This is the much better article for this audience. The submitted article is an expansion of tweets summarising this one.

This is a much better and more thorough read.

Thanks! We updated the link from http://www.citymetric.com/transport/londons-tube-has-been-ru... to this a while ago.

These are the first trains that I hear of with no regenerative braking.

> indeed, the use of regenerative braking now converts about half the heat loss back into electricity. However, that can only work where trains are accelerating and braking at the same time, on the same electricity sub-station loop.

Besides that, Tube tracks often rise slightly at stations, so that trains get a small gravity assist to both stopping and starting off again. (Unfortunately it also means that hot air from the tunnels tends to collect there, but you can't win 'em all.)

That is a pretty cool way to implement regenerative breaking that I honestly never thought of (even though the tram in my hometown feeds energy in the grid when driving downwards)

Correct me if i'm wrong, but it seems that regenerative braking is a bit troublesome because it is a third rail direct current system: a "regular" AC system can simply feed power back through the transformers to the power grid, but this is not possible here, so power must be consumed by another train fed by the same rectifier.

You're not wrong: However, that [regeneraative braking] can only work where trains are accelerating and braking at the same time, on the same electricity sub-station loop.

Or something like super capacitors to hold the braking energy until the train needs to a accelerate again

It would be much more difficult to feed power back into an AC grid from a regenerative brake. With a DC grid, no synchronization is needed.

That's not true.

1) modern railway is fully IGBT powered. In this case it is trivial to inject current.

2) with DC current you need a substation capable of converting AC to DC (easy: bridge rectifier) but also DC to AC (to given tolerances) which is much more cumbersome.

The first generation of Munich subway trains (manufactured from 1967-1983) uses resistor banks for braking, so the energy from braking goes right into heat.

Only the later generation B and the new C generation can move brake energy back into the grid.