What action must the Transmission Operator (TOP) perform to relieve an overloaded radial transmission line?

To relieve an overloaded radial transmission line, the Transmission Operator (TOP) typically needs to take action that reduces the current flowing through that line. Shedding load at the end of the line is an effective method for achieving this. When a load is shed, it decreases the demand on the transmission line, thereby reducing the overall current and helping to alleviate the overload situation. This is a direct intervention aimed at managing system reliability and preventing further issues such as equipment damage or system instability.

Increasing generation output, while it may provide more power to the grid, does not address the immediate concern of relieving the overload. In fact, it could potentially exacerbate the condition by increasing power flows on the already overloaded line.

Adjusting frequency regulation relates to the overall stability of the grid and does not focus specifically on managing localized overload conditions on specific transmission lines.

Notifying the regulatory authority is a procedural action that might be necessary for compliance or reporting purposes, but it does not contribute to the immediate physical solution to relieve the line's overload.

Thus, shedding load is the most effective and direct action that a TOP can take to relieve an overloaded radial transmission line.