I’ve taken the opportunity of a quiet space to extract some data over a 4-hour time range (and at 0.1 second cadence) to compile the following trend:
Unfortunately:
our ‘Device 2’ location was temporarily offline (following some power outages following Brisbane storms at the time)
so we had to revert back to the new ‘Device 1’ location … which (as noted on the image) we have observed appears to suffer from occasional noise (perhaps related to local intermittent power quality issues?).
So in the chart above we can’t really trust the specific details of the depth of the frequency drop, other than to note that the low point will have been around ~17:01 (NEM time) on Thursday 30th October 2025.
That should be enough for us to explore in a bit more detail….
Paul was one of the founders of Global-Roam in February 2000. He is currently the CEO of the company and the principal author of WattClarity. Writing for WattClarity has become a natural extension of his work in understanding the electricity market, enabling him to lead the team in developing better software for clients.
Before co-founding the company, Paul worked as a Mechanical Engineer for the Queensland Electricity Commission in the early 1990s. He also gained international experience in Japan, the United States, Canada, the UK, and Argentina as part of his ES Cornwall Memorial Scholarship.
We’ve already looked at how there was a drop in system frequency at ~10:41 NEM time (outside of the NOFB) in conjunction with trips of units at Yallourn Power Station. Well, believe it or not there was a couple drops – not as big – later in the day.
We follow on from A 292MW drop in “Market Demand” in Tasmania, on Saturday 16th August 2025 enlisting this “Part 2” to understand the sequence of events using 4-second data.
Whilst there were many things that went wrong on Tuesday 25th May 2021 (last week), guest author Allan O’Neil highlights that there were at least 4 things that went right – contributing to a much less severe outcome than would otherwise have been the case.
1 Commenton "A second look at the frequency drop on Thursday evening 30th October 2025"
Here’s the raw hz data from Melbourne. 49.84hz is the lowest I saw
https://www.dropbox.com/scl/fi/x1t4c6wku2fw6dt21c2m0/hz-data.csv?rlkey=vz5w7ppo8m8umf1md09jrelxw&dl=0 (note it also has noise but