Both units trip at Callide C on Wednesday 13th January 2021

A quick note today to flag the simultaneous trip of both units at Callide C in Queensland (I’ve put this article up quickly as it’s a pretty rare event that units trip simultaneously).  We can see this in the snapshot from ez2view time-travelled back to the 11:00 dispatch interval:


As noted before, we’re working in collaboration with others to provide more visibility of a range of additional data through the ez2view software (with more coming in 2021) so I thought it would be of interest to add in this snapshot of frequency trace on the mainland to see how frequency dropped around 10:57, presumably as a result of the loss of that ~830MW of supply:


Here’s a different representation from another source we are experimenting with, for inclusion in ez2view :


No surprise, really, that prices wobbled a bit as a result.  here’s the 11:10 dispatch interval snapped in NEMwatch v10 (our entry-level dashboard):



PS1 at 13:20 on Wednesday 13th January 2021

Worth noting that the AEMO published Market Notice 82117 at 11:41:24 (i.e. about 10 minutes after this article was published) speaking about the double trip, but not shedding any detail at this point:


From : AEMO
Creation Date : 13/01/2021 11:41:24


Notice ID : 82117
Notice Type Description : Emergency events/conditions
Issue Date : 13/01/2021
External Reference : Non-credible contingency event – Qld region – 13/01/2021


Reason :


Non-credible contingency event – Qld region – 13/01/2021

At 1057 hrs the Callide C3 and the Callide C4 units tripped.

AEMO did not instruct load shedding.

AEMO has not been advised of any disconnection of bulk electrical load.

The cause of this non credible contingency event is not known at this stage.

Manager NEM Real Time Operations




About the Author

Paul McArdle
One of three founders of Global-Roam back in 2000, Paul has been CEO of the company since that time. As an author on WattClarity, Paul's focus has been to help make the electricity market more understandable.

2 Comments on "Both units trip at Callide C on Wednesday 13th January 2021"

  1. Paul, do you have any insight into the logic AEMO uses to determine when to send out a ‘power system events’ market notice, or not? Large units trip with some regularity, but do not always attract a market notice flagging the event. For sure, an ~830 MW trip is a “very large” trip and significantly unusual, but a frequency drop to ~49.78 or so (as your screenshot suggests) is not particularly unusual or dramatic. Smaller unit trips have caused larger frequency drops in recent times, without prompting AEMO to send a market notice. Any insight into how AEMO decides to trigger notices, or not?

    • Double-checked with a couple more learned NEM junkies than me before responding …

      Yes, the reason this event was market notice worthy was because it was a “non-credible contingency”, not because of the level of the frequency nadir.

      Stations are designed to not have common points of failure across units, hence this contingency is “non-credible”. This event will trigger an investigation to ensure its cause is understood and not repeated.


      As an aside, even after a credible contingency, a frequency nadir below the frequency operating standard, i.e. 49.5Hz, will trigger a market notice.

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