Discontinuous Electrification - RUK's thoughts?

[StKeverne1497]

To provide battery EMUs to replace every one of the c5000 non pure EMU passenger vehicles on the network, with enough range for about an hour off the wire, would need roughly 750MWh of battery capacity. That‘s what Tesla produce every day for their cars.

I'm not sure that adds up, even if I'm right to assume you mean individual vehicles rather than "trains", and ignoring those trains that have unpowered vehicles.

750MWh divided by 5000 vehicles is 150kWh per vehicle. Elsewhere it looks as if a typical DMU uses about 10 times the amount of Diesel per mile as a car would. If you assume double the efficiency for a BEMU because of regeneration (no idea if that's an appropriate figure) and apply the resulting ratio (5 times the amount) to a rail vehicle, that's the equivalent of about a 30kWh battery in a car. Is that really enough for an hour of stop-start driving, fast acceleration and 60 - 75mph top speeds?

I mean, by my back-of-the-envelope you're possibly in the right ballpark if my assumptions are reasonable, but it's right at the low end I'd think.

The other question is whether a typical BEMU will need an hour of off-wires running. I gather TfW probably will, as the stretch between Queen Street and Penarth (for example) will not be wired, but is that a "normal" situation in the rest of the country , or is it more likely to be a few much shorter stretches, as happens north of Queen Street?

 

[Technologist]

I'm not sure that adds up, even if I'm right to assume you mean individual vehicles rather than "trains", and ignoring those trains that have unpowered vehicles.

750MWh divided by 5000 vehicles is 150kWh per vehicle. Elsewhere it looks as if a typical DMU uses about 10 times the amount of Diesel per mile as a car would. If you assume double the efficiency for a BEMU because of regeneration (no idea if that's an appropriate figure) and apply the resulting ratio (5 times the amount) to a rail vehicle, that's the equivalent of about a 30kWh battery in a car. Is that really enough for an hour of stop-start driving, fast acceleration and 60 - 75mph top speeds?

I mean, by my back-of-the-envelope you're possibly in the right ballpark if my assumptions are reasonable, but it's right at the low end I'd think.

The other question is whether a typical BEMU will need an hour of off-wires running. I gather TfW probably will, as the stretch between Queen Street and Penarth (for example) will not be wired, but is that a "normal" situation in the rest of the country , or is it more likely to be a few much shorter stretches, as happens north of Queen Street?

I wrote something similar, I did check the UK market is in the region of 1000 coaches per year, EMU, DMU, unpowered.

Either way the total amount of batteries to turn them into BEMUs is similar to hours of battery production at a single car marker. Even if the calc is off by an order of magnitude it doesn't change the fact that battery trains are unlikely to be a noticeable part of the battery market.

Especially as automotive is going to up it battery usage by more than 10x compared to today and grid storage will approximately equal that. Essentially batteries will be at least as big as oil is today and as batteries have relatively low negative externalities expect lots of new uses for batteries as they keep getting cheaper.

Regarding BEMU they are conceptually about where EVs were in 2000's a conventional vehicle with a battery box strapped in. By the 2010's we start seeing integrated battery packs being part of the structure, battery heat management, improved aero, more efficient motors/inverters and heat pumps for heating.

A ground up BEMU could use considerably less energy, not least from more diligent aero design. Most high speed trains trade accessibility/ not having to do masses of testing to prove aero features don't result in overheating or crud accumulation and the ability to use off the shelf components for aero efficiency. They can always just draw more energy from the OHW or fit a slightly bigger diesel tank.

The specs for the Class 801 train equate to a maximum consumption of 3.42KWh per coach going London to Kings Cross. That's a max consumption of 4600Kwh for the 5 car train.

Interestingly enough the bi modal 800 is 10 tonnes heavier than the electric model and carries 4.5 tonnes of fuel. A 14.5 tonne battery pack at 150Wh/kg (a good LFP chemistry pack) that gives us 2175KWh of battery or 125 miles at 125mph.

