Transmission Structures|Transmission Towers And Transmission Poles|Electric Tower

In this post, you will learn what are the different types of transmission line structures, Lattice Steel Towers (LST) , Tubular Steel Poles (TSP).

Contents

Transmission structures

Transmission structures 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).

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.Types of Transmission Towers|Electrical Tower Types

Types of transmission structures

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

Lattice Steel Towers (LST)
Tubular Steel Poles (TSP)

Lattice Steel Towers (LST)

Lattice Steel Towers consist of a steel framework of individual structural components that are bolted or welded together.

Tubular Steel Poles (TSP)

Tubular Steel Poles are hollow steel poles fabricated either as one piece or as several pieces fitted together.

Both LSTs and TSPs can be designed to carry either one or two electrical circuits, referred to as single-circuit and double-circuit structures.

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Double-circuit structures & single-circuit structures

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.

500–kV single-circuit LST-lattice-steel-tower — 500 kV single-circuit LST lattice steel tower

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

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.

Termination tower (overhead line to underground cable)

Transmission structure size

Structure sizes vary depending on voltage, topography, span length, and tower type.

For example, double-circuit 500-kV LSTs generally range from 150 to over 200 feet tall, and single-circuit 500-kV towers generally range from 80 to 200 feet tall.

Why Double-circuit structures are taller than single-circuit structures?

Double-circuit structures are taller than single-circuit structures because the phases are arranged vertically and the lowest phase must maintain a minimum ground clearance, while the phases are arranged horizontally on single-circuit structures.

As voltage increases, the phases must be separated by more distance to prevent any chance of interference or arcing.

Thus, higher voltage towers and poles are taller and have wider horizontal cross-arms than lower voltage structures.

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