New DMUs (Civity) - climate change

[Rhydgaled]

In a topic on future uses for the IC225 fleet, it was suggested that class 67s with mark 4 stock could have been an alternative to new DMUs for Manchester-Swansea serivces. I argued that, if this were to happen, fewer new DMUs should be ordered. However, 'hexagon789' was in favour of ordering all the new DMUs anyway, stating that "you can never have too much capacity!"

Since that discussion was moving off-topic, I've decided to continue in a new topic. Here's the latest post on the matter from the other topic:

Simply when you can electrify and buy new electric stock, I'd then cascade the new DMUs (which should be more efficient) to replace the older types still in service and keep cascading the newest types down to work to get rid of the oldest until the point where everything is electrified or perhaps run by battery or some other form of propulsion.

I had thought of that too. However, you cannot cascade the new Civity DMUs to replace older DMUs if you have replaced all the older DMUs. TfW rail services intends to replace the entire current fleet, mostly with new stock. The only older DMUs left would be just 12 units, which themselves are relatively new Turbostars. I suppose you could also count the 230s, but on this franchise the N.E.Wales Metro is probably second in line for electrification (or IPEMUs) after Cardiff to Penarth and Barry.

The strategy could work better for Northern, since I assume they have (or will soon have) all 50x class 150/1 units. Electrification (or partial electrification) of Northern Connect routes and introduction of new regional-express EMUs, IPEMUs or hydrogen-electric bi-modes would cascade the 195s to replace the 150/1s.

That said, I draw attention to hexagon789's comment that the new DMUs "should be more efficient". I assume this means 'fuel efficient' but I don't know whether this is actually the case. I understand that FOCs (or was it just GBRF?) rushed to order additional class 66s before the introduction of stricter EU emmisions standards because they feared that locos compliant with the new standards would burn more fuel. Modern standards seem to reduce emmisions that are directly harmful to human health, but increase fuel consumption and therefore greenhouse gas emmisions.

Going back to Wales (and the reason I put this in the 'Speculative Ideas' section), as well as reducing the number of new DMUs ordered I would retain either the 158s or the 175s. This is partly to introduce new services without needing to order more new DMUs but also to keep a larger pool of older DMUs on the franchise. The idea is that those older DMUs would provide an incentive to electrify other routes in order to cascade the new DMUs to eliminate the older stock.

 

[hexagon789]

However, 'hexagon789' was in favour of ordering all the new DMUs anyway, stating that "you can never have too much capacity

I'm afraid I will likely always think that!

I had thought of that too. However, you cannot cascade the new Civity DMUs to replace older DMUs if you have replaced all the older DMUs. TfW rail services intends to replace the entire current fleet, mostly with new stock. The only older DMUs left would be just 12 units, which themselves are relatively new Turbostars. I suppose you could also count the 230s, but on this franchise the N.E.Wales Metro is probably second in line for electrifica

My premises was you would eventually replace all the older types and cascade down in the meantime as it were.

That said, I draw attention to hexagon789's comment that the new DMUs "should be more efficient". I assume this means 'fuel efficient' but I don't know whether this is actually the case.

I was thinking both nore fuel efficient and perhaps hybrid or bi-modal with batteries and or 25kV capability.

 

[krus_aragon]

I know you suggested (in the other thread) changing the Manchester-Carmarthen/Milford service to Manchester-Swansea and Cardiff-Carmarthen/Milford services. Disregarding that for the moment, by my reckoning,the only Civity-operated routes that won't have portion working are Bangor-Manchester (and possibly Holyhead-Birmingham if the diagrams are separated from the Cambrian). That leaves Birmingham-Aberystwyth/Pwllheli, Liverpool-Llandudno/Shrewsbury(/Cardiff), and Manchester-Swansea/Carmarthen(/Milford) all designed around coupling units together.

Loco-hauled services from Manchester to Swansea may have been seriously considered. But from what I can tell (from ATW and TfW's actions), they've only opted for loco-hauled for one of three reasons:

• They want a full kitchen/buffet for First Class (Holyhead-Cardiff)
  
• They've been forced to by Westminster for competition/compensation reasons (WAG2 set)
• There's nothing else available, and capacity is needed urgently (Rhymney 37s)

I don't know how loco-hauled operations rank environmentally against DMUs, so can't offer much opinion on that. But I can toss in an observation that any cascade of Civitys (if new electric stock were bought) could include lengthening existing services in the future. They're well suited to that, with their end-corridor connections!

 

[Rhydgaled]

I was thinking both nore fuel efficient and perhaps hybrid or bi-modal with batteries and or 25kV capability.

Bi-modal / hybrid Civities would change the picture quite significantly. As I understand it though, the class 195s, 196s and TfW Civities are (intended to be) diesel-mechanical (or diesel-hydraulic?) which means they aren't easily adaptable to make use of electrification. Would it be worth campaigning for the TfW Civities to be diesel-electric, with space for pantographs, transformers etc. to be added later for easy conversion to bi-mode? I'd be less concerned about the long-term diesel use the order implies if that was the plan.

I know you suggested (in the other thread) changing the Manchester-Carmarthen/Milford service to Manchester-Swansea and Cardiff-Carmarthen/Milford services. Disregarding that for the moment, by my reckoning,the only Civity-operated routes that won't have portion working are Bangor-Manchester (and possibly Holyhead-Birmingham if the diagrams are separated from the Cambrian). That leaves Birmingham-Aberystwyth/Pwllheli, Liverpool-Llandudno/Shrewsbury(/Cardiff), and Manchester-Swansea/Carmarthen(/Milford) all designed around coupling units together.

Loco-hauled services from Manchester to Swansea may have been seriously considered. But from what I can tell (from ATW and TfW's actions), they've only opted for loco-hauled for one of three reasons:

• They want a full kitchen/buffet for First Class (Holyhead-Cardiff)
  
• They've been forced to by Westminster for competition/compensation reasons (WAG2 set)
• There's nothing else available, and capacity is needed urgently (Rhymney 37s)

I don't know how loco-hauled operations rank environmentally against DMUs, so can't offer much opinion on that. But I can toss in an observation that any cascade of Civitys (if new electric stock were bought) could include lengthening existing services in the future. They're well suited to that, with their end-corridor connections!

To be clear, I wasn't intending this topic to be a DMU vs LHCS debate. The bit I intended to be the focus of discussion was my suggestion that it would be better to retain 158s and/or 175s and reduce the number of new DMUs ordered. You make a good point about the about of portion working used in the Wales & Borders franchise; the unit-end gangways being the main advantage that 158s have over 175s.

 

[hexagon789]

Bi-modal / hybrid Civities would change the picture quite significantly.

Indeed and considering the electrification pause, I would've thought they would've been ideal.

As I understand it though, the class 195s, 196s and TfW Civities are (intended to be) diesel-mechanical (or diesel-hydraulic?) which means they aren't easily adaptable to make use of electrification.

Mechanical, six-speed gearbox I believe, so indeed not easily convertible if indeeed at all feasible.

Would it be worth campaigning for the TfW Civities to be diesel-electric, with space for pantographs, transformers etc. to be added later for easy conversion to bi-mode? I'd be less concerned about the long-term diesel use the order implies if that was the plan.

As would I, as acceleration is typically better and the transmission more efficient I'm surprised more new DMUs aren't Diesel-Electric.

 

[krus_aragon]

To be clear, I wasn't intending this topic to be a DMU vs LHCS debate. The bit I intended to be the focus of discussion was my suggestion that it would be better to retain 158s and/or 175s and reduce the number of new DMUs ordered. You make a good point about the about of portion working used in the Wales & Borders franchise; the unit-end gangways being the main advantage that 158s have over 175s.

Let me refocus on that area then.

My initial instincts at the franchise announcement were "why not keep the 175s instead of acquiring the 170s?" On digging through the numbers and looking at the timescales (as illlustrated here), I realised that the 170s are essential to make up the numbers between the Pacers going at the end of the year, and the new Civity stock arriving in 2022.

Given that some rolling stock is needed for the interim (be it 170s or otherwise), the question then changes to "what rolling stock shall we keep when the Civity stock gets delivered?"

I've written previously that I think it's a clever move by TfW to keep some old stock alongside the Civity fleet, as it allows some natural flexibility with the fleet in the future:

• Electrification means we don't need as many DMUs? Put the old stock off-lease, and cascade the Civitys.
• New services or growth in demand means we need more DMUs? We can order more Civitys (if the production line's still open), or look to transfer in more old DMUs instead

The key contenders for the old fleet are the 158s, 175s and 170s. As you note, the 158s have an advantage in gangways for portion working, but they will be over forty years old by the end of this franchise, and a bit long in the tooth. (Assuming a three-year timescale for delivery of new-build stock in the next franchise, they'd be pushing 45 years!) On that basis, I'll concentrate on the 170s and 175s.

