Discontinuous electrification to Penzance - Worked example for Cross-Country 80x Hitachi Trimode

[Nottingham59]

To help me understand what batteries and discontinous electrification would mean for the rail network, I've worked out what would be needed for XC to get to Penzance with 80x trimodes. The figures are based on the 802207 trial which had two diesel power units and one 577kWh battery pack. This gave 43 miles of range in normal operation on a hilly route. See discussion here:

802207 Hitachi testing battery power for Transpennine

Is 802207 in full use now? It’s my last 802 with TPE I’ve yet to ride on. No, it is currently sat doing nothing outside at Hitachi’s Merchant Park facility.

www.railforums.co.uk

BEMU SPECFICATION
I'm assuming a standard 5-car Hitachi 80x with two 577kWh battery units and one diesel power pack. This should have a maximum range of 86 miles on battery alone, which can be extended if necessary with the diesel engine to give effectively unlimited range in case of delays or emergencies. In practice, I would expect the operators to start up the diesel engine after around 64 miles off the wires, to avoid deep discharges. Given that the Stadler FLIRT Akku can recharge in 15 minutes on the wires, I've assumed that 20 minutes would be adequate to allow time a full recharge plus pan up and pan down time. Recharging 2 x 577kWk in 15 minutes requires a power draw of 4.6MW, which is well within the capability of modern OHLE.

ELECTRIFICATION ISLANDS
Assuming that MML is electrified to Sheffield, then battery operation from Edinburgh to Penzance could be done by electrifying the following sections of track:

• BRISTOL: Yate Station to Parson St Station: 13 route miles. XC transit time = 27 minutes, including 9mins at Temple Meads
• EXETER: Whiteball Tunnel to Exeter St Thomas: 21 route miles. Transit in 20 min
• PLYMOUTH: Laira Junction to St Germain station: 11 route miles. Transit in 21 min
• PENZANCE: Penzance station to St Erth: 6 route miles. Transit 8 min, plus terminus layover.

For redundancy, I would electrify each isolated OHLE section with two Static Frequency Converters, connected to different power lines at 33kV or higher, with no neutral section or sectioning cabinets needed between them.

UNELECTRIFIED GAPS
This leaves the following gaps, which are all within the assumed 86-mile range of the 80x:

• Moorthorpe/Doncaster to Sheffield: 30 miles
• Derby to Grand Junction (Birmingham): 40 miles
• Bromsgrove to Yate: 64 miles
• Parson St, Bristol to Whitehall Tunnel (Tiverton): 54 miles
• Exeter St Thomas to Laira (Plymouth): 50 miles
• St Germain to St Erth: 64 miles

So I reckon you could batterify all the way to Penzance by electrifying just 46 route miles of track, given that 5 miles is already done around Bristol Parkway. And by adding Westbury to Castle Cary (20 miles; 20 minutes) you could do the same for London Paddington traffic via the Berks and Hants.

Any thoughts?

 

[Zomboid]

For redundancy, I would electrify each isolated OHLE section with two Static Frequency Converters, connected to different power lines at 33kV or higher, with no neutral section or sectioning cabinets needed between them

Good luck getting 21 miles without any paralleling points... And you'll need to do the fast lines between Kings Norton and Barnet Green as well.

What state are you letting the batteries get to before getting a charge?

I think in the real world you'd need to look at wider service benefits, such as electrifying to Weston, and allowing local services to be EMUs (and not carrying the extra mass of a second power supply). That example would also reduce the distance to the next "island".

 

[zwk500]

I just can't seen the business case stacking up for 2 SFC connection points on 11 route miles, I really can't. The more likely scenario to me is continuous OLE on the GWML to Weston SM for Bristol suburban services, then continuous OLE from the B&H to Exeter and through to Plymouth. In Cornwall static charging at stations would be used to top up the batteries. On your distances, you'd probably want one about halfway along and then one at Penzance.

Penzance might, just might, get low-spec OLE for movements to/from Long Rock depot.

