Methodology for selecting operating points and contingencies for frequency stability studies

Transmission System Operators must regularly perform different stability studies in order to detect hazard situations in the system and to define proper corrective measures. Due to the high computational burden required by dynamic simulations, the number of study cases must be strongly limited to only a few cases. Ideally, only worst cases from a system stability point of view should be identified and used. However, the increased complexity of power system dynamics under high levels of variable generation technologies makes it more difficult to define worst-case scenarios for stability assessments. This paper proposes a novel methodology for selecting critical operating conditions (including operating point and contingency) for frequency stability studies. The methodology considers key factors influencing the system frequency stability, such as the power imbalance, the frequency nadir, the system inertia, the ROCOF and the short circuit level at the point of the contingency. The proposed methodology is validated considering the northern power system of Chile. The dynamic simulations show that the proposed methodology is able to identify critical operating conditions for frequency stability assessments. Furthermore, obtained results show that for the system under study, some of the selected critical operating points have a worse dynamic performance than the one that would be normally chosen with the traditional worst-case approach.