NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/sci/physics/19325

Text File | 1992-11-20 | 3.2 KB | 64 lines

Newsgroups: sci.physics
Path: sparky!uunet!ftpbox!mothost!lmpsbbs!areaplg2.corp.mot.com!bhv
From: [e-mail] (Bronis Vidugiris)
Subject: Re: Electric Power Transmission
Organization: Motorola, CCR&D, CORP, Schaumburg, IL
Date: Fri, 20 Nov 1992 19:16:57 GMT
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In article <[e-mail]> [e-mail] (John Hagerman) writes:
)In article <[e-mail]> [e-mail] (Leigh Palmer) writes:
)>
)> Wow. Thanks for the information, John. I hope someone will be able
)> to drop the other shoe and tell us where to learn more about this
)> twenty-year-old technology.
)
)Your ability to communicate sarcasm without a smiley is nice to see.
)But I fear that your comments may mask one important point of my post,
)which was to demonstrate that many of the questions asked here can be
)sufficiently answered by a tiny bit of research.  Need I explain why
)actually doing such research is useful?
)
)I have visited a hydroelectric plant, and it was rather interesting.
)Also of interest is the issue of grid phase maintenance, about which
)there have been many guesses and few facts posted, and about which my
)encyclopedia is mute.

The way I vaguely remember things from college, the phase of a generator
with respect to the 'grid' determined the direction and amount of power
flow.  The generator and grid were modelled as being connected together
by some inductance.

In one phase direction, the generator contributed power to the grid.  In
the opposite phase, the generator *took* power from the grid (and acted as
a motor).

An interesting analogy is a mechanical one.  Consider the grid to be like
a rotating shaft.  The coupling of the generator to the grid via an
inductor acts like connecting a (crank-driven) rotating wheel to the rotating
shaft via a spring.  In one direction, the spring adds energy to the shaft,
'pulling it along', in the other direction the spring acts as a load
on the shaft, taking energy away.

[The mathematical analogy is to assume voltage is like velocity and
that current is like force.  The vector product of voltage and current is
power.  v = L * di/dt across an inductor, so the intergal of the voltage
across an inductor is proportional to the instantaneous current.
Similarly the intergal of the velocity across a spring (the position) is
proportional to the force provided by the spring.  Capacitance acts
like mass with this mechanical analogy, resistance like some form of
friction damping.]

However, I'm not sure how global frequency/power regulation is done either.
Like the analogy with the rotating shaft, I'd expect that the grid frequency
and voltage would tend to rise when too much power was being fed into it
(compared to the total load on the grid), and drop when too little power was
being fed, but how the overall power regulation is done is something I don't
quite understand (I suspect that's what all those power engineering courses
are about :-)).