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Re: power-grid physics



At 10:57 AM 8/21/2003 -0400, James, you wrote:
///
I must take small exception to what Michael says in the portion below and I
will insert comments accordingly.

On Thursday 2003 August 21 08:45, Michael, you wrote:
....
> Contrary to what another respondent stated, the newly added generator
> will not slow down. When connected in this manner it neither supplies
> energy to the grid nor takes energy from the grid.

This is an inherently unstable (or at best, metastable)
condition. The risks
of motorizing a turbine generator are so great that, at least on the electric
plants I operated, the oncoming generator is brought on line while spinning
very slightly faster than the system's phase rotation.


Perhaps James would settle for "stressful" rather than "unstable".
Any motoring of a prime mover will torque its drive shaft into a reversal.
This could excite a rotary mode, and impact the control scheme too, I imagine.
Avoiding that case is evidently a high priority in subs.

Still, making a connection on two generators in phase and voltage identity
is at that moment, trouble free, it seems to me.

This is to ensure
positive loading of the generator. Usually, I observed only a few percent of
the load being picked up immediately upon closure of the generator's breaker,
but that was sufficient.

///
[Michael]
> .... After the connection has
> been made we can slowly raise the excitation current to raise the
> voltage of the new on-line generator. This is when the new generator
> begins to supply power to the grid. This is done slowly so that the
> governor-throttle can maintain the frequency and phase lock.

[James]
I cannot imagine this working well. Again, on submarines, we
controlled
relative loading of generators by moving their no-load speed settings up or
down,

///

regards,
Jim
James R. Frysinger


I think James And Michael's descriptions are not so far apart.
It is quite certain, that if a generator is to provide more power
over reasonable times, its throttles *will* be opened.
One is visualizing a putative phase advance, the other a putative
amplitude advance in two devices which may be in the same room,
and which are in fact, locked in phase and amplitude for
practical purposes....


Brian Whatcott Altus OK Eureka!