Evaluation of Frequency Reliability Standards by Determining Minimal Level of Inertia

Since the amount of power generated from inverter-based renewable energy affects the grid frequency, it is limited to maintain frequency reliability. In power system with two or more frequency standards, such as South Korea, the two standards should not be different for consistent system operation, so it is necessary to evaluate whether the frequency standards are appropriate for renewable energy accommodation. This paper proposes a methodology for evaluating the frequency standards by determining the minimum level of inertia required for the system operation considering the renewable energy generation. When inertia and frequency regulating reserve forces change as the operation of the generator changes, the minimal level of inertia can be calculated as the lowest inertia value that satisfies the frequency criteria. The minimal level of inertia was determined by conducting a frequency simulation by applying two frequency criteria in South Korea. The proposed methodology has been applied to 7080 operation time-based data extracted from Energy Management System. From the results, the minimal level of inertia for N-1 frequency criterion at the same situation was higher than the N-2 frequency criterion. The key finding of this study is that South Korea's two frequency criteria are applied differently based on the minimal level of inertia.