[time-nuts] Re: Has Line-Frequency Timekeeping Become Less Reliable in the U.S.?

[Francis Grosz]

Following up on Hal Murray's post, I have some data.  With all of the
discussions about AI and Data Centers connecting to the grid and looking at
the kind of load they represent, I became interested in what will happen to
power quality and reliability.  For several months I have been collecting
data from my power line.  This data consists of frequency over a short term
(1 second); maximum, minimum, and average frequency over a 20 minute block;
and long term frequency (drift of a power line clock vs. an accurate
clock); RMS voltage (at 5 second intervals); AC waveform; and power line
spectrum over 30 Hz to 1 kHz.

The long term frequency measurement is made by comparing a nominal 1 pulse
per minute from the power line (1 pulse per 3600 cycles of the line) to an
accurate 1 PPM from a Thunderbolt GPSDO and graphing that over time, one
measurement every minute so 1440 data points a day.  A 31 day graph of the
Eastern Interconnect time variation as seen in Louisiana is here:


[image: image.png]
There is no significance to the value of the difference, only the change is
significant.  The total variance is a bit over 35 seconds.  How significant
this is depends on the use case.

One additional note:  Last year I attended the IEEE Power & Energy Society
General Meeting in Austin to learn what was happening in this area.  There
was a lot of very interesting information at that meeting.  Unfortunately I
am not attending this year's meeting which begins Monday, 7/20/26.
However, many of the sessions will be streamed on IEEE TV.  I am not sure
if an IEEE account is needed to access them, but I don't believe so.  If
you are interested you can find the sessions at:

   https://ieeetv.ieee.org/2026pes-general_meeting

The Opening Plenary Panel Session begins at 9:30 AM EDT Monday.

                        Francis Grosz
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