On Sat, 16 Aug 2003 02:07:30 -0500, Jon Elson
wrote:


Eastburn wrote:

No, actually, the big turbo-alternator sets can't ever stop turning.
The alternator
rotors weigh 50 + tons, and the shafts will bend if they stop turning.
They have
a small motor called the turning gear that keeps the machine rotating slowly
when no steam is available. The air gap on the rotors is incredibly small
for such a huge machine, about .001" per side. The rotor on an 800 MVA
alternator is about 18-20" diameter and about 12 feet long. it is solid
steel,
with the shaft and rotor one piece. Grooves are cut into the face of the
rotor, and solid rectangular copper bars are fitted into the grooves, with
insulating paper surrounding them. They run some fantastic current through
these bars, something like 10,000 Amps at 100 V DC! They'd melt if it
wasn't for the Hydrogen cooling.

Jon

I have had the opportunity to be in a station (coal fired, Port Neal
on the Misouri River near Sioux City, IA) while a turbine was shut
down for maintenece and saw the drive system used to keep it turning,
that said, they were working on the turbine and it was stationary.
They had the bearing cap off it, big babbit style bearings. I've also
seen pictures of them slinging the rotors by big hoists to lift ehm in
and out of their cradles. So here is my question, do they actually
bend from their own weight or do they jsut keep them rotated to keep
the bearings lubrication working or something? If they do bend when
stationary then I assume this must take a while because I doubt they
have a good way of supporting the center while turning before stopping
rotation.

Dave