Elongation of overhead line conductors under combined mechanical and thermal Stress

For a high reliably and high-capacity electrical power supply, the most technical expedient and economized way is an intermeshed grid of power lines. For example in Europe, in the "Union for the Coordination of Transmission of Electricity" network (UCTE) are at the moment 24 countries with a providing area of 430 mil people with 200000 km of 230 and 400 kV lines. Parts of this grid are in operation since 1950 or earlier. Due to the operating time of more than 30 years each power grid operator must ask how reliable are the line components and how much load capability is remaining. Especially the components of an overhead line which are under mechanical stress and conducting the load current are critical parts for the personal safety and system protection. This combined stress is significant for the condition and behaviour evaluation of the equipment. This contribution gives an overview about the theoretical interrelationship of the mechanical and thermal behaviour of new and aged overhead line conductors. The behaviour of typical overhead line conductors will be shown. The mechanical and thermal elongations of the conductor influence the sag and thereby the required safety margins to the ground or objects. The knowledge of the sag behaviour is the base of an overhead line monitoring system based on thermal rating.