Pros and cons of different electrification schemes (e.g. 3rd rail / OHLE / battery power)

[Mikey C]

Possible 'North East to South East Chord' for through running to Strood (rather than via Gravesend). More strictly for a new area of housing part way along the branch rather than the Isle of Grain itself.

(My user name gives a clue to my interest.)

Surely you use a Tardis to get around anyway

Why would passengers in Hoo want to run through to Strood, wouldn't most of the demand be towards London (whether via Dartford or HS1)?

 

[O L Leigh]

As a climate researcher, I am often called upon to look at things on the "system" level.

Is that on a professional basis or as a personal interest?

I don't mean this to sound derogatory, but it might be helpful in your career/interest to do some research on engineering and the regulatory environment also. This would help enormously to inform what you do and might even give you some insights that other people might have missed. Unfortunately, I have to agree with others that some of your schemes are, although clearly well-intentioned, not necessarily realistic, practical or affordable. Electrification is always an expensive business (it may even be cheaper to build an entirely new electrified line than have to upgrade an existing one) and 25kV AC OLE definitely has it's place.

I am still curious to know whether the problems with the GWML scheme has artificially inflated the cost of future OLE schemes, and that the engineering and management lessons have been learned in order to make future schemes more affordable. In fact, I'm a bit concerned that these boys and girls don't yet appear to have been deployed to any other scheme yet. If we leave it much longer we could be facing a repeat of having to find the start-up costs all over again.

Trip out all the non-essentials. If it's a hot day, pop some windows open if your unit has them. If not, enjoy the temporary sauna. As long as the 'phantom draw' on the batteries isn't too high, you will be fine to resume when the line is clear. Electric cars can sit on drives unplugged for many weeks and still have plenty of charge, so an BEMU with significantly more battery capacity just needing to power it's radios, emergency LED lighting and compressors should be fine for a few hours.

Plus, I can't see the initial areas for BEMU's being anywhere but metro systems, so you should never be too far away from a station. Merseyrail will have at least one 777 fitted with plans for more if the trial proves successful and the Skem extension goes ahead, and that is the ideal location for this type of kit.

BEMUs only being used in metro areas is an assumption, and it's by no means a given. They are potentially just as suitable for some rural routes where the previous station could be quite far away. At the moment no-one knows.

Likewise, no-one yet knows quite what the capabilities of these trains will be or what working arrangements will be put in place to aid them in the event of a problem. All I will do is reiterate that it is rare for a train to go back to the previous station, and is something that I have never been asked to do. Until we actually see one and put it into real revenue-earning service it all remains speculative.

 

[HSTEd]

Is that on a professional basis or as a personal interest?

Well the EPSRC gives me quite a lot of money each month?

I don't mean this to sound derogatory, but it might be helpful in your career/interest to do some research on engineering and the regulatory environment also. This would help enormously to inform what you do and might even give you some insights that other people might have missed.

I am well aware of the travails of working in a safety case industry.
Indeed one of the themes of my research is how a narrow safety case culture can screw society over because it means that safety is optimised within an industry individually, rather than being optimised across society as a whole.

Unfortunately, I have to agree with others that some of your schemes are, although clearly well-intentioned, not necessarily realistic, practical or affordable.

Unfortunately one of the other themes of my research is struggling with experts who, having lived their entire career with one way of doing things, struggle to adapt to a situation that is radically different to the one in which their conceptions of what is and isn't practical developed.

Primarily this concerns the nuclear industry and it's ancillaries - people have spent so long optimising for "minimum electricity cost" or "best reactor" that they struggle to concieve that any other optimisation criteria can exist - or that they might lead to different results.
Which is a major problem if we truly are planning to radically change the way our energy, transport and wider societal systems function.
(Traditionally we have asked "how can we make nuclear electricity as cheap as possible?" whereas now we want to ask "how do we get lots of nuclear electricity as fast as possible?" which are fundamentally different questions that can, and probably do, give very different answers)

I am still curious to know whether the problems with the GWML scheme has artificially inflated the cost of future OLE schemes, and that the engineering and management lessons have been learned in order to make future schemes more affordable. In fact, I'm a bit concerned that these boys and girls don't yet appear to have been deployed to any other scheme yet. If we leave it much longer we could be facing a repeat of having to find the start-up costs all over again.

