When the NEM’s Largest Generating Unit Trips …

A quick followup from my post a few weeks ago on FCAS in action after the trip of a Loy Yang A unit.

On Wednesday evening this week the largest single generating unit in the NEM, the 750 MW Kogan Creek generator in Queensland, tripped from full load at 8:28 pm:


How did the power system cope? With the AEMO 4-second SCADA dataset released this morning, we can quickly look at the impacts on system frequency and the responses from other generators around the NEM, summarised in this chart:


Compared to the Loy Yang A trip covered in my earlier post, this was a larger unit losing output much more quickly – essentially inside one 4-second interval on the AEMO dataset. As a result the system frequency fell more rapidly and deeply, well below the lower operational frequency threshold of 49.85 Hz, the lowest value recorded in this data being 49.61 Hz. Nevertheless, the frequency fall was quickly arrested and then gradually recovered thanks to generator responses from right around the NEM, and quite possibly also responses from demand side FCAS providers who unfortunately don’t show up in the AEMO dataset.

The damped oscillations in frequency and in generator response are interesting, and weren’t evident in the “more graceful” trip of LYA3 previously covered, which took about 20-30 seconds to lose full output. These probably reflect the more rapid initial shock to frequency and are physically a bit like the reverberations of a struck bell (although much slower).

Finally, it’s worth looking at responses from a few individual generators around the NEM. First the relatively nearby Gladstone, also in Queensland:


Then at the other end of the system, Torrens Island B in South Australia:


And because everyone’s always interested, the big battery (Hornsdale Power Reserve) in South Australia:


– remarkably precise responses to movements in frequency, reinforcing some of AEMO’s observations in its recent report on the the battery’s operation.


About our Guest Author

Allan O'Neil Allan O’Neil has worked in Australia’s wholesale energy markets since their creation in the mid-1990’s, in trading, risk management, forecasting and analytical roles with major NEM electricity and gas retail and generation companies.

He is now an independent energy markets consultant, working with clients on projects across a spectrum of wholesale, retail, electricity and gas issues.

You can view Allan’s LinkedIn profile here.

Allan will be sporadically reviewing market events here on WattClarity

Allan has also begun providing an on-site educational service covering how spot prices are set in the NEM, and other important aspects of the physical electricity market – further details here.

1 Comment on "When the NEM’s Largest Generating Unit Trips …"

  1. Very interesting. I live in Adelaide. I fitted many years ago an over voltage and under voltage relay to my a/c. It has never tripped with over voltage set to 265V in 25 years. A few hours after that event at night with no neighbourhood PV feed the relay tripped. I measured the voltage with my multi meter and it was 268 V and stable. I went back to be bed and can add more more info. More than just Hz went feral that night.

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