I'm also working under the assumption that TfW would want to use one class of the other, and not both, in order to avoid the inefficiencies of microfleets. The current DMU fleet inherited from Arriva have two incompatible coupling systems: The 175s aren't compatible with the BSI couplers on the 158s (and Sprinters/Pacers). This means two separate ECS workings are needed from Chester to Llandudno Jn every morning, and that when a unit fails in North Wales or on the Marches, there's a good chance that the unit behind will be incompatible and unable to assist. Keeping both the 170s and 175s alongside the Civitys would result in three incompatible fleets.

So it's the 170s vs the 175s. You said you'd like to see fewer new trains ordered, and for more old trains to be used. Keeping the 175s instead would give you 15 extra units, so you could knock 15 units off the Civity order. But which services would be operated by the extra 175s instead of by Civitys? The current plan is for the old stock to be used mainly on West Wales services, so it'd be convenient for them to be on a nearby route. Unfortunately, TfW set a goal of introducing First Class provision on Manchester-Swansea, which 175s don't suit. Up in North Wales, most routes will see portion working, which doesn't suit the 175s or the 170s. In the south-east, the planned FLIRT DMUs (11 4-car) for Maesteg, Cheltenham and Ebbw services might be a more suitable target for knocking off the order list, though they'd need to double-up for some services.

If you chose to keep extra 170s instead, you'd need to acquire more of them before 2022, or keep some 158/175s for longer until you can get them. It seems only the 12 from Anglia were available this year, I don't know what's due to come off lease over the next few years. There'd also be the question of where to operate them, as above.

Having said all of the above, I can see a slim possibility that TfW will choose to keep the 175 fleet instead of the 170s, though with the existing Civity order size. There's talk of TfW applying for paths for a Swansea-Bristol TM service, and also plans for stations and increased service on the Swansea District line. My back-of-envelope calculations show that Swansea-Bristol would need four or five diagrams for an hourly service, and another unspecified number for District Line services. If no other franchise is chomping at the bit to snap-up the 175s, and the lease on the 170s is flexible, TfW could find that keeping the 175s is more convenient than finding extra 170s for these services.

 

[HSTEd]

The fuel burn of the railway is rather small compared to other sectors of the economy.
IIRC the railway uses about 530kT of fuel oil per annum, the airline industry uses something like 15,000kT.

 

[Rhydgaled]

I've written previously that I think it's a clever move by TfW to keep some old stock alongside the Civity fleet, as it allows some natural flexibility with the fleet in the future:

• Electrification means we don't need as many DMUs? Put the old stock off-lease, and cascade the Civitys.

I agree, I just don't think the balance of new stock to old is the right one given the large number of new DMUs on order and the (near) impossibility of converting them to bi-mode or EMU.

I'm also working under the assumption that TfW would want to use one class of the other, and not both, in order to avoid the inefficiencies of microfleets. The current DMU fleet inherited from Arriva have two incompatible coupling systems: The 175s aren't compatible with the BSI couplers on the 158s (and Sprinters/Pacers). This means two separate ECS workings are needed from Chester to Llandudno Jn every morning, and that when a unit fails in North Wales or on the Marches, there's a good chance that the unit behind will be incompatible and unable to assist. Keeping both the 170s and 175s alongside the Civitys would result in three incompatible fleets.

Is there anything the Civities are compatible with? ATOC's 2013 Key Technical Requirements for rolling stock specified "Diesel Multiple Units: compatibility with coupler type “BSI compact”"; incompatible coupling systems on new units really should be discouraged. Mind you, I already know that the class 195 is non-compliant with the Key Technical Requirements; the solid wall between windows is 3cm too big (the ATOC standard said 450mm, I measured the 195 at 48cm).

So it's the 170s vs the 175s. You said you'd like to see fewer new trains ordered, and for more old trains to be used. Keeping the 175s instead would give you 15 extra units, so you could knock 15 units off the Civity order. But which services would be operated by the extra 175s instead of by Civitys? The current plan is for the old stock to be used mainly on West Wales services, so it'd be convenient for them to be on a nearby route. Unfortunately, TfW set a goal of introducing First Class provision on Manchester-Swansea, which 175s don't suit. Up in North Wales, most routes will see portion working, which doesn't suit the 175s or the 170s. In the south-east, the planned FLIRT DMUs (11 4-car) for Maesteg, Cheltenham and Ebbw services might be a more suitable target for knocking off the order list, though they'd need to double-up for some services.

