installed from a point on the Reading to Basingstoke line to the existing electrification at Reading West, both of these examples being of how feeder cables running along non-electrified lines are used to boost power supply in other areas.

 

[SouthEastBuses]

I'd put forward the Harrogate Loop as a suitable candidate for discontinuous electrification. Its traffic is almost entirely self-contained with no freight, the exception being the already bi-mode Azuma services from London and there is a need for fast-accelerating EMUs on parts of the route with steep gradients and frequent stops.

However, there are many challenges to full electrification - Long and wet tunnels and a lot of viaducts, the one of which being the very scenic Knaresborough, with a discontinuous electrification approach not impacting the spectacle of the viaduct and the station. That being said this is counteracted by areas that ought to be very simple to electrify, such as the section between Knaresborough Tunnel and York. With that being said I could see it being difficult to justify complete electrification of the route given the likely high costs involved, but fairly easy to justify a discontinuous approach.

(I'm sure a lot of people remember the idea to use old Tube trains on the Harrogate loop with complete third rail electrification).

Regarding Knaresborough, the ECML Royal Border Bridge shows that if you use the correct type of catenary, then electrifying through listed structures isn't an issue.

 

[Bald Rick]

I'm not aware of any rolling stock being fitted with lithium titanate batteries,

Class 93 for starters

The passage specifically mentions track maintenance, your simply wanting it to say something it doesn't.

I’m not saying it doesn’t. I’m just saying that in my experience of maintaining track and doing electrification business cases, reduced track maintenance due to electrification barely registers.

Installing discontinuous requires the installation of expensive power supply feeder cables to continue the power supply to the OLE on the other side of the gap. Walmsley puts the cost of this at 10 times the cost of continuous OLE.

Walmsley’s wrong on this, mostly. He sometimes is (and we have spoken on that, and he does hold his hand up when he is !)

He’ll be right for short gaps, especially where there is mechanical clearance. But there isn’t always mechanical clearance. Nevertheless, Battery trains are not really about short gaps to clear dead sections under a bridge. You only need a small battery for that. Battery trains are about big gaps, measured in tens of kilometres, and for those you may not need a feeder cable to bridge it. Particularly for a ‘gap’ at the end of a branch line.

There's no reason to believe what you say, non of its backed up and multiple industry sources contradict you, you've repeatedly only tried to argue pointless pedantry which does nothing to argue against the issue you originally took exception to.

Feel free to disagree.

Signed, an industry source (who has actually done some of this stuff).

 

[D365]

Class 777s use LTi batteries also.

 

[tomuk]

He’ll be right for short gaps, especially where there is mechanical clearance. But there isn’t always mechanical clearance. Nevertheless, Battery trains are not really about short gaps to clear dead sections under a bridge. You only need a small battery for that. Battery trains are about big gaps, measured in tens of kilometres, and for those you may not need a feeder cable to bridge it. Particularly for a ‘gap’ at the end of a branch line.

I think the issue is what you define as discontinuous electrification. The Valleys will discontinuous electrification with earthed catenary under low bridges and parallel feeds cables where the clearance is too low for 25kv. That is a different philosophy to say running the whole of the Windemere branch on battery from Oxonholme.

 

[Nottingham59]

Can we agree that for some lines, full electrification is financially justified even if it does mean rebuilding all the overbridges and lowering tunnel floors? From the original case for MML electrification, I believe this point is reached when there are 8tph, maybe 6tph, each way during the normal day. But this may have changed since then with the increased costs of both electrification and diesel fuel.

(As an aside, I've not seen any business cases for the latest MML scheme(s), from which I assume that with 4 bimodes per hour on the MML, electrifying north of Kettering is not justified in purely financial terms - or else NR would have been boasting about it. Which makes MML electrification a political project, rather than a financial investment.)

On some other services, it is obvious that the decarbonised future is going to be battery. Especially minor branch lines with 1tph or less and no freight. A BEMU with just a few miles range would be able to do Matlock-Nottingham (after MML wiring), recharging between Nottingham and Ambergate. The Harrogate line seems to be a contender too. There are many others.

The interesting question then becomes how to decide between full electrification and battery operation for a given line? Ian Walmsley seems to suggest that full electrification is worth it for Cardiff-Swansea. But his argument makes too many assumptions about timetables and N-2 running to convince me.

