How should the AGC system be operated after losing tie-line RTUs with a neighboring BA?

To understand the correct approach when tie-line RTUs with a neighboring Balancing Authority (BA) are lost, it’s crucial to recognize the essential role of Automatic Generation Control (AGC) in maintaining system reliability and frequency stability.

When tie-line RTUs are unavailable, the AGC system loses real-time data regarding the imports and exports of power to and from the neighboring BA. This lack of information can compromise the AGC's ability to manage generation and balance load effectively. Therefore, placing all generating units on manual control mode becomes the prudent choice. This approach allows operators to have direct oversight and control over generation resources without relying on potentially inaccurate or incomplete data fed into the AGC system.

Operating in manual control mode shifts the responsibility of balancing the load and generation directly to human operators, enabling them to take immediate, informed actions based on their assessments and knowledge of the system. This manual approach aids in preventing frequency deviations that could otherwise destabilize the grid in the absence of reliable automated controls.

In this scenario, implementing a flat 60 Hz frequency control mode or leaving the AGC system in tie-line bias control would not be advisable because these methods presume accurate tie-line information and automated control, which is not available. Hence, manual control ensures that operators