Wacky Weekend: NERC to relax power grid frequency strictures
nanog.20110127 at jason.roysdon.net
Sat Jun 25 19:52:11 UTC 2011
On 06/25/2011 08:06 AM, William Herrin wrote:
> On Sat, Jun 25, 2011 at 10:49 AM, Jay Ashworth <jra at baylink.com> wrote:
>> Perhaps I read the piece incorrectly, but it certainly sounded to *me* like
>> the part that was hard was not hitting 60.00, but *staying in sync with
> Way I read it, when they occasionally run at 59.9hz for a few hours
> (and according to my UPS monitoring software this is a regular
> occurance), they're no longer going to run at 60.1 hz for a while so
> that the average comes out to 60.
> Bill Herrin
This paper describes what they currently do to keep clocks accurate with
Manual Time Error Correction (which is what they are going to suspect
for a year):
As I said in my last post, I'm not an EE, but just follow some of topics
on that side of the house.
What I gather is that Manual TEC, which is done by purposely running the
frequency away from 60Hz to correct an average deviation, can actually
cause more problems.
"NERC is investigating the possibility of eliminating Time Error
Corrections. NERC has been collecting data regarding Interconnection
frequency performance, including the number of clock-‐ minutes during
which actual frequency dropped below the low Frequency Trigger Limit
(FTL) of 59.95 Hertz. During the period of July 2005 through March 2010,
approximately 44% of the minutes during which clock-‐minute actual
frequency dropped below the low FTL occurred during Time Error
Corrections when scheduled frequency was 59.98 Hertz (1,875 of the 4,234
total minutes observed below 59.95 Hertz). Upon further investigation,
it was found that almost all of those minutes (1,819 of the 1,875 total)
represented frequency deviations that would likely not have dropped
frequency below 59.95 Hertz if the scheduled frequency had been 60
Hertz. In other words, approximately 97% of the Low FTLs were of such a
magnitude that if the Time Error Correction had not been in effect, the
exceedance of the low FTL would not have occurred.
These Frequency Trigger Limits in and of themselves are only indicators
of system behavior, but the nature of their relationship to Time Error
Corrections calls into question the potential impact that Time Error
Corrections can have on frequency behavior overall. While it is
intuitively obvious that any frequency offset that moves target
frequency away from the reference point to which all other frequency
sensitive devices (such as relays) have been indexed will have a
potential impact on those devices’ performance, the industry has by and
large regarded Time Error Corrections as harmless and necessary as part
of the service it provides to its customers. However, in light of this
data, NERC’s stakeholders are now questioning whether or not the
intentional movement closer to (or in some cases, further away from) the
trigger settings of frequency-‐based protection devices as is evidenced
during Time Error Correction events is appropriate.
Accordingly, NERC is planning a Field Trial during which the practice of
doing Time Error Corrections will be suspended. Because of the
fundamental nature of this 60Hz signal, NERC is reaching out to various
industries to get their thoughts on whether they anticipate any problems
with the elimination of Time Error Corrections. Those industries include
appliance manufacturers, software companies, chemical manufacturers,
companies that make automation equipment, computer manufacturers, and
The main point I gather is that trying to do manual Time Error
Correction actually makes the power grid less stable at times, and as
such they want to do away with it (thus making the power grid more stable).
Think of it the same as patch management risk assessment. If there are
no security or bug fixes that directly affect you or even feature
enhancements that you don't need, do you apply a patch/upgrade to
critical systems? Nah, you skip those, because we all know every
patch/upgrade carries with it risk of an unknown bug or even security flaw.
That's what they're doing here, opting to skip "patching" the time
error. They're not ignoring frequency altogether, but rather only
minding that aspects that have to do with grid stability, not your alarm
clock. This is for the better anyway, and NTP/GPS/WWV/WWVH is the way
to go to keep clocks accurate and hopefully will be the outcome of any
I've seen conversation in various forums and lists I read that they are
going to ignore or not care about the 60Hz standard. This is incorrect.
They just aren't going to purposely deviate from the scheduled
frequency to perform manual TEC.
Mind you, that they still care about why the frequency is off, and when
things are not able to quickly compensate, they want to know and be able
to pinpoint it and fix it:
Specifically, read this PDF:
The AP piece was focused on hype and word-spinning (I couldn't find an
AP.org link, so used one that I could find,
"The experiment would allow more frequency variation than it does now —
The NERC BAL standards already hold the NERC entities to very high
frequency standards, and this will be unchanged, except for manual TEC.
All it is doing is eliminating the corrections made purely for time's
sake, which actually eliminates more frequency variation. This may, or
may not, create more average frequency variation, and that is part of
"Officials say they want to try it to make the power supply more
reliable, save money and reduce what may be needless effort."
This is the real goal, and should have been the focus of the news story
- but that doesn't make headlines.
I'm going to go shop for a new clock. I had one that used the WWV/WWVH
stations, but then they messed with DST and it was off for a few weeks
around each DS change. That forced me me to pull it off the wall and
change the TZ at one time of the year to correct it, but the other time
of the year I could not correct it (as it only had 4 TZ settings), so I
took it down. Beware "Automatic Time Set" clocks which don't really
learn the time from the WWV/WWVH stations (like the Sony ICF-C218, which
has a preset time and battery, but still uses the frequency from the
wall to maintain time). The best bet is a clock that requires batteries
as you know it won't get time from the power grid.
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