Well with a laundry list of failings on that scheme, I have to question whether those teams are particularly useful moving forwards.
Other 25kV schemes, whilst extraordinarily expensive, actually managed to complete ratehr closer to their defined scope, time and budget.

 

[O L Leigh]

Well with a laundry list of failings on that scheme, I have to question whether those teams are particularly useful moving forwards.
Other 25kV schemes, whilst extraordinarily expensive, actually managed to complete ratehr closer to their defined scope, time and budget.

I was actually meaning the boys and girls with the spanners, not the ones with the clipboards. These people are trained for OLE work, but if they are not utilised we shall lose them and their expertise. This has happened before and the recruitment and training of these folk is a financial penalty that hopefully we won't have to pay twice.

Part of the societal issues that the railways face is the increasing view among the population that something is always someone's fault. Little Johnny generally doesn't get killed because he's titting about on the railways but because there were issues with a crossing gate or some signage was obscured or some other failing attributed to the railways (because, lets face it, Little Johnny is such an angel and would never ignore what his Mum and Dad tell him). As such, and in common with every other industry and area of life, the railway has to mind it's own house to ensure risks are minimised. This means being told to mind the gap, stand behind the yellow line, read the safety posters, etc, etc, because we cannot assume that the public has the sense it ought to have to work these things out for itself. We cannot be negligent in our duties and responsibilities towards society, including making good decisions about how to move the railway network forwards into the future.

And this is what this whole RSSB consultation is about. How can the industry continue to use CRE as an electrification system when the legislative and regulatory framework precludes it? It may be that the consultation throws up a whizzer new idea that will permit this, or it may be that the assembled minds conclude that there is no safe way to continue with it. It's purpose is not to come up with a third system. But then, this isn't simply a reactionary position based on traditional thinking, as the "one way of thinking" would just have said stuff it lets have the juice rails down. It may frustrate you, but the answer is not to come up with a whole new electrification system as the costs and practicalities of this preclude it to a far greater degree than simply plumping for 25kV AC OLE. As it stands we have a dual-voltage network with a very large stud of dual-voltage capable rolling stock.

 

[Domh245]

Well with a laundry list of failings on that scheme, I have to question whether those teams are particularly useful moving forwards.

"those who've made the biggest mistakes have learned the most" - or something to that effect

Also worth noting that in no small part that 'laundry list of failings' was done to a poor/shifting specification (from everybody's favourite govt department) and also the first major new build scheme in over a decade. It's quite an interesting approach to criticise GWEP for getting things wrong, and then go on to suggest new technologies should be used instead. HOPS ring a bell?

I was actually meaning the boys and girls with the spanners, not the ones with the clipboards. These people are trained for OLE work, but if they are not utilised we shall lose them and their expertise. This has happened before and the recruitment and training of these folk is a financial penalty that hopefully we won't have to pay twice.

Isn't it the case that quite a lot of them were simply brought over from Italy/Spain to do the work and have then subsequently just gone home again? That isn't to say however that the rationale behind that isn't bad, indeed a proper rolling scheme means that it makes sense to train locally rather than keep bringing expertise over.

 

[Bald Rick]

I am still curious to know whether the problems with the GWML scheme has artificially inflated the cost of future OLE schemes, and that the engineering and management lessons have been learned in order to make future schemes more affordable. In fact, I'm a bit concerned that these boys and girls don't yet appear to have been deployed to any other scheme yet. If we leave it much longer we could be facing a repeat of having to find the start-up costs all over again.

The problems were by no means confined to the GWML project. They occurred on almost every electrification project. Edinburgh-Glasgow was certainly more expensive than GWML on a normalised basis, as were many other jobs. The issue is that GWML was the first to go wrong, so took the flak first.

