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NYC Subways Testing Flywheels

Posted by michael on from the next-stop-42nd-street dept.

socolow writes "The New York Times (free registration required) has an article about the NYC subway system's use of flywheels to store the braking energy of trains approaching stations. Not only does this advance the development of flywheel energy storage, but it will help relieve a lot of the heat subways generate (always appreciated during the summer)."

8 of 363 comments (clear)

  1. I don't buy it by L.+VeGas · · Score: 5, Funny

    I still think my hamster could spin a wheel faster than some dumb fly.

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  2. Where to stick your flywheel.... by Sweetums · · Score: 5, Informative
    Several posts refer to the flywheel as being on the train. I don't think it explicitly says in the article, but I think it's clear that they are talking about stationary equipment in the stations, not flywheels on the trains. Lots of advantages to this.

    The modifications to the trains are actually significant to support this, but it's about how the braking systems work and how the motor controllers work on the trains. There are a class of motor controllers that are not really compatible with regenerative braking, and they are fairly commonly used since they are cheaper than the others. The conversion to regenerative braking may involve replacing a fair bit of gear on the rolling stock. They were considering this kind of thing in San Diego, which is where I picked up lots of this trivia.

    Many rail systems and streetcar systems have regenerative braking, but frequently they don't store the energy. What they do is have one unit braking while another is accellerating, so the excess power is in effect transferred via the wire to the other vehicle. Think of cable car systems where the guy at the top of the hill counterbalances the one at the bottom. This is hard to make work though, the timing issues being what they are.

    My $.02

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  3. Wow, 36,000 is a lot of RPM... by dpbsmith · · Score: 5, Informative

    and a million watts is a lot of power.

    Let's hope those flywheels are enclosed in something pretty solid.

    Storing that much energy is one thing. Accidentally releasing it is another. When I was a student at MIT there was a permanent display in a glass case in the hallway of the biology department showing a centrifuge rotor that exploded, just to remind everyone of what happens when something spins too fast.

    Let's also hope there's something to muffle that 600 Hz whine (which is close to the peak of human hearing sensitivity).

    And I thought the wheels on Boston's Green Line screeching when going around sharp turns was bad...

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    1. Re:Wow, 36,000 is a lot of RPM... by aeoo · · Score: 5, Informative

      Actually, modern flywheels are almost never solid. They are usually made from rings, or fiber. There is a Russian scientist named Gulia who invented and patented (to my knowledge) a way to wind fiber so that both ends end up inside the flywheel. This is critical because at high RPM a loose end can undo the entire flywheel. Using kevlar and other fiber like that allows you to have flywheels that can withstand incredible forces. In general, flywheels are far more efficient than any battery in terms of energy storage, and how fast they can store and release energy. Also, modern flywheels can fly on a magnetic suspension and in vacuum as well. Flywheels, in my opinion, are simply the best way to store energy. When fiber flywheel explodes, it does so one thread at a time. They are relatively safe and the only thing they generate when they explode is heat.

  4. More information here by brandonsr · · Score: 5, Informative

    Right here A very good article (with illustrations) that tells how flywheels work and store energy. Pretty neat stuff.

  5. Re:Regenerative braking by Waffle+Iron · · Score: 5, Informative
    clue me in please... why is the resistance such a problem, if the third rail is how they are powering the trains in the first place? Why does the braking energy from the trains get wasted, but the energy from the systems that are powering the third rail does not?

    IAAEE, so I'll hazard a guess. They say in the article that the 3rd rail uses 650V DC. For power distribution, this is a relatively low voltage. To minimize resistance losses, power is typically distributed at thousands of volts. To be able to easily convert voltages, you need AC, not DC so you can run it through a transformer.

    I'll bet that they have high-voltage AC power distribution throughout the system, and they step it down to 650 V and rectify to DC it at frequent intervals along the tracks. The distance the power needs to run at low voltage along a high-resistance steel rail would never be very long, so losses are minimal. (I assume they use DC becuase it's easier to design train motors for DC, or something like that.)

    The AC -> DC rectification is not reversible, however, so there would be no way for power generated by a train to get back into the main distribution grid, and the average distance the 650V DC would have to flow throught the 3rd rail to the next train would be too far to be economical.

    (Of course, I could be wrong about all of this, since I don't really know anything about their system.)

  6. Re:Regenerative braking by 4of12 · · Score: 5, Funny

    clue me in please... why is the resistance such a problem, if the third rail is how they are powering the trains in the first place?

    It's all tied together with social security.

    Politicians are often heard saying something along the lines of

    "Social Security is the third rail. Don't touch it."

    You've probably noticed that Social Security benefits are mostly received by old people.

    You've probably also noticed that those old people move slowly. The reason they move more slowly than you or me and the reason they can't drive more than 20 mph under the speed limit is simply because they are encountering resistance.

    Hope that clears it up.

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  7. Re:Regenerative braking by candover · · Score: 5, Informative

    That's how the system works, yes. The MTA has 214 substations around the city, which are fed something between 11-27 kV AC, transformed to 400 V AC, and rectified to 600 V DC.

    It's only within the last ten years that they finally retired all of the old pre-solid-state rotary converters in the system - running power backwards through them would have actually worked. :)

    The new cars actually have AC motors - the DC third rail powers a battery on board, I'm not sure exactly what the AC conversion tech is. There's still a couple thousand DC-motored cars riding the rails, so I'm not expecting to see the system switch over to AC distribution....