How much load needs to be shed for a 1 Hz frequency deviation when in an island?

• A. 1 to 2 %
• B. 3 to 5 %
• C. 10 to 12 %
• D. 6 to 10 %

Answer: (D)

In a system that is operating under isolated or islanding conditions, it is crucial to maintain frequency stability to ensure reliable operation. Frequency deviations occur due to an imbalance between generation and load. When there is a drop in frequency, indicating that the load exceeds the generation capacity, corrective actions must be taken, typically by shedding load.

To achieve the necessary balance for a 1 Hz frequency deviation, shedding a specific percentage of the load is essential. In general, for every 1 Hz frequency deviation, a rough guideline in frequency operating practices indicates that shedding around 6 to 10 percent of the load can stabilize the frequency back to its nominal operating point. This range is influenced by the system's characteristics, including generation mix and total system inertia.

This percentage is higher than some other ranges listed because islanded systems usually have less inertia and require a more aggressive approach to stabilize frequency deviations. Therefore, shedding 6 to 10 percent effectively aligns the generation and load balance, helping restore the system frequency to stable levels.