SOFIA (Bulgaria), January 8 (SeeNews) -Â Bulgaria's Electricity System Operator (ESO) said on Wednesday that it has signed two four-year contracts worth 1.7 million euro ($967,300/920,300 euro) combined with Plovdiv-based Filkab and Stara Zagora-based Contragent-35 for the delivery of 3,240 medium-voltage measuring transformers.Â