TABLE OF CONTENTS The first transmission lines utilised stranded copper conductors largely because of the good electrical conducting properties (volume resistivity at 20 C, 0.0177 ohm mm 2/m) and resistance to corrosion of the material.
Pure copper has a relatively low ultimate breaking strength of about 250 MN/m 2, and the maximum working tension of conductor manufactured from annealed copper must be limited so that the stress in the conductor does not exceed about 125 MN/m 2. Copper can be 'work-hardened', resulting in a material with an improved breaking load of about 420 MN/m 2 at the expense of a slight increase in resistivity. The increase in breaking strength allows higher working loads and longer span lengths. Alloys of copper, particularly cadmium copper, provide a material with a breaking strength of about 630 MN/m 2 but again an increase in resistivity to 0.0217 ohm mm 2/m results. Copper and cadmium copper are expensive and as a result these have largely been replaced by aluminum as a conductor material.
Aluminium has a higher resistivity than copper, being 0.0282 ohm mm 2/m. However, if the resitivity is expressed as mass resistivity at 20 C in ohm g/m, because of the lower density of aluminium, copper is seen to have a value of 0.1532 and aluminum 0.076 ohm g/m. Because aluminium has a low breaking strength of only 165 MN/m 2, in order to provide a conductor with an acceptable breaking strength, it...
