What is the primary AGC control mode that will indicate a Balancing Authority's generation-load-interchange balance?

The primary AGC (Automatic Generation Control) control mode that indicates a Balancing Authority's generation-load-interchange balance is Tie Line Bias. This control mode is crucial for maintaining system stability and reliability, as it focuses on the interchange of power between adjacent balancing authorities or areas.

Tie Line Bias operates by monitoring the power flows across interconnections with neighboring balancing authorities. When there is a discrepancy between generation and load within a balancing authority, adjustments are made based on the direct deviation of tie line flows from the scheduled values. This means that the control system will increase or decrease generation based on real-time conditions to ensure that the total load served, considering interchange schedules, is aligned, thereby achieving balance.

Utilizing Tie Line Bias assists in not only maintaining the balance within the authority but also in managing the overall system frequency. This mode is essential for dynamic adjustments when external imbalances occur, thereby supporting reliable operations.

Other control modes, such as Generators on Auto, Flat Interchange Control, and Constant Frequency, do not specifically target the interchanges between balancing authorities and therefore do not directly reflect the generation-load interchange balance as effectively as Tie Line Bias does.