David L Peterson wrote:

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.


I don't think the turbine, itself, is the problem. The complete turbine
rotor to
power an ~ 800 MW alternator is not all that large. Although it is
somewhere
near the size of the alternator rotor, it is mostly spindly blades on a
heavy
shaft. The low-pressure section does have some pretty large rotor
discs, though.

But, I think it is the alternator that is the problem. It is about
10-12 feet long,
and 18 - 24" or so in diameter. Using the largest of those dimensions, the
rotor (not including the shaft) weighs 9 tons (amazing, I thought it
would be
way more than that) and only clears the stator of the alternator by
about .001"!
If you let it sit, it will sag and crash into the stator. I'm not sure
what you do
to get it free again once that happens. The babbit bearings are
hydrostatic,
I think, and as long as the lube pump is on, there's no problem of it
setting
the shaft down onto the babbit.

Yes, I assume it takes some time for the steel to sag enough to crash
the rotor.

Jon