But yes, the lessons have been captured, and applied. Number 1 (on my list) is don’t issue an estimate or schedule until you are reasonably sure about it. Number 2 is don’t commit to projects where an ‘expert’ outside your organisation has decided how much it will cost. Number 3 is once you have a plan, don’t be pressured to change it.

Well with a laundry list of failings on that scheme, I have to question whether those teams are particularly useful moving forwards.

I’m afraid this is a misunderstanding regarding how electrification programmes are structured. I have posted on this before. Broadly, each electrification is formed of several projects:

Civils - altering bridges, planting concrete foundations, reprofiling cuttings and embankments
Property - station alterations, e.g. altering canopies and other buildings for the OLE
Signalling - any type of work but most often moving signals, changes to train detection
Telecoms & control - the SCADA system
Track - track lowering, and layout alterations to simplify the wiring
Power - grid connections
Electrification - masts, small part steel, wiring, switching, bonding.

Of these, all but the last are typically contracted to, and managed by, the teams and people that usually do that sort of work, and are doing it all the time. This usually accounts for well over half the programme costs.

It is only the electrification itself that needs specialist resource. Much is brought in from abroad - I’ve mentioned before that much of the recent Scottish electrification was built by Italians, who have long since returned home and working on projects there. However I’m sure they would be able to come back if required. Many of the people who have built some of the recent stuff are now maintaining it, and that has to be the way forward.

The most difficult part is co-ordinating and contracting all the different disciplines, and in particular how to get the design right up front within that. That is a skill of programme management, and not specific to electrification. It comes in handy for building new railways, which is of course where many of these people are now.

 

[NotATrainspott]

It might be slightly off-topic, but as a driver I’m a little nervous about some of the claims for battery units. Given that you’re relying on battery power for all systems, including A/C where fitted, I’d also like a little comfort about how long the charge can last off the juice as much as how far it can travel. The instance that I’m concerned about being a stranding due to, say, signal failure or an obstruction on the line.

I don’t know where Vivarail have been conducting their tests, but the only battery electric trial that I’m aware of happening on the mainline under mainline running conditions was carried out using a Cl379 on the Manningtree branch. As well as that train performed, it was never away from the OLE at any time and could simply raise it’s pan if it ran into trouble. What happens if you’re off the juice halfway down the Marshlink and you’ve got to wait a couple of hours while our orange friends get to and deal with a fallen mature tree blocking the line?

Tesla has added a 'camp mode' function to its cars which allows the air conditioning or heating to run while the vehicle is parked. It's probably a good analogy to a stopped train running hotel power. Moving a car or a train uses a huge amount more power than heating or cooling it. Unlike internal combustion, a battery vehicle won't waste a lot of energy idling just to run the 'hotel' services since the battery can efficiently deliver low levels of power. It shouldn't really be a problem.

Remember that the batteries we're talking about fitting to trains to make them run off the grid are a very different beast than the batteries that have typically been fitted to trains. Traction batteries will hold orders of magnitude more charge since they'll use the most modern battery chemistries. Traditional lead-acid batteries have been around for a long time and they're hardly the state of the art.

Range anxiety won't be a thing when battery trains are used in service. The operator will work out what the 99.9% percentile energy usage would be on a route, then add some buffer on top, and make that the minimum battery capacity for any train to run the service. I expect it'll be easier to have a fleet with a consistently large battery size than to have microfleets of varying battery size for specific routes, so most services will have space capacity beyond that.

The good thing about batteries is that they can end up being fitted as standard to any EMU. The New Tube for London trains will have batteries so they can crawl to the next station even in a power cut. The cost savings to NR through allowing EMUs to run short distances on battery power will be immense and more than enough to cover the cost of fitting them as standard.

