Updated list of events on 25th May 2021 that we’ll be investigating – time permitting

In this article on Friday 28th May, we identified a (relatively!) small frequency drop down to 49.879Hz.

We’ve not written any more about this – though we have been discussing some theories internally and we also have seen some speculation about this on some social media threads.

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Released late on Wed 2nd June 2021, the AEMO’s Preliminary Report notes in the Executive Summary that:

“Initial investigations show that at 1334 hrs on 25 May 2021, Callide C4 ceased exporting active power and was
observed to absorb approximately 50 MW and 300 megavolt-amperes reactive (MVAr) from the power system, …”

That’s not healthy…

This was first noted in the first article in the series.

I named it ‘Event 1’ the next day (Wed 26th May), and then wrote about it on Fri 28th May using ez2view snapshots.

The low point here was 49.773Hz.

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Mark Ludlow’s article in the AFR on Wednesday afternoon, 2nd June 2021 provides some excellent additional information I’d not seen before.

Just prior to 17:00 on Wednesday 2nd June, the AEMO’s Preliminary Report was released, provides more details of what went on here.

We identified this on 26th May, and then wrote about it on 28th May using ez2view snapshots.

The low point here was way down at 48.555Hz.

At this point QNI separated for ~20 seconds (as the Hornsdale frequency data confirmed) and Allan reminds us that some things went right.

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Just prior to 17:00 on Wednesday 2nd June, the AEMO’s Preliminary Report was released, and provides some details of Event 2.

We identified this on 26th May using ez2view snapshots, but have not yet had time to follow this one up.

There are a few questions there I’ll be delving into.

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Later on Wednesday afternoon (2nd June) I published this ‘Initial look at System Strength constraints’, but will have to wait for more time to do more….

Released late on Wed 2nd June 2021, the AEMO’s Preliminary Report includes a table on this constraint in section 5 (bottom of page 16).

In the lead-up to the evening we’d issued this warning, and then wrapped up later that night (with a sense of relief) when things had subsided.

Allan’s article showed some of the recovery – and, on Monday this week, I posted this first pass review of bidding on the day.

Carl Daley’s article on Monday 31st May also provided some details.

However there are other questions about this event that we have not explored.

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Released late on Wed 2nd June 2021, the AEMO’s Preliminary Report notes in the Executive Summary that:

“The large reduction of generation availability led to actual Lack of Reserve 1 (LOR1) and LOR2 conditions, and
forecast LOR3 conditions in Queensland. Actual LOR1 and forecast LOR2 conditions also occurred in New
South Wales.

As a result of the event, 15 MW of Reliability and Emergency Reserve Trader (RERT) capacity was activated in
Queensland.

Forecast LOR3 conditions in Queensland were subsequently cancelled at 1923 hrs. Investigation is underway
into the reasons for changes in forecast reserve conditions and will be discussed in a later report.“

The report also contains a discussion of this in section 6 (starts at the bottom of page 17).