If power is flowing from Station A through a radial transmission line that has exceeded its thermal limit, what action must the system operator take?

When power is flowing through a radial transmission line that has exceeded its thermal limit, it is critical to manage the load and generation in a way that reduces the stress on the transmission line to avoid potential damage or failure. Shedding load refers to reducing the electrical demand from consumers.

By shedding load in the area where power is being received (in this case, the area SE), the system operator effectively decreases the amount of power being drawn through the already stressed transmission line. This action alleviates the thermal overload on the line, ensuring that it operates within safe thermal limits, thereby protecting both the infrastructure and the reliability of the power system.

This is a key strategy in system operation—maintaining the balance between generation and load while ensuring the integrity of the transmission network. By focusing on the area that is causing the overload, the operator can make immediate adjustments to stabilize the system. Other options, such as increasing generation or shedding load at the originating station, do not directly address the overheating issue in the transmission line itself.