As well as cutting back the new fleet a little, I'd use the older stock (158s/175s) to enhance services at (presumably) lower lease costs than the new units. Thus, I envisage using the 175s (or 158s) on Swansea - Milford/Fishguard (hourly to Clarbeston Road, with some going to Fishguard and the rest to Milford), Swansea-Whitland (hourly, with alternate-hour extensions to Pembroke Dock) and Carmarthen-Cardiff (hourly via Swansea District Line, with extensions to Fishguard/Milford giving the latter a roughly hourly service when combined with the Swansea service). They would also work the Heart Of Wales, with the addition of 3 or 4 limited-stop trains per day.

It wouldn't actually reduce the new-build fleet that much, but it would provide a larger pool of older units to cascade out later if/when electrification expands. If you let the older trains go off lease, any new services would require yet more new DMUs (additional CAF units is at least an option in Prof. Stuart Cole's Swansea District Line service proposal).

If you chose to keep extra 170s instead, you'd need to acquire more of them before 2022, or keep some 158/175s for longer until you can get them. It seems only the 12 from Anglia were available this year, I don't know what's due to come off lease over the next few years. There'd also be the question of where to operate them, as above.

You see I'd keep the 12x 170s, perhaps instead of the diesel-only FLIRTs for Cheltenham services as you suggest (or on yet more new services, a Swansea metro in this case), in addition to the 158s or 175s (another advantage of keeping 158s instead of 175s is that 170s and 158s could rescue each other if needed).

 

[Rhydgaled]

I believe the Rail Industry Decarbonisation Task Force has recomended a net zero by 2050 target for the rail industry, and have also supported the withdrawal of all diesel-only trains by 2040.

However, construction of new trains involves a not insignificant amount of carbon emmisions (eg. in the smelting of aluminium) so it is prudent to maximise the viable working life of trains so that they are not replaced too often. Give Northern's class 195s a 30 year life and they'd be withdrawn in... 2049-2050. Would building a new fleet to replace them in 2040 cause more emmisions than allowing the 195s to run until 2050? The class 196 and Wales & Borders fleets, given that they are not yet even under construction as far as I know, could still be with us in the 2050s.

 

[LOL The Irony]

Bi-modal / hybrid Civities would change the picture quite significantly. As I understand it though, the class 195s, 196s and TfW Civities are (intended to be) diesel-mechanical (or diesel-hydraulic?) which means they aren't easily adaptable to make use of electrification.

Mechanical, six-speed gearbox I believe, so indeed not easily convertible if indeeed at all feasible.

It's just a case of replacing the gearbox with an alternator, isn't it? The bogies can come from a 331/397.

 

[AM9]

It's just a case of replacing the gearbox with an alternator, isn't it? The bogies can come from a 331/397.

DMU have an engine, a gearbox and shafts connecting to final drives in the bogies on the axles. DEMUs have an engine, a generator (alternator), control electronics and cables connecting electric motors on the bogies* driving the axles. A bit more than replacing the gearbox with an alternator.
* Very large DEMUs e.g. Voyagers might have ther motors mounted off the bogie like some locos but this discussion is abouit typical diesel mechjanical MUs being changed into diesel electric or bi-mode MUs.

 

[hexagon789]

It's just a case of replacing the gearbox with an alternator, isn't it? The bogies can come from a 331/397.

And traction motors too!

 

[Rhydgaled]

DMU have an engine, a gearbox and shafts connecting to final drives in the bogies on the axles. DEMUs have an engine, a generator (alternator), control electronics and cables connecting electric motors on the bogies* driving the axles. A bit more than replacing the gearbox with an alternator.

Interesting. Replacing shafts with cables might not be all that difficult, but:

• can a generator/alternator fit in the same space as a gearbox?
• do you need different bogies to be able to fit electric motors?

Also, what does an EMU have that a DEMU doesn't? A pantograph (or third rail shoe), obviously, and a transformer (or is that only required for dual-voltage stock?)... anything else? And how much space do you need to leave for these things if you want to build a DEMU with passive provision for bi-mode conversion (I'm guessing the amount of OHLE currently available on the Civity routes isn't enough to justify the weight of the transformer and pantograph initially).

 

[AM9]

Interesting. Replacing shafts with cables might not be all that difficult, but:

• can a generator/alternator fit in the same space as a gearbox?
• do you need different bogies to be able to fit electric motors?

