[RE-wrenches] National grid hertz adjustment

[Exeltech]

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 <reellison at gmail.com> wrote:

From: bob ellison <reellison at gmail.com>
Subject: Re: [RE-wrenches] National grid hertz adjustment
To: "'RE-wrenches'" <re-wrenches at 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-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at 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 ButlerNABCEP Certified Solar PV Installer®NYSERDA eligible PV & wind installerFour Winds Renewable Energy, LLC8902 Route 46Arkport, NY 14807607-324-9747  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 DuncanBy Seth Borenstein The Associated PressWASHINGTON -- 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
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