🚀 go-pugleaf

In article <5834@rsiatl.Dixie.Com> John G. DeArmond writes:

 >Shishin Yamada writes:

 >>
 > > I was suprised to learn when the plant was shut down that they didn't
 > > disconnect from the grid (for example, to clean the pipes and
 > > turbine valves).  They just let the grid power the generators as 
 > > large electric motors.  Said it was a whole lot easier than trying
 > > to bring them up from a dead stop and re-synch them to the grid
 > > (which had to be done by hand).  

I wrote:

  There's another reason that _very_ large horizontally-mounted generators are
  never stopped -- if they sat there for a long time, the weight would cause a
  permanent flat spot in the shaft and bearings!

John replies:

  >Both of these stories are silly.  

I will defend my own:  I used to receive the ASEA journal and news
magazines, and one of them says exactly that.  It dates from the early 70s
when I worked on large equipment (3-phase electric arc furnaces).  It
reported how the generator was turned at 1rpm (as you admit below) to
prevent permanent shaft distortion AND bearing flat spots.  I guarantee it,
John!  I'm not one to forget what I read and post what I don't know.  In
this case, I thought it was an interesting anecdote.

Note that the units I read about are probably still in use, (what's 20 years
to a power plant?) and that the technology does improve.

 >The 1200 MWE turbogenerator at the first nuclear plant that I worked at
 >was assembled fully 5 years before it was turned.  The shaft did indeed
 >sag but was easily reversed by turning it 180 degrees and allowing it to
 >sit for a couple of weeks.  We then spun it up on steam and dynamically
 >balanced it and away we went.  All turbines of any size are equipped with
 >turning gears and drives that rotate the shaft at perhaps 1 RPM.  The
 >turning gear is designed to equalize sag forces right before startup and
 >to allow the shaft to cool down equally after shutdown.  


Cheers.


Rich