NOTICE DATE: July 28, 2025

NOTICE TYPE: W-A022625-03 Operations

SHORT DESCRIPTION: Update Regarding Application of Hill County and Nearby 345-kV (SAMSW) Generic Transmission Constraint (GTC)

INTENDED AUDIENCE: ERCOT Market Participants

LONG DESCRIPTION: As detailed in Market Notice W-A022625-02, ERCOT identified a stability risk associated with additional inverter-based generation in the area impacted by the SAMSW GTC irrespective of the level of dispatch.  Any new inverter-based generators connecting at transmission voltage in this area are therefore required to (1) fully mitigate any stability risk associated with the interconnection or operation of the generator and (2) obtain confirmation of the effectiveness of the mitigation solution through an ERCOT or TSP study.

This Market Notice clarifies that all new inverter-based generators that will be subject to the GTC will need to obtain a TSP study consisting of additional TSP analysis conducted in an electromagnetic transient (EMT) tool such as PSCAD.  For generators whose Full Interconnection Study (FIS) stability studies have not yet been submitted to ERCOT, the TSP should conduct this EMT analysis as part of the FIS stability study.  For generators whose FIS studies have already been submitted to ERCOT, the TSP should conduct this analysis as part of the Subsynchronous Oscillation (SSO) study, since all units impacted by this GTC will also require SSO studies. The additional analysis is necessary for this area to refine stability risk and identify potential mitigation solutions required in paragraph (6) of Planning Guide Section 5.3.2.4.3 Dynamic and Transient Stability (Unit Stability, Voltage) Analysis. This SSO or stability study including the additional EMT analysis will require completion and approval to qualify for the Quarterly Stability Assessment (QSA) phase. Qualifying for the QSA is a prerequisite for the inclusion of the inverter-based generator in the ERCOT Network Operations Model in accordance with Nodal Protocol Section 3.10.  ERCOT will separately assess these stability risks as part of the QSA. 

The purpose of this Market Notice is to provide contemporaneous notice to all ERCOT Market Participants of these updates.  ERCOT will issue a subsequent Market Notice once it determines that the interconnection conditions described in this Market Notice are no longer necessary. 

Details of all GTCs (EMIL ID NP3-770-M, Report ID 11425) can be found on the ERCOT Market Information System (MIS) Grid Transmission page under the Generic Transmission Constraints Methodology Secured Area. A Digital Certificate with role ICE_M_VIEW_ECEII is required to access this ECEII data.

CONTACT: If you have any questions, please contact your ERCOT Account Manager. You may also call the general ERCOT Client Services phone number at (512) 248-3900 or contact ERCOT Client Services via email at ClientServices@ercot.com.

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