In ACE calculation, the AGC compares Net Actual Interchange to which quantity to determine ACE?

• A. Net Actual Interchange to Net Scheduled Interchange
• B. Net Actual Interchange to Frequency Bias
• C. Net Actual Interchange to Net Scheduled Interchange plus Frequency Bias
• D. Net Actual Interchange plus Frequency Bias to Net Scheduled Interchange

Answer: (C)

ACE measures how far actual interchange differs from what should have occurred when the schedule and the system’s frequency response are taken into account. The comparison is between Net Actual Interchange and Net Scheduled Interchange plus Frequency Bias. In formula terms, ACE = Net Actual Interchange − (Net Scheduled Interchange + Frequency Bias). This setup lets the AGC adjust generation to bring ACE toward zero, accounting for the bias that reflects how frequency deviations influence tie-line flows. If Net Actual Interchange is higher than Net Scheduled Interchange plus Frequency Bias, ACE is positive and adjustments are needed to reduce interchanges; if it’s lower, ACE is negative and the opposite adjustments are required.