In reviewing system frequency on the 16th of June, 2025, we observed a drop that reached below the NOFB.
The above chart provided us with the overview. To pin down the time of the excursion we charted the measurements from the logger (located in Brisbane, 100 millisecond sampling), zooming in . We find:
- The low-point was 49.832 Hz, at 15:40:19.
- Below the 49.85 Hz NOFB.
- The measurements took a bumpy ride to get to the low-point.
- A pattern of slowing-then-recovering cycles appears:
- 15:25 to 15:28 (3 mins, in the leadup to our zoomed-in chart)
- 15:28 to 15:33 (5 mins)
- 15:33 to 15:37 (4 mins)
- 15:37 to 15:44 (7 mins), the last one included the nadir.
- Frequency spent close to a minute at or near the lower NOFB, between 15:40 and 15:41.
We haven’t identified a material generator trip upon a quick scan of data available to us. So, identifying drivers of the dip is mere speculation until we find the time:
- Not currently aware of any large unit trip yesterday afternoon (no coal units, but not watching others).
- So (and here be speculation!) one suspects another VRE-driven event.
The last dip prior to this day that we’ve observed was on 13 June.
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