In the coming years, the Istrian electric power subsystem will face challenges in maintaining the safety and quality of electric power supply during the summer months, when electricity consumption significantly increases due to the tourist season. It is necessary to constantly invest in the development of the electric power subsystem by increasing the transmission capacity of existing power lines, replacing traditional aluminum/steel conductors with High-Temperature Low-Sag (HTLS) conductors, installing capacitor banks, and constructing new transformer stations and power lines. Simulations conducted using PSS®E software have analyzed potential technical solutions to improve the electric power subsystem to enhance the safety and reliability of electricity supply. These analyses include simulations for the scenario of the unavailability of the Plomin 2 thermal power plant, the only production facility in the Istrian subsystem, as well as the failure of the dual-system 220 kV Melina-Plomin and Pehlin-Plomin power lines. The simulations also cover the extreme scenario of simultaneous unavailability of the Plomin 2 thermal power plant and the failure of the dual-system 220 kV Melina-Plomin and Pehlin-Plomin power lines. Increasing the transmission capacity of the 110 kV Matulji-Lovran, Lovran-Plomin, and Buje-Koper power lines, and installing capacitor banks in the 110 kV Šijana and Poreč transformer stations will enhance the safety of the electric power subsystem and the quality of electricity supply during the tourist season. The construction of the new 220/110 kV Vodnjan transformer station further improves the quality of electricity supply, while the construction of the 110 kV Medulin-Lošinj power line/cable and the Matulji-Buzet power line provides alternative supply routes for the Istrian subsystem. Upgrading the Vodnjan transformer station to 400/220/110 kV and integrating it into the 400 kV Melina-Divača power line ensures safety and quality of supply in the event of simultaneous unavailability of the Plomin 2 thermal power plant and the dual-system 220 kV Melina-Plomin and Pehlin-Plomin power lines.