750v D.C. OLE is all very well for trams that weigh 40t, travel at 50mph max and draw at most half a megawatt for half a minute at most. It is absolutely not suited for trains that weigh 10 times as much, with 10 times the power, travelling at 70mph, as would be the case at Uckfield. Clearances would need to be the same as well - it’s the pantograph that triggers most clearance issues, not the wire.

Of course, there's the tram OHLE side and then there's the 750V DC side of that. Tram OHLE is deliberately designed to be cheaper and better suited for urban areas and simple environments. Powering a mainline train off that sort of voltage is definitely possible but it seems that multiple pantographs become required to provide enough conductivity for the amount of current. I think the Eurostar 374s have to put up most of their pantographs when they run on the Dutch 1500V DC OHLE network. However, as you say, it's the total power consumption of the train that matters as much as the electrical supply method.

 

[Bald Rick]

Of course, there's the tram OHLE side and then there's the 750V DC side of that. Tram OHLE is deliberately designed to be cheaper and better suited for urban areas and simple environments. Powering a mainline train off that sort of voltage is definitely possible but it seems that multiple pantographs become required to provide enough conductivity for the amount of current. I think the Eurostar 374s have to put up most of their pantographs when they run on the Dutch 1500V DC OHLE network. However, as you say, it's the total power consumption of the train that matters as much as the electrical supply method.

To put it in context, a 12 car Class 700 on AC draws roughly as much power through its 2 pantographs as 4 x Class 76s would do through 8 pantographs (and a much thicker contact wire, requiring much more metal to hold it up).

 

[AlastairFraser]

It’s a possibility.

Oh,OK. I had no idea. Could you provide links to show where this has been discussed recently?

 

[A0wen]

Number 1 (on my list) is don’t issue an estimate or schedule until you are reasonably sure about it.

As an project manager - in the IT field - that is my first statement to any and every "eager beaver" new junior project manager.

Yes, you will have stakeholders and project owners demanding costs and timelines that they can go and sell to important people - and that's all very interesting, but the moment you give a suggestion of a cost or timeline you're a hostage to fortune.

The problem, to be fair, is too many organisations go straight to full business case and include the spec and design costs in that business case - which is where the problem begins. What *should* happen is design and spec work delivered as a scoping / sunk cost. And change control needs to be rigourously enforced - it doesn't matter how "easy" it might appear to add a little bit here and a new feature there - they all cost and need to be agreed and accounted for.

Too often project teams are blamed for cost and time over-runs but the reality is most of the time the project owner and stakeholders are the root cause of the problems.

 

[AlastairFraser]

Possible 'North East to South East Chord' for through running to Strood (rather than via Gravesend). More strictly for a new area of housing part way along the branch rather than the Isle of Grain itself.

(My user name gives a clue to my interest.)

Well, I suppose if new housing was built around Hoo, it might just about justify the provision of passenger services on the Isle of Grain branch but,apart from Hoo, the other settlements seem to be relatively close to Higham(Cliffe/Cliffe Woods)/already served by reasonably frequent buses to Chatham and Gravesend

 

[big all]

Of course in both those cases it was one company and the electrocutions occurred from OHLE not 3rd rail.

There remains a problem in that the 3rd rail doesn't just electrocute humans, it does a fair bit to wildlife which doesn't tend to respect trespass laws. Yes, I know OHLE can take out birds - I've seen a pigeon lose a fight with the OHLE, but that's much less common than foxes etc on 3rd rail - and part of the risk there is when the power gets knocked out when Foxy Woxy wanders over the lines, bringing all trains to a halt.

As a driver man and boy there was virtually no dead creatures along the line indeed you may see an animal on a monthly basis at most?

Now some, like pheasants, would spar with trains in places like Balcombe station to the Ouse Valley viaduct but these were flying debris but would of course be food for foxes and to be honest seeing a dead fox was a perhaps few year apart event so they must have learnt and pass on dangers to offspring so avoiding the conductor rail?

Indeed, creatures like badgers had gaps in the conductor rail cut on known runs on the Redhill - Tonbridge electrification of the 90s because they will stubbornly follow their "run" even when deadly!

