Its mission is to operate and maintain the power transmission installations - the substations and overhead lines (OHLs) of 220 kV and 400 kV which it owns.
Within the activity developed by ST Sibiu it is worth mentioning that over 50 % of the total length of its 220 and 400 kV OHL (987 km) stretches across the mountains, in hardly accessible areas, operating under special weather conditions, with high operational and maintenance exigencies. Through these lines, the power generated in the large power plants of Lotru, Mintia and Iernut, is transmitted. 
Achievements:
- promoting some pilot projects, such as: Reliability-based maintenance - RCM- OHL inspection by helicopter, Live treatment of electro-insulating oil, Applying the live work, GIS technologies;.
- extending the live actions in the power transmission grid and participation in the technical and scientific events and organizations, such as: international conferences, CIGRE, ICOLIM, CIRED;
- an important contribution to the power grid development is brought by the protection systems specialists within ST Sibiu , both by the activity they carry out in the work groups of CIGRE - member of Scientific Committee B5 and by periodically organizing conferences, symposiums in the protection and automation fields.
Investment projects guidelines 
- rehabilitation of the substations in Sibiu south, iernut, Fantanele and Gheorghieni.