6 ms·

Regenerative braking would improve a lot with not just the heat issue, but also air quality. Commuters on the London Underground get a characteristic grey/black

Regenerative braking would improve a lot with not just the heat issue, but also air quality. Commuters on the London Underground get a characteristic grey/black snot from the brake dust they inhale. If you stare into the tunnel after a train left you can literally see a haze of brake dust in the air.

bombcar 4y ago
Yeah, they mention it with a "grid balancing issue" but it seems that could be solved by adding under-floor battery packs to the trains or the stations themselves - store braking energy to restart the train afterwards.
- msandford 4y ago
  Less batteries and more ultra capacitors. You might need to handle power requirements in the range of 5-20MW, albeit for just a minute or so.
  - mnw21cam 4y ago
    Definitely. The bonus is that they wouldn't have to be on the train. And the tube electric system is DC already as well. This sounds like an engineering problem that is largely already solved.
pbhjpbhj 4y ago
I wonder if you could fit a magnetic braking system mainly at platforms, when engaged trains would be slowed. That could reduce weight on the trains themselves? Thinking wildly, tube trains are like pistons (they're actual plungers, I guess) if you had a smooth walled section of tunnel then you could have a seal at the head of the train that fans out and provides pneumatic braking, you could maybe use the pressure to drive the ventilation system. Unlikely to be practical (you'd have to have a pre-platform door to prevent all the passengers from getting exposed to the pressure increase, I think).
- jaywalk 4y ago
  Magnetic (eddy current) brakes work by converting kinetic energy into heat, which doesn't really solve the problem here. I'm not sure if anyone has devised a system that actually captures electrical energy from the braking action, or if such a thing is even plausible.
  - bushbaba 4y ago
    It'd at least solve the dust break-pad dust issue
  - zorlack 4y ago
    You could put the braking resistors above ground, no? Or if the braking resistors have to be close the the coils, then you could use a heat-exchanger to move the heat somewhere else...
  - jamincan 4y ago
    Regenerative braking generates electricity and there's really no reason modern trains wouldn't use them. Another approach that can be used when initially building the system is to have a slope leading into/out of stations so that energy can be stored as gravitional potential. I know the Montreal Metro was built this way.
    - dtgriscom 4y ago
      Your second point was stated exactly in the parent of your parent comment.
      - jamincan 4y ago
        I don't think that's correct. @pbhjpbhj talks about magnetic braking and some sort of pneumatic braking. The sibling to his comment by @fredley mentions it, but I don't recall seeing that yet when I posted mine.
  - namibj 4y ago
    Yes. It's called "electric generator" and can be performed by almost all electric motors.
konschubert 4y ago
It seems they have been testing it out? https://arstechnica.com/cars/2015/09/london-tube-gains-regenerative-braking-tech-that-can-power-whole-stations/ https://arstechnica.com/cars/2015/09/london-tube-gains-regen...
- Symbiote 4y ago
  The new trains on the deep lines should also bring a big improvement, from 2025. https://en.wikipedia.org/wiki/New_Tube_for_London https://en.wikipedia.org/wiki/New_Tube_for_London
fredley 4y ago
It's already got a primitive version of regenerative braking! The deep-line tubes—those that have the heating problem—are designed so that the stations are at peaks in the line. As the train is approaching the platform the uphill slope helps it decelerate, and the downhill helps it accellerate again.
- andbberger 4y ago
  hardly primitive, it's by far the most efficient form of regenerative braking
na85 4y ago
>Commuters on the London Underground get a characteristic grey/black snot from the brake dust they inhale. Well that's horrifying. Is there no health and safety monitoring being conducted?
- calcifer 4y ago
  It is continuously monitored, but then what? There are no feasible solutions as yet.

bombcar 4y ago

Yeah, they mention it with a "grid balancing issue" but it seems that could be solved by adding under-floor battery packs to the trains or the stations themselves - store braking energy to restart the train afterwards.

msandford 4y ago
Less batteries and more ultra capacitors. You might need to handle power requirements in the range of 5-20MW, albeit for just a minute or so.
- mnw21cam 4y ago
  Definitely. The bonus is that they wouldn't have to be on the train. And the tube electric system is DC already as well. This sounds like an engineering problem that is largely already solved.

pbhjpbhj 4y ago

I wonder if you could fit a magnetic braking system mainly at platforms, when engaged trains would be slowed. That could reduce weight on the trains themselves? Thinking wildly, tube trains are like pistons (they're actual plungers, I guess) if you had a smooth walled section of tunnel then you could have a seal at the head of the train that fans out and provides pneumatic braking, you could maybe use the pressure to drive the ventilation system. Unlikely to be practical (you'd have to have a pre-platform door to prevent all the passengers from getting exposed to the pressure increase, I think).

jaywalk 4y ago
Magnetic (eddy current) brakes work by converting kinetic energy into heat, which doesn't really solve the problem here. I'm not sure if anyone has devised a system that actually captures electrical energy from the braking action, or if such a thing is even plausible.
- bushbaba 4y ago
  It'd at least solve the dust break-pad dust issue
- zorlack 4y ago
  You could put the braking resistors above ground, no? Or if the braking resistors have to be close the the coils, then you could use a heat-exchanger to move the heat somewhere else...
- jamincan 4y ago
  Regenerative braking generates electricity and there's really no reason modern trains wouldn't use them. Another approach that can be used when initially building the system is to have a slope leading into/out of stations so that energy can be stored as gravitional potential. I know the Montreal Metro was built this way.
  - dtgriscom 4y ago
    Your second point was stated exactly in the parent of your parent comment.
    - jamincan 4y ago
      I don't think that's correct. @pbhjpbhj talks about magnetic braking and some sort of pneumatic braking. The sibling to his comment by @fredley mentions it, but I don't recall seeing that yet when I posted mine.
- namibj 4y ago
  Yes. It's called "electric generator" and can be performed by almost all electric motors.

konschubert 4y ago

It seems they have been testing it out? https://arstechnica.com/cars/2015/09/london-tube-gains-regenerative-braking-tech-that-can-power-whole-stations/ https://arstechnica.com/cars/2015/09/london-tube-gains-regen...

Symbiote 4y ago
The new trains on the deep lines should also bring a big improvement, from 2025. https://en.wikipedia.org/wiki/New_Tube_for_London https://en.wikipedia.org/wiki/New_Tube_for_London

fredley 4y ago

It's already got a primitive version of regenerative braking! The deep-line tubes—those that have the heating problem—are designed so that the stations are at peaks in the line. As the train is approaching the platform the uphill slope helps it decelerate, and the downhill helps it accellerate again.

andbberger 4y ago
hardly primitive, it's by far the most efficient form of regenerative braking

na85 4y ago

>Commuters on the London Underground get a characteristic grey/black snot from the brake dust they inhale. Well that's horrifying. Is there no health and safety monitoring being conducted?

calcifer 4y ago
It is continuously monitored, but then what? There are no feasible solutions as yet.