 

[Skie]

BEMUs only being used in metro areas is an assumption, and it's by no means a given. They are potentially just as suitable for some rural routes where the previous station could be quite far away. At the moment no-one knows.

I did say initial areas (and metro systems, not areas). The 777 trial (and then potential usage in service) isn’t too far away. Gain confidence in “safer” areas and they will prove the technology can be confidently used in other areas and with more mixed traffic.

 

[Bald Rick]

Oh,OK. I had no idea. Could you provide links to show where this has been discussed recently?

It was mentioned in a thread somewhere, but my forum search skills are ‘in need of improvement’. However I’m better at google:

Future Hoo | Medway Council

Hoo Peninsula – Housing Infrastructure Fund

www.medway.gov.uk

 

[stuu]

Other 25kV schemes, whilst extraordinarily expensive, actually managed to complete ratehr closer to their defined scope, time and budget.

Why are they extraordinarily expensive? They may be compared to some of the optimistic estimates pre-GWR wiring perhaps, but £2m per km for a new piece of long term infrastructure doesn't seem that bad to me. Especially as so much of the cost is on replacing bridges and civil works that generally need doing anyway at some point over the life of the OHL.

Every new railway all around the world chooses 25kV overhead, there must be a good reason why

 

[gallafent]

Every new railway all around the world chooses 25kV overhead, there must be a good reason why

Not quite: https://en.wikipedia.org/wiki/Gotthard_Base_Tunnel for example uses 15kV, 16 2/3 Hz AC, per the older system in Switzerland that it connects to. I was interested by that, I'd assumed they would just go for 25kV, 50Hz AC and be using traction capable of switching between the two. Maybe there's just too much Swiss traction around that can only do the former, still. Or maybe there's just plenty of generation in the alps which is amenable to the former. Would be interesting to find out!

 

[edwin_m]

Not quite: https://en.wikipedia.org/wiki/Gotthard_Base_Tunnel for example uses 15kV, 16 2/3 Hz AC, per the older system in Switzerland that it connects to. I was interested by that, I'd assumed they would just go for 25kV, 50Hz AC and be using traction capable of switching between the two. Maybe there's just too much Swiss traction around that can only do the former, still. Or maybe there's just plenty of generation in the alps which is amenable to the former. Would be interesting to find out!

At a guess, 25kV would have required a new infrastructure with duplicated feeder stations etc, whereas going for 15kV would allow the infrastructure either end to feed into the tunnel section. There probably still are quite a few trains in Switzerland that can't operate on 25kV. 15kV is probably not quite as good as 25kV for supplying high power with minimum losses, but it's leagues ahead of any of the DC systems.

Every new railway all around the world chooses 25kV overhead, there must be a good reason why

I think it's true that since the 25kV system was invented virtually every main line railway with no existing electrification has gone for that system, with a few exceptions where they have gone even higher to 50kV. Some railways with existing electrification at lower voltages have chosen 25kV for new electrification and some have started conversion, but the advantages of 25kV over 15kV don't seem to be enough to justify changing in Germany/Switzerland/Austria. According to Wikipedia even the high speed lines in Germany still use that system - not sure how they get away with that when the EU requires 25kV for new high speed lines.

 

[HSTEd]

Every new railway all around the world chooses 25kV overhead, there must be a good reason why

Because until about 2000-2010 it was probably the best choice.
It is impossible to understate the epochal changes wrought by power electronics improvements in the last decade or two.

Also worth noting that I am not proposing we build an ECML equivalent on a new system.
I am proposing what are, in tonnage terms, minor secondary routes.

And if 25kV was a magical panacea, we wouldn't see newbuild metro systems being built with other systems, everything woudl be built like the Delhi Metro and use 25kV wouldn't it?

 

[A0wen]

And if 25kV was a magical panacea, we wouldn't see newbuild metro systems being built with other systems, everything woudl be built like the Delhi Metro and use 25kV wouldn't it?

Well Metro systems inhabit that strange world between light rail and full on heavy rail - you could argue Manchester Metrolink is a Metro system, yet 25kv would be completely and utterly inappropriate given it's routes.

For 'heavy' rail lines, there seems little doubt 25kv OHLE is the right solution. Where this isn't appropriate e.g where there are tunnels with clearance problems then 3rd rail of 600-750v DC seems to be the way forward.

For light rail it's a different matter - if there's street running, then oddly enough 3rd rail probably isn't appropriate - whereas a system like the DLR it makes perfect sense for it to have adopted a 3rd rail system.

The 3rd rail system in use in the UK dates back over a century - it was done because it was relatively cheap, simple to install and because there weren't any practical alternatives at the time - yes 6600v OHLE had been tried and discounted. Even before WW2 the only practical alternative was 1500V DC OHLE - indeed that's what the LNER was planning to use to electrify it's mainlines with.

There was only limited AC overhead electrification pre WW2 - a couple of lines at the most, it wasn't until after the war that 25kv became practical - and a good chunk of that was driven by technology progress - mainly around the manufacture of Mercury Arc rectifiers.

Suggesting going backwards and extending 750v 3rd rail in all but exceptional circumstances is daft - it's akin to suggesting going back to using gas lights in housing and offering DC mains supplies into domestic properties.

 

[HSTEd]

There was only limited AC overhead electrification pre WW2

Extensive networks of ~25-16.7Hz systems were deployed prior to WW2.

Such low frequency systems don't have to have rectifiers, which is why they were deployed.

Large system in the Northeastern US, 16.7Hz systems in Germany, Austria and Scandinavia, and the three phase AC system deployed quite extensively in Italy.

offering DC mains supplies into domestic properties.

Substantial research going on into just that........
Power electronics like we have today change everything.
(400Vdc microgrids replacing the low voltage AC distribution system)

 

[AlastairFraser]

It was mentioned in a thread somewhere, but my forum search skills are ‘in need of improvement’. However I’m better at google:

Future Hoo | Medway Council

Hoo Peninsula – Housing Infrastructure Fund

www.medway.gov.uk

Oh okay, it's interesting how they think £65 million will deliver a direct service to a London terminal and why they're not opening the line the whole way through to Grain. But it does explain why they're going for 3rd rail.

 

[stuu]

Because until about 2000-2010 it was probably the best choice.
It is impossible to understate the epochal changes wrought by power electronics improvements in the last decade or two.

Also worth noting that I am not proposing we build an ECML equivalent on a new system.
I am proposing what are, in tonnage terms, minor secondary routes.

And if 25kV was a magical panacea, we wouldn't see newbuild metro systems being built with other systems, everything woudl be built like the Delhi Metro and use 25kV wouldn't it?

So railway engineers are slow to catch up? What would the ideal solution be today, assuming no backward capability needed?

There are other factors when it comes to metros, as they are generally entirely segregated, and high power is less of a requirement. Also there is things like tunnel dimensions, and aesthetics e.g. Singapore doesn't allow any wires on poles of any sort

 

[HSTEd]

So railway engineers are slow to catch up?

Well given the glacial pace at which the railway adopts technically innovations..... often it is

For example the transition to semi-centralised control centres for signalling was not, last time I checked, projected to complete until 2060.

The railway industry seems to work on drastically extended timescales

What would the ideal solution be today, assuming no backward capability needed?

I woudl argue that would very based upon the speed and demand regime the railway must operate in.
I would argue for 1500Vdc bottom contact third rail (Guangzhou metro style) for low speed/lower traffic density operation and probably 6-12kVdc or 50kVac (if not higher voltage!) for high speed/high traffic density operation. If you can't provide enough power with a high voltage DC system, you should go AC, at which point you should build the highest voltage AC system you can possibly manage.