 

[HSTEd]

ELECTRIFICATION ISLANDS
Assuming that MML is electrified to Sheffield, then battery operation from Edinburgh to Penzance could be done by electrifying the following sections of track:

• BRISTOL: Yate Station to Parson St Station: 13 route miles. XC transit time = 27 minutes, including 9mins at Temple Meads
• EXETER: Whiteball Tunnel to Exeter St Thomas: 21 route miles. Transit in 20 min
• PLYMOUTH: Laira Junction to St Germain station: 11 route miles. Transit in 21 min
• PENZANCE: Penzance station to St Erth: 6 route miles. Transit 8 min, plus terminus layover.

For redundancy, I would electrify each isolated OHLE section with two Static Frequency Converters, connected to different power lines at 33kV or higher, with no neutral section or sectioning cabinets needed between them

I'm skeptical that redundant Static Frequency Converters (especially as it would have to be 2x100% to be redundant) would be more economic than interconnecting the charging points with a wood pole 25-0-25kV power line.
Construction and maintenance of such a line could be contracted out to the local DNO and would be able to use most of the existing 33kV hardware (albeit with longer insulators).

The necessary autotransformers are already in the NR parts catalogue after all.

Then again, if every train is going to have a diesel generator regardless, is there any need to have redundancy?
If one of the feeders trips just tell every train to start its engines until it is restored.

A more likely scheme in my view would be a single SFC positioned as near as possible to the Indian Queens Supergrid substation, then feeding the charging islands from there in combination with a tap on the 25kV lines at Bristol Parkway.

 

[Zomboid]

Then again, if every train is going to have a diesel generator regardless, is there any need to have redundancy?
If one of the feeders trips just tell every train to start its engines until it is restored

There'll depend on the capability of the train in that mode to meet the timetable. If it's purely an emergency backup to keep the lights on and get to a platform then the trains will need a resilient supply.

That could be managed by the design not permitting the batteries to drop below (for example) 35% in normal operation, and speed restrictions being applied to keep charge levels up if charging is disrupted.

I think the Bromsgrove - Yate gap is a bit wide for comfort, so I'd extend the wires from one end or the other. Which end would depend on where the tricky bridges are, but ideally get it down to no more than 50 miles off the wires.
Bristol to Weston SM seems like it would really be worthwhile to sightly close that gap and allow a Cardiff - Bristol - Weston stopping service to run with straight EMUs, as well as helping the London service (which may also have batteries).
Further west it'd make more sense to electrify the general Exeter suburban area (at least Exmouth and Paignton, there's no need to be scared of Dawlish), and the big hills between Exeter and Plymouth would benefit from wires.
Further west still it's harder to picture, static charging is probably the way to go, and that'll be provided in several places for the local services as they'll probably go over to BEMU operation in due course, so some splash and dash charging (3-4 minute dwell times) at places like St Austell and Truro might be enough to keep the batteries in good enough shape to make it to Penzance.

 

[MatthewHutton]

There’s probably value in speeding up Exeter to Penzance anyway. So probably worth starting out the new sections at least with electrification. Certainly Exeter to Plymouth is slow.

 

[HSTEd]

There'll depend on the capability of the train in that mode to meet the timetable. If it's purely an emergency backup to keep the lights on and get to a platform then the trains will need a resilient supply.

Assuming the diesel power pack is the one currently fitted to the 80x series trains, even a single one will give the train 700kW.

With the batteries available, the generator can be run essentially flat out at all times.
That should provide enough to allow the train to keep to timetable through a feeder outage, especially given the rather low speeds on the bulk of this route.

 

[Nottingham59]

Good luck getting 21 miles without any paralleling points...

I thought paralleing points are needed to accommodate different phases being fed to different sections on the line. But SFCs can all deliver the same phase, without causing phase imbalances in the grid supply, so they won't need parallelising as much. But I guess would be helpful to have the capability of isolating parts of the route, to bypass faults etc.

And you'll need to do the fast lines between Kings Norton and Barnet Green as well.

True. I'd forgotten about that. But all the masts are in place, so it will be a relatively easy job.

What state are you letting the batteries get to before getting a charge?

