'COMPUTER AIDED ANALYSIS AND DESIGN OF TRANSMISSION LINE TOWERS

Abstract

The construction of large thermal power stations,remote Hydro Electric power plants and interconnection of state grids have given rise to the need for Extra-High Tension (E.H.T.) transmission lines. Before the advent of computers the analysis and design of transmision line towers was a most challenging job for engineers. After spending several engineering man-days, -63 the design was considered unreliable such that prqtype testing was thought of as a necessity. Errors involved in the analysis 6 were more due to various simplifying aspmptions. Three Dimensional analysis in those days was a remote possiblity if not impossible. With the availability of digital computers, the analysis and design of these towers can be done in few minutes of CPU time. 3-D analysis using computers is so reliable and accurate that prototype testing can altogether be done away with. In this way it is evident that use of computers and development of an efficient computer program for analysis and design of towers will be very useful. In this dissertation, a digital computer program has been developed which performs the analysis and design of transmission line towers. The computer program includes : (1) Calculation of various tower loads. (2) Analysis of tower as 3-D pin jointed structure for various loading conditions. (v) (vi) (3) Design of Single Circuit and Double Circuit towers. (4) Design of towers by working stress method and ultimate load method. Analysis of tower is done for different load conditions, that is, normal condition, broken wire conditions and dead-end condition and design force for each member is found. The analysis and design is done within core memory of the computer and final angle sizes for different members are printed out A 132 kV transmission line tower with following characteristics, which have been already constructed in field, has been designed by using digital computer program by working stress as well as ultimate load method. Type of tower : Single circuit Deviation angle of tower: 30 degree Normal span 320 m. Wind span 320 m. Weight span : 500 m. The computer program has been found very efficient and versatile. It can be used for designing new towers and also for checking already designed towers, thus ensuring safe and economic structure. CPU time on DEC 2050 computer was 3 min 41 seconds. The design of the comlete tower, that is, preparation of data-sheet and interpretation of the results, can be completed within few days. After analing various towers for different initial dead weights, it has been noticed that final weight of tower is almost independent from initial weight assumed. Convergence from initial weight to final weight has been found very rapid and number of cycles required for the purpose in various cases do not vary much.