Dynamic under frequency load shedding in power systems

This paper proposes a dynamic under-frequency load shedding scheme allowing faster frequency re-establishment and system restoration. The proposed scheme is based on a combination of two criteria: frequency pre-defined minimum thresholds and the rate of change of frequency (ROCOF). The scheme comprises a fault detection stage, an initial shedding stage, and an accelerated shedding stage. The amount of load to be shed and its critical acting time are anticipated from the first stage frequency gradient. The proposed load shedding method was tested on the IEEE 9 bus 3 generators power system for loss of generation contingency, under different loading conditions. The simulation results demonstrate the advantages of the proposed technique in terms of avoiding unnecessary load shedding, and faster re-establishment of stable operation.