Hi Dave, Just got back from from four weeks overseas plus a two-week domestic road trip and am still unwinding (decompressing?). Need to readjust the caffeine intake accordingly.
I accidentally multiplied the 20 minutes by 60. Your value is correct .. and an even smaller error. Thanks for keeping on top of things.... Dan --- On Mon, 6/27/11, Dave Click <davecl...@fsec.ucf.edu> wrote: > From: Dave Click <davecl...@fsec.ucf.edu> > Subject: Re: [RE-wrenches] National grid hertz adjustment > To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org> > Date: Monday, June 27, 2011, 2:26 PM > 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> > > > > > > > > _______________________________________________ > > List sponsored by Home Power magazine > > > > List Address: RE-wrenches@lists.re-wrenches.org > > > > Options& settings: > > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > > > List-Archive: > > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > > > List rules& etiquette: > > www.re-wrenches.org/etiquette.htm > > > > Check out participant bios: > > www.members.re-wrenches.org > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
