Sag and tension calculations for overhead transmission lines athigh temperatures-modified ruling span method

摘要

The ruling span concept is widely used to calculate sags andntensions for new overhead transmission lines and for upgrading existingnlines. It provides satisfactory results for a level line with relativelynuniform spans at any temperature, or for any span length of a level linenat low temperature. The ruling span concept may result in annunacceptable error if it is used to calculate sags and tensions in anline segment with significantly unequal spans at high temperature. Thisnpaper presents a method to calculate sags and tensions of multi-spannline segments at different temperatures based on the rotationalnstiffness of suspension insulator strings. A simple equation, based onnthe parabolic approximation, is derived to calculate changes in the spannlengths and conductor sags and tensions. The method follows the rulingnspan concept but relaxes the fundamental assumption of the ruling spannmethod. The accuracy of the method is compared with the more complex,nnonlinear, finite element method