On 06/13/2010 06:35 PM, Jon Elson wrote:
I was at the local ice cream place that is adjacent to one of the local
train tracks.
The Amtrak pulled up to exchange passengers at the nearby station. A bit
after it stopped, I heard a very familiar and unexpected sound.
It was a large air compressor driven by a 60 Hz 3-phase motor. I'd guess
from the sound it very well could be a Quincy, and I'd guess maybe 15-25
Hp 4-cyl 2-stage, with pneumatic unloaders.

Anyway, it struck me as just a tiny bit odd they'd use an electric
compressor, as they have mechanical power available off the Diesel engine.
I also noticed the Diesel didn't seem to change speed when the train
accelerated, so I'm guessing they run a single engine at 60-Hz
synchronous speed all the time, so they can distribute 60-Hz power for
air conditioning, etc. to the coaches. So, no aux engine for the
non-traction power.

Anybody know anything about this?

If you're generating a 60Hz three-phase rail anyway, a switch to a motor
is a heck of a lot easier to design, manufacture and maintain than a
shaft to distribute power and a bunch of clutches to turn it on and off.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com