Static and dynamic under-frequency load shedding: a comparison

Safe operation of a power system requires that system frequency is kept within a specified range. When the generation is insufficient due to disturbances, the frequency might fall under the minimum allowable value which may lead to system blackout if not properly counteracted. This frequency decline may be corrected by shedding certain amount of load so that the system is back into balanced state. In this paper several under-frequency load shedding schemes are reviewed. Comparison are made between static scheme which shed a fixed, predetermined amount of load at each stage and a dynamic system which shed the load by taking into account the size of the disturbance and the voltage and frequency characteristics. Simulations were done on a five buses power system to obtain the amount of load shed, minimum under-frequency, number of stages and completion time. Results from the dynamic scheme appear to give a better frequency recovery.