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Off in the distance
my journal
May 2016

The Bellinghman
Date: 2009-12-23 15:49
Subject: Old tech saves the day
Security: Public
As seen here: Passengers rescued by Tornado.

It's rather wonderful in its way that when the electric-driven trains were being disabled by ice and snow, a good old-fashioned A1 Pacific steam loco could carry the stranded passengers to London.

He said: "It was a nice way to finish for Christmas, though I think some of the rescued passengers didn't realise they'd even been travelling on a steam train until they got off."

Hmm. I wonder what they thought the plume flowing back along the train from the front was, then.

(Steam trains are wondrous things, but I wouldn't really want them back in bulk. Electrics can run in almost any weather, as the Swiss can demonstrate, and they don't have to run on hydrocarbons.)
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Tony Finch
User: fanf
Date: 2009-12-23 17:08 (UTC)
Subject: (no subject)
I believe TGVs use regenerative braking. Trains can't rely on regenerative brakes, though, because there must be some other load on the line into which the slowing train can pump its power. If that isn't the case, trains use rheostatic braking instead (or some combination of the two if the line can take part of the braking load). TGVs have stacks of resistors and cooling fans on top of the power cars for this purpose.

TGVs only use their disc brakes below a certain speed.
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User: furrfu
Date: 2009-12-23 17:13 (UTC)
Subject: (no subject)
Yes, indeed. I should have phrased it better.

"how many trains use regenerative braking with the express purpose of feeding energy back into the grid."

(I know the Brussels Metro switched to such a system not that long ago, and became quite a bit more efficient because of it. But that's not big trains.)

(Incidentally, huge dump trucks as used in open cast mining also use resistive braking. Because disc brakes just can't cope.)
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Tony Finch
User: fanf
Date: 2009-12-23 17:19 (UTC)
Subject: (no subject)
Ah right, I see what you mean. The need for rheostatic brakes rather implies that there's no feedback to the general grid.

Speaking of brakes not coping, the French have been investigating magnetic brakes for very high speed braking, which work by transferring energy to the rails by heating them up using induced eddy currents. You can't use this technique at lower speeds because you don't want to heat the rails up too much, i.e. you want to spread the heat out as much as possible.
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