Amtrak's order of the latest attempt to replace the GG-1 is rolling out, and the greenies are enthusiastic about regenerative braking.
Each engine centers on a regenerative braking system that can recover up to 5MW of energy, much of which goes back to the power grid. The machinery is smarter, too: it can self-diagnose problems and mitigate the impact until repairs are possible. Commuters won't immediately notice the difference when ACS-64 trains reach the rails between this fall and 2016, but there should be important behind-the-scenes savings.
With a simple enough locomotive, sufficient instrumentation, and a competent engineer, you can cut out the misbehaving circuits and roll on. Regeneration is a simple flick of a switch.

Contemporary control circuitry, with a.c. transmission and thyristors, achieves results that the traction pioneers could only dream about.

You put all that technology over fewer wheels and less unsprung weight.

On the other hand, that Bi-Polar is more distinctive than the beefed-up Class 87 profile of Amtrak's latest power.


David Foster said...

I know that regenerative braking was invented and deployed a long time ago; I've seen articles about its use in mountainous areas in the US about 80 years ago. I thought it was generally used on electrified passenger likes aka Amtrak, and also for mass transit. Has this really not been the case? If so, why?

Stephen Karlson said...

Regenerative braking is relatively simple if the motors are running directly off the overhead wire, as was the case with Milwaukee's two mountain electrifications.

With more complex circuitry, it is easier to dissipate the energy of braking as heat, the dynamic braking employed by diesels, and also on some of the early rectifier electrics.

Only recently have the electrical engineers come up with enough wizardry to invert and chop the direct current and put induction motors under rapid-transit cars, and add even more wizardry to put something resembling direct current back onto the third rail. The latest Chicago L cars do so.

As far as I know, the regenerative feature is on Amtraks's motors for the first time. The Pennsylvania Railroad was mostly a flatland operation, hence not on the GG-1s. The first electrics built for Amtrak used silicon rectifiers, and the invert-de-invert technology was still experimental. The HHP-60s might be new enough to have that in them, although the additional cost of the circuitry combined with the flatness of the railroad might not have made it cost-effective.

David Foster said...


How about urban rapid transit? These lines may not have hills, but they have a lot of start/stop, so regeneration should still have a high payoff.

Stephen Karlson said...

Urban transit may have more potential than you think. Good design practice puts slight downgrades out of the stations, and upgrades into the stations, so as to get the help of gravity with both accelerating and braking. Most modern transit cars now have regeneration. The circuitry takes up less space. The event recorders might be an updated version of the coasting clock Chicago Rapid Transit once used (kept track of how much of the run the motorman had the controller off).