From this morning at 08:00 NEM time the AEMO split the ‘x5 constraint’ into two … as had been telegraphed ahead of time in Market Notice 106643 as follows:

*__________________________________________________ *

*Notice ID : 106643
Notice Type ID : New/Modified Constraints
Notice Type Description : MARKET
Issue Date : Wednesday, 15 March 2023
External Reference : Updated NSW system normal voltage stability limit
__________________________________________________ *

*AEMO ELECTRICITY MARKET NOTICE *

*Refer to market notice 105936? *

*The Murraylink Very Fast Runback (VFRB) scheme was modified to increase the capacity of the network due to the increase in generation in the area. The scheme was changed so Murraylink VFRB could be activated / de-activated depending on the time of day on the monitored 220kV lines in north-west Victoria.?*

*Transgrid has advised AEMO on a revision to the X5 voltage collapse limit with this change to VFRB. This will now be managed by two limits.?*

*The following constraint equation changes will be implemented at 0900 hrs on Thursday 16th March 2023:
N^^N_NIL_X5_BEKG (replaces N^^N_NIL_3)
N^^N_NIL_X5_BESH (new)? *

*For full details on the factors on constraint equations and all the constraint equation changes – these have now been loaded into AEMO’s pre-production systems.?*

*Ben Blake
AEMO Operations*

Time permitting, we hope that Allan O’Neil might find some time in the near future to take a deeper dive into the implications of this change (because his Case Study Part #1 and Case Study Part #2 were much appreciated from our readers) … but I thought I would have a quick look this morning…

## (A) Changes seen in ez2view

Using the ‘Constraint Dashboard’ widget in ez2view v9.6 I’ve taken a very quick and cursory look at how these different constraints look, as follows:

### (A1) Out with the old … (i.e. N^^N_NIL_3)

Here’s the way the constraint has looked since it was initially invoked at 10:00 on Friday 20th November 2020 (albeit that some newer appearing DUIDs have been added in over time as they have been commissioned):

The constraint description here was:

*‘Out= Nil, limit power flow on line X5 from Balranald to Darlington Point (X5) to avoid voltage collapse at Balranald for contingency trip of any major 220kV line in NW Victoria’*

### (A2) In with the new … (i.e. N^^N_NIL_X5_BEKG and N^^N_NIL_X5_BESH )

Instead of the above, from 08:00 (NEM time) this morning, this constraint has been split into two different constraints … here is the ‘N^^N_NIL_X5_BEKG’ constraint equation:

The constraint description here is:

*‘Out= Nil, limit power flow on line X5 from Balranald to Darlington Point (X5) to avoid voltage collapse at Balranald for contingency trip of Bendigo to Kerang 220kV line and other nearby lines in NW Victoria’*

… and here is the companion ‘N^^N_NIL_X5_BESH’ constraint equation:

The constraint description here is:

*‘Out= Nil, limit power flow on line X5 from Balranald to Darlington Point (X5) to avoid voltage collapse at Balranald for contingency trip of Bendigo to Shepparton 220kV line in NW Victoria*

## (B) Tabulating the changes on the LHS

Out of curiosity, I mashed the **LHS terms and factors** together in the following table to help me quickly gauge one aspect of ‘what’s changed’ and quickly see that (unless I have made a mistake in transcribing … which is always possible) the LHS for all three constraints are calculated

*identically*:

… so I conclude that it must be the RHS formulation that’s changed … but will need to leave that to Allan to explore and explain in further detail…

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