Martin,
That is very interesting. I didn't have a clue about this.

Ron Miller
N6MSA
Dunedin, Fl.
USA
SKYPE: arjay1
-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of Martin G. McCormick
Sent: Monday, August 20, 2012 9:16 AM
To: [log in to unmask]
Subject: Re: Moderating you off the list!

	The power grid is pretty much what you describe but it is
surprisingly complex, also.

	As a student in the late seventies, I had a part-time job involving
the development of instructional materials for the training of power line
workers. Somewhere along the way, we discussed what has to happen when you
connect an AC generator to the grid or more accurately, the grids.

	We have more than one large power network in North America which
includes the United States, Canada and Mexico.

	A very large grid runs all the way from Quebec and New York State
all the way across the nation to the Rocky Mountains and down to Texas.

	There is a Western grid from the Rockies to the West Coast and then
Texas has its own grid.

	This is based on what I learned in the seventies and it could be
that some of these grids have merged. Here's the problem. You know how, in
radio, you can tune a transmitter to the exact same frequency as another
transmitter and they are said to be at zero beat. These generators are just
extremely low-frequency transmitters. When you start one up, it may be a
cycle or two too fast or slow and its signals will beat with the rest of the
grid at some low frequency like two musical instruments that aren't quite in
tune.

	You may wonder how they connect AC generators in parallel. After
all, they do it all the time and here is where theory meets practice.

	The word heterodyne means to mix forces. If two people are on a
tandem bicycle, they must both peddle at the same speed or nothing much good
happens. Generators are like motors, so much so, that a motor can be a
generator under the right conditions and vice versa. If you have two AC
generators running at the exact same speed, you can connect them together
and they will run as one. The trick is making them run exactly the say
speed.

	What they have to do is connect an instrument to both generators
that can tell when both are close to being in phase.
When they are, it is safe to hook them together.

	When you do this, they keep each other in phase because if one tries
to lag a little, the energy from the other will force it back to speed. It's
just like the tandem bike.

	If they have to take a generator off line, they disconnect it from
the grid, first and then they can safely stop it.

	Think about this. In New York City, you could put a mark on the
armature of a generator at a power plant and do the same thing on a
generator in Oklahoma City and come back a week later and find both marks in
the same relationship to each other that they were when you made them
because all the generators in the Eastern grid must phase lock with each
other or terrible things will happen. I'm talking about destroyed equipment
and lots of fire.

	I honestly do not know how one keeps the whole grid from drifting
slowly up or down in frequency, but I have heard that the long-term
frequency stability of the American power grids is superb. I think they use
atomic standards to set the whole thing.

	That few months I worked in that job was really interesting and
amateur radio theory made it much more easy to understand this material.

Martin WB5AGZ


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