[time-nuts] Low cost synchronization
phk at phk.freebsd.dk
Sun Aug 21 14:24:47 EDT 2005
In message <20050821.193225.53123034.cfmd at bredband.net>, Magnus Danielson writes:
>> For the NordPool area (Norway, Sweden, Denmark, Finland) nobody tried to keep
>> the average at 50Hz.
>Which is what I recalled that you where saying. This is again my point, that
>just because it is in one place, that is not universally true for all places.
>The reasoning why people don't care as much should be fairly evident from the
>discussion so far.
Just got off the phone with a guy who writes for the same paper as me,
has been teaching this stuff for ages.
As a regulation domain gets larger, (and "larger" is measured in
[MW * km * s] in this context), the inherent regulation mechanisms
may develop instabilities for which the only currently known cure
is a external frequency reference.
The reason they don't do that in NordPool is because they don't
think they are big enough to need it *and* because they have a
couple of HVDC lines to other larger regulation domains where they
can dump surplus or pull deficit on very short notice.
However, external frequency references are not the perfect cure because
they tend to trip more generators on faults in the network than the
traditional mostly MVAR (reactive power allocation) based regulations.
He said that the places he knew off that used it, had a two state
mode, in one state, the frequency locked state, the delta-frequency
(not delta-phase!) is limited relative to the external reference, and
an effort to keep the delta-phase low was purely manual. The other state
gives up on all external references and just tries to avoid a collapse
of the grid.
As usual with big systems, the big problem is that they never get to test
and they're never ready when they get a chance to collect experience :-)
>Also, how do you encode a leapsecond over 50 Hz, 60 Hz or whatever and has it
Well, since they don't encode UTC in the first place, they can just encode
leapseconds just like any other second :-)
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
>BTW, measuring the 53rd overtone frequency may not give a clear picture of the
>frequency deviations at the base frequency.
Even worse, it may not be a "real" overtone in the first place, it could be
a PWM tone from some regulated async motor.
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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