December 23 (SeeNews) - Montenegro's state-controlled power transmission system operator Crnogorski Elektroprenosni Sistem (CGES) has shortlisted six international firms and consortia in the tender for consultancy services for the planned 36 million euro ($37.4 million) upgrade of the Brezna electrical substation in the country's north-west, the European Bank for Reconstruction and Development (EBRD) said.