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From: smh@mit-eddie.UUCP (Steven M. Haflich)
Newsgroups: net.analog
Subject: Re: Selling Energy to the Utilities
Message-ID: <5210@mit-eddie.UUCP>
Date: Thu, 5-Sep-85 11:42:58 EDT
Article-I.D.: mit-eddi.5210
Posted: Thu Sep  5 11:42:58 1985
Date-Received: Sat, 7-Sep-85 05:21:50 EDT
References: <482@petrus.UUCP> <2550001@csd2.UUCP> <387@rti-sel.UUCP> <442@phri.UUCP>
Reply-To: smh@mit-eddie.UUCP (Steven M. Haflich)
Organization: MIT, Cambridge, MA
Lines: 43

In article <442@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>	First, get your generator running as close to line frequency as you
>can with mechanical speed control.  Once you have it matched to within a
>few cycles per minute, you take a standard light bulb and attach one side
>to the power grid and the other side to your generator (after appropriate
>step-down, of course!).  As the two sources drift in phase, the bulb gets
>brighter and dimmer (it sees the beat frequency of the two sources).  When
>the bulb goes out, you throw the switch to connect your machine to the
>grid (and cross your fingers and/or hide someplace far away).

About 25 years ago I was fortunate enough to witness the local electric
power company prepare for the evening load by bringing online to the
power grid an additional generator -- a steam-driven armature the size
of a small building, spinning at 60Hz.  (Generators are not normally
spun down when offline because it takes days for their bearings to reach
operating temperature, and to cool during careful spindown.)  When
offline, the generator spins free at approximately 60Hz, and bringing it
online requires synchronizing its rotation with the grid.  The
monitoring devices was a simple lightbulb connected between the grid and
the generator, along with a nifty rotating arrow to indicate phase angle
and looking for all the world like something from a 1930's Frankenstein
set.  (Remember, this particular generator was an already considered
aged when I saw it sometime in the 1950's.)

The single operator carefully adjusted a servo controlling the steam
valve for the turbine, finally getting the generator within about .5Hz,
with the arrow rotating and the light varying along with the phase
error.  The generator was then `cut in' with remote control switches
which connect it's output to the grid.  His art consisted of
compensating for the delay of the large mechanical switch mechanism -- a
significant fraction of a second -- so that connection would be made at
nearly zero phase difference.

He explained that the generator must be riunning at nearly the correct
speed, or else the mechanical impulse of the sudden speed change could
destroy it machanically.  The generator must also be cut in at
approximately zero phase, or else the sudden electrical surge from the
phase angle difference could destroy it (and/or the swtches)
electrically.

Remember, large generators are measured in megawatts and tens on tons.
On the whole, I'm glad I have a job where I can recompile after a
careless mistake :-).