Regenerative Braking

A recent trip out west and seeing some substations along the old Milwaukee Road ROW got me thinking. I know that the substations got A.C. from outside sources and with motor-generators converted that A.C. (I don't recall the voltage) to 3000 v D.C. that went to the trolley for the locomotives. I also know that when the locomotives went into regenerative braking mode that the electricity they produced went back into the trolley . So far, so good. I remember reading about how the first Milwaukee train ended up costing the power company something like $15.00 for the electricity produced by the train in regen.

My query is this: how did thhat DC voltage coming from those box cabs and Little Joes get converted to AC voltage to be redistributed to the grid at the substations? Did the motor generator set at the substations also have an alternator?

Nothing major, just curious.

I suspect this is a case of comparing apples & oranges, otherwise it makes a pretty good perpetual motion machine - LOL.

That sounds like a reasonable question to me. I would suspect an alternator as Black Dog suggested. As for a perpetual motion machine, I don't think so. My guess is that first train which more than offset the cost of electricity was going down a longer grade that it went up. In other words a train of the same tonnage going the opposite direction would use more electricity than it made going down the opposite side of the hill. Or maybe the first train had steam helpers on the way up so not all the energy was supoplied by electricity.

BlackDog wrote: ...
$15.00 for the electricity produced by the train in regen.

My apologies, I missed this part "in regen" when I first read the post.

Found a brief account from the Milwaukee Road Historical Association

Excerpt:
"It wasn't long before the rail­road found that steam operation in the mountains was difficult for several reasons, one being temperatures that could go as low as 40 degrees below zero.

Keeping in mind that water power for generating electricity was abundant in the Northwest, and that large supplies of copper for electric wire were available at Anaconda, Montana, the Milwaukee's board first studied, then approved, plans to construct an electrified operation in the Northwest.

Contracts were made for electric power in 1912, and in 1914, work was begun on 440 miles of electrification between Harlowton, Montana, and Avery, Idaho. On November 30, 1915, the road's first electrically hauled train ran from Three Forks to Deer Lodge in Montana, over 112 miles of track.

The early stages of electrified operation proved so successful that in 1917 it was decided to go ahead with electrification between Othello and Tacoma in Washington. The first test run on that track was on November 11, 1919, and formal operation began in March 1920. Considerably later, a 10 mile electrified section between Seattle and Black River was constructed and went into operation on July 5, 1927.

One interesting aspect of this operation is that electric locomotives are equipped with regenerative braking. This means that when the electric motors are reversed for braking, they become generators of electricity, so that about 12 per cent of the power used by the trains is recovered during braking. Some of these first locomotives are still in use today, proving their durability and efficiency. The Milwaukee's 656 miles of electrified operation is the largest such operation in the U. S."
[http://www.mrha.com/history.cfm]

Didn't see anything about the power being sent all the way back to the utility, but could happen.

More info:
http://www.northeast.railfan.net/classic/MILWdata5.html
Includes an interesting quote from Michael Sol:
"We could not find equivalent modern equipment that was able to provide the 100-200% overload capacity that the Milwaukee rotating machinery could provide, and still absorb regeneration at a reasonable cost."

As Aji-tater suggests, if the start point was at a higher elevation than the end point, the loco would have spent more time in Regen.

With the technology of the time, I would deduct the Milwaukee Road sub-stations utilized what is now termed a "Synchronus Motor" to rotate the DC Traction Generator supplying the cantanary power. If the first train was the only unit on the wire, the traction motors (if they were called that in 1915) would generate power (because of gravity) raising the cantanary voltage. This voltage increase would motor the generator at the sub-station, and the motoring generator would overhaul the AC motor and speed it up until it produced power. This will not be the case with today’s "Squirrel Cage" motors. I am not betting the house on this, but with the technology of 1915 it is very possible...