Loads to which a transmission line tower is subjected are briefly described and it is shown that notwithstanding the higher factor of safety stipulated under normal condition, it is the broken conductor condition, with resultant torque on tower shaft, which is generally the governing criterion for the design of transmission line towers. At present transmission line towers in this country are designed to withstand a broken conductor tension computed on the assumption of maximum wind coincident W th minimum temperature. It is shown that this design requirement is very rigorous and unrealistic. A more realistic approach is described and certain factors such as actual simultaneous incidence of wind and temperature, limited front of gust of wind acting on considerably long transmission line spans, and rare occurrence of conductor breakages, and the effects of these on unbalanced conductor pull, are discussed. Some practical methods to eliminate or reduce longitudinal pull on tower such as use of release clamps, adoption of rotating cross-arms and provision of weak connection between cross-arm and tower shaft, used on recent transmission lines are dealt with.
