On Wednesday 19th August 2026 we posted a number of articles, including two pertaining to PEC Stage 2 … and particularly how it’s represented in MT PASA modelling results (for the first time!) in modelling results released on Monday 17th August 2026:

• first was this ‘… first look at PEC Stage 2 in AEMO’s MT PASA weekly data set’.
• which was followed by ‘One more view of that (first results from) this week’s MT PASA data, relating to PEC Stage 2’
• … and now this article follows on…

Current hypothesis

Some conversations with clients and readers ensued, and (after one of our engineers did some digging), we present the current hypothesis to explain the seemingly too-smooth trend of modelled results for Export Limit and Import Limit on NSW1-SA1 in the MT PASA results

1)  Remember that the slated ‘go live’ date for the interconnector is 1st October 2026

(a)  which is now less than 6 weeks away

(b)  readers can refer to:

i.  the final Go-Live plan the AEMO released on 7th August 2026;

ii.  which superseded the draft Go-Live plan we featured here on 24th June 2026;

2)  In order to provide for this, AEMO needs to do many things ahead of 1st October:

(a)  with loading of a significant number of new and/or modified constraint equations into the MMS (i.e. Production (or PROD) systems) to deal with limits, including loop flows

(b)  but, prior to that time, firstly into Pre-Production (or PREPROD) systems.

3)  The AEMO is only part-way through this process:

(a)  There are a number of new/modified constraints in PREPROD;

(b)  But nothing really in PROD systems at this point.

4)  With the absence of these new ‘real world’ constraints in PROD at this point:

(a)  MT PASA modelling defaults back to ‘boilerplate’ hold point constraints;

(b)  which is what we saw in this first look, on Wednesday.

Looking into the final Go-Live plan, we read (on  p7/21) that the plan includes this milestone:

‘mid-September 2026 – Planned production deployments in AEMO Market Systems including Dispatch and Negative Residue Management changes ’

… and also (p8/21):

‘Participants now have visibility of constraint equations in Pre-production with Production to follow (from mid-September).’

From which we’re presuming that ‘simplified’ limits might persist in the MT PASA modelling results for a couple more weeks yet…

An illustration, using ez2view …

… in Pre-Production Systems

Here’s an illustration of a snapshot of ez2view time-travelled to 10:45 on Wednesday 19th August 2026 to illustrate some of the above:

1)  With this image, two important caveats:

(a) This image comes from an (earlier) pre-release copy of ez2view v9.20:

i.  Our September upgrade to the software

ii.  Which an increasing number of the team are testing

iii.  So may still have bugs at this point (though hopefully not)

(b)  and it has also been pointed to PRE-PROD, and not PROD

2)  From this image:

(a)  We can see some imagined flow on PEC even on Wednesday 19th August 2026 … given the inputs in PRE-PROD (which is ‘the wild west’, in some ways)

(b)  But we can also see some of the newer constraints with NSW1-SA1 on the left-hand side (which are in PRE-PROD and not PROD).

… in Production Systems

One of our engineers was curious, so manually matched these new constraints to existing constraints (where they existed … albeit obviously different in lacking NSW1-SA1) … as a result of which he’s pointed ez2view:

• to PROD MMS
• and time-travelled to the same point (10:45 on Wednesday 19th August 2026)

With this, we (and now readers) can compare in this second image:

Our expectation is that these existing constraints will be retired at the same time as the new (though obviously this plan has not yet been loaded into AEMO’s PROD systems).

For those readers who were (like us) initially confused/concerned about what we saw in MT PASA results for PEC earlier this week, we hope that (assuming our hypothesis is correct, or at least mostly so) this clears things up?