== ==
The issue of shortish neutral sections under low bridges is separate. As I understand it, there are in-line neutral sections on existing electrified mainlines. I assume that whatever arrangements they have to avoid flashovers at 125mph would work on longer in-line neutral sections under a bridge. I don't believe Walmsley's contention that this means a train would have to isolate its pan 5km before such a bridge. (Pehaps someone could explain to me why he says this? And what procedures are currently used to cross neutral sections on the ECML and WCML?)

I suggest that all future EMUs orders should specify at least a small traction battery - just 1km range at low speed would be enough to ensure the train never got stranded under a low bridge. And not rebuilding bridges can easily save a quarter of the cost of full electrification.

 

[MarkyT]

I suggest that all future EMUs orders should specify at least a small traction battery - just 1km range at low speed would be enough to ensure the train never got stranded under a low bridge. And not rebuilding bridges can easily save a quarter of the cost of full electrification.

Fully agree with that but the range should be rather more than 1km so short isolations and diversions can be handled as well as depot movements. Once entire fleets are so equipped, then some simplification of conductor rails through junction areas can be considered in 3rd rail areas, as gapping risk is removed. I've heard Cardiff is using a similar approach around complex layouts for OHLE, with gaps in wiring rather than earthed conductors and an automatic pan control system activated by digital Eurobalises.

 

[Lawner]

Class 93 for starters



I’m not saying it doesn’t. I’m just saying that in my experience of maintaining track and doing electrification business cases, reduced track maintenance due to electrification barely registers.



Walmsley’s wrong on this, mostly. He sometimes is (and we have spoken on that, and he does hold his hand up when he is !)

He’ll be right for short gaps, especially where there is mechanical clearance. But there isn’t always mechanical clearance. Nevertheless, Battery trains are not really about short gaps to clear dead sections under a bridge. You only need a small battery for that. Battery trains are about big gaps, measured in tens of kilometres, and for those you may not need a feeder cable to bridge it. Particularly for a ‘gap’ at the end of a branch line.




Feel free to disagree.

Signed, an industry source (who has actually done some of this stuff).

What is your basis for saying Walmsley is wrong? Feeder cable is very expensive, its big and heavy due to the large amount of insulation and installing it isn't cheap. Discontinous electrification wasn't about big tens of kilometers long gaps, the biggest gap on CVL is barely 4km. It was brought in from what I saw as a knee jerk reaction to the problems on GWEP by trying to save costs through not wiring the parts that were considered hard.

I've spent most of my working life on electrification.

The issue of shortish neutral sections under low bridges is separate. As I understand it, there are in-line neutral sections on existing electrified mainlines. I assume that whatever arrangements they have to avoid flashovers at 125mph would work on longer in-line neutral sections under a bridge. I don't believe Walmsley's contention that this means a train would have to isolate its pan 5km before such a bridge. (Pehaps someone could explain to me why he says this? And what procedures are currently used to cross neutral sections on the ECML and WCMLWCML

Walmsley in this section is writing about sections which are not wired where you need to able to safely raise and lower the pantograph the problem here is the train may have to travel some distance to be able to do this if the bridge is in a complex area and the distance of simple railway needed to be able to safely raise the pan increases with speed.
I think you're thinking of neutral sections which are used to seperate different electrical phases. In these neutral sections the train passes over an APC magnet which opens a circuit breaker stopping the pantograph from drawing power this let's the pan switch between the live wire to the earthed wire in the middle of the neutral section without drawing an arc, the train then passes onto the wire carrying the new phase where another magnet closes the circuit breaker. The pan stays up throughout this process. Designers are limited in where they can place neutral sections, they're ideally in places where there's nothing complicated nearby, no signals, nothing to prevent a train from safely coasting through.
Section insulators also exist which are installed in-line with the wire but their impact on the dynamic performance is not good, so are only used where speeds are low, they do experience arcing. If you want to read about these things I suggest Garry Keenor's book which is linked in the resource thread at the top of the infrastructure forum.

And not rebuilding bridges can easily save a quarter of the cost of full electrification.

There's been a lot of work in reducing the cost of electrification which has meant that far fewer bridges need to be rebuilt, have track lowers etc.

