NOTICE DATE: March 2, 2018

NOTICE TYPE: M-A021618-02 Operations

SHORT DESCRIPTION: Update - Variation discovered with Day-Ahead Market (DAM) Hub Bus modeling affecting DAM Hub Settlement Point Prices (SPPs)

INTENDED AUDIENCE: ERCOT Market Participants

DAY AFFECTED: March 2, 2018

LONG DESCRIPTION: Following additional analysis of the pricing discrepancy with respect to published DAM Hub SPPs, ERCOT has also identified impacts to Load Zone modeling. ERCOT initially believed that an emergency system change could be implemented to address the pricing outcome, but has determined that an Urgent Nodal Protocol Revision Request (NPRR) to modify the current Hub Bus and Load Zone definitions and their related formulas would allow for the most consistent solution across Congestion Revenue Right (CRR) Auctions and the DAM. Please see NPRR868, As-Built Hub and Load Zone Calculation. Approval of this NPRR will allow for a thorough discussion on the most appropriate and consistent solution across CRR Auctions, the DAM, and the Real-Time Market (RTM).

ADDITIONAL INFORMATION: This issue was discussed at the February 28^th Wholesale Market Subcommittee (WMS) meeting under agenda item 7. The presentation for that discussion can be found on the WMS meeting page.

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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NOTICE DATE: February 16, 2018

NOTICE TYPE: M-A021618-01 Operations

SHORT DESCRIPTION: Variation discovered with Day-Ahead Market (DAM) Hub Bus modeling affecting DAM Hub Settlement Point Prices (SPPs)

INTENDED AUDIENCE: ERCOT Market Participants

DAY AFFECTED: December 1, 2010 - present

LONG DESCRIPTION: ERCOT recently became aware of a pricing discrepancy with respect to published DAM Hub SPPs. ERCOT has investigated pricing variations in published DAM Hub SPPs compared to manual calculations based on published Electrical Bus Locational Marginal Prices (LMPs) and the Electrical Bus to Hub Bus mapping that comes from the Common Information Model (CIM). In some stations, the DAM software detected a split bus based on network topology in the base case, and in those cases added a new bus, and included that new bus in the Hub Bus list. By including that new bus in the Hub Bus list, it was ultimately used to determine both the Hub SPP and the Hub MW distribution. This outcome results in pricing and award differences compared to the outcomes based solely on the CIM Electrical Buses. ERCOT Protocols Section 2.1 states that Hub Buses are composed of energized Electrical Buses.

ERCOT is working on an emergency system change to address this outcome by ensuring that only CIM Electrical Buses are included in the Hub Bus list for the DAM. A follow-up Market Notice will be sent when a production release date for the system change has been set.

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 cannot be determined because without a software change immediately available, the market cannot be rerun with the correct Hub MW distribution. Therefore, ERCOT will not correct prices.

This logic has been in place since nodal go-live (i.e., December 1, 2010). However, had only CIM Electrical Buses been included in the Hub Bus list for the DAM since the beginning, pricing and award differences may have only occurred on certain Operating Days and/or at some Hubs.

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