That of course assumes that a class 800 is the bleeding edge of all technology. It clearly isn't, there's plenty of scope for aerodynamic improvements. I doubt very much whether house loads have been ruthlessly designed to be minimised. It is also not a particularly light train.

1 hour of operation and 20 minutes charging means that you only need 1/3 of a trains route to be electrified and you have basically unlimited range.

Conclusion; I don't see why we don't have a national strategy for getting rid of diesel very rapidly using partial electrification and ambitiously designed BEMUs nicking as much tech out of EVs. Frankly everything should be accelerating at 1.3m/s/s whatever the top speed, larger high power motors are cheap commodities now there's no reason to not make every train gloriously overpowered.

 

[Nottingham59]

Conclusion; I don't see why we don't have a national strategy for getting rid of diesel very rapidly using partial electrification and ambitiously designed BEMUs nicking as much tech out of EVs.

I agree. For remote destinations like Penzance and Oban, we should have convertible trimodes, with a small but high-power battery (100kWh/2MW) and a small (~100-200kW) diesel engine running on HVO biofuel. To be converted to pure BEMU as islands of OHLE get built.

 

[Trainbike46]

I wrote something similar, I did check the UK market is in the region of 1000 coaches per year, EMU, DMU, unpowered.

Either way the total amount of batteries to turn them into BEMUs is similar to hours of battery production at a single car marker. Even if the calc is off by an order of magnitude it doesn't change the fact that battery trains are unlikely to be a noticeable part of the battery market.

Especially as automotive is going to up it battery usage by more than 10x compared to today and grid storage will approximately equal that. Essentially batteries will be at least as big as oil is today and as batteries have relatively low negative externalities expect lots of new uses for batteries as they keep getting cheaper.

Regarding BEMU they are conceptually about where EVs were in 2000's a conventional vehicle with a battery box strapped in. By the 2010's we start seeing integrated battery packs being part of the structure, battery heat management, improved aero, more efficient motors/inverters and heat pumps for heating.

A ground up BEMU could use considerably less energy, not least from more diligent aero design. Most high speed trains trade accessibility/ not having to do masses of testing to prove aero features don't result in overheating or crud accumulation and the ability to use off the shelf components for aero efficiency. They can always just draw more energy from the OHW or fit a slightly bigger diesel tank.

The specs for the Class 801 train equate to a maximum consumption of 3.42KWh per coach going London to Kings Cross. That's a max consumption of 4600Kwh for the 5 car train.

Interestingly enough the bi modal 800 is 10 tonnes heavier than the electric model and carries 4.5 tonnes of fuel. A 14.5 tonne battery pack at 150Wh/kg (a good LFP chemistry pack) that gives us 2175KWh of battery or 125 miles at 125mph.

That of course assumes that a class 800 is the bleeding edge of all technology. It clearly isn't, there's plenty of scope for aerodynamic improvements. I doubt very much whether house loads have been ruthlessly designed to be minimised. It is also not a particularly light train.

1 hour of operation and 20 minutes charging means that you only need 1/3 of a trains route to be electrified and you have basically unlimited range.

Conclusion; I don't see why we don't have a national strategy for getting rid of diesel very rapidly using partial electrification and ambitiously designed BEMUs nicking as much tech out of EVs. Frankly everything should be accelerating at 1.3m/s/s whatever the top speed, larger high power motors are cheap commodities now there's no reason to not make every train gloriously overpowered.

While I agree with you on most things here, I'm not sure you're being entirely fair when comparing a BEMU with early EV cars. BEMUs are typically based on EMUs, so starting from a train that is optimised for electric usage. Some of the improvements of newer EV cars, like heat pump heating, are used on trains already (and have been for years - NS was retrofitting it to some inctercities in the early 2010s). Of course these improvements in energy efficiency should be more universally applied, and more improvements should be sought.