... Take the class 195, - I would imagine that a 390 kW alternator is slightly larger than the existing transmission but it would be easier to accommodate as it does not need to have a mechanical drive to the bogie(s).
The passive design of the bogies can be similar but the mountings, pinion drive and suspension design might make conversion not cost effective.

Also, what does an EMU have that a DEMU doesn't? A pantograph (or third rail shoe), obviously, and a transformer (or is that only required for dual-voltage stock?)... anything else? And how much space do you need to leave for these things if you want to build a DEMU with passive provision for bi-mode conversion (I'm guessing the amount of OHLE currently available on the Civity routes isn't enough to justify the weight of the transformer and pantograph initially).

All mainline EMUs now must have structural provision for a pantograph, and a location for a transformer. Where a family has models supplied both for OLE and 3rd rail, it is often easier to fit a dummy transformer (typically concrete) to allow a common suspension setup in that vehicle. Third rail provision has little effect on the desgns of EMUs now that designs like the 700s have incorporated collector shoes on lightweight inside frame bogies.
Virtually all ac or ac/DC EMUs since the MKIII class 317s have a 750VDC'ish DC bus. That is how the 319s manage to be dual voltage capable. A new design for an EMU family could easily make provision for alternative power sources to feed the DC bus, diesel genset or batteries, (or even both) just need to be connected onto that bus. The traction control and motor drives are then operating in the same way except that under regeneration conditions where kinetic energy in the moving train is converted back to electrical energy, it is then:

1) fed back through the transformer to the OLE
2) fed through tbe collector shoes directly to the 3rd rail
3) used to charge the batteries
4) or wasted as heat in resistor banks on a pure DEMU train.​

A well designed DEMU, whilst wasting energy and probably carrying slightly more weight than a diesel mechanical MU, should make better use of the diesel engine's power curve to give better fuel economy, and have lower maintenance costs.

 

[squizzler]

I see that CAF have developed a bi-mode for the New South Wales rail network in Australia. Presumably the technology can be rolled into other products, although in this instance the low voltage DC of the Sydney network means the electrification it can use is more akin to third rail than UK OLE.

According to the International Rail Journal:

IN a surprise announcement, the New South Wales (NSW) state government says that the new rolling stock ordered to replace the NSW Trains regional passenger fleet will be now delivered with bi-mode capability.

The 29 new trains will now be delivered by Momentum rolling stock partner CAF with bi-modal capability, to operate as a diesel-electric multiple unit to operate over the bulk of the NSW Trains regional network and draw power from 1.5kV dc overhead lines where available.

 

[Meerkat]

The fuel burn of the railway is rather small compared to other sectors of the economy.
IIRC the railway uses about 530kT of fuel oil per annum, the airline industry uses something like 15,000kT.

You can have all the stats you like but the ordinary bod on the street is going to hear “green trains” but be thinking “that noisy, rattly, thing belching out fumes in my local station?”

 

[HSTEd]

You can have all the stats you like but the ordinary bod on the street is going to hear “green trains” but be thinking “that noisy, rattly, thing belching out fumes in my local station?”

It will be a long time before a Class 195 is like that.

 

[Meerkat]

It will be a long time before a Class 195 is like that.

Class 195s are quiet and belch no fumes?? I live a long way from their gaff

 

[HSTEd]

Class 195s are quiet and belch no fumes?? I live a long way from their gaff

Compared to all previous diesel units..... yes.

They actually have modern diesel engines in them after all, I believe complete with SCR (AdBlue)

 

[Meerkat]

I have yet to experience a diesel on the road or rail that isn’t noisy and smelly.
Even expensive cars are a bit nasty in diesel format

 

[Rhydgaled]

I see that CAF have developed a bi-mode for the New South Wales rail network in Australia. Presumably the technology can be rolled into other products, although in this instance the low voltage DC of the Sydney network means the electrification it can use is more akin to third rail than UK OLE.

CAF do advertise bi-mode as an option for the Civity on their website, but it's interesting to hear that somebody has now ordered some. Two big questions remain however:

• is bi-mode an option for the Civity UK (keeping in mind the loading guage, is New South Wales' as constrained as just plain old Wales?)?
• is bi-mode an option for 2/3-car units?

With regard to these, the only major difference between a DMU and a bi-mode listed in the various posts above appears to be the need to find space for a transformer (I'm assuming control electronics for the traction motors are just a few computer chips, but that might be a poor assumption). On that basis, it seems sensible to ask what are the dimensions of a typical UK EMU transformer and whether there could be space for this on a Civity UK?

