BEMUs vs. full electrification of lines?

[HSTEd]

Then you would be extremely naïve.
We apparently can't afford to finish the last few miles of the GW electrification project. Similarly Midland Main line to Leicester and Sheffield. HS2's eastern leg is abandoned as is north of Birmingham. Yet some people imagine billions are to be found to provide a new high speed line from Leeds via Bradford and Huddersfield across the Pennines.

mods note - split from this thread

How do you solve a problem like Bradford?

Please move this thread if it is in the wrong place but with the news today that Bradford Interchange will close in 2028 due to end of life expectancy. What is the solution for a fully integrated transport network in the UK’s fastest-growing city in terms of population? Rather than having two...

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I really don't want to derail the thread, but yhe GW electrification project and HS2-East failed due to massive cost runaways, which is why they were cut back. The Midland Main Line electrification was axed because it doesn't actually achieve anything commersurate to the cost of 25kV electrification in the modern era.

In a world where electrodiesels exist, there is very little additional track on which electrification can be justified at the cost at which the railway appears able to deliver.
The network effect is dead, and electrification is almost (if not totally) complete - especially with the arrival of practical battery trains.

It's not really a "there is no money" issue, its a "its not really worth it any more" issue.
A new line is still potentially justifiable if it actually delivers benefits that can offset its cost.

Wherever NPR is proposed to be routed will be a construction nightmare because of the nature of the terrain. It would have to be lots of viaducts, tunnels, bridges etc. i.e. a very high cost/mile. And if the other projects aren't financially viable then this doesn't stand a chance.

I'd argue that the lesson of HS2 is that it is surface construction that is a nightmare with a very high cost per mile.
Tunnels are now the easy (and probably fast) way to build railways in the UK, and the cost differential is smaller than it has ever been, even in good terrain. In bad or expensive terrain the tunnel will be cheaper.

If anything happens at Bradford (or at all) I would not discount a new line, but I think by far the most likely course is that nothing will happen
.

 

[HSTEd]

What are you on about?

The main reason for electrification is that it allows for much quicker acceleration which is vital for a mixed traffic, mixed service density route like the Calder Valley.

That was true 30 years ago, but diesel trains have way higher performance now. In any case, battery trains will eliminate any limitations on acceleration - and their arrival is likely inevitable at this point.

It will also remain the main route for East to West freight across the Pennines.

I am very skeptical electric freight is suddenly going to take off.
I think the freight operators are going to cling to their two stroke EMD diesel engines until they are pried from their hands by the government.

 

[The Pelican]

I am very skeptical electric freight is suddenly going to take off.
I think the freight operators are going to cling to their two stroke EMD diesel engines until they are pried from their hands by the government.

As in America- the pre-war Pennylavania Railroad proves the advantages of a four-track electrified mainline- only for the rest of the country not to progress to it!

 

[Noddy]

In any case, battery trains will eliminate any limitations on acceleration

Much as I am a fan of battery powered vehicles this simply isn’t true. The weight of the battery will slow you down. With small gaps in electrification and small batteries that just need to plug these short gaps this won’t be that noticeable. But if you call it quits now on electrification of the network you are going to need BEMU with large, heavy batteries to cover all the extended gaps in electrification.

 

[HSTEd]

Much as I am a fan of battery powered vehicles this simply isn’t true. The weight of the battery will slow you down. With small gaps in electrification and small batteries that just need to plug these short gaps this won’t be that noticeable. But if you call it quits now on electrification of the network you are going to need BEMU with large, heavy batteries to cover all the extended gaps in electrification.

The BEMU will be heavier, it is true. But it will also have no real limit on available traction power. The power to weight ratio of batteries is very high, so it would be able to brute force the acceleration.

Unlike with a 25kV EMU with a transformer with a limited rating, it can just pump out as many kilowatts as it can use without spinning the wheels.

Acceleration will trend towards the wheelslip imposed limit.

 

[Noddy]

The BEMU will be heavier, it is true. But it will also have no real limit on available traction power. The power to weight ratio of batteries is very high, so it would be able to brute force the acceleration.

Unlike with a 25kV EMU with a transformer with a limited rating, it can just pump out as many kilowatts as it can use without spinning the wheels.

Acceleration will trend towards the wheelslip imposed limit.

Of course there is a limit to the ‘traction power’. Batteries can’t just output an unlimited number of kilowatts or megawatts. For a start you’ll run into significant voltage sag and overheating issues if you try to output everything all at once-this is controlled by the battery management system limiting the output. But more importantly you’re using the same electric motors whether the power comes from the battery or via the pantograph.

 

[HSTEd]

Of course there is a limit to the ‘traction power’. Batteries can’t just output an unlimited number of kilowatts or megawatts. For a start you’ll run into significant voltage sag and overheating issues if you try to output everything all at once-this is controlled by the battery management system limiting the output. But more importantly you’re using the same electric motors whether the power comes from the battery or via the pantograph.

Modern lithium batteries are capable of such output powers that they may as well be unlimited from this perspective.

Electric car batteries are rated for peak draws that would drain them flat in around 15 minutes. This is how high performance electric cars have such stunning and dangerous acceleration performance. The battery bank in a significant range BEMU will be capable of the sorts of power outputs that are normally found in high speed trainsets, at least for a few minutes.

As for electric motors, modern motors have reached such high power to weight ratios (peak outputs of several kW per kg) that they won't constitute a large fraction of the train's mass, almost regardless of power outputs.

The limiting factor in the achievable performance of an EMU with modern technology is going to be the traction transformer and the ability of the upstream power supply to cope. Battery trains remove both of these restrictions.

But this is wandering off topic, but I really can't see a compelling case to spend the hundreds of millions of pounds required for Calder Valley electrification any time soon.

 

[Noddy]

Electric car batteries are rated for peak draws that would drain them flat in around 15 minutes. This is how high performance electric cars have such stunning and dangerous acceleration performance. The battery bank in a significant range BEMU will be capable of the sorts of power outputs that are normally found in high speed trainsets, at least for a few minutes.

As for electric motors, modern motors have reached such high power to weight ratios (peak outputs of several kW per kg) that they won't constitute a large fraction of the train's mass, almost regardless of power outputs.

EVs have great performance because of the electric motor. It doesn’t matter where the source of the electricity comes from. Peak discharge performance of an EV battery might be high (maybe 3 or 4C) but that comes with thermal degradation as well as voltage sag issues which are especially noticeable at low temperatures and low states of charge. At 0 degrees Celsius my Cupra Born starts to limit power at around 30% state of charge to prevent this happening. And even at high states of charge and temperatures they’ll only do peak performance for very short bursts. My standard range Born has faster acceleration (and I would imagine braking) than the long range Born with larger batteries precisely because it has a smaller, lighter battery pack, even though the larger pack could (theoretically) output more. The limiting factor here is the electric motor, not the battery pack, but the extra weight of the larger battery is a performance penalty (for acceleration and probably braking).

Repeatedly crossing the pennies all day everyday with a BEMU in winter is going to require very large batteries to avoid encountering these issues, especially as the battery ages and the resistance increases. This is perfectly possible and BEMUs are definitely the way forward. But without further electrification they won’t give the same performance benefits as pure EMUs if in effect they have to be BMUs and carry around lots of batteries (and I imagine will also incur higher track access fees than their lighter equivalents).