ACE. The instantaneous difference between net actual and scheduled interchange.
Last Updated: June 20, 2025
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The instantaneous difference between an entity’s Actual Net Interchange (NIA) and Scheduled Net Interchange (NIS), taking into account the effects of Frequency Bias, of correction for meter error, and of Inadvertent Interchange Management (IIM) if operating in the IIM mode. For compliance usage, refer to the term Reporting ACE.
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Demand and supply are constantly changing within all BAAs. This means that a BA will usually have some unintentional outflow or inflow at any given instant. This mismatch in meeting a BA’s internal obligations, along with the small additional “bias” obligation to maintain frequency, is represented via a real-time value called Area Control Error (ACE), with units of MW.