Transmission

In addition to modelling traditional inter-state interconnectors, the framework treats select intra-state transmission lines that cross substate boundaries as functionally equivalent to interconnectors due to their significant role in regional power flow and price formation. These transmission paths - particularly those connecting high renewable zones with load centres - can materially impact local supply demand balances and price volatility.

A key focus area in the model is the Southern NSW (SNSW) to Central NSW (CNSW) transmission corridor. This cluster includes critical 330kV lines such as Collector to Marulan, Collector to Yass, and Yass to Marulan. This is a particularly weak part of the grid, and outages on these lines can cause significant transmission constraints and volatility.

Given their importance, the model applies extra care when representing availability on these links. Historical outage data is mapped to each line, then any periods of reduced availability are reflected appropriately in the modelled transmission between substates. This ensures the model captures the downstream impacts on dispatch outcomes and price volatility, especially during periods of high demand or high renewable output in affected zones.

Outages

The model applies load factors to both inter-state interconnectors and intra-state transmission lines to account for outages. For historical assets, it uses AEMO data to calculate the proportion of nominal capacity available at each interval. For intra-state lines, outage records are mapped to specific sub-regional paths, and reduced availability is applied when components are flagged as in outage.

For new or future transmission infrastructure, the model synthesises outages by replicating and time-shifting patterns from similar existing assets. This creates realistic availability profiles for new lines without relying on overly simplistic assumptions.

Outage data is aligned to the modelling period. In backtesting, actual historical outages are used. For forecasts, outages from a chosen “weather year” are shifted to match the target forecast period.

These availability factors are merged with each interconnector’s nominal capacity to calculate final available capacity at each interval. This approach ensures that transmission limits are realistically represented in the mode.