Protection systems on major transmission lines should be coordinated with whom?

Protection systems on major transmission lines should be coordinated with the interconnected systems because these systems often share common infrastructure and can directly affect one another's stability and reliability. Proper coordination ensures that if a fault occurs in one system, the protection mechanisms will work harmoniously to isolate the issue without causing unnecessary disruptions to the interconnected networks. This is essential for maintaining the overall integrity of the grid, as it helps prevent cascading failures that can lead to widespread outages. The successful operation of these protection systems relies on mutual understanding and alignment between the different operators and systems involved. Coordination enhances system reliability and protects against potential hazards that might arise from an outage in one segment affecting others.

The other options, while relevant to various aspects of the electric power sector, do not directly address the critical need for coordination among interconnected systems, which is vital for effective protection and operation of transmission lines.