[time-nuts] Daft idea with the National Grid

Tue Feb 9 14:31:43 UTC 2021

Hi,

zero cross detection is not the best way to track grid frequency. 
I built my grid frequency tracker with a uC sampling the grid at 160ks/s 
and 12Bit. It is clocked by a TCXO. I fit a sine wave for every cycle of 
the grid. 

Fitting a sinewave is a linear problem, you do not need any approximations 
and it is doable with a small uC. The samples of a sinewave are the 
solution to the difference equation sig(n+1)=2*cos(w)*sig(n)-sig(n-1), 
which is a linear equation for the unknown cos(w). That is straight and 
simple linear algebra. I get a precision in the range of 4E-4 Hz.

>>>>>>>>>>>>>>>>>>>>>>
Years ago I recall reading accounts of efforts in the U.S. and perhaps 
Canada to track down the cause(s) of small but noticeable changes in the 
frequency of certain regional power grids that seemed to occur at more or 
less the same time each day. 

In the european grid you have stable frequency changes in a 15min 
timeframe, frequency being high in the morning and at night and low in the 
afternoon. The 15 min timeframe is due to the 15min trade periode of the 
European Energy Exchange trading platform located in Leipzig. The energy 
brokers show a deterministic under/over-estimation of the european power 
consumption which results in power shortage/surplus and thus frequency 
rise or fall. 

If I were a stock exchange geek I'd turn this information into money, much 
money :))

Cheers
Detlef 

"time-nuts" <time-nuts-bounces at lists.febo.com> schrieb am 08.02.2021 
23:59:07:

> Von: joekokker at epios.eu
> An: time-nuts at lists.febo.com
> Datum: 09.02.2021 00:05
> Betreff: Re: [time-nuts] Daft idea with the National Grid
> Gesendet von: "time-nuts" <time-nuts-bounces at lists.febo.com>
> 
> Dear all,
> 
> it is quite an interesting premise. I think one of the challenges is to 
> even measure these small deviations in frequency. The time correlation 
> can be achieved with GNSS but the actual determination of the 
> zero-crossing might be the problem. I think the ZCD must be better than 
> 100ns for this in each cycle. Local noise and environment conditions 
> render it quite difficult. When constructing a filter for the 50Hz, the 
> components must be very well designed to cope with the different 
> temperature, local noise and voltage amplitudes at two different places.
> 
> Regarding disruptions in the grid: there are various regulation 
> mechanisms. Generally the first 10-20 seconds physical effects stabilize 

> the grid. Afterwards the automatic control takes over.
> 
> - saved rotational energy: an initial frequency drop due to a unexpected 

> change in load or production is smoothed out by the inertia of all the 
> generators, motors, pumps, etc. For a 10% mismatch in power without 
> additional measures, the initial frequency drop would be about 1Hz per 
> 30 seconds.
> 
> - self-regulation: a 1% drop in frequency leads to a ~2% reduction of 
> load due to frequency dependent loads;
> 
> - primary, automatic load-frequency control takes about 30 seconds to 
> activate
> 
> After this rather short timescales, as Poul-Henning mentioned the human 
> factor (trading) has the biggest impacts on grid stability. It is 
> clearly visible with a periodicity of 15 minutes and more pronounced in 
> the evenings.
> 
> A small note on the recent frequency drop in the European grid:
> https://www.entsoe.eu/news/2021/01/26/system-separation-in-the-
> continental-europe-synchronous-area-on-8-january-2021-2nd-update/
> 
> Best
> Joe
> 
> On 2/8/21 8:46 PM, Mark Spencer wrote:
> > Years ago I recall reading accounts of efforts in the U.S. and 
> perhaps Canada to track down the cause(s) of small but noticeable 
> changes in the frequency of certain regional power grids that seemed
> to occur at more or less the same time each day.
> > 
> > 
> > Mark Spencer
> > mark at alignedsolutions.com
> > 604 762 4099
> > 
> >> On Feb 8, 2021, at 6:48 AM, Lux, Jim <jim at luxfamily.com> wrote:
> >>
> >>> On 2/8/21 12:02 AM, Poul-Henning Kamp wrote:
> >>> --------
> >>> Lux, Jim writes:
> >>>
> >>>> If you happen to own something like a steel mill running electric
> >>>> furnaces or an aluminum refinery, so you can manipulate the load...
> >>> More scary:  Several independent studies have shown that even 
relatively
> >>> moderate bot-nets in the hands of somebody who knows the math of 
grid
> >>> stability would mean no grid stability.
> >> This is a generalized concern with distributed generation (i.e. 
> rooftop solar panels on houses), because a bug in the controllers 
> for the line connected inverter could really screw things up. I 
> suppose there's also concerns about  malicious activity, but fiascos
> like the NEST thermostats stopping  in winter of 2015/2016 are more 
likely.
> >>
> >>
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