Replaying four dispatch intervals on Wed 3rd April 2024 with the ER01 and ER02 trip (Part 2)

I noted earlier about the ‘Simultaneous trip of ER01 and ER02 drops mainland frequency in the NEM’, which occurred between 13:20 and 13:25 NEM time today (Wednesday 3rd April 2024).

Time-Travelling one of my ez2view windows back to earlier today, we can quickly see a broader view of what was happening in the NSW region at the time:


13:20 dispatch interval … prior to the trip

Here’s the snapshot of the 13:20 dispatch interval… remembering the NEM works on an ‘end of interval’ basis, and that (in time-travel) all output measures revert to FinalMW (i.e. SCADA snapshots at the end of the interval):


Note that:

1)  there are 3 x Eraring units running (ER01, ER02 and ER03)

2)   … with ER04 offline on an unplanned outage, which we see in the ‘Generator Outages’ widget (but not shown here)

3)  Aggregate output at the 13:20 time point being 1,358MW (i.e. aggregate FinalMW).


13:25 dispatch interval … ‘bridging’ the trip

In this snapshot for the 13:25 dispatch interval we now know that we’re straddling the trip, in that:

1)  Output values are SCADA snapshots from 13:25, so show the physical effect of the trip; but

2)  Target values (e.g. for price, demand and interconnector flow) reflect AEMO’s expectations in the SCADA run at 13:20 … and so before the trip occurred

Keeping this in mind:


As alluded two above:

1)  Three widgets shown here (the NSW Schematic, the Notifications and the GenChange widget) all reflect the change in FinalMW for ER01 and ER02

(a)  interestingly, the third unit (ER03) stays online

(b)  we presume this is related to a separation between how Units 1 & 2 (on 330kV) and Units 3 & 4 (on 500kV) connect into the NEM:


network diagram from AEMO, supplied with their permission in the ‘Station Details’ widget in ez2view.

2)  But this change has yet to filter through to dispatch outcomes – so:

(a)  No significant change in prices

(b)  No significant change in target for flow, etc…


13:30 dispatch interval … first NEMDE run taking account of the trip

Five minutes later, this is what we see:


From a NEMDE run point of view:

1)  AEMO knows that the output of ER01 and ER02 are zero (because they come automatically from SCADA snapshot):

(a)  so prices and target flows on interconnectors have adjusted to take account of the gap to be filled from generation from elsewhere.

(b)  but it does not yet know the availability of ER01 and ER02 are zero …

2)  … because there’s no rebid yet received from Origin for the two units

(a)  perfectly understandable, as …

i.  The trip happened between 13:20 and 13:25

ii.  ‘Gate Closure’ for rebids for the 13:30 dispatch interval would be ~13:24:40 or so

iii.  Hence insufficient time to submit!

(b)  so the aggregate Available Generation for NSW has not dropped.


13:35 dispatch interval … second NEMDE run taking account of the trip

Five minutes later, this is what we see:


We deduce that Origin has submitted a rebid for a few different units before the 13:30 ‘gate closure’ for this dispatch interval, because we see:

1)  Available Generation for NSW dropping by ~1,000MW

… which would be because ER01 and ER02 have had MaxAvail set to 0MW in their rebids;

2)  Additionally, we see URAN11 starting up.

… this unit’s normally bid up towards the Market Price Cap, except if Origin wants it to run, as we see in the pattern for the last 7 days in the ‘Bids & Offers’ widget in ez2view (and remembering that the bids data is only ‘next day public’:


That’s all for now…

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.

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