THE NEW TGV M

[Austriantrain]

But then Switzerland doesn't do very-high-speed rail either really. The FV-Dosto is a 200km/h train. Their higher speed RABe 503s (250km/h) and RABe 501s (300km/h) are both single deckers (and can they reach their maximum speed in Switzerland? Have the GBT and CBT been authorised for 250km/h?).

Cheers,
Ewan

That’s not what I meant, I was talking about boarding times on long-distance Double Deck Stock. That shouldn’t depend on the train‘s maximum speed (but will certainly depend on the amount of luggage being carried, which surely will be more in Germany than in Switzerland).

 

[WizCastro197]

2024 debut dans le sud est?
I am not sure if I like it, it doesn't fit in well with the other TGVs
Assuming when this stock is introduced the Oldest TGVs will be removed?

 

[XAM2175]

The super-long windows on the trailers look interesting, but potentially complicated from a seat-alignment perspective.

And unfortunately the power cars don't look any less hideous now then they did at the Amtrak rollout

But the Swiss - with frequent stops and very high passenger turnover - are doing well with their Double Deck Stock

With a proportionally larger number of doors compared to the TGV Duplex, though.

 

[Austriantrain]

With a proportionally larger number of doors compared to the TGV Duplex, though.

Indeed. That was the point I was trying (and apparently failing) to make.

 

[Technologist]

Because you still need to find room for main transformers and inverters etc (most are triple or quadruple voltage to work to Belgium, Netherlands, Germany, Switzerland and Italy). Each power car is around 5MW (about 6500HP) and even modern inverters of that rating aren’t going to fit under a low floor trailer car. I use term trailer, but actually distributed motors mean some might be motored. A typical 12car British EMU has less power than a single power car, and obviously lot less than 2 power cars so lots of electrical equipment to fit in.

When the TGV Duplex was designed, the catering car had higher floor (there are slopes up in corridor each end), and space underneath housed lots of of the trains auxiliaries as couldn’t fit them in the double deck cars.

The designers of EVs are having a snigger in the corner.....

Plenty of EVs manage to get 1MW or over packaged into a medium sized passenger car, now obviously there is a different duty cycle in those vehicles vs a train, but even accounting for that they are clearly producing much denser components and systems than those built to rail patterns, they are obviously also delivered at volumes and costs unheard of in rail service.

Even rail designers are beginning to notice, and look at adapting EV components, at least according to a few things I've got through from IMECHE.

 

[HSTEd]

Plenty of EVs manage to get 1MW or over packaged into a medium sized passenger car,

1300hp medium sized passenger cars?

I'm not aware of any of those myself.


As for loading times on double deck trains - the RER A called.

 

[AdamWW]

As for loading times on double deck trains - the RER A called.

Not a very appropriate layout for a long distance train though, I'd have thought.

 

[HSTEd]

Not a very appropriate layout for a long distance train though, I'd have thought.

A very similar layout in passenger terms is used for 2hr30 journeys from Brighton to Cambridge on the Class 700s!

And whilst no, I would prefer tables and other such comforts, it does demonstrate that once passengers get used to having to move quickly at these stations, these things can be done quickly. I am skeptical that the dwell time claims often made with regards double deck stock are truly tenable - especially given double-decker bus experience.

 

[AdamWW]

A very similar layout in passenger terms is used for 2hr30 journeys from Brighton to Cambridge on the Class 700s!

And whilst no, I would prefer tables and other such comforts, it does demonstrate that once passengers get used to having to move quickly at these stations, these things can be done quickly.

I thought this was a reference to the double deck trains used on the RER A which have three sets of (large) doors per side on a coach, and consequently two separate double floor sections each with stairs at both ends.

(Of course the 700s do offer a nice area in standard class with seating round tables, it's just very small. And I presume the vast majority of passengers aren't going all the way between Brighton and Cambridge.)

 

[Technologist]

1300hp medium sized passenger cars?

I'm not aware of any of those myself.


As for loading times on double deck trains - the RER A called.

Tesla Model S Plaid has about 1100bhp peak and manages to fit that into a practical 5 door hatchback packaging with storage space under the bonnet.

More exotic stuff like the Rimac Nevara manage to get 1900bhp into a 2 seat mid engined form factor.

Even accounting for a significant derate for different usage cycles they are fitting a lot of electrical power into extremely compact spaces by rail standards. There is much less volume for electrical systems in an EV that you could fit in a bogie never mind a carriage body.

They are also doing some fascinating stuff in the domain of charging cables with the next generation chargers putting out more than a 1MW (at 900v) and flowing that down a cable the same size as a regular car charger.

 

[AdamWW]

How does the

Tesla Model S Plaid has about 1100bhp peak and manages to fit that into a practical 5 door hatchback packaging with storage space under the bonnet.

More exotic stuff like the Rimac Nevara manage to get 1900bhp into a 2 seat mid engined form factor.

Even accounting for a significant derate for different usage cycles they are fitting a lot of electrical power into extremely compact spaces by rail standards. There is much less volume for electrical systems in an EV that you could fit in a bogie never mind a carriage body.

They are also doing some fascinating stuff in the domain of charging cables with the next generation chargers putting out more than a 1MW (at 900v) and flowing that down a cable the same size as a regular car charger.

Would a car perhaps be required to produce the peak output for a less sustained time than a high speed train?