Dunno.

In reality it would be easier to specify a battery big enough to deliver 64 miles at full linespeed in the coldest winter without getting degraded by over discharge. My best guess is that is around 2x577kWh. In real life the optimum battery capacity for XC might be a bit more or a bit less than this.

The interesting thing is that this battery capacity is well within the capability of existing BEMUs.

 

[Zomboid]

I thought paralleing points are needed to accommodate different phases being fed to different sections on the line. But SFCs can all deliver the same phase, without causing phase imbalances in the grid supply, so they won't need parallelising as much. But I guess would be helpful to have the capability of isolating parts of the route, to bypass faults etc.

You need paralleling to keep the voltage within tolerance, and sectioning to allow for subsections to be isolated and for a fault to not take the whole lot out at once.

How far is Coventry (or New Street if going via Solihull) to Didcot? Assuming these trains can be specified to also take a 750V supply they'd be better suited to the Bournemouth to Manchester run, since most of that is already electrified in one form or another.

 

[HSTEd]

You need paralleling to keep the voltage within tolerance, and sectioning to allow for subsections to be isolated and for a fault to not take the whole lot out at once.

Conceptually you can provide paralleling without paralleling huts, if you connect the overhead lines in the tramway fashion and surrender the ability to isolate one line from the other.
Deleting all this extra hardware may be worthwhile if the trains all have high power auxiliary generators regardless. The proposed electrification scheme has islands only a few miles long in any case.

If you had a scheme chained together with power lines, you could, conceptually, feed from both ends, providing only a handful of sectioning circuit breakers at the ends of the charging islands.

That would allow one fault to be endured without losing any non faulted segments entirely.

One circuit breaker at each end of a charging island would allow a fault to be isolated whilst only losing a maximum of one charging island. No islands would be lost if the fault occurs on the interconnecting pole line.

 

[Zomboid]

Conceptually you can provide paralleling without paralleling huts, if you connect the overhead lines in the tramway fashion and surrender the ability to isolate one line from the other.
Deleting all this extra hardware may be worthwhile if the trains all have high power auxiliary generators regardless. The proposed electrification scheme has islands only a few miles long in any case.

If you had a scheme chained together with power lines, you could, conceptually, feed from both ends, providing only a handful of sectioning circuit breakers at the ends of the charging islands.

That would allow one fault to be endured without losing any non faulted segments entirely.

One circuit breaker at each end of a charging island would allow a fault to be isolated whilst only losing a maximum of one charging island. No islands would be lost if the fault occurs on the interconnecting pole line.

True, I think horses for courses in this kind of thing. But you can't just run a 21 mile section with nothing on between to provide paralleling or sectioning, no matter what hardware you use there needs to be something.

 

[Nottingham59]

How far is Coventry (or New Street if going via Solihull) to Didcot?

62 miles. That's a pleasing coincidence.

== Doublepost prevention - post automatically merged: 8 May 2025 ==

I'm skeptical that redundant Static Frequency Converters (especially as it would have to be 2x100% to be redundant)

These would be very small and I hope relatively cheap. In Penzance for instance, I'd expect that two 3MVA SFCs would be enough. I'd site one where 33kV line crosses the railway to St Ives (500m from St Erth station), and the other near Marazion where a 33kV double circuit lines cross the railway. (See https://openinframap.org/#14.15/50.13352/-5.47438)

Those would cost perhaps one twentieth of the MML grid feeder at Braybrooke (2 x 80MVA, fed from two 400kV circuits on the same pylon).

Plymouth and Exeter would need perhaps 2 x 10MVA, to handle more trains at once and charge local BEMU services too.

 

[Grecian 1998]

Whilst electrifying the major stations has obvious benefits, it would also take rather longer and be more complex than electrifying the sections in the countryside. It would also realistically require multiple total shutdowns of those stations for prolonged periods of time to put the wires up.

Further west it'd make more sense to electrify the general Exeter suburban area (at least Exmouth and Paignton, there's no need to be scared of Dawlish), and the big hills between Exeter and Plymouth would benefit from wires.

