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A Good Set of Results!

A project log for Grid-2-Audio

A convenient adapter to view the electrical grid waveform through your PC's sound card.

David ScholtenDavid Scholten 01/01/2019 at 02:360 Comments

Okay, I know it's been a while (I'm a Daddy now!), but I have obtained the longest stretch of results that I possibly could without leaving the computer unattended.

Everything on the right side is just the final instantaneous snapshot of the measurement run and isn't that interesting. However, everything on the left is a running set of results where each time division (1x10^4) represents almost 4 hours of time.

The results started recording about 10am in the morning and ran till about 12am (~14 hours).

What I've learnt from this is that yes, I can see any time that a heavy load is turned on in the house (hair dryer, compressor, kettle or microwave). This can be seen on the Vrms plot as little sharp drops of 2-3 volts). I also see larger slower drops that must be from local industry (there is a vehicle works shop 3 houses down the road).

The grid frequency over that day is its own thing and is primarily controlled by the collective behaviour of all of the customers and the generation regulation.

The peak voltage is interesting in that is sometimes seems to capture some little transients. However, this will never be reliable as the sampling by MATLAB goes long periods without actually looking at the grid (it's luck if I grab a transient peak really).

The THD is great as it seems to vary in an interesting way in reaction to loads. For example, a linear load (resistor) like a kettle will simply drop the voltage across all frequencies. However, a heavy load with power factor correction and input filtering SHOULD (as far as I can casually comment) only draw fundamental current. Thus, the fundamental voltage component of the grid will sag a few volts, but the harmonic ripples will NOT. As a result, the ratio of the harmonics to the fundamental voltage (i.e. the THD) will increase. As a result, such fundamental current only devices should increase the grid voltage THD when they are turned on. Good luck observing this! And good luck separating such an effect from other variables that may overwhelm and make the opposite occur!

I'll also upload this MATLAB plot, along with others that are okay or decent.


When taking these results I have also noticed some very strange frequencies that seem to shift in reaction to THD or Vrms thresholds (cause and effect confusion maybe?). To show this to you I plan on getting the harmonic waterfall plotting working. This should allow a nice visual representation of what's going on over a day.

As you may have guessed, I'm certainly looking to wrap this project up (it's been a long time and I've lost interest).

Before I finish I'd like to:
-->Have some waterfall plots.
-->Video output of the grid.
-->Some kind of audio representation.
-->Raw data file for others.


Oh and here's the hair dryer turning off:


This also shows some mysterious 5kHz and 10kHz signals (bottom right black spectrum).

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