[time-nuts] 60hz disciplined watch

Jim Lux jimlux at earthlink.net
Wed Apr 20 16:34:21 UTC 2011


On 4/20/11 8:53 AM, Jim Lux wrote:
> On 4/20/11 8:26 AM, Poul-Henning Kamp wrote:
>> In message<BANLkTimuxPs8gBxP99ra8iJzvhEotp8ong at mail.gmail.com>, paul 
>> swed writ
>> es:
>>
>>> Thats what I also thought though did not plan to test it.
>>> As for mains stability. They are indeed stable over time weeks and 
>>> months
>>> and are corrected.
>> Are you sure ?
>>
>> Here in europe that was lost in the "privatization" of the grid: Nobody
>> was charged with paying for the extra power needed to capture lost
>> cycles, so now they just try to keep it close to 50.0Hz and don't
>> care about the integral.
>>
>> I would be surprised if it were any different in USA.
>>
> It's probably somewhat better, because there are long distance 
> transmission lines which rely on careful management of relative phases 
> (and by extension frequencies) to control the power flow on the line.  
> California consumes about 50 GW (peak)   (26 GW for Ca Independent 
> System Operator as I type this).  The two Pacific Intertie lines (one 
> AC and one HVDC) carry 7GW-ish.  That AC line is quite the challenge 
> to stabilize (it's 1000km long, and I've heard that transients take 
> hours to die out). (and, of course, they use GPS heavily to provide an 
> accurate time reference for reporting instantaneous phase and 
> amplitude of the lines)
>
> I seem to recall a site somewhere that gave statistics (in quasi real 
> time) of the system frequency here in Southern California.

I found this in a generator interconnection agreement:

This frequency response control shall, when enabled at the direction of 
CAISO, continuously monitor the system frequency and automatically 
reduce the real power output of the Asynchronous Generating Facility 
with a droop equal to a one-hundred (100) percent decrease in plant 
output for a five (5) percent rise in frequency (five (5) percent droop) 
above an intentional dead band of 0.036 Hz

---

Here's a nice training presentation about how they measure and manage 
system frequency and relative phase (to fractions of a degree)
http://www.phasor-rtdms.com/downloads/guides/CAISO_RTDMS-Training01312006.pdf

There's some pictures of actual frequency disturbances during 
transients, and I leave it as an exercise for the reader to turn that 
into an AVAR spec.

That's all about short run (taus of tens/hundreds seconds)...
The system generally regulates frequency over 100k seconds (a day) to 
keep electric clocks reasonably "on time". I think the standard is "no 
more than 2 seconds deviation from UTC" which implies, what, something 
like 5E-4 ADEV for tau of 100,000 secs?

tvb's data at http://leapsecond.com/pages/mains/  seems to show similar 
statistics.  His plot of "phase data" is labeled seconds, and if that's 
right, then his local power is substantially worse than the "2 second 
error" metric.



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