I appreciate Jim Frysinger's comments on my recent post. I've read a
lot and toured a few facilities, but I've never done the things Jim has
done.
Jim's comment about bringing the generator on line a little fast makes
sense. It is my understanding that when the synchroscope is used, an
exact frequency match is not achieved. It's the slight frequency
difference that allows the phase to vary and therefore provides periodic
opportunities for closing the switch. Once the phase is varying
sufficient slowly (ie frequencies matched close enough), the generator
is brought on-line during one of the times that the synchroscope
indicates an in-phase condition. This could be done with the generator
running either a bit slow or a bit fast. But having the generator
running a bit fast makes better sense than having it running a bit slow.
As Jim said, having the generator come on line as a motor would be more
harmful than having it come on line as a generator with a small load.
I'm still a bit confused about power sharing. It is clear to me that a
generator hooked to a grid could provide power to the grid either by
have a voltage slightly higher than the grid, or by having a phase that
slightly leads the grid. I always assumed adjustment of the voltage was
how the loading was adjusted. I understand that a temporary speed
increase of the generator can make it lead the grid and thus increase
its power contribution to the grid. But why would one do that as
opposed to keeping the phases matched and raising the voltage?
Another area that seems complicated and confusing to me is the
relationship between the power plant and the attachment to the grid that
takes place some distance away and after traversing several
transformers. The synchronization procedure that is most clear to me is
when the power plant is already on the grid and we are bringing an
additional generator on line within the already functioning power plant.
How does a power plant make its initial connection to the grid? Do we
have to have some sort of synchroscope connected to the grid and
power-plant output at the high-voltage end (after the transformers and
at the location where the connection to the grid takes place)?
As I try to learn more about this, some of the things I read seem to
indicate that the GPS system is now being used to help in this
synchronization process.
Can anyone shed any light on what happens beyond the power plant?
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu