A case study on voltage uprating of overhead lines - air clearance requirements

Voltage uprating is a reliable method for increasing the power transfer capability of an existing overhead line. It is essential to meet the primary air clearance requirements for power frequency, switching and lightning overvoltages while evaluating the suitability to uprate the line to a higher voltage level. In this paper, a method is discussed to establish the necessary clearance envelopes for power frequency, switching and lightning overvoltages. The results are based on an investigation into the clearance requirements for IEC-60071. A case study based on uprating a 275 kV overhead line with L3 towers design to 400 kV is presented. Finally, issues and opportunities associated with uprating the L3 tower to 400 kV are explored.