Transmission

Nodal Transmission Network

Description

Up until 2034, we work with a detailed representation of ERCOT transmission network based on all individual transmission lines between substations. Each of these has a thermal limit and reactance/susceptance value.

Historical line ratings are informed by ERCOT’s CIM rating reports. For future network evolution, the topology upgrades outlined in ERCOT’s Regional Transmission Plan (RTP) studies — particularly the 2026 and 2029 economic start cases — are incorporated. These planned topologies are held static for the interim years. In addition, insights from ERCOT’s Permian Basin Reliability Planning Study are used to supplement assumptions in key high-growth regions.

To capture dynamic congestion effects, we monitor congestion rents across all lines for both the 2026 and 2030 network configurations. Lines exhibiting extreme congestion levels are selectively uprated, where the most heavily congested lines have their thermal ratings adjusted to reflect a more plausible operating scenario.

Assumptions and caveats

• Transmission expansion decisions are made exogenously to the model and are not determined by economic optimization algorithms.
• No speculative transmission buildout is included beyond published ERCOT plans and targeted congestion-driven adjustments.

Data sources

Generic Transmission Constraints

Description

Generic Transmission Constraints (GTCs) are groups of transmission lines for which directional flow limits are imposed on the total flow across the interface. These constraints are designed to reflect grid stability limits and are pre-defined ahead of real-time dispatch to allow ERCOT’s SCED to maintain system reliability without requiring full stability analysis during dispatch.

GTCs are modeled by mapping ERCOT’s published definitions — which specify both the constituent lines and the flow restrictions — onto the network represented in the model. Each GTC aggregates the flow across its defined set of lines, and enforces a maximum allowable directional flow limit.

Assumptions and caveats

• GTC flow limits are held flat over time and do not evolve with transmission network upgrades.
• Only the base case contingency limits are used for all GTCs.
• No speculative future GTCs are added beyond those currently published.
• Beyond 2034, when the model transitions to zonal granularity, GTCs are no longer explicitly represented.

Data Sources