Calculation of overhead line sags

Abstract: The liberalisation of the energy market in Europe leads to change in operation of the transmission network. Diagnostic tools for the condition evaluation get more importance. Based on the changed stress and the large expansion of the network of the line components a considerable effort for condition evaluation and maintenance is necessary. In the centre of Europe the Austrian transmission line system at the level 230kV and 400kV has an important role for the energy exchange and was built up in 50’s to the70’s of the last century, therefore parts of the system are more than 40 years old. Based on this situation this paper focuses on the operation behaviour of ageing overhead lines with special regard to the sag calculation of span sections. The sag of a transmission line will increase by increasing conductor temperature caused by the electrical load and specific environmental conditions or additional rope forces (e.g. ice load). In addition, the permanent mechanical forces (everyday stress) elongate the conductor irreversible during its live time.