[time-nuts] Logging the grid frequency....
nerd at verizon.net
Fri Feb 22 23:52:58 EST 2013
I think you have to ask what is the use that is going to be made of that
number. Do you want to know how well an old synchronous clock will keep time or
do you want to know when there's been an (inductive) phase shift that signifies
the loss of a transmission line? Are you interested in how phase relates at
various parts of the system (synchrophasors)? How fast do you need to detect
and how fast do you need to react (if that is your intent). Or do you just want
to log and make pretty graphs later? You have to answer questions like this
before you can say what is appropriate or not as a measurement means, and that's
where this is heading, yes?
On 2/22/2013 11:21 PM, Bill Hawkins wrote:
> The grid contains a massive amount of inertia in the rotating
> synchronous machinery that generates power. The 'springiness'
> of the transmission lines allows local noise and even phase
> noise that is caused by loads added to or dropped from the
> line. Hal Murray (ICBW) had pictures of individual cycles
> that were badly distorted by changing taps on distribution
> So it is not correct to measure one point to a gnat's nose
> hair and call it "the grid frequency."
> It might be more accurate to put a flywheel on a synchronous
> motor and measure its speed, because the time constant of that
> system is a whole lot closer to that of the real grid frequency.
> Now, I understand that nobody build things like that any more,
> so perhaps a mathematical model of such a system could be solved
> by a computer that samples the line voltage at about 100 times
> line frequency.
> But perhaps I have misunderstood what you have been talking about.
> Bill Hawkins
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