For clarity, I fully agree with your conclusion that we should be replacing diesel trains with (B)EMUs quickly. Let's hope the new orders (Northern, GWR Churchward, Chiltern, etc.) recognise this and only order (B)EMUs

 

[zwk500]

A ground up BEMU could use considerably less energy, not least from more diligent aero design. Most high speed trains trade accessibility/ not having to do masses of testing to prove aero features don't result in overheating or crud accumulation and the ability to use off the shelf components for aero efficiency. They can always just draw more energy from the OHW or fit a slightly bigger diesel tank.

This is true, but the design process for trains is far longer and requires far more certification than new designs for cars. I don't think it's quite as bad as planes, which can take 30 years of development and testing for a new airframe, but it's long and therefore very expensive. A co-ordinated strategy would be identifying the long-term need for BEMUs while strapping battery packs under existing EMUs in the short term, to allow the extension of electrification to match the long-term strategy.

Interestingly enough the bi modal 800 is 10 tonnes heavier than the electric model and carries 4.5 tonnes of fuel. A 14.5 tonne battery pack at 150Wh/kg (a good LFP chemistry pack) that gives us 2175KWh of battery or 125 miles at 125mph.

Worth mentioning the traction power design on the 80x series is modular - you can switch the diesel gensets out for batteries if you wish (GWR made some noise about trialling just such an arrangement for air quality and efficiency on the West Country routes).

Conclusion; I don't see why we don't have a national strategy for getting rid of diesel very rapidly using partial electrification and ambitiously designed BEMUs nicking as much tech out of EVs.

Agree

 

[Bald Rick]

I'm not sure that adds up, even if I'm right to assume you mean individual vehicles rather than "trains", and ignoring those trains that have unpowered vehicles.

750MWh divided by 5000 vehicles is 150kWh per vehicle.

Essentially, yes I meant vehicles. 150kWh per vehicle, 600kWh for a generic 4 car unit with 1.2MW installed power. Gives it half an hour st full power, but there isn’t a DMU on the network that ever does that in a duty cycle. A typical cycle sees a unit on full power for 20-30%, lower notched power for 30-40%, and idling for 30-40%. And for a BEMU when braking, that will be recovering a decent proportion of the energy used for acceleration. So a reasonable assumption is that a battery capacity of half the installed power of a unit will give it an hour off the wire.

A 600kWh battery of LiTo type (that chemistry is used in the Clss 93 batteries) will weigh around 6 tonnes. On a 4 car unit weighting 160 tonnes, thats essentially noise, especially when weight doesnt matter so much in terms of energy consumption on a battery unit.

 

[Peter Wilde]

A few further thoughts:

Gap-bridging is not necessarily bad. But carrying batteries for many miles under the wires in order to deal with an un-wired stretch towards the end of a long route is not desirable. Really it would be better to deal with that situation by (1) bringing the cost of electrification down with a sensibly expanded rolling programme (like the Southern pre-war - not really such a difficult concept to grasp!); or if that is still too expensive, (2) dragging the EMUs over the non-electrified far end of the route by attaching a battery powered front end. Surely it is not beyond the wit of man to provide this in the form of a low vehicle, like the 1950s diesel brake tenders? This could then be attached at the front of the train at the changeover station, eliminating any shunting or the need for any extra cabs and controls. A quick process, as was done routinely on the Southern Region when Weymouth services attached/detached Class 33s at Southampton … but this time with electric traction. (Of course some clever-ish new engineering would be needed, to deal with automated coupling/uncoupling of power cables, and how to move un-cabbed battery vehicles off to a charging or repairs siding. Not exactly rocket tech though is it?).

Yes, the world can probably manufacture lots and lots of high-tech batteries, eventually. But there will be a long transitional phase in which there will be a shortage. At that time the priority will be for the available batteries to be used in road transport.

For calculating the required battery powers, remember that trains moving onto branch lines will encounter more hills, steep curves, station stops and speed restrictions; so average power figures will not apply.

 

[Dr Hoo]

The brake tenders weren’t ‘diesel’ or powered or drivable in any other way. They were just a ‘dumb’ wagon that had a high, dead, weight and brake force, to supplement the locomotive on unfitted trains.

 

[aavm]

Back to the original question.

