Assemble the transmission lines structure steel tower

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transmission lines structure steel tower

500kv Self Supporting Lattice Steel Tower

Transmission structures are one of the most visible elements of the electric transmission system. They support the conductors
used to transport electric power from generation sources to customer load. Transmission lines carry electricity over long
distances at high voltages, typically between 115 kV and 765 kV (115,000 volts and 765,000 volts).

There are many different designs for transmission structures. Two common types are:

 Lattice Steel Towers (LST), which consist of a steel framework of individual structural components that are bolted or welded together
 Tubular Steel Poles (TSP), which are hollow steel poles fabricated either as one piece or as several pieces fitted together.

The foundation part of the structure is placed within the foundation excavation, it is centred and fixed, and then the concrete is cast in the foundations. Further assembly is made after the concrete solidifies. The structure can be mounted element by element (one element at the time), in parts (sections) or in one piece (complete).

Assembling the structure

Sections of the towers are composed of main legs of max. length 6m connected with diagonals, and the same section is used for towers of different heights without requiring additional works on the structure as such. In this way the storage (number of positions) and assembly of towers is simplified. It makes possible to very simply use them on different locations in case the existing tower is to be disassembled, as also makes possible to use then for lower heights, that is the foundation section can be used for both equal and for higher towers.

Both LSTs and TSPs can be designed to carry either one or two electrical circuits, referred to as single-circuit and doublecircuit structures (see examples above). Double-circuit structures typically hold the conductors in a vertical or stacked configuration, whereas single-circuit structures typically hold the conductors horizontally. Due to the vertical configuration of the conductors, double-circuit structures are taller than single-circuit structures. On lower voltage lines, structures sometimes carry more than two circuits.

A single-circuit alternating current (AC) transmission line has three phases. At low voltages, a phase usually consists of one conductor. At high voltages (over 200 kV), a phase can consist of multiple conductors (bundled) separated by short spacers.

A double-circuit AC transmission line has two sets of three phases.

Dead-end towers are used where a transmission line ends; where the transmission line turns at a large angle; on each side of a major crossing such as a large river, highway, or large valley; or at intervals along straight segments to provide additional support. A dead-end tower differs from a suspension tower in that it is built to be stronger, often has a wider base, and has stronger insulator strings.

Steel lattice towers for 10, 20 and 35 kV transmission lines

In order to comprise all requirements of distributors, and at the same time use the simplest possible storage solutions and to reduce maintenance costs i.e. to unify the construction, a suitable group of steel lattice towers was designed for assembling 20 (10 and 35) kV distribution lines. Towers were designed between 1980 and 1983 for the requirements of the Elektroprivreda company, as part of the medium voltage tower standardisation program for ZEOH at that time, and are now part of the Jielian STEEL TOWER d.d. Zagreb manufacturing assortment.

By using extensive experience in design, production and construction of transmission line towers and data on their use, 3 suspension (N – NAH, NAL and NAP) and 5 tension (Z – ZAE, ZAH, ZAJ, ZAL and ZAM) towers were designed, in line with the “Regulation on Technical Standards for Construction of Overhead Power Lines of Nominal Voltage Between 1 and 400 kV” Official Gazette 65/88 (O.G.RH 55/96), where each of them can be used in different conditions present on the transmission line route.

For each tower type a structure prototype was made and it was tested under test load. Based on the examination of the project documentation (calculations and manufacturing blueprints), examination of the prototype structure, testing results and by participation in tests, IGH as the authorised organisation issued attests on testing.

Over 25 years of experience in using towers indicated all structural advantages, precisely because of the possibility of their differentiated use, their suitability to most common situations and deployment requirements. Accordingly, new types of accessorises and new manufacturing technology improvements were made to: the structure itself, presentation of acceptable loads and methods for control and selection of the structure model for the relevant load of each single tower design type group. To the names of towers the additional mark 2 was added, (N – NAH2, NAL2 and NAP2) and (Z – ZAE2, ZAH2, ZAJ2, ZAL2 and ZAM2).

For each single tower type a project documentation was prepared according to the currently valid technical regulations and professional HEP standards (Steel Lattice Tower Standardisation for 20(10) kV Network, mark N.022.03, class no. 4.08/92).