[time-nuts] Mains frequency
hmurray at megapathdsl.net
Thu Mar 13 02:17:17 EDT 2014
[Context is maybe(?) withdrawing the proposal to stop keeping time on the US
wb4gcs at wb4gcs.org said:
> Since then, large amounts of generation (primarily coal) has been shut
> down, so I was not at all surprised by the request.
> I missed the announcement that the request was withdrawn, and actually
> thought it had been approved and enacted -- all my line-frequency based
> clocks are now erratic and not very accurate.
I could easily be wrong on the withdrawing part. I haven't seen any recent
comments either way.
Where are you located? Did you notice when your clocks started acting
erratic? Do you have any solid data?
I have 2 old, synchronous, line clocks (stove and clock-radio). They seem to
be working normally, but I don't pay a lot of attention to how accurate they
I'm in Silicon Valley. I do monitor the line with a typical time-nut setup.
That's using the Linux PPS stuff to count cycles. Here is an updated graph
covering the last 12 weeks.
The 0 on the left is arbitrary. Peak-to-peak is 15 seconds. So if I set my
mechanical clock correctly, even at the worst time, it would still be within
15 seconds of correct.
That's from counting cycles and dividing by 60. A single cycle is a big
event. Off by one is easy to spot if you look at the right graph. Here is a
sample of a glitch:
I've only seen one event where a cycle was picked, none for dropped. I might
have missed something interesting. Look at the longer graph above. It's
pretty clear I haven't missed a huge pattern either way.
I saw one comment (don't remember where) that the problem was that the power
companies had to file a lot of paperwork whenever the line frequency dipped
below X. (I don't remember the numbers.) If they were running slow, (say
targeting 59.98) to catch up for running too fast, and an event that dropped
the frequency happened, it was much more likely to trigger the paperwork.
(Seems like they should fix the paperwork-filing rules to allow for that case, but maybe it's more complicated than I can see.)
> This is what initiated the 2003
> blackout in parts of the US & Canada. A utility had a paucity of reactive
> generation on a day with large reactive load, and one of its generators
> tripped on over-excitation to prevent damage to the generator and voltage
> regulator. This initiated the cascading events that left many in the dark.
> (The Joint US/Canada task force on that event is a /fascinating/ read!)
Do you have a URL?
In the late 70's there was a big blackout in NYC. I remember reading the IEEE article on it. I don't remember any frequency graphs. Did they archive that sort of data back then? The deal was that an important line bringing power in to NYC was knocked out by lightning. Power lines have several load capacities, depending on time. Thus they can carry X forever, X+x for a half hour, and X+xx for 5 minutes. A line from Long Island was carrying it's 5 minute rating for way more than 5 minutes. Somebody in the control room had their thumb on the "shut up" button. They knew that line was a critical resource, but they couldn't shift any load. Eventually, it sagged enough to hit a tree. Then that line when out and so did all of NYC. (That's my memory from 35 years ago.)
the same song recordings played at normal speed reveal that approximately six minutes before blackout the line frequency was 56 Hz, and just two minutes before the blackout that frequency dropped to 51 Hz.
51Hz ??!! Wow. It would be interesting to see that on a graph.
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