If lines apart were OHE'd apart from (too expensive) bridges, tunnels, etc, could a train
- run at line speed, (say) 125mph
- lower the pantograph automatically to go through a tunnel / under a bridge
- and raise it automatically afterwards

What typical percentage difference would skipping the bridges/tunnels make to the cost?

 

[Snow1964]

Back to the original question.

If lines apart were OHE'd apart from (too expensive) bridges, tunnels, etc, could a train
- run at line speed, (say) 125mph
- lower the pantograph automatically to go through a tunnel / under a bridge
- and raise it automatically afterwards

What typical percentage difference would skipping the bridges/tunnels make to the cost?

Any section where pantographs are raised on the move needs extra strength wiring.
In many cases there is a need to continue the wire with a dummy section, a non conductor bar or wire, to avoid a problem if the pantograph fails to drop then strikes something (something like this happened few weeks ago near City Thameslink, and blocked line for hours)
It's also not good idea to be dead in a tunnel and if something happens and train brakes and stops on dead section, then got risk of not restarting it in a tunnel.

By time you have done this, it is often cheaper to install one of the modern slim fixed bar type contact wire in structure than have the dead section, especially nowadays that special insulating materials, and even non conducting paint can be between pantograph and structure.

 

[Irascible]

But carrying batteries for many miles under the wires in order to deal with an un-wired stretch towards the end of a long route is not desirable.

Why would you assume batteries are dead weight under wires? you can even out demand ( supply too, don't have to dump all regen power into the wires either ) through the fixed infrastructure if you draw off batteries as well as the supply when you're accelerating, and you can still regen into them - this'd be even more beneficial on 3rd rail. In the interests of keeping the system simple it'd make some sense to *always* run off the batteries - you're insulated from any supply side failure ( up to the point you run out of battery, obviously ). Your entire traction package is somewhat seperate from power supply modules which helps commonality. Whether battery tech can manage that I don't know yet, but there are other applications that are going to want that behaviour ( I'd think the national grid would be eyeing that sort of capability too ).

To answer the initial question - if the choice is between some electrification or none, then good grief yes.

 

[HSTEd]

A few further thoughts:

Gap-bridging is not necessarily bad. But carrying batteries for many miles under the wires in order to deal with an un-wired stretch towards the end of a long route is not desirable. Really it would be better to deal with that situation by (1) bringing the cost of electrification down with a sensibly expanded rolling programme (like the Southern pre-war - not really such a difficult concept to grasp!)

There have been several attempts to reduce the capital cost of electrification, they have pretty much all failed miserably.
At some point we are going to have accept the evidence that exists, which is £4m/stkm is about the best that can be done.

And a rolling programme will not achieve much in the time available.

; or if that is still too expensive, (2) dragging the EMUs over the non-electrified far end of the route by attaching a battery powered front end. Surely it is not beyond the wit of man to provide this in the form of a low vehicle, like the 1950s diesel brake tenders? This could then be attached at the front of the train at the changeover station, eliminating any shunting or the need for any extra cabs and controls. A quick process, as was done routinely on the Southern Region when Weymouth services attached/detached Class 33s at Southampton … but this time with electric traction. (Of course some clever-ish new engineering would be needed, to deal with automated coupling/uncoupling of power cables, and how to move un-cabbed battery vehicles off to a charging or repairs siding. Not exactly rocket tech though is it?).

To do that you need a bunch of extra trackwork, signalling and control systems and you add piles of extra mass onto the non electrified sections because this power unit has to generate tractive effort to haul the entire EMU around.

Yes, the world can probably manufacture lots and lots of high-tech batteries, eventually. But there will be a long transitional phase in which there will be a shortage. At that time the priority will be for the available batteries to be used in road transport.

The train system will not consume a measurable number of batteries compared to the demand for the road system.

 

[Nottingham59]

Back to the original question.

What typical percentage difference would skipping the bridges/tunnels make to the cost?

I understand that raising bridges etc. is typically one-third of the total cost of electrification.

