More pain ahead for non-synchronous units … a bigger ‘rhombus of regret’ in western NSW & VIC

Coincident with today’s draft rule from the AEMC on Semi-Scheduled plant we also noticed AEMO’s Market Notice  80103 published today, which reads as follows:

Notice ID : 80103
Notice Type ID : New/Modified Constraints
Notice Type Description : MARKET
Issue Date : Thursday, 19 November 2020
External Reference : New system normal constraint equation in NSW for voltage collapse at Balranald

TransGrid has advised AEMO of a new voltage collapse limit in south west NSW, which is required to prevent voltage collapse at Balranald following a loss of a 220 kV line in north-west Victoria (either Bendigo to Kerang, Kerang to Wemen or Buronga to Red Cliffs lines). The limit applies to pre-contingent flow on Balranald to Darlington Point (X5) 220 kV line. The constraint equation is likely to bind when there is high generation in south-west NSW

The constraint equation includes generators in south-west NSW and north-west Victoria on the left-hand side as well as Murraylink and VIC1-NSW1.

The following constraint equation will be implemented at 1000 hrs Friday 20th November 2020:


For full details on the factors this constraint equation has now been loaded into AEMO’s pre-production systems.

For further details on this new constraint equation please contact ben.blake “at” you-know-where (our simple attempt to protect Ben from the bots)

Ben Blake

AEMO Operations


(A)  Key points

For background see this ‘work in progress’ page on Constraint Equations and Constraint Sets in evolving Glossary.  The key points are:

1)  The constraint equation to look out for (in ez2view, or other) is ‘N^^N_NIL_3 ’ (also referred to as the ‘X5 constraint’ because of TransGrid’s line numbering).

2)  It goes live from tomorrow morning (i.e. 10:00 on Friday 20th November 2020).

3)  It’s in a ‘System Normal’ constraint set … so will always be invoked (and hence have the potential to bind)…

… at least until some action (network upgrades perhaps?) is taken to rectify.

4)  It could significantly ‘constrain down’ a number of non-synchronous (and Semi-Scheduled) units:

(a)  the effect will be worst in south-western NSW; but

(b) also in western VIC.

(c)  but some units will see a slight positive effect

5)  It will probably bind on most occasions when it’s very sunny over the affected solar farms (and a wind farm or two).


(B)  Who’s going to be affected?

Picking apart the Left-Hand Side of the constraint, it appears that the following will be the general effect:

DUIDs that will probably be adversely affected

(i.e. have positive factor,
with form of the constraint LH
S ≤ RHS)

DUIDs that might benefit (slightly)

(i.e. have negative factor,
with form of the constraint LH
S ≤ RHS)

Significant impacts at SW NSW:

Broken Hill Solar Farm, Silverton Wind, Limondale 1 & 2, Sunraysia

Smaller impacts in NW Victoria:

Ararat Wind Farm, Bulgana Wind Farm, Crowlands Wind Farm, and others……

Coleambally SF, Darlington Point SF, Murray Hydro, Gannawarra BESS consumption.


From tomorrow morning (when the constraint is in AEMO’s Production systems) the constraint equation will be visible in ez2view.

Just search for it with the constraint ID:


Of course, the actual effect will depend (amongst other things) on how each of the above bids … which will be particularly complex because this constraint spans two regions and affects Murraylink!

This will inevitably give rise to:

1)  Bids down at the Market Price Floor (except when the regional price is negative) … otherwise known as ‘disorderly bidding’; but also

2)  Increased push, by some, for the introduction of nodal pricing in the NEM … not that the general thrust of COGATI does not have many who oppose.

Pain ahead, no matter which way we look…


(C)  One more reminder…

At the bottom of this article here (also today) I added a few comments about why we are so interested in these kinds of developments … which also applies here as well.

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.

2 Comments on "More pain ahead for non-synchronous units … a bigger ‘rhombus of regret’ in western NSW & VIC"

  1. This problem sounds like a local lack of reactive power. I wonder if it can be improved by?
    a) installing a static synchronous compensator (STATCOM).
    b) Requiring Voltage Source Converter (VSC) based inverters remain synchronized and provide voltage control, even when not generating active power (currently on trial in the United Kingdom).
    c) series compensation capacitors to reduce AC line impedance.
    d) additional transmission lines or synchronous condensors to increase local system strength.
    e) follow b) but additionally investigate voltage support from (Doubly-Fed Induction Generator) wind farms.

    Unfortunately I suspect economic rules like the RIT-T will slow down technical fixes.

  2. For anyone curious about N^^N_NIL3 the constraint is published here^^N_NIL_3 (an extensive public dataset, no connection to it)

    At time of posting it hasn’t bound today.

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