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Cables Over Head Essay

2076 words - 9 pages

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 ...view middle of the document...

Numerous other electrical, mechanical and structural applications of aluminium in electrical industries developed along with the growth of aluminium wire and cable.

Wire and Cable

The positive attributes of aluminium for electrical applications are: reasonably high electrical and thermal conductivities, low density, nonmagnetic properties, ease of drawing down to the smaller wire sizes and high resistance to weathering.
Because of technological advances and good price as compared to copper, there has been permanent expansion in the volume, sizes and varieties of aluminium conductors.

Aluminium Conductor Materials
It was early learned that the electrical resistivity of aluminium is markedly increased by impurities; electrical conductor grade (EC) metal, containing approximately 99.5% Al, was established for most conductor uses. At present,
The utilisation of aluminium has increased quickly since World War II, in no doubt by the change in the aluminium-copper price relationship. Aluminium has over twice the conductivity of copper on a weight basis, and aluminium conductor is used for almost all overhead sub transmission and distribution lines.

There are some great reasons because in numerous countries aluminium has taken the place of copper for main conductor material of all components of the transmission and distribution systems.
Aluminium is much lighter than copper. The density of aluminium is about 30 % that of copper. Especially in overhead line construction this factor is very important because heavy conductors lead to heavy and expensive pole structures. Handling and transportation of aluminium conductors and cables are also easier compared with heavy copper conductors and cables. The lightness of aluminium gives advantages in many ways
Aluminium is the most common metal in the earth surface - its amount is about 8 %. Today copper are limited and diminishing so the price of copper has been high and rising. The price of aluminium was low and rather steady state for years, but some rising can be noticed in it, too. Because of lightness of aluminium, the price of aluminium conductors and cables are clearly smaller than those of copper conductors and cables.
Long-distance overhead conductors use aluminium in first choice to copper - the inferior electrical conductivity being more than compensated by the lower density and cost. In composite steel-Al Cables, the steel carries largely or all of the mechanical load, and the Al the electrical current. Aluminium is frequently now used throughout, serving both electrical and mechanical purposes.

Aluminium is about a third the weight than equal volume of copper, steel or brass.
Aluminium can supported heavy loads and heavy pressures.
The strength when alloyed approaches that of steel.
Corrosion resistance - The creation of a microscopic film of aluminium oxide on the surface of the metal protects it against corrosion and also makes a good insulation.


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