But I would use insulated contact rods to push the Pantograph down to get the required physical clearance. If the bridge were too low for that to be possible, or in an acceleration zone, I'd raise the bridge.

 

[zwk500]

Gap-bridging is not necessarily bad. But carrying batteries for many miles under the wires in order to deal with an un-wired stretch towards the end of a long route is not desirable.

Actually, it is. They provide an emergency resource for either traction or hotel power should there be a need to turn the power supply off, and they can be used to supplement the train's power in areas of specific load without needing expensive management of the power supply system, as well as providing an additional reservoir for regenerative braking so that energy doesn't need to be burned off.

Really it would be better to deal with that situation by (1) bringing the cost of electrification down with a sensibly expanded rolling programme (like the Southern pre-war - not really such a difficult concept to grasp!);

While this would be good - and is being pursued in Scotland - it's not going to eliminate the need for batteries nor obviate major costs of rebuilding infrastructure.

or if that is still too expensive, (2) dragging the EMUs over the non-electrified far end of the route by attaching a battery powered front end. Surely it is not beyond the wit of man to provide this in the form of a low vehicle, like the 1950s diesel brake tenders? This could then be attached at the front of the train at the changeover station, eliminating any shunting or the need for any extra cabs and controls. A quick process, as was done routinely on the Southern Region when Weymouth services attached/detached Class 33s at Southampton … but this time with electric traction. (Of course some clever-ish new engineering would be needed, to deal with automated coupling/uncoupling of power cables, and how to move un-cabbed battery vehicles off to a charging or repairs siding. Not exactly rocket tech though is it?).

It's far easier to just have the same vehicle be able to turn a switch. 30 seconds not 5 minutes. Even if you attach at only one end with cab controls you still have an operational dependency at the changeover station (either the loco shunting from up to down platform or all trains using the correct platform) whereas if you have all BEMUs no such limitations.

Yes, the world can probably manufacture lots and lots of high-tech batteries, eventually. But there will be a long transitional phase in which there will be a shortage. At that time the priority will be for the available batteries to be used in road transport.

Tbh the priority should be on rail transport, and trying to encourage shift from road to rail.

For calculating the required battery powers, remember that trains moving onto branch lines will encounter more hills, steep curves, station stops and speed restrictions; so average power figures will not apply.

Equally if you go up the hill, you must come down, and if you're braking you're storing the potential energy for the acceleration the other side. F1 has done rather well out of a rechargable battery in various guises - it's done everything from provide momentary boosts of power to extra braking force to allowing drivers to start and stop the car away from the garage.

 

[Richard Scott]

In the interests of keeping the system simple it'd make some sense to *always* run off the batteries - you're insulated from any supply side failure ( up to the point you run out of battery, obviously ). Your entire traction package is somewhat seperate from power supply modules which helps commonality.

If you constantly run off of the batteries you will have a more inefficient system due to losses charging and discharging. It would soon add up.

Equally if you go up the hill, you must come down, and if you're braking you're storing the potential energy for the acceleration the other side. F1 has done rather well out of a rechargable battery in various guises - it's done everything from provide momentary boosts of power to extra braking force to allowing drivers to start and stop the car away from the garage.

Yes, but not all of it. Some will still be lost as heat during charging and discharging, admittedly it won't be a massive amount but it's still important to take it into account.

 

[edwin_m]

Why would you assume batteries are dead weight under wires? you can even out demand ( supply too, don't have to dump all regen power into the wires either ) through the fixed infrastructure if you draw off batteries as well as the supply when you're accelerating, and you can still regen into them - this'd be even more beneficial on 3rd rail. In the interests of keeping the system simple it'd make some sense to *always* run off the batteries - you're insulated from any supply side failure ( up to the point you run out of battery, obviously ). Your entire traction package is somewhat seperate from power supply modules which helps commonality. Whether battery tech can manage that I don't know yet, but there are other applications that are going to want that behaviour ( I'd think the national grid would be eyeing that sort of capability too ).

To answer the initial question - if the choice is between some electrification or none, then good grief yes.

