The curious case of a frequency spike (outside of the NOFB) on Friday 10th April 2026

A quick first article with the following 4-hour trend of mainland frequency in the NEM

Very briefly:

1)  The highest point was (at 50.174Hz) was at 10:30:41.5 NEM time on Friday 10th April 2026:

(a)  which was outside of the Normal Operating Frequency Band, OFB

(b)  and presumably triggered Contingency FCAS responses.

2)  This spike does not look like any of the causes that we’ve encountered before (sometimes documenting in other articles about frequency disruptions):

(a)  With a frequency spike, they can sometimes be caused by a sudden trip of a large load:

i.  In years gone by, an aluminium smelter

ii.  But in the new world we’re steaming towards, perhaps a Data Center?

…in either case, the spike would be close to vertical

(b)  Occasionally they might be due to some energy resource issue across a fleet of VRE plant.

… though that’s much more likely to be a low frequency event caused by under-performance of VRE.

(c)  Occasionally they have been data or operational glitches

… like what happened on 19th August 2025 (for instance).

What’s particularly curious here is that the spike seems to center on 10:30, and is quite short in duration (i.e. a dispatch interval or two).  So this prompts me to zoom into a one-hour period as follows:

This chart helps:

1)   it makes it clear that the excursion was focused in the 10:30 (excursion) and 10:35 (recovery) dispatch intervals NEM time on Friday 10th April 2026.

2)  also, intriguingly, it looks to ramp fairly steadily up, and then steadily down ... almost like it’s linked to some linear trajectories of unit outputs?

We’ll come back to this in subsequent articles…