As well as much longer acceleration times I would have thought that a high speed train would need a much greater fraction of total power when at it's maximum speed than a car.

 

[HSTEd]

The real thing holding back high-speed trains in terms of power equipment compactness is depressingly the decision to adopt 50Hz AC power supplies of such high voltage.

Until we get to the point where you can practically fit a 25kV direct converter into a high-speed train (we are getting close but we are not there yet), we will be limited by the enormous transformer the train has to lug around.

If we were using 9kV DC or similar we could really pack the horsepower in. After all the AGV motor assemblies are entirely within the bogies, so it's all converter/transformer volume at this point.

 

[MarkyT]

The real thing holding back high-speed trains in terms of power equipment compactness is depressingly the decision to adopt 50Hz AC power supplies of such high voltage.

AC was the only realistic option back in the mid-20th century, and exploited the standards being adopted for general-purpose distribution. It is what is there today and changing to something else would be very difficult logistically and no doubt expensive. Also what are the relative reliability and worst-case failure modes for cutting-edge static converters vs established (albeit heavy) traditional transformers? At least at 50Hz the transformer losses are lower than Germanic and Scandinavian systems have to endure at their lower frequency.

If we were using 9kV DC or similar we could really pack the horsepower in. After all the AGV motor assemblies are entirely within the bogies, so it's all converter/transformer volume at this point.

Regardless of the AC/DC argument, there would be greater line losses at the lower voltage, or heavier cable and support structures would have to be provided for the same load. Possibly more supply substations too.

 

[mike57]

Regardless of the AC/DC argument, there would be greater line losses at the lower voltage, or heavier cable and support structures would have to be provided for the same load. Possibly more supply substations too.

I think the other issue with DC would arcing at the point of contact. An AC supply is zero volt crossing multiple times a second. (twice the supply frequency) and tends to self extinguish arcs. I am not sure how 3kV DC systems cope, but I would think that with higher DC voltages it would be an issue.

AC also suffers from the skin effect where very large conductors and currents are in use, and this is another source of losses, the 16.7Hz German system actually suffers less in this regard, but at the expense of much larger magnetic components e.g. transformers.

Hopefully technology will develop to the point where direct 25kV input and conversion electronics will become available to replace the transformer, in much the same way as switched mode supplies have revolutionised domestic and light industrial systems.

No doubt you could model solutions for each route and come up with the optimum supply strategy for each route, but that defeats the object of a standard system. 25Kv AC is probably as close as we will get to a one size fits all for the foreseeable future for intercity routes, and lower voltage DC for high density urban routes where it makes more sense to do the transformation and rectification before sending the power to the train to avoid lugging the transformer around.

One advantage of DC over AC which is being eroded is the ability to balance the load on the 3 phase supply, because static convertors are becoming available which can take 3 phase input and give a single phase output. This issue has hindered upgrading supplies where there is no large feeder from the grid.

 

[HSTEd]

AC was the only realistic option back in the mid-20th century, and exploited the standards being adopted for general-purpose distribution. It is what is there today and changing to something else would be very difficult logistically and no doubt expensive. Also what are the relative reliability and worst-case failure modes for cutting-edge static converters vs established (albeit heavy) traditional transformers?

The transformer probably burns prettier than the electronics ever could! They are full of resin after all.

Regardless of the AC/DC argument, there would be greater line losses at the lower voltage, or heavier cable and support structures would have to be provided for the same load. Possibly more supply substations too.

SNCF has come to the conclusion that line losses at 9kVdc are comparable to 25kV, and substation spacings would be similar. Once you get to these sorts of voltages ohmic losses in the conductors is no longer the predominant loss mechanism.

Conductor weight is also comparable, because at these currents it is far less important.

Which is why SNCF is currently developing 9kV conversion of its 1500V system rather than conversion to 25kV, which has been ruled out due to ruinous costs.

But you are correct that conversion of 25kV is unlikely to ever occur, so at this point we just have to wait for converter technology to advance to the point where the voltage issues can be overcome.

 

[Technologist]

How does the


Would a car perhaps be required to produce the peak output for a less sustained time than a high speed train?

As well as much longer acceleration times I would have thought that a high speed train would need a much greater fraction of total power when at it's maximum speed than a car

Yes, discount a car's quoted peak power to about 60% for a sustained number, a high power EV cannot run a peak power for more than 10's of seconds anyway as it will hit top speed (gearing limited) and the power will regulate down to the amount required to sustain this top speed. A Model 3 would need only around 190bhp to sustain its maximum speed but has just under 500bhp.

The real thing holding back high-speed trains in terms of power equipment compactness is depressingly the decision to adopt 50Hz AC power supplies of such high voltage.

Until we get to the point where you can practically fit a 25kV direct converter into a high-speed train (we are getting close but we are not there yet), we will be limited by the enormous transformer the train has to lug around.

If we were using 9kV DC or similar we could really pack the horsepower in. After all the AGV motor assemblies are entirely within the bogies, so it's all converter/transformer volume at this point.

That's a bit which cars generally don't include, however there are a few exceptions which probably means that the technology will become widespread.

Generally EVs change their batteries with DC power at their battery voltage 400-900V. However there are a few cars which can take charging at different voltages for compatibility reasons. Given that they charge at ~200KW that would normally equate to a 200-400kg transformer, not acceptable! Instead they use the power electronics which feed the motor to generate a high frequency AC which is stepped to the battery voltage and then rectified.