Using the batteries for regen probably does have a benefit on third rail, particularly in less busy areas where a receptive unit may be a long way away, and much of the regenerated energy will be lost in voltage drop over that distance or dumped into resistors because that voltage drop pushes the voltage over the maximum allowed. Much less so for 25kV because the lower current means the power can travel much further.

I don't know how you "always run off the batteries" - they only have two terminals so you can't be putting power in and taking it out at the same time, unless you have several batteries and switch them on and off line in turn. Anything like that would also waste a significant proportion of the power to inefficiencies in the charge/discharge cycle.

 

[zwk500]

Yes, but not all of it. Some will still be lost as heat during charging and discharging, admittedly it won't be a massive amount but it's still important to take it into account.

Very true, no conversion is 100% efficient.

 

[Technologist]

This is true, but the design process for trains is far longer and requires far more certification than new designs for cars. I don't think it's quite as bad as planes, which can take 30 years of development and testing for a new airframe, but it's long and therefore very expensive. A co-ordinated strategy would be identifying the long-term need for BEMUs while strapping battery packs under existing EMUs in the short term, to allow the extension of electrification to match the long-term strategy.

Worth mentioning the traction power design on the 80x series is modular - you can switch the diesel gensets out for batteries if you wish (GWR made some noise about trialling just such an arrangement for air quality and efficiency on the West Country routes).

Agree

Nit picking but the design process for a type approved car in Europe runs to about €0.5 billion due to the amount of requirements.

It's also why virtually every car in a segment looks the same once you've covered the sight lines, crash test and pedestrian impact requirements.

The key difference is the much more constrained requirements of permanent way and the individual cost of the item. A major new car will have more prototypes, pre-prod and development vehicles than many rail vehicles total production runs. They can run them on the roads without constraint, ship them to the arctic, the desert and write off multiple ones in crash and durability tests. Ergo they can take much bigger development risks. It helps that the market is orders of magnitude bigger and has common standards across multiple nations.

Planes aren't that bad, if they don't go wrong civil airliners can get from go-ahead to flying in 4-5 years and enter service about 1 year after that. Technology development and agreeing how it will be certified is really open ended/ decades long bit that happens before the main programme happens.

My point re; heat pumps and energy efficiency is one of efficiency. I doubt very much that existing trains are quite as optimsed as EV cars with regards to reducing house loads even if they have heat pumps etc. It would be more efficient if they focused on heating and cooling the seats for example and with far more responsive zonal controls.

As to how you might get more dynamism into rail vehicles, I suspect that having the users own them (death to ROSCO) and having contracts where at certain hold points passenger feedback was incorporated into modifications would go a long way. You'd almost need some sort of guiding mind....

 

[Irascible]

they only have two terminals so you can't be putting power in and taking it out at the same time, unless you have several batteries and switch them on and off line in turn

The latter. Pluses would be redundancy, ( potentially ) easier servicing, rotating them spreads "wear" or if the system is clever enough allows different use patterns for different ages of battery... and I was going to say something else but forgot. Disadvantage is extra complication & extra points of failure. Removing the power source switching would be a pretty big potential benefit, but it would as has been said come at the cost of efficiency loss. The major thing is though that batteries aren't useless even with an external power source.

 

[zwk500]

The latter. Pluses would be redundancy, ( potentially ) easier servicing, rotating them spreads "wear" or if the system is clever enough allows different use patterns for different ages of battery... and I was going to say something else but forgot. Disadvantage is extra complication & extra points of failure. Removing the power source switching would be a pretty big potential benefit, but it would as has been said come at the cost of efficiency loss. The major thing is though that batteries aren't useless even with an external power source.

Tbh it'd be better to have the batteries as a backup/extra boost when needed and charging when not. Switching between OLE and battery sources isn't really a problem - it's raising pans on the move or firing up a genset from cold that's a problem.

 

[Technologist]

There have been several attempts to reduce the capital cost of electrification, they have pretty much all failed miserably.
At some point we are going to have accept the evidence that exists, which is £4m/stkm is about the best that can be done.