 

[Trainbike46]

What is your basis for saying Walmsley is wrong? Feeder cable is very expensive, its big and heavy due to the large amount of insulation and installing it isn't cheap. Discontinous electrification wasn't about big tens of kilometers long gaps, the biggest gap on CVL is barely 4km. It was brought in from what I saw as a knee jerk reaction to the problems on GWEP by trying to save costs through not wiring the parts that were considered hard.

I've spent most of my working life on electrification.

Walmsley in this section is writing about sections which are not wired where you need to able to safely raise and lower the pantograph the problem here is the train may have to travel some distance to be able to do this if the bridge is in a complex area and the distance of simple railway needed to be able to safely raise the pan increases with speed.
I think you're thinking of neutral sections which are used to seperate different electrical phases. In these neutral sections the train passes over an APC magnet which opens a circuit breaker stopping the pantograph from drawing power this let's the pan switch between the live wire to the earthed wire in the middle of the neutral section without drawing an arc, the train then passes onto the wire carrying the new phase where another magnet closes the circuit breaker. The pan stays up throughout this process. Designers are limited in where they can place neutral sections, they're ideally in places where there's nothing complicated nearby, no signals, nothing to prevent a train from safely coasting through.
Section insulators also exist which are installed in-line with the wire but their impact on the dynamic performance is not good, so are only used where speeds are low, they do experience arcing. If you want to read about these things I suggest Garry Keenor's book which is linked in the resource thread at the top of the infrastructure forum.



There's been a lot of work in reducing the cost of electrification which has meant that far fewer bridges need to be rebuilt, have track lowers etc.

Bald Rick is one of the most knowledgeable people on this forum. If Bald Rick says Walmsley is mistaken, then Walmsley is in fact mistaken

 

[Nottingham59]

I think you're thinking of neutral sections which are used to seperate different electrical phases. In these neutral sections the train passes over an APC magnet which opens a circuit breaker stopping the pantograph from drawing power this let's the pan switch between the live wire to the earthed wire in the middle of the neutral section without drawing an arc, the train then passes onto the wire carrying the new phase where another magnet closes the circuit breaker. The pan stays up throughout this process. Designers are limited in where they can place neutral sections, they're ideally in places where there's nothing complicated nearby, no signals, nothing to prevent a train from safely coasting through.

That's what I meant. I understand they use PTFE-coated non-conducting contact rods in neutral sections to provide the sliding characteristics needed.

In many cases a low over-bridge will not have clearance to allow sufficient gap between the pantograph and the structure, and between the pantograph and the vehicle. But a non-conducting contact wire or rod that could push the pan down enough to achieve mechanical clearance would be enough not to have to rebuild the bridge.

Provided that all electric stock on the line had a traction battery with sufficient range to self-rescue a stranded train, I still don't see why neutral sections longer than two train lengths cannot be used to save the cost of rebuilding low bridges when appropriate to do so.

 

[John R]

What is your basis for saying Walmsley is wrong?

There might be a few hints here:-

Signed, an industry source (who has actually done some of this stuff).

Having been responsible and a budget holder for track maintenance in the past, I can confirm that the changes to track maintenance costs from electrification are there on paper…. But not on steel, ballast and concrete. It doesn’t reduce inspection frequencies, nor tamping frequencies or the rate of track faults. The cost changes are essentially negligible in the whole scheme of things,

and an electrification business case (Which I have also been responsible for writing).

Sounds as though Bald Rick has a lot of experience from which to make his statements. As an observer of this particular discussion, I'm wondering if you have anything similar on your CV, or, like me, are just an lay observer?

Oh, and a reminder that IW didn't mention the Cardiff Valleys discontinuous electrification once in the article you cited as evidence. As the only such scheme well under way, I find it curious that he didn't reference it at all, as it would have been the obvious thing to do.

 

[eldomtom2]

Sounds as though Bald Rick has a lot of experience from which to make his statements.

Asking people to show their work and not coast on their alleged reputation is generally a sensible thing to do.

 

[GRALISTAIR]

Bald Rick is one of the most knowledgeable people on this forum. If Bald Rick says Walmsley is mistaken, then Walmsley is in fact mistaken

We all have our strengths and proven fields. Ian Walmsley has his, but so does Bald Rick.

In this instance I would back Bald Rick.