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Re: electrical power



At 12:27 PM 2/21/02, you wrote:
Can I ask for a little more detail about AC commercial power distribution.

I took a look for useful sites dealing with power distribution. It was a
little disappointing. There were two simple descriptions and at the other
end a government preprint site. I didn't find a middle of the road effort:
Siemens described their motor driven, tap changing regulators but this was
too isolated for me to want to offer it here.

How is the voltage regulated with changing loads? The 'howthingswork' web
site shows a bank of regulators on the 7200V line, but says nothing about
how they work.

These are tap changers, which step at about 1/2% of nominal voltage per step
to +/- 10%


Does the High Voltage/Low Current of the main transmission
lines buffer the plant itself? I can see this because the voltage drop in
the transmission line would be a very small fraction of the voltage.
However, that isn't necessarily the case once through the substation
step-down transformers. It would also seem that the generators produce a
fixed voltage--is that right? Is there any where else in the distribution
system where the voltage is regulated? If so how?

In my understanding, turning up the power really means bringing more
generators on line and if the demand is less than the capacity of the
running generators, the excess is dumped back to ground. Again is this
right?


Not sure about the 'dump to ground' concept - if you want less power from a
prime mover, you supply less fuel.


Another Web site talked about DC transmission being more efficient than
AC--but I think they were talking about at the same voltage. The particular
Canadian DC line was running at 900K! Why is this so?

At the highest AC transmission voltage, resonance and peak voltage becomes
a problem, so with the advent of high efficiency converters/invertors it
becomes attractive to use DC.

Any good on-line references to how this all works--at a level beyond
'howthingswork'?

A basic diagram & description of transmission & distribution.
<http://www.chipcenter.com/columns/rci/tesla/acbasics.html>

Another one in the same vein:
<http://www.windows.ucar.edu/spaceweather/power_to_home.html>

Here's the preprint site.
<http://www.osti.gov/preprint/powertrans.html>

Other things I don't know (amongst many, many) is how the various power
plants on a grid synchonize frequency and phase as their output is merged?
How do you add in the output of a bunch of wind turbines--for that matter
how is the frequency regulated in these?

Thanks,

Rick

I understand plants use phase indicators to match
frequency and phase before connecting to the grid - the consequence of not
doing so are apparently expensive.

Where generator speed cannot be well controled - as in a windmill, the
power is routed through a solid state converter/inverter.

This response was not as thorough as I would want to offer, but I just did
not find the sources I would have wanted you to see.


Brian Whatcott
Altus OK Eureka!