miracle ACS-64 locomotive regen braking defies physics

[Patrick Boylan]

http://qz.com/107394/the-regenerative-p ... ive-fleet/" onclick="window.open(this.href);return false;

The ACS-64 is incredibly energy-efficient.The fleet’s braking system is regenerative, potentially returning all of the energy used to stop the train back to the overall power grid.

Can some folks with greater expertise than me explain how it's possible to move ALL energy from one system to another?

[DutchRailnut]

It does not, the Regenerative braking is only part of braking, as all cars use Air brakes at same time.
So out of total energy to get train moving only about 1/8th gets recovered, with most of that energy being used to feed HEP.
So if any energy is fed back into overhead its very little.

[Fan Railer]

http://qz.com/107394/the-regenerative-p ... ive-fleet/

The ACS-64 is incredibly energy-efficient.The fleet’s braking system is regenerative, potentially returning all of the energy used to stop the train back to the overall power grid.

Can some folks with greater expertise than me explain how it's possible to move ALL energy from one system to another?

Sloppy writing is all this is. What the writer of the article is reading is that none of the energy produced by the motors during braking in the ACS-64 is going to be dissipated through a resistor grid, since the locomotive isn't equipped with any. All of that braking energy is either going to HEP, or back into the overhead wires. However, the way the writer of that article puts it makes it sound like the only thing that is stopping the train is going to be the regenerative brake of the locomotive, which we all know is definitely not true.

[25Hz]

It dumps braking energy into resistor, HEP, and back into the overhead wire, so in essence the locomotive is not taking any energy from the wire, plus dumping it back into the wire...

While air on the car brakes does account for something, the cars do not draw power from the overhead wire via the locomotive during the braking process, so in theory the weight of the train is being converted into electricity and heat on the braking surfaces.

This sounds like a good way to save money on braking surfaces (pads, shoes, treads, discs), and get some savings in power generation, and maybe, just maybe, keep over-load situations and save the system from a trip that wold have messed up everyone's day.

[Patrick Boylan]

So out of total energy to get train moving only about 1/8th gets recovered, with most of that energy being used to feed HEP.

Dutch, sorry I wasn't clear, I'm much more interested in "energy used to stop the train", so I'd expect they recover a lot more than 1/8th of that. I doubt even a streetcar that stops at every corner uses as much energy to brake as they do to move.

And as 25hz mentions, one can't discount savings on pads, shoes, treads, discs.

And as Fan Railer hints, I was poking fun at the sloppy reporting, which says "potentially returning all of the energy used to stop the train", when my grade school physics at Our Lady of the Evening taught me that one can never convert 100%.

[Fan Railer]

Imagine using only regen brake to stop an 8 car regional train going at 125 mph though lol... that probably takes at least 8-10 miles

[Adirondacker]

... get some savings in power generation....

In one of these threads there was a link to a Siemens/Amtrak document that listed how much electricity it would save. Which I'm not in the mood to go find. At ten cents a kilowatt hour, they probably pay less, the fleet is going to save them 300,000,000 dollars over their lifetimes.

[mtuandrew]

Moderator's Note: Moved to Amtrak.

Also, agreed on sloppy reporting. Unless it's a trade publication or from one of a small number of mainstream writers, such articles tend to include a lot of fluff meant to go unnoticed by 99.99% of readers.

[NHAirLine]

Imagine using only regen brake to stop an 8 car regional train going at 125 mph though lol... that probably takes at least 8-10 miles

It should be just a bit less than the acceleration distance to the same speed, as it should be able to pull back the same horsepower it's taking during acceleration, plus friction, wind resistance (friction basically), electrical, and other losses. However, it's still not 100%, nothing's 100%, there's always friction losses, electrical conversion losses, etc, etc. I have no clue what the percentage efficiency would be for something like this, but I'd be shocked if it's any more than 80%, and I highly doubt it's that high. However, they may want to stop even faster than just a bit less than the acceleration distance, in which case, they would use regular brakes alongside regen braking.

[hi55us]

Moderator's Note: Moved to Amtrak.

Also, agreed on sloppy reporting. Unless it's a trade publication or from one of a small number of mainstream writers, such articles tend to include a lot of fluff meant to go unnoticed by 99.99% of readers.

worth noting:

This article was produced on behalf of Siemens by the Quartz marketing team and not by the Quartz editorial staff.

The way I interpret it is Quartz wrote up the whole article, got paid by Siemens, and got the rubber stamp from Siemens.

[jstolberg]

Imagine using only regen brake to stop an 8 car regional train going at 125 mph though lol... that probably takes at least 8-10 miles

There's quite a bit of braking that is less than 125 mph to dead stop. Braking for curves, bridges, and numerous stations that have an approach speed of less than 125 mph.

[kitn1mcc]

wonder how there gonna back feed AC like that

[BandA]

Imagine using only regen brake to stop an 8 car regional train going at 125 mph though lol... that probably takes at least 8-10 miles

using the same traction motors, the 125-0 distance should equal the 0-125 distance

It should be just a bit less than the acceleration distance to the same speed, as it should be able to pull back the same horsepower it's taking during acceleration, plus friction, wind resistance (friction basically), electrical, and other losses. However, it's still not 100%, nothing's 100%, there's always friction losses, electrical conversion losses, etc, etc. I have no clue what the percentage efficiency would be for something like this, but I'd be shocked if it's any more than 80%, and I highly doubt it's that high. However, they may want to stop even faster than just a bit less than the acceleration distance, in which case, they would use regular brakes alongside regen braking.

The addition of large flux capacitors allows recovery of up to 105% of the stopping power.

[BuddSilverliner269]

Imagine using only regen brake to stop an 8 car regional train going at 125 mph though lol... that probably takes at least 8-10 miles

Yes this has already been tested and works very well. Just an FYI, the NJT ALP 46 locomotives are capable of stopping the train using simply the dynamic brake.

[Patrick Boylan]

mtuandrew, although this example's about a statement about ACS-64, the concept's dynamic-regenerative braking in general. I offer as evidence that the comments so far talk about other operations besides Amtrak.
I'm sorry I included ACS-64 in the title.