ERCOT: Variation Discovered w/Day-Ahead Market Hub Bus Modeling Affecting DAM Hub SPPs
ERCOT said in a February 16 market notice that it 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 stated in the market notice
"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 stated in the market notice
"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," ERCOT stated in the market notice
"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," ERCOT stated in the market notice