[time-nuts] Daft idea with the National Grid

[Hal Murray]

andy.g4jnt at gmail.com said:
> I can probably measure the grid frequency to a few micro Hz   over a period
> of tens of seconds. So I make a continuous recording of this, averaged over
> say 10 second periods. Now take a 7kW load (the maximum reasonably possible
> on a domestic circuit) and switch it on and off at intervals of perhaps 10
> minutes, precisely timed so it can be correlated with the frequency log.
> That 7kW load will be about 0.2ppm of the average for that for the whole of
> the UK.    By post processing, and some deep correlation covering days worth
> of cycles of load on-off with the frequency, I wonder if it would be possible
> to see the loading, the mean frequency changing by a few uHz. Not sure what
> the time constant of the grid control is, but for* small signals* I doubt it
> can be faster than a few minutes. 

I'd expect an ADEV type pattern.  For long tau, the wander in the system will 
dominate.  We have lots of long term data so should be able to plot that part 
of the graph.  For short tau, the noise will dominate.  I don't have any data 
below 10 seconds.  But I do have a TICC.  I wonder if the middle is the 
classic V or has some wiggles.

How much energy is in the rotating turbine and generator?  That should provide 
a lower limit on the time constant of the control loop.

If the ADEV pattern is a clean V and the signal is 2 levels, I'd expect the 
optimal modulation pattern is a homework problem for the right course.  We can 
synchronize the transmit and receive clocks with GPS.

This feels like I have to use something like 8B/10B with lots of transitions 
so the receiver can track the system frequency?




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