If your generation isn't tied to a wider-area grid, all you really
care about is coarse instantaneous frequency and keeping the long-term
average as precise as possible, the latter is specifically so your
customers' clocks run at the right speed.
The former is doable with reeds, the latter requires exactly the kind
of integration over time that a clock compared with another time
reference provides... This is just a PLL with a minutes-to-hours time
constant and human phase comparators controlling the generator speed.
Matthew Kaufman
(Sent from my iPhone)
On Apr 10, 2010, at 8:31 AM, Eric Garner <[email protected]> wrote:
My question is why is it done that way at all? It seems impractical
in the extreme. Why not use a meter? Or the afore mentioned
vibrating reeds?
What happens when the clock rates sync up again, since the wall
clock time will still be ahead/behind the sat clock? Do they reset
the wall clock? Or is it only the rate that matters?
Given the sophistication of the rest of the network there must be a
reason.
Sent from my Banana Jr. mobile device
On Apr 8, 2010, at 3:48 PM, "Bill Hawkins" <[email protected]> wrote:
Brooke,
There are some interesting misconceptions here.
Yukon Power did not cause time to slow down. They did what every
generating
station does, which is to adjust drive power to make a synchronous
power
line
clock match a precision reference clock. The tolerance is seconds
because
the
means for controlling drive power has a time constant of several
seconds.
The real problem is the way demand varies. If you pour mechanical
power into
a generator, it will speed up when lightly loaded or slow down when
heavily
loaded. This is less of a problem when many generators are tied
together by
a power grid, as they are all synchronous machines. Central
dispatching
stations compare line and reference clocks, and direct plants with
capacity
to do so to make up lost cycles, or buy less from the most
expensive sources
when extra cycles are generated.
If you have a 5 digit counter (or more) tied to a computer, you can
plot the
deviation of line frequency for 24 hour intervals. TVB had this on
his site.
What I saw in MN was that generators speeded up in the early
morning to make
up cycles so there was no reference error at 6 AM. Then the loads
turned on
and the cycles fell behind and recovered as power was dispatched,
within +/-
6 seconds. This is good enough for social time, where the mundanes
don't
know
about time-nuts.
The Alaskan network is probably too sparse for central direction,
so each
power plant makes its own adjustments. Note that this doesn't
necessarily
produce stable control, ever.
In this case, the reference clock appears to refer to GPS satellite
time,
but
uses a standard wall clock to display it. It is the reference clock
that
slowed down when it should have failed to work at all. Perhaps the
wall
clock
(maybe it was really a HP 113) needed oil. There's the real
question for
time
nuts: How did the reference clock slow down?
The first comment to the article shows what happens when your ego
fails to
shame you into silence when you don't know what you're talking about:
"I don't understand how the amount being generated has anything to
do with
what happens to household electronics." [see above]
"It would make more sense if the plant was generating at 55Hz
versus 60Hz
as some electronics will use the line frequency rather than
integrated
oscillators to set clocks." [The plant probably has breakers that
take it
off line when the frequency gets below 58 cycles, to keep it from
dragging
the network down.] [I thought that all electronics today converted
the line
to DC without sampling it, and ran timing from a crystal. Anyone
know?]
"Regardless, it shows YEC continues to be a bunch of bumbling
oafs." [People
who live in glass houses shouldn't stow thrones, or something like
that.]
Thanks, Brooke. I had some fun explaining all this.
Bill Hawkins
-----Original Message-----
From: Brooke Clarke
Sent: Thursday, April 08, 2010 12:58 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Yukon Energy causes time sync problems
Hi:
http://whitehorsestar.com/archive/story/time-passed-more-slowly-over-the-eas
ter-holiday/
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
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