A quick article with this 6-hour-long view of NEM Mainland Frequency measured in Brisbane, with the snapshot taken at ~15:11 on Thursday 13th February 2025:
With respect to the two periods of wandering noted:
1) Happening at the time of the snapshot (~15:11) and then roughly 90 minutes earlier.
2) Important to note that this wandering was not outside of the NOFB
3) But, with respect to Linton’s statistical analysis (part 1 and part 2) we note that it’s relatively rare that frequency wanders outside the range of (approx) 49.95 to 50.05
… so I thought, whilst I saw it happening, we might document contemporaneously so that we’d have something to refer back to later if required…
If the frequency is wandering it is clear indication that there is not enough governors active on the system. For turbogenerators to have effective governors the machine must be above minimum load and below maximum load. From my experience as a AEMO Load Dispatcher (retired), AEMO needa to apply some constraints to get better regulation of frequency.
My (uncalibrated) measurements has them dropping ever so slightly under for a very brief time.
https://www.dropbox.com/scl/fi/rmz78wijwdn4g0d7otgk7/Screenshot-2025-02-13-at-9.03.56-pm.png?rlkey=p8hbrcwwpf08ytxq47ogawxp8&dl=0
Roughly 10 seconds?
Governors respond in less than 6 sec and adjust steam flow to compensate for change in steam pressure (rise or fall) to keep turbine speed at 50Hz. Fuel flow is determined by Steam Pressure and Flow rate and is slower than the Governor response and should not change until the governor demands more average steam flow which takes more than 60 sec. So the problem is that System frequency is on a slow trend up/down which is causing the fuel flow to oscillate in response to the slow change in frequency. This will be found to be caused by largish slow load changes which were not traditional in load caused by consumer demand (diversity) but changes in large solar and wind generation caused by cloud patterns and wind variability. As solar and wind farms in common localities get larger the problem will get worse. Have you ever watched the output of your rooftop solar panel for a few minutes? You will notice the power level change by up to 30% for very little change in solar brightness. So imagine a 1000MW solar farm with some wispy high cloud passing by, the change in output can be around 300MW. This kind of change system wide on a diversified basis will become more noticeable as large solar farms in a common locality become more prevalent (eg. on the Darling Downs and New England areas)
Absolutely, Ian McG.
Trends to more variable (wandering) grid performance is a serious matter.
Meanwhile, records are being set and AEMO’s messages are about the past; mothing done to reduce “wandering” to historical levels.
This will end in tears.