International competitive bids are invited for the supply of digital relay protection for the 110 kV and 400 kV connections to be installed in relay cabinets of Madara, Teteven, Troyan 2, Zlatna Panega, Boichinovtsi, Kaliste, Stara Zagora, Hristo Botev, Uzundjovo, Karlovo 2 and Sofia West substations.