Comparative Study on 4-Legged Transmission Line Tower with Different Bracings by using STAAD Pro

India has a large population residing all over the country and the electricity supply need of this population creates requirement of large transmission and distribution system. Also, the disposition of the primary resources for electrical power generation viz., coal, hydro potential is quite uneven, thus again adding to the transmission requirements. Transmission line is an integrated system consisting of conductor subsystem, ground wire subsystem and one subsystem for each category of support structure. Mechanical support of transmission line represents a significant portion of the cost of the line and they play an important role in the reliable power transmission. They are designed and constructed in wide variety of shapes, types, sizes, configuration and materials. The supporting structure types used in transmission line generally fall into one of the three categories: lattice, pole and guyed. The supports of high voltage transmission lines are normally steel lattice towers. The cost of tower constitutes about quarter to half of the cost of transmission line and hence optimum tower design will bring in substantial savings. The selection of an optimum outline together with right type of bracing system contributes to a large extent in developing an economical design of transmission line tower. The tall structure with relatively small cross-section and with a large ratio between the height and the maximum width are known as tower or masts. Tower is also known as pylon. A tower is a single cantilever freely standing self.

For the present study, 220KV transmission line towers of different types of bracing are considered. First model of tower is tower with X-bracing, second model is of tower with K-bracing and third model of tower is tower with composite bracing. The tower is square base self-supporting type.

The transmission line towers are subjected to the following loads: (a) Vertical loads

(d) Torsional loads

(1) To analyse and design the transmission line tower using STAAD Pro software. (2) To analyse and design the transmission line tower for different types of bracing. (3) To compare different towers for its structural stability.

INTRODUCTION TO STAAD Pro SOFTWARE

STAAD or (STAAD. Pro) is a structural analysis and design computer program originally developed by Research Engineers International at Yorba Linda, CA in year 1997. In late 2005, Research Engineers International was bought by Bentley Systems. An older version called STAAD-III for windows is used by Iowa State University for educational purposes for civil and structural engineers. Initially it was used for DOS-Window system. The commercial version STAAD Pro is one of the most widely used structural analysis and design software. It supports several steel, concrete and timber design codes. analysis. It can also make use of various forms of dynamic analysis from modal extraction to time history and response spectrum analysis. In recent years it has become part of integrated structural analysis and design solutions mainly using an exposed API called Open STAAD to access and drive the program using a VB macro system included in the application or other by including Open STAAD functionality in applications that themselves include suitable programmable macro systems. Additionally STAAD Pro has added direct links to applications such as RAM Connection and STAAD. Foundation to provide engineers working with those applications which handle design post processing not handled by STAAD Pro itself. Another form of integration supported by STAAD Pro is the analysis schema of the CIM steel Integration Standard, version 2 commonly known as CIS/2 and used by a number modeling and analysis applications.

TRANSMISSION LINE COMPONENTS:

The following parameters for transmission line and its components are assumed from I.S. 802: Part 1:Sec: 1:1995, I.S. 5613: Part 2: Sec: 1:1989.

A substance or a material which allows the electric current to pass through its body when it is subjected to a difference of electric potential is known as Conductor.

The earthwire is used for protection against direct lightning strokes and the high voltage surges resulting there from. There will be one or two earthwire depending upon the shielding angle or protection angle.

Insulators are devices used in the electrical system to support the conductors or to support the conductors carrying at given voltages.The insulators separate thecurrent carrying conductors of a transmission line from their support structures to prevent the flow of current through the structure to ground and to provide necessary mechanical support to the conductors at a safer height above the ground level.

In result analysis we compare the three tower of different bracing for displacement of member, displacement of nodes, axial forces and maximum tensile and compressive stresses. In this paper an attempt has been made to compare the same transmission line tower with different bracing system i.e X- bracing, K- bracing and Hybrid bracing system. Following conclusions are drawn on basis of STAAD Pro analysis. ● Stresses developed in hybrid bracing are less as compared to X and K- bracing. ● Axial forces developed in hybrid bracing tower are very less as compared to other types of bracing. ● Displacement of nodes is more for K- bracing and lesser for hybrid bracing. ● Displacement of members of K- bracing tower is more as compare to X and hybrid bracing. ● Maximum bending moment is greater for wind load than dead load. ● Tower structure with least weight is directly proportional to deduction of cost. Tower of X- bracing gives least weight.

D.B. Sonawal, J.D. Bharali, M.K. Agarwalla, N. Sarma, P. HazarikaAnalysis and Design of 220 kV Transmission Line Tower (A conventional method of analysis and Indian Code based Design) Dr.B.C.Punmia, Ashok Kumar Jain, Arun Kumar Jain, ―COMPREHENSIVE DESIGN OF STEEL STRUCTURES‖, Laxmi Publications. F. Albermani, M. Mahendran and S. Kitipornchai (2008). ―Upgrading of Transmission Towers Using a Diaphragm Bracing System‖ International Journal of Civil and Structural Engineering Volume2, No. 2. G. Visweswara Rao (1995). ―Optimum Designs For Transmission Line Towers‖ Computer & Structures vol.57.No.1.pp.81-92, 1995 I.S 800: 2007 General Constructions in Steel - Code of Practice. IS 5613 (Part1/ Sec1): 1985 Code of Practice for Design, Installation and Maintenance of Overhead Power Lines (Part 1 Lines up to and including 11kv Sec 1 Design).

11kv and up to and including 220kv Sec 1 Design). IS 802 (Part1/ Sec1): 1995 Use Of Structural Steel in Overhead Transmission Line Towers - Code of Practice (Part 1 Materials, Loads and Permissible Stresses Sec 1 Materials and Loads). M. Selvaraj, S.M. Kulkarni, R. Ramesh Babu (2012). ―Behavioral Analysis of built up transmission line tower from FRP pultruded sections‖ ISSN 2250-2459, Volume 2, Issue 9, September 2012 N. Prasad Rao, G.M. Samuel Knight, S.J. Mohan, N. Lakshmanan (―Studies on failure of transmission line towers in testing‖ Ram Chandra, ―DESIGN OF STEEL STRUCTURES‖,VolumeII,Standard Book House,Delhi,110006. S. Christian Johnson 1 G.S. Thirugnanam (2010). ―Experimental study on corrosion of transmission line tower foundation and its rehabilitation‖ International Journal of Civil and Structural Engineering ISSN 0976 – 4399 Volume 1, No 1, 2010 V. Lakshmi, A. RajagopalaRao ― Effect Of Medium Wind Intensity On 21M 132Kv Transmission Tower‖ISSN: 2250–3676 Volume-2, Issue-4, pp. 820 – 824 Y. M. Ghugal, U. S. Salunkhe ―Analysis and Design of Three and Four Legged 400KV Steel Transmission Line Towers: Comparative Study‖ International Journal of Earth Sciences and Engineering691 ISSN 0974-5904, Volume 04, No 06 SPL, October 2011, pp. 691-694

Department of Civil Engineering, JSPM‘s Imperial College of Engineering and Research Wagholi, Pune-412207