[142444] in North American Network Operators' Group
Re: Wacky Weekend: NERC to relax power grid frequency strictures
daemon@ATHENA.MIT.EDU (Leo Bicknell)
Sun Jun 26 08:28:39 2011
Date: Sun, 26 Jun 2011 05:27:10 -0700
From: Leo Bicknell <bicknell@ufp.org>
To: nanog@nanog.org
Mail-Followup-To: nanog@nanog.org
In-Reply-To: <4E0661E9.7040602@rollernet.us>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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In a message written on Sat, Jun 25, 2011 at 03:32:09PM -0700, Seth Mattine=
n wrote:
> Most of these come in open, delayed, or closed transition models:
> http://www.gedigitalenergy.com/powerquality/ATSHome.htm
I think we're missing something, which is where these ATS's are
installed.
I don't think most utilities allow (largeish) ATS's to do a closed
transition from a genset to the utility grid, but I may be wrong.
There may be other ATS's in your facility that do a closed transition
though. For instance, consider this (somewhat simplified) dual UPS
design:
Utility Generator
| \/ |
| /\ |
ATS #1a ATS #1b
| |
UPS #1 UPS #2
| |
\ /
\ /
ATS #2
|
Load
ATS's 1a, 1b, sense utility power for quality. Should the utility
power quality not meet specs (e.g. go out), they disconnect from
utility, tell the generator to spin up, wait 5-15 seconds for the
generator(s) to spin up and then close to the generator. They are
in an open state for perhaps 20+ seconds, generators are never
closed to the utility. Going back the drop may be shorter, perhaps
10 seconds, but there's still a long-ish open gap. Definately not
sub-second.
ATS #2 takes the dual UPS output (from synchronized UPS's) and does
a closed transition between the two sources. Indeed, a previous
employer had ATS's at this location that could switch between sources
in less than 1/4 wave, the equipment never knew the differenece. Very
impressive.
It's not that you couldn't install a closed transition ATS in the
ATS 1a/1b location from an electrical point of view, but I don't
think codes, power companies, or common sense make it a good idea.
As others have pointed out, the grid can do weird things because
your neighbors did something stupid, or a car hit a power pole and
shorted 3 phases together. Syncing to it is, well, crazy.
Maybe small plants are different, but I've never seen a 1MW+ plant
where the generators synced to utility. I can imagine CoGen might have
some different requirements, and I've never worked with that, but I
don't think that's what we are discussing.
--=20
Leo Bicknell - bicknell@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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