And a rolling programme will not achieve much in the time available.



To do that you need a bunch of extra trackwork, signalling and control systems and you add piles of extra mass onto the non electrified sections because this power unit has to generate tractive effort to haul the entire EMU around.



The train system will not consume a measurable number of batteries compared to the demand for the road system.

Yes:

Even with a rolling programme there are still limitations as to how fast you can build capacity and there is likely a lower ceiling to costs.

Implementation of BEMU and Bimodal can be done both at replacement and when trains are cascaded/refreshed.

I suspect that the most effective intermittent electrification isn't to try to drop pantographs for bridges but to electricfy decently long stretches where it is comparatively easy and then have relatively long stretches where obstacles are more frequent left free of electrification, 5-20 miles on, 5-20 miles off. Where we have optimised BEMUs like that Battery IET I scoped out it could already do a partially electrified route like London to Sheffield on MML already.

Assuming it leaves the wires at Kettering with 100% charge, it goes down to 80% charge by Leicester, gets 4% charge when standing still, burns 24% to get to Derby (60%). Puts 7% in at Derby (charge rates go up as battery depletes) and burns 36% getting to Sheffield, to arrive with 24% SOC.

If we back fit to a 10% SOC at Kettering returning from Sheffield, we need to do a 24-64% charge, which takes 15 minutes at Sheffield.

Obviously batteries and charging speeds are only getting better, all those performance figures were against LFP types which trade energy density for cost, cycle life and more resistance to deep discharge and fast charging at either end of the state of charge. Also our BEMU IET could have aerodynamic improvements, not least losing 5-10% of drag by stowing the pantograph away.

 

[Richard Scott]

Obviously batteries and charging speeds are only getting better, all those performance figures were against LFP types which trade energy density for cost, cycle life and more resistance to deep discharge and fast charging at either end of the state of charge. Also our BEMU IET could have aerodynamic improvements, not least losing 5-10% of drag by stowing the pantograph away.

I seriously doubt a pantograph being stowed away will reduce drag by 5-10%. I think be hard pushed to make it 1%.

 

[Technologist]

I seriously doubt a pantograph being stowed away will reduce drag by 5-10%. I think be hard pushed to make it 1%.

Influence of pantograph fixing position on aerodynamic characteristics of high-speed trains - Railway Engineering Science

To study the influence of the pantograph fixing position on aerodynamic characteristics of high-speed trains, the aerodynamic models of high-speed trains with eight cars were established based on the theory of computational fluid dynamics, and eight cases with pantographs fixed on different...

link.springer.com

Influence of pantograph fixing position on aerodynamic characteristics of high-speed trains, Liang Zhang et al, 2017.

"When the train speed reaches 200–300 km/h, the aerodynamic drag accounts for 70% to 85% of the total drag of the train [1, 2]. The aerodynamic drag of pantographs accounts for 8% to 14% of the total aerodynamic drag".

The drag of a cylinder is more than 10x that of an aerodynamic shape of the same frontal area. It's why modern racing bikes hide the brake cables and modern bike wheels have blade like spokes.

 

[Bald Rick]

But carrying batteries for many miles under the wires in order to deal with an un-wired stretch towards the end of a long route is not desirable

Why not?

expensive, (2) dragging the EMUs over the non-electrified far end of the route by attaching a battery powered front end.

So ‘carrying batteries for many miles under the wires’ isnt desirable, but having them lie around at a changeover station is?

 

[edwin_m]

"When the train speed reaches 200–300 km/h, the aerodynamic drag accounts for 70% to 85% of the total drag of the train [1, 2]. The aerodynamic drag of pantographs accounts for 8% to 14% of the total aerodynamic drag".

The quote refers to pantographs plural. In the context we are discussing there will be a maximum of two. How many are actually assumed in that paper?

Also there is a broad reference to 200-300km/h. Aerodynamic drag generally varies as the square of train speed, so that speed range potentially introduces a factor of more than 2. Again, the context we are discussing will be at or below 200km/h. If we are talking about energy consumption we are concerned with absolute energy loss to drag, not to what proportion it is of the total energy loss. So I don't believe this quote is particularly useful in enforcing the situation.

