daestrom wrote:

You seem to be laboring under the idea that all the AC generators tied to
the grid have to be carefully regulated to stay in sync with each other
through some incredibly precise timing.


I never said that at all, but I did say that the sped and phase have
to match to connect a new generator to a grid.


That isn't the case. A generator is brought on-line by carefully regulating
the speed and getting it in phase. That is a bit tricky. But once tied to
the grid, 'keeping in sync' is done by the load current and physics. In
fact, base load units don't even have frequency control once on-line. The
speed set-point for the governor is run several hz up out of the way and the
turbine controls are controlled by a 'load' setting. The operator dials in
the amount of MW load they are supposed to carry, and the controls monitor
MW and steam flow. They don't respond at all to frequency changes unless
the frequency rises to the point the unit is in danger of over-speeding.


If you would have read the entire thread, I described how the
generators are synched, and that the grid keeps them in sync unless
something goes wrong. I also stated that the generator was fed more
fuel or water to actually produce power for the grid rather than just
coasting along, in phase, one it was connected to the grid. I studied
the subject with college textbooks on power generation and distribution
when I was 13.


During grid disturbances, base load units will naturally speed up/slow-down
as grid frequency changes, maintaining their load output based on
'load-set'. Only 'regulating duty' plants monitor generator speed/freq and
make any sort of adjustment based on changes in speed/freq. And
'regulating' units make up a fairly small fraction of all AC units.

The vast majority of AC generators will 'stay in sync' just by virtue of the
physics of synchronous machines. Only if under-excited, or significant
reactance in their output line are they likely to 'pull out' of sync with
the grid. (and that's a *bad thing*)


Of course the larger the spinning mass in the generator, the more the
inertia, and the less likely to be kicked out of phase. The
experimental nuclear power plant at Ft. Greely, Alaska was steam driven
and unable to adapt to rapid load changes so they blew out quite a few
bearings in the turbines before they finally gave up and shut it down.
They would barely get it running an synchronized to the Alaskan power
grid when someone would fire up another generator and switch it on line
without contacting other providers on the grid. The system was
unstable, in frequency, voltage and a lot of outages. I watched my 120
VAC feed climb to over 190 volts one day, as circuit breakers all over
the complex were tripping out. It took me a couple hours to get all the
studio equipment and transmitters back in service that day. It was one
of the few times that I was happy that the towers were too short to need
lights.


daestrom

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