Certainly if discontinuous electrification is used, the place with the most obvious benefit by far is on the steep inclines between Newton Abbot and Plymouth. An 80x with an engine knocked out tends to be trundling by the time it reaches Dainton / Wrangaton / Hemerdon summits. I'm not sure if there's still a general policy of cutting out stops at Totnes for trains running on reduced power but there certainly was for HSTs. I was an eastbound 80x with this problem a few weeks ago and at one point it seemed 50-50 whether we'd get up Hemerdon.

If summers are going to get hotter, not having to rely on an 80x on diesel to get up the hill without the air con or anything else conking out on a hot day seems like a definite win. It should aid acceleration as well, particularly westbound from Totnes where the climb starts rapidly.

Taunton - Whiteball Tunnel westbound is also a fairly steep incline, and there are several short but fairly sharp climbs in Cornwall.

 

[HSTEd]

62 miles. That's a pleasing coincidence.

== Doublepost prevention - post automatically merged: 8 May 2025 ==


These would be very small and I hope relatively cheap. In Penzance for instance, I'd expect that two 3MVA SFCs would be enough. I'd site one where 33kV line crosses the railway to St Ives (500m from St Erth station), and the other near Marazion where a 33kV double circuit lines cross the railway. (See https://openinframap.org/#14.15/50.13352/-5.47438)

Those would cost perhaps one twentieth of the MML grid feeder at Braybrooke (2 x 80MVA, fed from two 400kV circuits on the same pylon).

Plymouth and Exeter would need perhaps 2 x 10MVA, to handle more trains at once and charge local BEMU services too.

The SFCs would be cheap individually, but would it be cheaper than a single 16MVA SFC at Indian Queens or somewhere and a tap off the existing GWML scheme at Bristol Parkway etc?

The traffic density is quite low and fundamentally the overhead line is "only" ~160 miles from end to end.

 

[brad465]

Certainly if discontinuous electrification is used, the place with the most obvious benefit by far is on the steep inclines between Newton Abbot and Plymouth. An 80x with an engine knocked out tends to be trundling by the time it reaches Dainton / Wrangaton / Hemerdon summits. I'm not sure if there's still a general policy of cutting out stops at Totnes for trains running on reduced power but there certainly was for HSTs. I was an eastbound 80x with this problem a few weeks ago and at one point it seemed 50-50 whether we'd get up Hemerdon.

Yes I was just thinking going to Penzance on discontinuous electrification and not including the South Devon Banks is missing a big trick, particularly as the 50 mile distance quoted above from Exeter-Laira would be cutting range fine when including those sustained gradients.

I can also see all the branch line interchange stations wanting electrification too in this instance, as a means to provide battery power to the branch line services. St Erth was included in the OP idea, but Liskeard, Par and Truro would certainly value it, particularly the latter as the Maritime line is the most intensively used branch in Cornwall, to the point I could see other parts of the branch electrified too (which also has steep gradients). The Atlantic Coast line may also need electrification at the Newquay end, to facilitate with the regular service and the summer specials, including XC services if they were to return.

I just can't seen the business case stacking up for 2 SFC connection points on 11 route miles, I really can't. The more likely scenario to me is continuous OLE on the GWML to Weston SM for Bristol suburban services, then continuous OLE from the B&H to Exeter and through to Plymouth.

If Exeter was to receive electrification from Cogload Jct, as part of the B&H being done, you might as well infill W-S-M to Cogload, which would have the added benefit that if Filton Bank is electrified, Cardiff-Exeter could be done with EMUs.

 

[deltic08]

To help me understand what batteries and discontinous electrification would mean for the rail network, I've worked out what would be needed for XC to get to Penzance with 80x trimodes. The figures are based on the 802207 trial which had two diesel power units and one 577kWh battery pack. This gave 43 miles of range in normal operation on a hilly route. See discussion here:

802207 Hitachi testing battery power for Transpennine

Is 802207 in full use now? It’s my last 802 with TPE I’ve yet to ride on. No, it is currently sat doing nothing outside at Hitachi’s Merchant Park facility.

www.railforums.co.uk

BEMU SPECFICATION
I'm assuming a standard 5-car Hitachi 80x with two 577kWh battery units and one diesel power pack. This should have a maximum range of 86 miles on battery alone, which can be extended if necessary with the diesel engine to give effectively unlimited range in case of delays or emergencies. In practice, I would expect the operators to start up the diesel engine after around 64 miles off the wires, to avoid deep discharges. Given that the Stadler FLIRT Akku can recharge in 15 minutes on the wires, I've assumed that 20 minutes would be adequate to allow time a full recharge plus pan up and pan down time. Recharging 2 x 577kWk in 15 minutes requires a power draw of 4.6MW, which is well within the capability of modern OHLE.

ELECTRIFICATION ISLANDS
Assuming that MML is electrified to Sheffield, then battery operation from Edinburgh to Penzance could be done by electrifying the following sections of track:

• BRISTOL: Yate Station to Parson St Station: 13 route miles. XC transit time = 27 minutes, including 9mins at Temple Meads
• EXETER: Whiteball Tunnel to Exeter St Thomas: 21 route miles. Transit in 20 min
• PLYMOUTH: Laira Junction to St Germain station: 11 route miles. Transit in 21 min
• PENZANCE: Penzance station to St Erth: 6 route miles. Transit 8 min, plus terminus layover.

For redundancy, I would electrify each isolated OHLE section with two Static Frequency Converters, connected to different power lines at 33kV or higher, with no neutral section or sectioning cabinets needed between them.

UNELECTRIFIED GAPS
This leaves the following gaps, which are all within the assumed 86-mile range of the 80x:

• Moorthorpe/Doncaster to Sheffield: 30 miles
• Derby to Grand Junction (Birmingham): 40 miles
• Bromsgrove to Yate: 64 miles
• Parson St, Bristol to Whitehall Tunnel (Tiverton): 54 miles
• Exeter St Thomas to Laira (Plymouth): 50 miles
• St Germain to St Erth: 64 miles

So I reckon you could batterify all the way to Penzance by electrifying just 46 route miles of track, given that 5 miles is already done around Bristol Parkway. And by adding Westbury to Castle Cary (20 miles; 20 minutes) you could do the same for London Paddington traffic via the Berks and Hants.

Any thoughts?

I have already posted on this subject the other day. To repeat, I suggested extending electrification from Bromsgrove around Worcester loop and to Malvern for Birmingham-Hereford and Paddington services, continue to Standish Junction for long distance XC battery bimodes, XC Nottingham-Cardiff bimodes as far as Gloucester, Paddington-Cheltenham trains and Malvern-Gloucester-Bristol battery bimodes. This would leave gaps Standish Junction to Yate, Gloucester to Severn Tunnel Junction and Swindon-Standish Junction.
I suggested electrifying Derby-Birmingham after MML electrification is completed, Moorthorpe/Doncater-Sheffield for converting Leeds-Sheffield and Adwick-Sheffield local trains to EMUs.
I thought electrifying Bristol TM to Weston too much to ask but agree with those who want to.
Battery Trimodes for Manchester-Bournemouth when Oxford is wired

 

[zwk500]

Yes I was just thinking going to Penzance on discontinuous electrification and not including the South Devon Banks is missing a big trick, particularly as the 50 mile distance quoted above from Exeter-Laira would be cutting range fine when including those sustained gradients.

The banks would certainly be a prime target for OLE.

I can also see all the branch line interchange stations wanting electrification too in this instance, as a means to provide battery power to the branch line services. St Erth was included in the OP idea, but Liskeard, Par and Truro would certainly value it, particularly the latter as the Maritime line is the most intensively used branch in Cornwall, to the point I could see other parts of the branch electrified too (which also has steep gradients). The Atlantic Coast line may also need electrification at the Newquay end, to facilitate with the regular service and the summer specials, including XC services if they were to return.

The issue is that to have a substantial body of electrification to justify the scale of investment electrification requires, you are now talking about fully electrifying through to Penzance, not discontinuous.

