Dan, I think we're only looking at an error of 20 minutes per (8760 hrs
x 60 min / hr) = 0.00381%, well within the frequency drift allowed under
UL 1741. So as you point out, it would only be the shorter excursions
away from 60.0Hz that would be the issue. This shift isn't the easiest
thing in the world to do (and then maintain)!
On 2011/6/27 15:08, Exeltech wrote:
A max of 20 minutes error per year (as stated in the article)
equates to an error of 0.228%.
Whether grid-tied inverters stay on line or not depends on
the ultimate range of the frequency excursions permitted
during the tests. UL1741 limits are 59.3 to 60.5 Hz for
fixed frequency settings. The cumulative error shown
above is well within those bounds. 59.3 Hz = -1.16%;
60.5 Hz is +0.83%.
However, I could see cases where they may allow 60.6 Hz
one day and 59.4 Hz the next. The overall net difference
would be zero for a frequency-dependent clock - but a
grid-tied inverter would spend the first day of this example
totally offline.
This would have to be a grid-wide frequency difference,
else they'd end up with some seriously large power flows
from one part of the grid to another, with potentially disastrous
results.
It will be interesting to see how they handle this.
Thanks for the post.
Dan
--- On *Sun, 6/26/11, bob ellison /<reelli...@gmail.com>/* wrote:
From: bob ellison <reelli...@gmail.com>
Subject: Re: [RE-wrenches] National grid hertz adjustment
To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org>
Date: Sunday, June 26, 2011, 6:40 PM
This will make it interesting to everybody with a grid tie inverter,
can we open up the specs to let them work with the “new test
variation”? The other option is that the inverters will spend a lot
more time off line.
Bob Ellison
*From:*re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of
*Roy Butler
*Sent:* Sunday, June 26, 2011 1:45 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] National grid hertz adjustment
I saw this as well, came over the AP news wire on Friday, June 24th.
I've been trying to figure out what they hope to gain by allowing more
frequency variation.....puzzling at best!
Roy Butler
NABCEP Certified Solar PV Installer®
NYSERDA eligible PV& wind installer
Four Winds Renewable Energy, LLC
8902 Route 46
Arkport, NY 14807
607-324-9747
www.four-winds-energy.com <http://www.four-winds-energy.com>
Although no trees were killed in the sending of this message,
a large number of electrons were terribly inconvenienced.
On 6/26/2011 1:31 PM, North Texas Renewable Energy Inc wrote:
This article in the local paper sounds a little like potential
trouble for grid connected inverters. I looked around on the NERC
www site without finding the report mentioned. Any other wrenches
seen anything about this experiment?
Jim Duncan
By Seth Borenstein The Associated Press
WASHINGTON -- A yearlong experiment with the nation's electric
grid could mess up traffic lights, security systems and some
computers -- and make plug-in clocks and appliances like
programmable coffee makers run up to 20 minutes fast.
"A lot of people are going to have things break, and they're not
going to know why," said Demetrios Matsakis, head of the time
service department at the U.S. Naval Observatory, one of two
official timekeeping agencies in the federal government.
Since 1930, electric clocks have kept time based on the rate of
the electrical current that powers them. If the current slips
off its usual rate, clocks run a little fast or slow.
Power companies now take steps to correct it, keeping the
frequency of the current as precise as possible.
The North American Electric Reliability Corp., which oversees
the U.S. power grid, is proposing an experiment that would allow
more frequency variation without corrections, according to a
June 14 company presentation obtained by The Associated Press.
The test is tentatively set to start in mid-July.
Tweaking the power grid's frequency is expensive and takes a lot
of effort, said Joe McClelland, head of electric reliability for
the Federal Energy Regulatory Commission.
"Is anyone using the grid to keep track of time?" McClelland
said. "Let's see if anyone complains if we eliminate it."
No one is quite sure what will be affected. This won't change
the clocks in cellphones, GPS or even on computers.
But wall clocks and those on ovens and coffee makers -- anything
that flashes "12:00" when it loses power -- may be a bit off
every second, and that error can grow with time.
VCRs or DVRs that get their time from cable systems or the
Internet probably won't be affected, but those with clocks tied
to the electric current will be off a bit, Matsakis said.
According to the June presentation, East Coast clocks may run up
to 20 minutes fast over a year, but West Coast clocks are only
likely to be off by eight minutes. In Texas, it's only an
expected speedup of two minutes.
Read more:
http://www.star-telegram.com/2011/06/24/3178359/test-of-electric-grid-could-be.html#ixzz1QOzHwezw
<http://www.star-telegram.com/2011/06/24/3178359/test-of-electric-grid-could-be.html#ixzz1QOzHwezw>
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