When a transmission line is overloaded, which generator should be increased if its GSF is -0.4 and the overloaded line is affected by it?

To understand which generator should be increased when a transmission line is overloaded, it's important to analyze the concept of Generator Shift Factor (GSF). The GSF indicates how much the power output of a generator affects the flow on a specific transmission line. A negative GSF, like -0.4, suggests that increasing the generation output from this generator will actually reduce the flow on the overloaded line.

In this case, the overloaded line is influenced negatively by the Grand River generator, meaning that increasing the output from this generator will help alleviate the overload condition. Given that the GSF is -0.4, this indicates that a change in output from the Grand River generator will help counteract the overload and bring the line back to an acceptable operational level.

Evaluating the other options, the St. Clair generator's relationship with the overloaded line is not addressed in the question. Without the GSF for the St. Clair generator provided, it cannot be concluded that it would alleviate the overload as effectively as the Grand River generator, which has a known negative GSF impacting the line. Therefore, the increase in output should focus on the Grand River generator, making it the appropriate choice to address the current overload situation on the transmission line.