If Exeter was to receive electrification from Cogload Jct, as part of the B&H being done, you might as well infill W-S-M to Cogload, which would have the added benefit that if Filton Bank is electrified, Cardiff-Exeter could be done with EMUs.

Filton absolutely should be electrified, and yes infill would be an obvious next step but there are limits as to how fast things can move and if bi modes are being used, then the justification for Weston to Cogload is lower.

 

[Zomboid]

Maybe the way to look at it is too ask where electrification will help the most. In terms of the Western area, Bristol Parkway to WSM would help both the local XC and GW intercity service groups. Finishing the job to Oxford needs to happen, too.

Then Whiteball through to Plymouth is hilly enough to be worthwhile, and would help XC, GW intercity and potentially BEMUs on the Waterloo line, and if Exmouth and Paignton were included that's a local service helped, too. How far is it from there to the end? Doing St Par to Penzance would help everything that runs around there, and I think you could fully decarbonise Cornwall with static charging added at Newquay and BEMU trains. The Looe branch might need some dynamic charging infrastructure given the minuscule turn round allowances.

The trains then need to be able to cope with that (including, I would imagine, running past Dawlish with the juice off).

 

[6Gman]

The technical stuff is well beyond me, but ... would wiring the Royal Albert Bridge be acceptable to the heritage people?

 

[Zomboid]

The technical stuff is well beyond me, but ... would wiring the Royal Albert Bridge be acceptable to the heritage people?

Possibly not, but if we're running BEMUs then it wouldn't need to be. (The same may apply through Bath, if the GWML trains are going to need batteries in general then that would avoid that problem - but it would then force any pure electrics going to Bristol to run via Filton.

Though there's no reason why a suitably sympathetic design couldn't be developed if necessary.

 

[zwk500]

Possibly not, but if we're running BEMUs then it wouldn't need to be. (The same may apply through Bath, if the GWML trains are going to need batteries in general then that would avoid that problem - but it would then force any pure electrics going to Bristol to run via Filton.

Though there's no reason why a suitably sympathetic design couldn't be developed if necessary.

It's been addressed before - a solution for OLE in Bath *was* agreed. It was a bespoke design but was apparently accepted by the relevant bodies for the tricky bit through Sydney Gardens.

The technical stuff is well beyond me, but ... would wiring the Royal Albert Bridge be acceptable to the heritage people?

Fundamentally it's national infrastructure and if needed the heritage provisions can be overridden at a political level. Enough other heritage structures have wires there's no real reason not to. The Royal Albert Bridge is probably one with less visual impact than most given it's already a fairly big structure. The heritage objections always feel a bit hypocritical to me as if those objecting had been alive when the line was built there'd be no bridge to protect! Add in the fact that Brunel was always keen to experiment with the latest technology, and I'd argue that wiring his bridge was the least we could do to honour the historic legacy of such a structure.

 

[brad465]

It's been addressed before - a solution for OLE in Bath *was* agreed. It was a bespoke design but was apparently accepted by the relevant bodies for the tricky bit through Sydney Gardens.

Canning this part of the GWML electrification was the second-most stupid bit (after Oxford), given all the prep work that went into it for nothing. Box tunnel was shut for 6 weeks in 2015, with 4 of those also closing Sydney gardens. There was a 2-week possession in 2016 for Bath-Bristol, then 2017 Bath station itself was half-closed to realign the platforms for OHLE installation. They'd practically done over half the work by the time it was canned. There were other benefits, including track renewal work that timed well with life expiry, but beyond that little was gained from what I can see.

 

[Zomboid]

It's been addressed before - a solution for OLE in Bath *was* agreed. It was a bespoke design but was apparently accepted by the relevant bodies for the tricky bit through Sydney Gardens

So I've heard, but if the trains are to have batteries it may end up simpler to not bother.

Personally I wouldn't choose that path, for me trunk routes need continuous wiring from end to end, and it's only the secondary routes/ add-ons that should be considered for discontinuous electrification. In terms of the GWML, the trunk routes in my opinion are London - Oxford, Bristol & WSM (both ways) and Swansea; wires should also reach Bedwyn, and from there to Penzance discontinuous electrification should be considered.

