Abstract
In a power system, contingencies like the outage of an interconnection or a generator cause the system frequency to decline rapidly. It may lead to system wide collapse if appropriate frequency control measures are not adopted. During inadequate primary frequency response, Under Frequency Load Shedding (UFLS) schemes are deployed to restore system frequency followed by the contingency. To determine the appropriate location and amount of load shedding in such schemes, voltage stability indices of the load buses may serve as a reliable indicator since it helps in identifying the critical areas that are vulnerable to sudden collapse. In this context, a new under frequency load shedding scheme is proposed in this paper, which utilizes the Fast Voltage Stability Index (FVSI) of the load buses to divide the network into several zones. Then, a higher amount of load shedding is applied at a higher frequency threshold in relatively weaker zones. The concept of an equivalent zonal FVSI is developed that can be normalized to quantify the amount of load shedding in different zones. The proposed scheme is validated by applying it to the IEEE 39-bus system. The performances of the proposed scheme are analyzed at different load and generation levels. Simulation results reveal that the proposed method yields better frequency response and causes lower amount of load cut compared to the conventional scheme.
Published Version
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