 

[Richard Scott]

Influence of pantograph fixing position on aerodynamic characteristics of high-speed trains - Railway Engineering Science

To study the influence of the pantograph fixing position on aerodynamic characteristics of high-speed trains, the aerodynamic models of high-speed trains with eight cars were established based on the theory of computational fluid dynamics, and eight cases with pantographs fixed on different...

link.springer.com

Influence of pantograph fixing position on aerodynamic characteristics of high-speed trains, Liang Zhang et al, 2017.

"When the train speed reaches 200–300 km/h, the aerodynamic drag accounts for 70% to 85% of the total drag of the train [1, 2]. The aerodynamic drag of pantographs accounts for 8% to 14% of the total aerodynamic drag".

The drag of a cylinder is more than 10x that of an aerodynamic shape of the same frontal area. It's why modern racing bikes hide the brake cables and modern bike wheels have blade like spokes.

But that's at high speed, you'll never achieve that with batteries so effect is negligible.

 

[Irascible]

That is also the entire pantograph installation, not just the arm. Having a bunch of odd shaped items on what is basically a hole in the roof ( aerodynamically ) does not do wonders for reducing turbulence. The drag they're showing isn't just from having an arm up in the air, it's the disruption to the smooth flow over the entire train from a break in the contour which is why there's different levels of drag depending on where the pantographs are.

 

[Technologist]

But that's at high speed, you'll never achieve that with batteries so effect is negligible.

That's your assumption not mine, my worked case was using an IET and power consumption from a London to Newcastle run so significant time at 125mph or (200kph) which was within the working range of that estimate.

I would assume that running multiple pantographs is covered in the pretty large spread of drag. Looking at Chinese and Japanese high speed trains they generally operate with two pantographs on very large 16 cars trains.

However in those circumstances we are talking about much longer trains with commensurately more drag. Ergo the % of drag attributable to a pantograph for 400m long train with two pantographs and 200m train with one is likely very similar. In fact the proportion of drag attributable to the pantograph is only going up as the train gets shorter than the max length supportable with a single pantograph.

Baked into my assumption was also that a purpose built BEMU would be designed for aero efficiency ergo the relative proportion would be the same or higher than for a high speed train.

The velocity at which the train travels also won't change the % split of aero drag between the pantograph and the rest of the train, once the flow is turbulent the CD of the train components aren't going to appreciably change.

The only factor that will change is the proportion of energy use associated with aeo drag Vs rolling friction. However at the speeds we are talking about for mainline trains under OHL the vast majority of energy consumption will be aero drag.

That is also the entire pantograph installation, not just the arm. Having a bunch of odd shaped items on what is basically a hole in the roof ( aerodynamically ) does not do wonders for reducing turbulence. The drag they're showing isn't just from having an arm up in the air, it's the disruption to the smooth flow over the entire train from a break in the contour which is why there's different levels of drag depending on where the pantographs are.

On my optimised BEMUs, I would assume that the pantograph sowes like aircraft undercarriage. Given said percentage of drag it would be worth it.

 

[Irascible]

On my optimised BEMUs, I would assume that the pantograph sowes like aircraft undercarriage. Given said percentage of drag it would be worth it.

I'd be interested in the engineering soluition for that - to stay in gauge you'd need a sliding cover for the whole pan area. Not sure that'd be worth it for anything but proper HSR, and given nobody has apparently done it yet I guess it's not been thought worthwhile there either. The aero industry ( and motorsport ) have a lot of aerodynamic tricks which might help to some extent, you don't necessarily have to blank the "hole", just control the boundary layer ( of air ) better.

 

[zwk500]

On my optimised BEMUs, I would assume that the pantograph sowes like aircraft undercarriage. Given said percentage of drag it would be worth it.

I'd love to see where your fairing is stored while the Pan is deployed that doesn't negate any advantage for efficiency when running on batteries.