3 ms·

Absolutely hearsay here but a family member worked for SNCF as a mechanic for TGV trains (but not the locomotive) and has said that the pantograph was the limit

Absolutely hearsay here but a family member worked for SNCF as a mechanic for TGV trains (but not the locomotive) and has said that the pantograph was the limiting factor they had designed the last generation around. That it was designed as a wear part and the top and optimal speeds were chosen based on thresholds for unacceptable wear on the transmission lines themselves, which are much more difficult and expensive to replace. He told me never to expect TGV speeds to increase significantly until we saw them ripping out the powerlines and replacing them with an entirely new system. Again I don't know if this is true! But it seems reasonable enough to me. That conversation was about twenty years ago and plenty has changed with TGV in the mean time but sure enough no top speeds have increased on any line in the system in that timeframe, and new lines are deployed with the same speeds as the older ones.

bombcar 4y ago
I've often wondered why a wheel rolling against the wire wouldn't be better, after all at those speeds you have a wheel rolling against the track and bearing the weight of the train.
- pmyteh 4y ago
  Having a low sprung weight is important for pantographs, and getting the 25kV off a rotating contactor would introduce another unhelpful electrical interface I suspect. If you want to know far more than you did before about overhead line electric systems for railways, from a predominantly British perspective, I can strongly recommend Gary Keenor's (free) book: https://archive.org/details/overhead-line-electrification-for-railways-6th-edition https://archive.org/details/overhead-line-electrification-fo...
crocal 4y ago
This correct. Power lines wear induced by pantographs is the limiting factor for TGV top speed. The engineer that can solve this problem will allow top speeds in the range of 400/500 kph on /existing/ TGV tracks. Much better problem to solve than hacking a lame hyperloop.
- deleted 4y ago
  [deleted]
- q-big 4y ago
  > The engineer that can solve this problem will allow top speeds in the range of 400/500 kph on /existing/ TGV tracks. How is this problem solved in China? > https://en.wikipedia.org/wiki/Fastest_trains_in_China https://en.wikipedia.org/wiki/Fastest_trains_in_China
  - fhrow4484 4y ago
    They're maglev trains, so there's no pantograph involved there. https://youtu.be/_ZZMViMDjto https://youtu.be/_ZZMViMDjto at 16:40 explains the problem. It's in french, but you can get the gist visually as it's a for-kids documentary. Tldr is a wave on the cable is created at high speed, making it impossible for the train to stay in contact with the cable. The documentary also touches on another top speed limitation: how agressive the turn angles are, limiting the top speed.
    - q-big 4y ago
      > They're maglev trains, so there's no pantograph involved there. The linked wikipedia article also lists speeds of Chinese non-maglev trains.
      - fhrow4484 4y ago
        Ah true, maybe they have higher operating costs on pantograph and/or the power lines maintenance? (I don't fully believe GP's comment of "The engineer that can solve this problem will allow top speeds in the range of 400/500 kph on /existing/ TGV tracks.", as narrow turns is probably a bigger contraint than the pantograph problem. Maybe a few of the more straight lines can benefit, but there's more constraints to solve before taking turns at 400/500 kph!)
  - ThePowerOfFuet 4y ago
    >However, on July 1, 2011 in order to save energy and reduce operating costs, the maximum speed of Chinese high-speed trains was reduced to 300 km/h, and the average speed of the fastest trains on the Wuhan-Guangzhou High-Speed Railway was reduced to 272.68 km/h (169 mph).
flyinghamster 4y ago
Wear and tear is always going to be a limiting factor. Back in 1955, SNCF began its early high-speed research with a record-setting 331 km/h run - this under 1500V DC catenary, boosted to 1800V for the run. Some aerial footage of the run shows spectacular arcing, and they switched pantographs when first one became too damaged. Newsreel in three parts (in French): 1 https://www.youtube.com/watch?v=0AyPGkMoGE0 https://www.youtube.com/watch?v=0AyPGkMoGE0 2 https://www.youtube.com/watch?v=FpLf4M5OXeQ https://www.youtube.com/watch?v=FpLf4M5OXeQ 3 https://www.youtube.com/watch?v=cHWjelxe_MU https://www.youtube.com/watch?v=cHWjelxe_MU

bombcar 4y ago

I've often wondered why a wheel rolling against the wire wouldn't be better, after all at those speeds you have a wheel rolling against the track and bearing the weight of the train.

pmyteh 4y ago
Having a low sprung weight is important for pantographs, and getting the 25kV off a rotating contactor would introduce another unhelpful electrical interface I suspect. If you want to know far more than you did before about overhead line electric systems for railways, from a predominantly British perspective, I can strongly recommend Gary Keenor's (free) book: https://archive.org/details/overhead-line-electrification-for-railways-6th-edition https://archive.org/details/overhead-line-electrification-fo...

crocal 4y ago

This correct. Power lines wear induced by pantographs is the limiting factor for TGV top speed. The engineer that can solve this problem will allow top speeds in the range of 400/500 kph on /existing/ TGV tracks. Much better problem to solve than hacking a lame hyperloop.

deleted 4y ago
[deleted]
q-big 4y ago
> The engineer that can solve this problem will allow top speeds in the range of 400/500 kph on /existing/ TGV tracks. How is this problem solved in China? > https://en.wikipedia.org/wiki/Fastest_trains_in_China https://en.wikipedia.org/wiki/Fastest_trains_in_China
- fhrow4484 4y ago
  They're maglev trains, so there's no pantograph involved there. https://youtu.be/_ZZMViMDjto https://youtu.be/_ZZMViMDjto at 16:40 explains the problem. It's in french, but you can get the gist visually as it's a for-kids documentary. Tldr is a wave on the cable is created at high speed, making it impossible for the train to stay in contact with the cable. The documentary also touches on another top speed limitation: how agressive the turn angles are, limiting the top speed.
  - q-big 4y ago
    > They're maglev trains, so there's no pantograph involved there. The linked wikipedia article also lists speeds of Chinese non-maglev trains.
    - fhrow4484 4y ago
      Ah true, maybe they have higher operating costs on pantograph and/or the power lines maintenance? (I don't fully believe GP's comment of "The engineer that can solve this problem will allow top speeds in the range of 400/500 kph on /existing/ TGV tracks.", as narrow turns is probably a bigger contraint than the pantograph problem. Maybe a few of the more straight lines can benefit, but there's more constraints to solve before taking turns at 400/500 kph!)
- ThePowerOfFuet 4y ago
  >However, on July 1, 2011 in order to save energy and reduce operating costs, the maximum speed of Chinese high-speed trains was reduced to 300 km/h, and the average speed of the fastest trains on the Wuhan-Guangzhou High-Speed Railway was reduced to 272.68 km/h (169 mph).

flyinghamster 4y ago

Wear and tear is always going to be a limiting factor. Back in 1955, SNCF began its early high-speed research with a record-setting 331 km/h run - this under 1500V DC catenary, boosted to 1800V for the run. Some aerial footage of the run shows spectacular arcing, and they switched pantographs when first one became too damaged. Newsreel in three parts (in French): 1 https://www.youtube.com/watch?v=0AyPGkMoGE0 https://www.youtube.com/watch?v=0AyPGkMoGE0 2 https://www.youtube.com/watch?v=FpLf4M5OXeQ https://www.youtube.com/watch?v=FpLf4M5OXeQ 3 https://www.youtube.com/watch?v=cHWjelxe_MU https://www.youtube.com/watch?v=cHWjelxe_MU