 

[CdBrux]

So I reckon you could batterify all the way to Penzance by electrifying just 46 route miles of track, given that 5 miles is already done around Bristol Parkway. And by adding Westbury to Castle Cary (20 miles; 20 minutes) you could do the same for London Paddington traffic via the Berks and Hants.

Any thoughts?

I do like this way of thinking!
I suppose a next step would be to run a similar exercise for other, local, services sharing the same infrastructure to see how many of them you could change to BEMU operation with these wires or just a little more. How much spare time do you have?

 

[HSTEd]

Is there anything preventing a two track railway having its two tracks on "opposite" phases using autotransformer feeding?

Obviously it would make crossovers more complicated, but with short charging sections it may be possible to avoid those complications entirely.

It would simplify the wiring on railway property further.

 

[zwk500]

Is there anything preventing a two track railway having its two tracks on "opposite" phases using autotransformer feeding?

Obviously it would make crossovers more complicated, but with short charging sections it may be possible to avoid those complications entirely.

It would simplify the wiring on railway property further.

Doesn't this require 2 AT connections, so double the tricky bit of connecting to the grid?

 

[Nottingham59]

Is there anything preventing a two track railway having its two tracks on "opposite" phases using autotransformer feeding?

Would that bring any benefit? At 21 miles, the longest OHLE island won't need AT boosting, I would have thought.

Using SFCs avoid the problem of trying to balance out phases. Having the island all one phase makes things so much simpler.

 

[Zomboid]

Would that bring any benefit? At 21 miles, the longest island won't need AT boosting, I would have thought.

Using SFCs avoid the problem of trying to balance out phases. Having the island all one phase makes things so much simpler.

It's probably not related to your straw man.

Electrically the circuit would work with the up line at +25 and the down at -25, but that would probably create a lot of complications in the real world. Double length neutral sections on crossovers and the like, which would get very complicated in station areas.

 

[HSTEd]

Doesn't this require 2 AT connections, so double the tricky bit of connecting to the grid?

As far as the grid or frequency converter is concerned it remains a single phase load, it is just that the traction side of the transformer has a centre tapped winding rated for 50kV end-to-end. The rail return is coupled to the centre tap and the two contact wires are connected to the end windings.

== Doublepost prevention - post automatically merged: 9 May 2025 ==

Would that bring any benefit? At 21 miles, the longest OHLE island won't need AT boosting, I would have thought.

Using SFCs avoid the problem of trying to balance out phases. Having the island all one phase makes things so much simpler.

Within an island, no.
But if you use AT feeding you can use an inexpensive distribution line to interconnect all the islands and feed them either with two SFCs at different sites, or with a single SFC and a single phase feed from an existing 25kV installation.

Given the discontinuous nature of the installation and the provision of large traction batteries (and in this case, a 700kW generator) on all trains, we can accept significantly lower redundancy in the system.

Six islands would require a total of twelve two pole circuit breakers and one SFC (Assuming the SFC output is protected by a circuit breaker). If you are willing to accept a distribution line fault taking out a charging island, you only need six circuit breakers. Ofcourse this assumes that a suitable phase can be selected for feeding from the GWML, otherwise you will need a second SFC.
Any single fault could knock out at most one charging island.

 

[Sir Felix Pole]

I understand the St. Ives and Looe branches are not suitable (yet) for battery operation as the turnaround times are too tight. It could be done with extra units on 'charge', swopping them over during the day, but of course, adversely affecting the economics.

One option is 'tram-train' conversion, with lightweight catenary on the branch, but vehicles capable of running on the mainline to get back to their depots or perhaps offering a through service St. Ives to Penzance. (Buses are often heavily delayed on the gridlocked A30). A tramway style passing loop on the dunes at Lelant would enable a more frequent service for this popular line.

For Looe, the line could be extended a couple of hundred metres to reach the town bridge and perhaps even the quayside.