The scan rate values of a Balancing Authority Area’s (BAA) Area Control Error (ACE) measured in MW includes the difference between the Balancing Authority Area’s Actual Net Interchange and its Scheduled Net Interchange, plus its Frequency Bias Setting obligation, plus correction for any known meter error. In the Western Interconnection, Reporting ACE includes Automatic Time Error Correction (ATEC).
Reporting ACE is calculated as follows:
Reporting ACE = (NIA − NIS) − 10B (FA − FS) – IME
Reporting ACE is calculated in the Western Interconnection as follows:
Reporting ACE = (NIA − NIS) − 10B (FA − FS) – IME + IATEC
• NIA = Actual Net Interchange.
• NIS = Scheduled Net Interchange.
• B = Frequency Bias Setting.
• FA = Actual Frequency.
• FS = Scheduled Frequency.
• IME = Interchange Meter Error.
• IATEC = Automatic Time Error Correction.
All NERC Interconnections operate using the principles of Tie-line Bias (TLB) Control and require the use of an ACE equation similar to the Reporting ACE defined above. Any modification(s) to this specified Reporting ACE equation that is(are) implemented for all BAAs on an Interconnection and is(are) consistent with the following four principles of Tie Line Bias control will provide a valid alternative to this Reporting ACE equation:
1. All portions of the Interconnection are included in exactly one BAA so that the sum of all BAAs’ generation, load, and loss is the same as total Interconnection generation, load, and loss;
2. The algebraic sum of all BAAs’ Scheduled Net Interchange is equal to zero at all times and the sum of all BAAs’ Actual Net Interchange values is equal to zero at all times;
3. The use of a common Scheduled Frequency FS for all BAAs at all times; and,
4. Excludes metering or computational errors. (The inclusion and use of the IME term corrects for known metering or computational errors.)