There are other factors when it comes to metros, as they are generally entirely segregated, and high power is less of a requirement. Also there is things like tunnel dimensions, and aesthetics e.g. Singapore doesn't allow any wires on poles of any sort

I'm not sure modern metros can really be characterised as having lower power demands.
They tend to run at very high frequencies with (relatively, compared to secondary railways in the UK) long trains.

Comparing a modern metro train to a 3 car 100mph EMU will probably not end with the main line EMU enormously ahead.

 

[stuu]

Well given the glacial pace at which the railway adopts technically innovations..... often it is

For example the transition to semi-centralised control centres for signalling was not, last time I checked, projected to complete until 2060.

A fair point!

I woudl argue that would very based upon the speed and demand regime the railway must operate in.
I would argue for 1500Vdc bottom contact third rail (Guangzhou metro style) for low speed/lower traffic density operation and probably 6-12kVdc or 50kVac (if not higher voltage!) for high speed/high traffic density operation. If you can't provide enough power with a high voltage DC system, you should go AC, at which point you should build the highest voltage AC system you can possibly manage.

Nowhere has gone with HV DC, that I'm aware of, I don't think anything goes above 3kV does it? What would be the advantage compared to high voltage AC?

I'm not sure modern metros can really be characterised as having lower power demands.
They tend to run at very high frequencies with (relatively, compared to secondary railways in the UK) long trains.

True, I was thinking more of freight trains and high(er) speed trains... I also wonder if city centres often don't have the grid capacity to support 25kV, although that is idle speculation

 

[HSTEd]

Nowhere has gone with HV DC, that I'm aware of, I don't think anything goes above 3kV does it? What would be the advantage compared to high voltage AC?

There was a lot of work done in the Soviet Union in the 80s with regards to building a 6kV system, because rural areas were having serious trouble supporting single phase 25kV loads, and 3kV was not considered to allow a long enough substation spacing.

There was even work on 12kV, although as far as I know that never went beyond a single test train.
This work got aborted in ~1990 for obvious reasons.

Obvious advantages, beyond the less important phase problems, is you can get more power for a given "peak" voltage, since voltage-time curvei s flat and not a sine wave. So you can operate better at a given set of electrical clearances.
You can also use lightweight electrical converters based on power electronics without trying to massively overbuild them to switch the ~45kV peak seen on 25kVac systems. No huge, heavy, bulky transformer to lug.


Either way, if we were starting from scratch, even if we went for a single phase AC system, it is unlikely we would adopt anything like what we have.
Thanks to practical electronic power converters we could build a single phase AC system where all parts of the network could be operated in parallel, which would allow substations to split loads over very long distances, especially if 50kV+ was adopted as the contact voltage.

You can split a three phase power supply into a two phase one with a Scott-T transformer, and then feed half the power through a static converter.
That gievs you a single phase AC from a balanced there phase supply and only half the power goes through the power electronics.

If you fit a quadrature booster upstream of the scott-t you can even shift the phase of the generated supply, so you can control how much each substation contributes to a given load.

 

[O L Leigh]

The problem is that you cannot always be going for the "next big thing", as it undermines the principle of running a network. Instead you adopt a standard and stick to it otherwise you're just going to end up with a patchwork of different electrification systems with all the operational headaches that this brings. As I mentioned above, we have a dual-voltage network with a large stud of dual-voltage capable trains to operate it. 25kV AC OLE was the best system when it was adopted as the standard in the 1960s and still remains fit for purpose. It's good enough for dense inner-city operations as well as being suitable for high speed rail and freight haulage.

You've already bemoaned the costs of 25kV AC OLE schemes and yet the adoption of a new standard would grossly inflate the costs even of that. I'm sure that there are better systems out there, but that is not the topic of this thread because, as I've already said more than once, it is not within the scope of the RSSB Consultation to consider.

The ROC programme is not a good example of failing to adopt to new technologies. It is my impression (and I'll be happy to be corrected by someone more in the know) that the expansion of ROC areas is linked to re-signalling/signal renewals, which actually makes good financial sense. Also the projected completion date includes bringing all those areas still controlled by mechanical signalling into the scheme, and there is a fair bit of work to be done along those routes to even permit ROC control.

