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Grid problem ?

broadgage
At about 03-00 today I had another power cut, this happens fairly regularly and is not normally worthy of much comment.

However I noted that after the supply was restored, that the UPS was still making unhappy sounds due to "mains out of tolerance"

I then observed the "dynamic demand" website, upon which there is a real time display of UK grid frequency. This looked very unstable with the frequency "bouncing around" a great deal.

There was nothing remarkable about the actual frequency attained, it remained generally within the usual operating limits of 49.8 cycles to 50.2 cycles.

What was however most exceptional was the speed of the frequency variations, less than a second for a 0.3 cycle change, and the number of these sudden frequency changes, at least a dozen such rapid changes in a minute.


I then observed the national grid website "frequency for the last 30 minutes" chart. This showed nothing unusual, but I suspect that the chart has insufficient resolution to display frequent and very brief events.
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  • 0
    Do you mean this website ?
    http://www.dynamicdemand.co.uk/grid.htm

    here ?

    It is showing quite large flutters now as well.

    A caution.

    It is not quite clear how they make the readings - traditionally to measure to 1/10 of a Hz you have to wait for at least 10 seconds worth of waveform-  given they quote to 1/1000 of a Hz  (about quarter of an hour to slip a whole cycle) this is presumably using the period of a few cycles, maybe as little as one, and then deducing the frequency from the time interval. If this is the case, then this method is vulnerable to any noise near the zero crossing, as even if small in amplitude, will move the instant of the zero-crossing and appear as a frequency error. It does not mean the frequency has instantaneously changed.

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  • 0
    Do you mean this website ?
    http://www.dynamicdemand.co.uk/grid.htm

    here ?

    It is showing quite large flutters now as well.

    A caution.

    It is not quite clear how they make the readings - traditionally to measure to 1/10 of a Hz you have to wait for at least 10 seconds worth of waveform-  given they quote to 1/1000 of a Hz  (about quarter of an hour to slip a whole cycle) this is presumably using the period of a few cycles, maybe as little as one, and then deducing the frequency from the time interval. If this is the case, then this method is vulnerable to any noise near the zero crossing, as even if small in amplitude, will move the instant of the zero-crossing and appear as a frequency error. It does not mean the frequency has instantaneously changed.

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