A very similar spike in frequency (outside the NOFB) on Saturday 11th April 2026

In recent days we’ve already written:

1)  Several articles about a notable Frequency Spike at 10:30 on Friday 10th April 2026:

(a)  which appears to be due to some glitch in UIGF forecasting at the AEMO

… possibly compounded by some ‘Games that Self-Forecasters can Play’.

(b)  and led to frequency spiking up outside the Normal Operating Frequency Band for a Dispatch Interval.

2)  And we also observed a very similar large aggregate over-performance from Semi-Scheduled units on Saturday 11th April 2026 at 14:20 (NEM time):

…which we mused also delivered a similar frequency disruption.

It’s Monday morning 13th April 2026 and we’ve been able to extract a 4-hour run of NEM Mainland Frequency measured at 0.1 second cadence from our ‘Device 2’ in Brisbane for back on Saturday 11th April 2026:

As we did with the frequency spike on Friday 10th April, below we’ve also zoomed into a 1-hour span to show that the spike on Saturday afternoon was remarkably similar to the spike on Friday morning:

In both cases we see:

1)  An almost linear ramp up (within a dispatch interval) and an almost linear ramp down (within the next dispatch interval);

2)  Peaking just outside of the NOFB (50.176Hz on Saturday, compared with 50.174Hz on Friday)

3)  With the peak occurring ~30-40 seconds within the second dispatch interval

… remembering the significance of the first 20-40 seconds within each Dispatch Interval (in terms of receipt of new Dispatch Targets):

(a)  As we noted in this ‘(… first step into the complexities of) the Dispatch Interval in the Real World’; and

(b)  As AEMO showed  as noted in their ‘NEM Dispatch Timing Fact Sheet’.

The similarities between these two spikes, and the other factors above (e.g. linear ramps, and timing) point to some gremlins in the dispatch process (specifically related to UIGF systems) that caused both spikes.