[142448] in North American Network Operators' Group
RE: Wacky Weekend: NERC to relax power grid frequency strictures
daemon@ATHENA.MIT.EDU (Matthew Huff)
Sun Jun 26 11:03:25 2011
From: Matthew Huff <mhuff@ox.com>
To: 'Seth Mattinen' <sethm@rollernet.us>, "'nanog@nanog.org'" <nanog@nanog.org>
Date: Sun, 26 Jun 2011 11:03:17 -0400
In-Reply-To: <4E06820D.3000704@rollernet.us>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Another couple of reasons to use a delayed transition ATS:
1) Motor lock. Delays on HVAC equipment never get triggered if the system n=
ever goes offline. Having a correct "open" period allows the motors to spin=
down, and start back up on the delays that are programmed keeping them fro=
m being synchronized
2) Allowing transformer fields to collapse. Even in phase, without a delaye=
d transition ATS you can end up with a partially collapsed transformer fiel=
d with a new field being created at non-ground state. This can cause a tran=
sient back wave that can snap circuit breakers. Yep, this one happened to u=
s a few times before we switched to a delayed ATS, was a PITA to debug and =
resolve.
-----Original Message-----
From: Seth Mattinen [mailto:sethm@rollernet.us]=20
Sent: Saturday, June 25, 2011 8:49 PM
To: nanog@nanog.org
Subject: Re: Wacky Weekend: NERC to relax power grid frequency strictures
On 6/25/2011 16:43, Paul Graydon wrote:
> On 6/25/2011 12:32 PM, Seth Mattinen wrote:
>>
>> For open and closed transitions you'll most certainly want to sync to
>> utility to transition between the two. For the delayed transition model
>> it'll stop at the intermediate "open" point for a configurable amount of
>> time during which the load is disconnected from everything (i.e. let all
>> the motors spin down first).
>>
>> ~Seth
>>
> Take a guess what the datacenter our equipment is currently hosted in
> uses. Yet another reason to be glad of a datacenter move that's coming u=
p.
>=20
Also depends on the operator, so ask to see their xfer switches and how
they're programmed if that's a concern. All of the non-residential
models in that link for three-phase have motor/load disconnect signaling
capability. If the operator is clued enough to use it then it's all
good: shut off signal to motor/compressor loads, phase sync and switch,
signal reconnect after delay. But if they're not... run away.
Even with the delayed transition models the "hold open" delay can be too
short and end up re-energizing the motors too quickly. There's always
plenty of ways to f*ck things up good.
~Seth
