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NOTICE DATE: Jan 22, 2021

NOTICE TYPE: M-A012221-01 Operations

SHORT DESCRIPTION:  Correction of software error impacting calculation of certain transmission limits in the DAM

INTENDED AUDIENCE: All Market Participants

DAYS AFFECTED: December 1, 2010 - January 22, 2021

LONG DESCRIPTION: Effective for Operating Day (OD) January 23, 2021, ERCOT is implementing a correction to its Day-Ahead Market (DAM) systems to fix a recently-discovered software error that in certain, limited cases impacted the calculation of transmission limits used for clearing in the DAM. In the unique circumstance where a contingency definition splits a Hub Bus, this software error could result in a constraint erroneously showing as binding in the DAM. This error did not impact clearing in Real-Time.

This software error has existed since Nodal go-live. ERCOT is aware of only one constraint that showed as binding in error due to this issue. The most recent OD in which this constraint showed as binding in error was December 9, 2020.

Because this error impacted clearing in the DAM, it may have impacted prices. ERCOT Protocol Section 4.5.3(4) requires ERCOT to correct prices when (i) a market solution is determined to be invalid, or (ii) invalid prices are identified in an otherwise valid market solution, unless accurate prices cannot be determined. In this case, accurate prices could not be determined until after the software error was corrected. Further, pursuant to ERCOT Protocol Section 4.5.3(5), DAM prices can only be corrected if ERCOT determines that prices are in need of correction and notifies Market Participants no later than 30 days after the impacted OD. Because the most recent OD impacted by this error is outside of this 30-day window, ERCOT will not be correcting prices.

ADDITIONAL INFORMATION: ERCOT staff expects to discuss the issue described in this Market Notice in more detail at the February 3, 2021, meeting of the Wholesale Market Subcommittee (WMS).

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 [log in to unmask].

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