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. In the first part of the paper we deal with the frequency dynamic model that was developed to simulate the impact of the most important system parameters on the frequency response after a major disturbance. Next, we determined the optimal number of load-shedding steps and the amount of load to be shed in each step. We also checked whether it is necessary to use the frequency decline gradient in the underfrequency relaying scheme, which is currently not implemented. 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.