Following an area blackout, what must the TOP ensure when re-energizing transmission lines?

When re-energizing transmission lines following an area blackout, it is crucial for the Transmission Operator (TOP) to ensure that protective relay polarization is maintained. This is important because protective relays are critical for monitoring and safeguarding the integrity of the electrical system during re-energization. They are designed to detect faults and protect equipment from damage by isolating problematic sections of the network.

Maintaining proper relay polarization helps prevent unwanted operations and ensures that the relays function as intended when the system is re-energized. This can help minimize the risk of further cascading failures or additional outages, ensuring a safe and orderly restoration process.

Other options, while relevant to specific operational aspects, do not focus on the preservation of system integrity in the same way as maintaining protective relay polarization. For example, re-energizing tie lines first or relying on generation buses for support entails their own operational considerations, but they do not directly address the critical role of protective measures during the re-energization process. Similarly, keeping transformers hot and ready is an operational strategy, yet it does not replace the necessity of ensuring protective devices are properly polarized and functioning.