 

[NotATrainspott]

Engineering is also not about picking what's conceptually best today, regardless of what came before. It's also about understanding why the decisions were made back then, and how those decisions (whether right or wrong) can have implications today. There is basically zero possibility of any new mainline electrification standards being created in the world right now. 25kV AC is ubiquitous and works for pretty much every mainline circumstance. Any new railways or infrastructure need built for other good reasons with the clearances required for OHLE at this voltage. Any new and fundamentally incompatible system would need to also be fundamentally better than 25kV AC at the job of making trains run.

The primary novel technology in play is battery power. You can put your fingers in your ears but 99% of rubber-tyred vehicles are going to switch to EV technology in the coming decades, just as quickly as ICE vehicles replaced horses. If batteries are running everything from long-distance lorries to cars, and then down into the world of consumer electronics, it would look a little stupid to say that they fundamentally cannot work for trains too.

The only viable circumstance I can see special high-voltage DC being introduced will be for rapid charging of battery trains at stations. 25kV AC provides more than enough power capability to charge and drive battery-electric trains at the same time. In areas too distant from the 25kV AC network (as in, well beyond where even an insulated feeder cable could reach through gaps in OHLE power due to obstacles) the need will shift to being able to charge trains, when stopped, as quickly as possible. Any area without an easy way to provide a 25kV AC connection is also likely one which can't handle big, bursty power requirements when a train needs to charge up. Therefore, the likely solution will be a trickle grid charge of static batteries which then discharge rapidly to provide the power to charge up the train. At that point, the losses from converting from static battery DC, to 25kV AC, and back to DC for the batteries will probably be quite large. Since the charging sections would be very distant from the rest of the network, running HV DC through them means bypassing the conversion stages. Modern EV fast chargers depend on DC power for this reason. The crucial big two pins on a CCS charger carry a DC current. The pins used for AC charging aren't even connected at fast chargers, other than the communication ones.

 

[Bald Rick]

Engineering is also not about picking what's conceptually best today, regardless of what came before. It's also about understanding why the decisions were made back then, and how those decisions (whether right or wrong) can have implications today. There is basically zero possibility of any new mainline electrification standards being created in the world right now. 25kV AC is ubiquitous and works for pretty much every mainline circumstance. Any new railways or infrastructure need built for other good reasons with the clearances required for OHLE at this voltage. Any new and fundamentally incompatible system would need to also be fundamentally better than 25kV AC at the job of making trains run.

The primary novel technology in play is battery power. You can put your fingers in your ears but 99% of rubber-tyred vehicles are going to switch to EV technology in the coming decades, just as quickly as ICE vehicles replaced horses. If batteries are running everything from long-distance lorries to cars, and then down into the world of consumer electronics, it would look a little stupid to say that they fundamentally cannot work for trains too.

The only viable circumstance I can see special high-voltage DC being introduced will be for rapid charging of battery trains at stations. 25kV AC provides more than enough power capability to charge and drive battery-electric trains at the same time. In areas too distant from the 25kV AC network (as in, well beyond where even an insulated feeder cable could reach through gaps in OHLE power due to obstacles) the need will shift to being able to charge trains, when stopped, as quickly as possible. Any area without an easy way to provide a 25kV AC connection is also likely one which can't handle big, bursty power requirements when a train needs to charge up. Therefore, the likely solution will be a trickle grid charge of static batteries which then discharge rapidly to provide the power to charge up the train. At that point, the losses from converting from static battery DC, to 25kV AC, and back to DC for the batteries will probably be quite large. Since the charging sections would be very distant from the rest of the network, running HV DC through them means bypassing the conversion stages. Modern EV fast chargers depend on DC power for this reason. The crucial big two pins on a CCS charger carry a DC current. The pins used for AC charging aren't even connected at fast chargers, other than the communication ones.

An excellent post, and the definitive word on the matter. Exactly what will happen.