Subway cars have been equipped with similar systems for many years.

What's new here?

What happens to the extra electricity ?

if you have 500 tons of train braking from 100 kph to 0, that is a huge spike.

How is this absorbed or does the voltage just go up locally?

Or are there short term things like flywheels that can absorb the power and release it over the next 5-10 minutes ?

Or do you just brake more slowly so as to release a longer lower spike of electricity into the grid?

Normally, there would be a number of trains running on the same power source for the third rail, enough so that whatever energy is fed back into the rail from one train will be used somewhere else to accelerate a different train.

It's possible (albeit expensive) to take excess DC and use an inverter to go back to AC if necessary, but if the main power for the rail is supplying power to a big enough system that has enough trains in it, it shouldn't be needed.

@HarveyD: Joe Biden is the Dem's VP candidate.

It would seem somewhat short-sighted to restrict innovation only to recovery of lost kinetic energy through regenerative braking. I previously have suggested gathering and reusing kinetic energy could occur not only by electricity generated when electric motors become generators while being used for braking, but also from application on rail cars of Bose Suspension® or the like.

Years ago some NYC subway cars had flywheels.

One company had a recent contract to build stationary flywheels for the subway electrical supply somewhere. (urenco) now out of the business.

Flywheels have been demonstrated in europe.

During WWII some UK electric locomotives had large flywheels to bridge the gaps in third rails.

High speed flywheels with no iron core in their alternator/motor are a very good option.

General Electric has demonstrated a locomotive with ZEBRA batteries for regeneration.

If ZEBRA batteries get a lower price as predicted the should be used in the cars. Or flywheels should be used with smaller ZEBRA batteries. ..HG..

For periods of light use, the hybrid flywheel Parry People Movers should be considered. A number of prototype versions have been tested in actual service. Two bespoke units will enter service on a commuter branch railroad this year. ..HG..

Lightrail with flywheels?
Look here- http://www.parrypeoplemovers.com/

Bombardier actually demonstrated that the usual regenerative braking (already in wide-spread use all across europe; with modern semiconductor inverters, implementing this is almost a cost-free option) only 40 % of the recovered kinetic energy actually get used to power another train. All the rest is lost to the resistance of the third rail or catenary.

Of course, if none of the US electric trains is currently equipped with this cheap system, I really wonder where your engineers have been the past 40 years...

Using an on-board energy storage device (battery, flywheel, ultracap, ...) to store the recovered energy boosts the efficiency up to about 80%. For one thing, the resistive losses in the power network are removed, and you don`t have to have another train nearby, which is currently accellerating.

Bombardier has provided a small number of light trains to some german municipalities some years ago (2002/2004 i think), and as a nice side-effect they could reduce the number of power distribution stations to the rail network by a factor of three, while reducing the overall power usage by a factor of four...

So, I have to agree, where is the news here? Just because someone came up with a prooven-good idea and takes government money to "further develop" it?

You do not need to put the flywheels on the trains, you can put them in substations on the rail network.

I guess the trick is to work out what the maximum "charging" rate is and try to keep the braking to or below this.

Then you can absorb your braking energy into the flywheel or whatever, as long as you can plan your braking properly. However, it could result in slower journey times if you had to brake for longer.

So it is a case of balance.

Hybrid fright train currently have no ability to storage energy form dynamic breaking. I read that batteries take quite beating on trains great reduce there life. Maybe for long distance freight trains can use pneumatic system to strong energy.

Virgin trains in the UK has reported 15% savings and does this operationally on its high speed Pendolino services. The AC overhead system allows distribution back into the National Grid as well as to other trains.

http://www.railwaygazette.com/features_view/article/2007/07/7577/regenerative_braking_boosts_green_credentials.html

jcwinnie, The rail bogies we see on the mainline do not operate with shock absorbers. So there is no damping requirement to supply the linear accumulator as you are suggesting.(for simplicity)
Some passenger rail carriages may have damping for pitch and yaw and there could be some opportunity there.
I am unaware if any light rail operate single axle systems, But for automotive applications not using walking beam axles, this would make sense for recuperating some useful amounts of energy.
Further more Ferrari? Aermacci? had active suspension designs that would lift a wheel out of the way of approaching bumps. Effectively the wheel never actually contacted the bump but 'flew ' over it.
Any system along the line you suggest could combine 3 elements of design and be at least self powering.

An "old school" tech described regeneration being fed from one train going down long steep grade with the opposite pair travelling up grade. Hence timing was essential.
This was said to be required to to supply the over load.
Not sure whether this was actual or theoretical.

Freight trains don't store dynamic braking energy because thus far there hasn't been a practical, cost effective way to do it and still slow the train down in an acceptable distance. Freight cars have mechanical brakes on every axle, but drive motors (with regen capability) only in the locomotive. Normally, the idea with freight trains is to get them up to speed once, drive for the longest possible distance, and minimize speeding up and slowing down. Batteries (or compressed air tanks, or a flywheel) to store the entire amount of kinetic energy in a mile long freight train, would be colossal. Not saying it can't be done, it's just not necessarily the most beneficial application.

Passenger trains are a different matter, because they are speeding up and slowing down all the time (and they're usually shorter, and either have individual drive motors on each car or have a locomotive but it's a much greater percentage of the total train's weight). The flywheel idea is interesting ... on a subway or other local train system, maybe the place for it is at each subway stop.

The green energy/electricity generated form the on board Alternators, which uses the KE of the moving trains be pooled through the transmission lines laid, and be distributed through the pooling sub-stations and receiving stations.