Dynamic analysis of a transmission line tower modeled in staad pro.

Abstract

Transmission line towers carry heavy electrical transmission conductors at a sufficient and safe height from ground. In addition to their self-weight they have to withstand all forces of nature like strong wind, earthquake and snow load. Therefore transmission line towers should be designed considering both structural and electrical requirements for a safe and economical design. This paper introduces different types of transmission tower and its configuration as per Indian Standard IS-802. A typical type of transmission line tower carrying 220kV double circuit conductors is modeled and analyzed using STAAD-Pro considering forces like wind load, dead load of the structure and earthquake load as per Indian Standard IS1893:2000(part 1). The transmission tower has height of 40m which includes the ground clearance(h1),maximum sag of the lower most conductors wire(h2),vertical spacing between the conductors wires(h3) and vertical distance of earth wire from the uppermost conductor wire(h3).The earth wire or ground wire is always located at the top of the transmission tower. It has a square base width of 11.5m The type of transmission tower considered is a tangent tower having no deviation located on a plain landscape with minimal obstacles. It is located at the wind zone 6 with basic wind speed of 55m/s. The wind pressure on the tower depends on the gust response factor (GT) which increases with height. The transmission tower is situated in the most seismic sensitive region i.e. Zone V where response reduction factor steel frame with concentric braces is of 4 and the damping for steel structures is 2%. The members are designed for maximum deflection and load for the most critical load combination as per code IS802. The members are also grouped for better fabrication. Steel optimization has been carried out to find the most suitable and economical section for the design.