The Chaira Pumped Storage Hydro Power Plant (Chaira PSHPP) was built in the Rila mountain range, about 100 km southeast of Bulgaria's capital city, Sofia. Part of the major Belmeken–Sestrimo–Chaira Hydropower Cascade, Chaira has generating capacity of 864 MW and a pumping capacity of 788 MW. The power plant is equipped with four reversible Francis pump-turbines, each rated at 216 MW in the generating mode, and 197 MW in pumping mode. Units 1 and 2 have been in operation since 1995, and at that time Chaira was the largest pumped-storage plant in southeast Europe with the highest head in the world for a single-stage pump turbine (690 m generating and 701 m pumping). Units 3 and 4 came online in 1999. The pump-turbines and motor-generators were supplied by Toshiba, and three of them were manufactured under Japanese supervision in Bulgaria. The upper basin for Chaira is formed by the Belmeken Dam which connects to the pumped storage plant by two headrace tunnels with a diameter of 4.2 m and two penstocks with diameter 4.4 m, reducing to 4.2 m. Outflow from the Belmeken reservoir supplies the Sestrimo Hydro Power Plant