On Jun 26, 6:51*pm, Jon Elson wrote:
Cydrome Leader wrote:

What is the poing of the frequency variation in the first place? it's
never explained in the links.

A control systems group at our university tried to understand the stability
of the electrical grid. *This was a big, multi-year DOE grant. *They wrote
a software simulation, with generating plants, loads and transmission lines.
As I understand it, they eventually found that the problem is essentially
mathematically intractable, but that they were able to establish certain
bounds to the solution. *What that all means is that the grid is not really
very stable at all, somewhat like a whole bunch of masses tied together by
a network of springs, and energy being added and subtracted here and there.
Resistance of the transmission lines and the huge resistance of resistive
loads (incandescent lights and toasters) may be the only thing keeping it
from going wildly unstable. *They do experience periods of smaller
instability now and then, and sometimes have to pull a generating station
offline to break the cycle of reactive power bouncing back and forth from
one region to another.

So, with that background, **I THINK** what is going on is they think there
may be a way to reduce some of these stability problems if they don't
try to maintain exact frequency all the time, TOO. *Stability is a LOT
more important than minor frequency variations.

Jon

Think about a 60 HZ standing wave....
HOW can that be applied to the grid? It cannot.

Say for example, you had a reference signal leaving Minneapolis, and
the peak of that wave will arrive in Chicago some time later. If there
is only One single line between these two centers, no problem...

Now add in the grid. The peak of that 60 HZ sine wave arrives at
Chicago, and the peak is also traveling from Minneapolis to Denver,
then on to Chicago.... The time is not the same for the two possible
paths.. There needs to be power moving back and forth...

With the wavelength of signal smaller than the possible distances in
the grid, you cannot have it all tied together without recirculating
power...

Even if a reference signal was assigned to one point in that example,
the reference cannot arrive at various points in the grid intact
because being a grid, there are multiple paths for it to follow.
Now add in multiple sources driving the grid, and you are left with
recirculating power... There is no way to have a "master" reference
for the grid...

The ONLY way that I can think of it working would be if all the
connecting points were assigned a time stamp reference from a MASTER
signal, and you would need tapped Delta transformers at each end of a
line.
Moving the delta taps could force power to flow in either
direction...

A tapped Delta transformer can change the phase angle, without
changing the voltage.

Can anyone illuminate this situation?
Anytime I have talked to electric power guys, they have never heard of
or thought about the fact that the grid cannot be in sync, without
having recirculating power..

They always refer to the grid has an infinite source and sink of
reactive power... it gobbles up the MVARS, or supplies them to keep
the generator perfectly in sync. You can open or close the wicket
gates to push more or less power to the grid. The voltage and
frequency are locked, but pushing harder against it will push more
amps... or pushing softer will push less amps...