Key takeaway: The model solves a transmission network of over 200 nodes, limiting each line to its thermal rating and the net flow across 19 corridors to the Australian Energy Market Operator's (AEMO) secure transfer limits. The network grows over the forecast horizon as projects from AEMO's final 2026 Integrated System Plan (ISP) enter service.
The network is built from Geoscience Australia’s transmission topology, giving each modelled line its own voltage, length, thermal rating and electrical characteristics. Generators and loads connect at the network node closest to their physical location, so the model captures how power flows between generation, demand centres and interconnectors.
Line ratings and transfer limits
Every modelled flow is limited in two ways at the same time:
- Thermal ratings: each line can carry power up to its thermal rating, the maximum flow before its conductors overheat. This determines where individual lines congest.
- Secure transfer limits: the net flow across each of 19 flow corridors is capped at AEMO’s secure transfer limit for that corridor, which varies by direction and season. AEMO sets these limits to keep the network secure if any single line or generator fails, so they stand in for N-1 outages.
Secure transfer limits on flow corridors
AEMO’s ISP divides the National Electricity Market (NEM) into sub-regions, such as Central New South Wales, or Sydney, Newcastle and Wollongong. A flow path is the set of lines that connects one sub-region to the next, and AEMO publishes transfer limits for each. The model’s 19 corridors follow these flow paths, with a separate corridor wherever AEMO publishes a separate limit, plus one AEMO group limit on flows into Adelaide. They cover the interconnectors between states and routes within states, such as the southern approach into Sydney.
Network projects
The base network reflects transmission assets as they exist today. Projects from AEMO’s final 2026 ISP are added on top, so transfer capability grows over the forecast horizon.
- Named projects: committed and anticipated upgrades add or upgrade lines in the nodal network. They include HumeLink, VNI West (Victoria–New South Wales Interconnector West), Project EnergyConnect, Marinus Link, Queensland–New South Wales Interconnector (QNI) Connect and Renewable Energy Zone (REZ) network augmentations.
- Smaller ISP projects: projects not modelled as new lines add their capacity to the highest-rated existing lines in the affected area, in proportion to each line’s rating.
- Corridor limit increases: where a project reinforces a corridor, the corridor’s secure transfer limit rises from the day the project enters service.
Renewable Energy Zones
Each REZ is mapped to the transmission nodes within it that are eligible to host new generation and storage. New wind, solar and battery capacity built by the capacity expansion can connect only at these nodes.
Congestion in forecast outputs
When a corridor reaches its limit, the model dispatches more expensive generation on the importing side and less of the cheaper generation on the exporting side.
- Price separation between regions: when an interconnector corridor binds, prices in the importing region rise relative to the exporting region.
- Price separation within a region: when a corridor inside a state binds, nodal prices on the exporting side fall below those on the importing side. Where the Regional Reference Node (RRN) sits on the importing side, exporting nodes price below the RRN.
- Curtailment: wind and solar behind a binding corridor are curtailed when the corridor cannot carry their output, which lowers nearby nodal prices and affects how batteries there are dispatched.
How the gap between a battery’s local price and the RRN price affects its revenue is covered on the Curtailment and Grid Risk page. How this network produces a distinct price at every node is covered on the Nodal Pricing page.