T&W Metro: Nexus won't extend DB Regio contract past 2017

[nerd]

A single voltage 1500V rail vehicle can be built far more simply than an AC or dual voltage version of the same.
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Is that really the case HSTEd? As all LRVs are now equipped with AC power; any LRV product that is likely to be available off-the-shelf (which is an so essential requirement for Nexus, as I understand it), will require, for Metro use, an inverter to convert from OLE DC to AC anyway. I can see that dual voltage is likely to be a bit more costly - though I understand, much less so now than formerly - but otherwise, the simplest option will be 750v DC, as that is always what would be the original specification. If Metro don't want that; then other voltage options are much of a muchness.

 

[HSTEd]

Is that really the case HSTEd? As all LRVs are now equipped with AC power; any LRV product that is likely to be available off-the-shelf (which is an so essential requirement for Nexus, as I understand it), will require, for Metro use, an inverter to convert from OLE DC to AC anyway.

Well yes, but it does not need a line frequency transformer to produce AC (although in future I would not be surprised if a lot of power to auxiliaries was provided as DC at some arbitrary voltage anyway, given that LED lighting and computers much prefer DC).
You just get an off the shelf inverter of a type similar to one you can buy in a shop for any components that have to be AC. For example an air conditioning unit motor. Although even those are tending to be replaced with VFD driven motors that can accept DC power.

I can see that dual voltage is likely to be a bit more costly - though I understand, much less so now than formerly - but otherwise, the simplest option will be 750v DC, as that is always what would be the original specification. If Metro don't want that; then other voltage options are much of a muchness.

All you need to do to convert a 750v DC traction package to a 1500v DC one is fit higher rated IGBTs and tweak the software.
You need 3 IGBTs for a three phase traction inverter and one to convert 1500vDC into something more reasonable for auxiliary use. Any downstream inverter can use low rating MOSFETs which are cheaper and easier to drive.
Fitting 25kV requires either a second pantograph or extra high rating circuit breakers [the 1500V side one has to hold off 25kVac], a main transformer, a main rectifier and numerous other components, all of which have to be built to a far higher voltage tolerance than anything on a pure DC design. And the transformer is going to weigh some ridiculous amount.

 

[edwin_m]

It becomes a question of how much you are willing to spend to retain this capability that might be needed fifty years from now.
Unless you chose to depend on PETTs becoming available in the future you effectively have to design the trains to accept a transformer of the types available today which is a significant design compromise.
A single voltage 1500V rail vehicle can be built far more simply than an AC or dual voltage version of the same.

The Rotherham tram-trains are being supplied with 25kV capability due to the likelihood of the shared route being converted to that voltage in future. Due to the prevalance of high voltage electrification on most railways across Europe, tram-train designs (which is what the Metro replacement stock is) are likely to have this capability at little extra cost. And it's worth noting that all EMU classes ordered since privatisation for DC operation, excepting only classes 458 and 460, have provision for AC conversion.

It is also worth noting that any fleets likely to be operating the Durham Coast line will probably be self contained and therefore the service could simply be operated by a handful of dual voltage units should the need arise.

The service operating the Coast line runs through to the Hexham-Carlisle line today and who's to say both might not be electrified in 50 years time? In that sort of timescale there is also the possibility of electric passenger services to York and beyond, and widespread use of electric freight with the Coast providing an alternative route to avoid the ECML. In my view any of these contingencies justifies the minimal cost of providing 25kV capability on the Metro units.

Provision of a non-standard micro-fleet with 1500V capability, with all the necessary standards, design and safety case activity, doesn't bear thinking about. And who would pay for it, given that it would only be needed to accommodate the non-standard Metro operation?

 

[HSTEd]

Provision of a non-standard micro-fleet with 1500V capability, with all the necessary standards, design and safety case activity, doesn't bear thinking about. And who would pay for it, given that it would only be needed to accommodate the non-standard Metro operation?

But that provision can be discounted into the future, as opposed to the modifications that have to be made now to ensure metrocars can use 25kV.
And since traction packages are increasingly off the shell drop in devices it is highly unlikely that the cost would really be much greater considering it would just be swapped with a French or similar pack with 1500V capability built in.

And it's worth noting that all EMU classes ordered since privatisation for DC operation, excepting only classes 458 and 460, have provision for AC conversion.

These vehicles are not standard EMUs though.

The service operating the Coast line runs through to the Hexham-Carlisle line today and who's to say both might not be electrified in 50 years time?

And who says the service pattern will look anything like it does now?

In that sort of timescale there is also the possibility of electric passenger services to York and beyond, and widespread use of electric freight with the Coast providing an alternative route to avoid the ECML. In my view any of these contingencies justifies the minimal cost of providing 25kV capability on the Metro units.

Ah yes the magical electric freight that is just waiting to materialise and for which we have been waiting for since privatisation.
Electric freight simply isn't going to happen in our lifetimes.
And through services to York could be handled by a much smaller dual voltage fleet of heavy rail units.
Either 50+ dual voltage units now or 5-10+ in the future.
If we order dual voltage units now they will use more energy and have more maintenance requirements due to greater internal complexity and the carriage of all the extra weight, even if no transformer is fitted you will still require a concrete ballast weight along the lines of the ones fitted to the 450s.

 

[edwin_m]

But that provision can be discounted into the future, as opposed to the modifications that have to be made now to ensure metrocars can use 25kV.
And since traction packages are increasingly off the shell drop in devices it is highly unlikely that the cost would really be much greater considering it would just be swapped with a French or similar pack with 1500V capability built in.


These vehicles are not standard EMUs though.

And who says the service pattern will look anything like it does now?

Ah yes the magical electric freight that is just waiting to materialise and for which we have been waiting for since privatisation.
Electric freight simply isn't going to happen in our lifetimes.
And through services to York could be handled by a much smaller dual voltage fleet of heavy rail units.
Either 50+ dual voltage units now or 5-10+ in the future.
If we order dual voltage units now they will use more energy and have more maintenance requirements due to greater internal complexity and the carriage of all the extra weight, even if no transformer is fitted you will still require a concrete ballast weight along the lines of the ones fitted to the 450s.

You must have a very accurate crystal ball to know exactly which options to rule in and out over a 50 year period.

 

[nerd]

You must have a very accurate crystal ball to know exactly which options to rule in and out over a 50 year period.

agreed edwin. But the general trend towards the specification of tram-train functionality is becoming pretty clear. So we can tell how light rail systems (and their counterpart heavy rail lines) are currently being respecified for future tram-train opertion; and that itself establishes a set of parameters that future route improvement options are likely to operate within.

Once current estimations of a likely future establish the specifications of a standard product; then it is more likely than not, that future line investment will be undertaken so as to conform with the requirements of that product.