A Transmission line is loaded at 125% of its System Operating Limit. What action would be acceptable under these conditions?

• A. Re-dispatch generation to decrease loading on the line
• B. Open the overloaded line immediately
• C. Decrease the voltage setpoints on the generators in the area
• D. Wait until the parallel line is restored

Answer: (A)

When a transmission line is loaded beyond its System Operating Limit, it is critical to take appropriate actions to ensure the reliability of the bulk power system. Re-dispatching generation to decrease the loading on the line is a proactive and effective approach in this situation. This method involves adjusting the output of nearby generation sources to reduce the amount of power flowing over the overloaded transmission line, thereby bringing it back within safe operational limits. This action not only alleviates the immediate overloading condition but also helps uphold overall system reliability and stability.

In contrast, immediately opening the overloaded line can lead to disruption and possible cascading effects in the power system, potentially causing blackouts in other areas. Decreasing the voltage setpoints on generators, while it might seem like a feasible approach, could further complicate the situation and potentially exacerbate loading issues. Lastly, waiting for a parallel line to be restored does not address the critical need to manage the current overloading problem and risks maintaining an unsafe operational state for an extended period. Therefore, re-dispatching generation stands out as the most responsible and effective action to mitigate the overload while maintaining system reliability.