What is the immediate action a System Operator should take after a unit separates due to underfrequency relay operation?

The immediate action a System Operator should take after a unit separates due to underfrequency relay operation is to immediately pick up load. This is crucial because an underfrequency event indicates that the system frequency has dropped below acceptable levels, typically due to an imbalance between generation and load. By picking up load, the operator can help restore the frequency to normal levels.

When a unit separates, it often removes a significant amount of generation from the grid. Picking up load helps to stabilize the system and supports the remaining generation in balancing supply and demand. This action is part of the operator's responsibility to maintain system reliability and ensure the security of the electrical grid.

Other options, while they have their place in system operations, do not address the immediate need to stabilize frequency and balance the generation-load relationship as effectively as picking up load does. Reporting to the Reliability Coordinator would be important, but it is a follow-up action after addressing the immediate frequency issue. Deactivating auxiliary loads may be relevant in a broader context of managing system resources but does not directly respond to the urgency of trying to stabilize the frequency post-separation. Securing all transmission lines is not a direct response to the underfrequency situation and would not immediately assist in addressing the imbalance created by the unit's separation