Revision of the underfrequency load-shedding scheme of the Slovenian power system

The main motivation for the study presented in this paper was the numerous blackouts that occurred in 2003. After the Italian blackout, which almost caused a collapse of the Slovenian power system as well, it became clear that some automatic procedures, with underfrequency load-shedding being one of the most important ones, need to be thoroughly revised. The paper studies three different load-shedding schemes. Two of them use the frequency decline gradient, which is currently not implemented in the Slovenian power system. The first two schemes have fixed maximal amount of load to be shed, while the third one sheds more loads if the frequency gradient is greater, which makes this scheme successful also in those case where the first two fail due to insufficient load-shedding. This is application of known techniques to a specific case of finding the best load-shedding scheme in Slovenian power system to avoid blackout. The simulations were performed on a detailed model of the Slovenian power system using the software package EUROSTAG. The proposed underfrequency relays’ settings conform to the UCTE Operation handbook.