A quick view into constraints on the Heywood interconnector, on Tuesday 22nd July 2025

Arriving at the office this morning, our congestion map offered some interesting patterns. With outages on the Heywood–South East line this week — and strong winds along the south coast this morning — a noticeable regional divide appeared in this view of the market.

Source: ez2view’s Congestion Map widget

In the screenshot above, we can see the ‘SA_ISLE_STRENGTH’ equation is currently binding, as at the 09:20 dispatch interval. This equation places a 1,900MW limitation on non-synchronous generation in SA, based on system strength requirements when SA could be at risk of separation or when islanded — and in this case, the binding equation is providing a negative local price adjustment to a number of semi-scheduled wind and solar units in South Australia.

We can also see that the ‘V::N_HYSE_V1’ equation is also binding in this interval, with a large number of units in Victoria receiving a positive price adjustment. This equation prevents a transient instability in the case of a fault on the Hazelwood-South Morang 500kV line in VIC.

Both of these equations are within the ‘I-HYSE’ constraint set, which has been invoked since yesterday morning due to a planned outage on the 275kV Heywood-South-East transmission line (forming part of the SA-VIC interconnector).

Below shows the schedule for the ‘I-HYSE’ constraint set. It is currently scheduled to be invoked until tomorrow afternoon.

Source: ez2view’s Scheduled Constraint Sets widget

The screenshot below shows all current outages within SA’s scheduled fleet, where we see the 210MW Torrens Island B4 Unit is currently on a planned outage and 522MW Pelican Point Gas Turbine is experiencing a planned derating. The 210MW Torrens Island B1 Unit has been mothballed since October 2021. Four syncons in South Australia are currently in service.

Source: ez2view’s Scheduled Constraint Sets widget

The ongoing outages on the Heywood–South East line continue to pose risks of elevated energy and FCAS prices, so we’ll be closely monitoring market outcomes until the outage concludes.