TABLE OF CONTENTS The tower or supporting structure is required to carry the overhead line conductors and earth conductors, each of which will be subjected to a variety of forces. These range from normal still air load, extreme wind loads, ice loads in some parts of the world, and any additional loads during erection and maintenance of the conductors or insulator sets. The tower must be capable of safely withstanding all the various forces applied to it and at the same time the electrical clearances between the live conductors and the earthed metal must be maintained under all loading conditions.
The tower may be designed to cater for a single 3-phase circuit, double 3-phase circuits, multiple voltage circuits and, with direct current transmission, either a monopolar (with earth return) or bipolar construction.
Single circuit (SC) towers are generally of one of three forms: horizontal, delta or triangular conductor configuration. Some typical towers are shown in Figure 5.4.
Towers equipped with horizontal configuration conductors require a lower tower height than an equivalent vertical configuration tower but, because of the clearance requirements between phases, they require a wider strip of ground. If the region in which the line is to be constructed has a high lightning level (isoceraunic level) it is usually necessary to install two overhead earth wires to provide proper shielding of the line...
