Transmission

Overview of our ERCOT transmission modeling.

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 sourced from the daily published Network Operations Model for the Day-Ahead Market (DAM). These are primarily used to ensure accurate backtest results by reflecting the real operational state of the network on any given day. For future network evolution, the topology upgrades outlined by ERCOT’s Steady State Working Group cases are used. In addition, insights from ERCOT Regional Transmission Plan are used to supplement assumptions in key high-growth regions.

We ensure the network is well calibrated in terms of producing the right amount of congestion in the right places by cross-referencing with nodal basis patterns in our backtest. The following map shows how topology evolves over the course of the nodal horizon. One notable feature is the addition of 765kV lines which are essential in alleviating congestion between Far West Texas and the rest of the ERCOT grid.

DISCLAIMER: We apply noise to all node locations to protect sensitive lat/lon information

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 changes modeled in the Steady State Working Group (SSWG) or Regional Transmission Plan (RTP) cases.

Data sources

For data sources that require ERCOT MIS permissions we provide the EMIL ID in the absence of a shareable link.

Generic Transmission Constraints

Description

Generic Transmission Constraints (GTCs) are groups of transmission elements for which flow limits are imposed on the total flow across the entire group of lines and transformers, also known as an interface. These constraints are designed to reflect grid stability limits. Some GTC limits are pre-determined under different topology configurations, while others involve real-time voltage stability assessments. ERCOT conducts quarterly stability assessments that produce these pre-determined limits and evaluate whether new or existing GTCs are still needed.

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.

The following map shows the transmission lines making up each of the GTC interfaces. Note that some low voltage/rating lines can cross the interface without being part of a GTC — this is consistent with how ERCOT defines GTCs. Where additional local transmission or upgrades to monitored elements increase capacity across GTC interfaces, less conservative limits can be enforced. This is reflective of future stability assessments which re-evaluate GTCs as system conditions evolve. ERCOT-specified “GTC exit plans” are also considered — that is, whether a GTC should still be enforced given the transmission upgrades present in the model’s evolving network topology.

DISCLAIMER: We apply noise to all node locations to protect sensitive lat/lon information

Assumptions and caveats

• 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