transmission lines

[joeajay]

types of conductors used in transmitting electricity

[chakka35]

Overhead power lines have a core of steel wires for strength surrounded by aluminium wires for conductivity.

Underground cables, where they are practicable, have copper, which is a better conductor than aluminium, as a core. This reduces heat losses which don't matter overhead because the air acts as a coolant but is a problem underground.

High voltage underground cables also have to masses of insulation (again supplied by the atmosphere when overhead) plus electric and magnetic screens to reduce interference. The core has a hole through its centre to allow cooling oil to be pumped through.

[beso]

Overhead conductors used to be copper. But it got very expensive and they get stolen a lot.

Although copper is a better conductor by volume, aluminium is a better conductor by weight and much better by dollar. Steel is a comparatively poor conductor but it is very strong.

Silver is the best conductor by volume but obviously too expensive to be used anywhere.

Copper is normally used where volume matters like inside motors windings. However the rotor conductors of inductions motors use aluminium because it can be cast into the lamination slots. Some motors use aluminium in the stationary field windings because size is less important than in the rotating parts and cost is important.

The weight is important in the design of the support pylons so aluminium is used in long distance power transmission lines, apparently with steel cores. However fully aluminium conductors are used in smaller power lines where maximum span capabilities are not so important such as in the street.

In remote parts of some countries like Australia, a plain steel conductor is used for Single Wire Earth Return (SWER) systems. Transmission is usually at 33kV so the current is very low and conductivity is not important. The conductor is a single wire (the return conductor is the ground) to the span between ploes can be as much as 400 metres because there is no danger shorting.

Gold is used where minimum volume, high reliability and good conductivity is important such as inside computer chips. Gold does not corrode and can be drawn into extremely fine wires. It is also used to plate connectors becuase it doesn't corrode.