Design specification
High voltage overhead power lines must comply with several requirements. We need to consider various factors for the design specification, mechanical and electrical and also the sites where the cables will be fixed.

The site is very important because its span varies enormously depending on the nature of the terrain and climate. Also important to the requirements are the lowest electrical resistance (to cut down losses), safe clearance over the ground, adequate strength for the applied loads, good mechanical strength able to manage the stresses and weights involved and convenient cost for the 100 or 1000 of km the lines regularly installed.

It is vital that appropriate environmental protection is provided and that recyclable materials are used as much as possible. This is achieved through specifying a thermal expansion limit, corrosion resistance and apt wind resistance for the cables. Numerous varieties of cable specifications are offered to meet the demands for distinct currents. There are a number of important specifications to consider:

• Need to meet transfer capacity requirements • Life cycle period • Reliability • Transmission • Distribution • Wind loading • Ice loading • Load factors • Loaded tension limits • Extreme wind loading • Environmental aspects • Low weight • High strength and flexibility • High mechanical load with extreme cold • Corrosion behaviour • Impact resistances • Required safety factors • British Standards (1970BS/215)

Introduction

As copper was the first material to be used in this capacity and aluminium is the most commonly used material used today I have decided to compare these two metals.

Conductor Material Properties

Materials usually used in conductors are aluminium, copper, and steel. Steel wires are joint with aluminium in the most frequent type of overhead conductor. Aluminium Conductor Steel