I can't help feeling I'm missing something here, given that I'm not aware of any 25kv EMU or bi-mode in the UK with only 2 coaches and there is often a mixture of vehicle types in the formation with the different kit distributed between the vehicles (eg. the class 800 driving vehicles, with the pantograph, have no traction motors). Is that just due to weight distribution or is there some massive component that won't fit on a vehicle unless other components are moved elsewhere in the train?

 

[squizzler]

I can't help feeling I'm missing something here, given that I'm not aware of any 25kv EMU or bi-mode in the UK with only 2 coaches and there is often a mixture of vehicle types in the formation with the different kit distributed between the vehicles (eg. the class 800 driving vehicles, with the pantograph, have no traction motors). Is that just due to weight distribution or is there some massive component that won't fit on a vehicle unless other components are moved elsewhere in the train?

Regarding the packaging of a bi-mode transmission in a two car unit I imagine it is probably easiest to accommodate the weight, slightly harder to do accommodate the volume and most difficult of all to justify the cost per seat.

 

[edwin_m]

Another problem is pantograph spacing if two units are coupled together, where the first one sets the wires wobbling which affects pickup on the second one. It would probably require a significant speed restriction or for one unit to be dead with pan down.

 

[HSTEd]

Another problem is pantograph spacing if two units are coupled together, where the first one sets the wires wobbling which affects pickup on the second one. It would probably require a significant speed restriction or for one unit to be dead with pan down.

The alternative now we are allowed 25kV bus lines is probably to put two pantographs on a unit, as close to the cab ends as possible.
That way you can raise pans and have them be four cars apart.

 

[edwin_m]

The alternative now we are allowed 25kV bus lines is probably to put two pantographs on a unit, as close to the cab ends as possible.
That way you can raise pans and have them be four cars apart.

Yes that's a possibility - the separation would be as good as a pair of standard 4-car EMUs in the worst case orientiation, which as far as I know are unrestricted up to at least 100mph. I guess the problem would be finding the space for all the cab equipment if that part has a flat roof.

 

[Rhydgaled]

Another problem is pantograph spacing if two units are coupled together, where the first one sets the wires wobbling which affects pickup on the second one. It would probably require a significant speed restriction or for one unit to be dead with pan down.

Ah, that could be an issue. That said, how is power for heating and lighting transmitted through the Mark 5 sleeper stock*? I'm guessing that wouldn't be suitable for traction power, but if it could then couldn't both units get all their power from one (raised) pantograph?

* singled those out because I'd read they are switching from the old couplings on the mark2/3 stock (which I assume involves a member of staff manually connecting power cables between each car when the portions are coupled together) to auto-couplers

 

[gazthomas]

A 456 is a 2 car EMU, albiet DC

 

[edwin_m]

Ah, that could be an issue. That said, how is power for heating and lighting transmitted through the Mark 5 sleeper stock*? I'm guessing that wouldn't be suitable for traction power, but if it could then couldn't both units get all their power from one (raised) pantograph?

* singled those out because I'd read they are switching from the old couplings on the mark2/3 stock (which I assume involves a member of staff manually connecting power cables between each car when the portions are coupled together) to auto-couplers

There are standard plugs and sockets for feeding auxiliary supplies through a train. 25kV or 750V traction supplies can be fed through a bus wire within a unit not to or from other units coupled to it.

The only example I can think of where traction power is transferred via a plug and socket is the "slug" units in the US, which are (or were) "locomotives" with traction motors but no engine, plugged in to an actual locomotive and taking power from it to increase tractive effort at low speeds. I don't know the voltage used but it would be in the hundreds of volts as supplied to the motors, certainly not 25kV. In principle something like that might be possible with the "DC Link" in a modern traction package, but highly likely to be a manual plug and socket not through an autocoupler.

 

[HSTEd]

There are standard plugs and sockets for feeding auxiliary supplies through a train. 25kV or 750V traction supplies can be fed through a bus wire within a unit not to or from other units coupled to it.

Well 25kV lines are still detachable in the case of TGV power cars.

I believe there was an RSSB scoping project on a 25kV autocoupler a couple of years back, don't know if anything has come of it.

 

[anamyd]

A 456 is a 2 car EMU, albiet DC

what context are you referring to 2-car EMUs (like 456s and 466s) in...?