Sag and tension calculations for mountainous terrain

While normal sag and tension calculations based on the `equivalent-span¿¿ concept are satisfactory, when applied to transmission lines located in a reasonably undulating terrain, the answers obtained by this method are inaccurate for mountainous terrain. An alternative method of calculation, which is based on the analysis of the change of state equation for each span of a section in turn, is given. It is shown that when using this new approach the full effect of both the suspension and tension insulators can be included together with the influence of the running-out blocks on the sag of the conductor. The paper also shows how this concept can be adapted to the function of line design and gives several examples of critical areas where existing methods may give unacceptable results. When stringing conductors in mountainous terrain, it is not always practical to measure the conductor sag using conventional techniques and the paper gives three additional means which may be used, and discusses the advantages and disadvantages of each.