Bulgaria's Electricity System Operator (ESO) said on Wednesday that it has launched a tender for awarding a contract for rehabilitation of a section of 110 kV overhead transmission line Ayazmo, in the city of Stara Zagora, worth an estimated 3.5 million levs ($2 million/1.8 million euro).The contract envisages upgrade of the line connecting power substations Samara and Trayana, ESO said in a tender notice.The deadline for submitting offers is April 19.Bids will be ranked solely based on price.