Applications of Aluminium

Aluminum in electrical engineering

Aluminum for the electrical industry

It happened so many years ago, that most engineers, constructors and designers in the electrical industry believe copper and steel substantially only materials, you can work with. This is attributed, in particular, so as, that at the end of the 19th century, originated when the electrical industry, available aluminum almost was not yet.

At present, the situation is completely different: aluminum is produced in the world about twice as much as copper and the volume of aluminum production is second only to the volume of steel production..

In recent years, prices for steel and copper are growing significantly faster, than aluminum prices. As a result, some consumers, which are traditionally used copper, switching to aluminum. However, comparison of the physical and economic characteristics of these metals, "shouts" that, that substituting steel and copper to aluminum should be much more. Therefore it is not surprising, what The use of aluminum in the electrical industry is steadily increasing.

Material properties as the electrical conductor

For an electrical engineer the most important properties and the characteristics of the materials are:

  • density,
  • electrical conductivity,
  • strength,
  • thermal expansion and
  • corrosion resistance.

Aluminium alloys, steel and copper

Comparison of aluminum properties, steel and copper [1]:

  • Density (g / cm3):
    Aluminium alloys 1350: 2,70
    Steel: 7,86
    Copper (annealed): 8,93
  • bulk conductivity (% IACS):
    Aluminium alloys 1350: 61
    Steel: 8
    Copper (annealed): 100
  • Conductivity (per unit mass):
    Aluminium alloys 1350: 100 %
    Steel: 4 %
    Copper (annealed): 50 %
  • Tensile strength (MPa):
    Aluminium alloys 1350: 125
    Steel: 300
    Copper (annealed): 235
  • Yield strength (MPa):
    Aluminium alloys 1350: 110
    Steel: 170
    Copper (annealed): 104
  • Linear thermal expansion (10-6 m / m ° C):
    Aluminium alloys 1350: 22
    Steel: 13
    Copper (annealed): 17

Electrical properties

Annealed copper has a conductivity 100 % IACS. Reduction in IACS - stands for "International Standard for annealed copper" – comparative unit of measurement of electrical conductivity. The electrical conductivity of aluminum by purity 99,99 % at 200 ° C is 63,8 % International Annealed Copper Standard (IACS). Due to the low specific gravity, the mass electrical conductivity of pure aluminum is more than twice as high., than annealed copper, and higher, than any other metal (Fig. 1). Resistivity at 200 ° C is 2,69 μΩ cm [2].

Сonductivity, reciprocal resistivity, is one of the most sensitive properties of aluminum, which is affected by both compositional changes, and heat treatment. The addition of other metals to aluminum alloys reduces the electrical conductivity of aluminum, so this should be offset by any additional benefits, which can be obtained, such as increased strength. Heat treatment also affects conductivity, since alloying elements in solid solution produce more resistance to electrical current, than they are in the undissolved state.

Aluminum 1350-H116 has conductivity 61 % IACS, i.e. the equivalent conductivity of copper is achieved when larger cross-sectional aluminum. However, since aluminum is much lighter than copper, this enlarged aluminum conductor will weigh half as much as copper (8.93 / 2.70 × 0.61 = 2.02). As a result, one kilogram of aluminum will provide the same conductivity as two kilos of copper. therefore, when there is no hard limits on the size of the conductor, for busbars, cables and wires instead of copper, aluminum is increasingly used [2].

Strength

Under identical cross sections and copper, and steel, of course, stronger than aluminum. However, the strength of aluminum can be increased by alloying and thermomechanical processing, and increase its thickness. Moreover, since the aluminum pressing technique allows to obtain a difference, for example, from steel, cross-sections of a very complex shape. Therefore, the aluminum member may be so designed, to be more structurally efficient, than steel elements.

corrosion resistance

Unlike steel aluminum surface is not necessary to paint or coat, for example, zinc, and then follow, that it is not rusted. Natural aluminum oxide layer isolates the metal from further contact with air and prevents further oxidation. The slightest damage to this layer, he instantly recovered himself.

Misconceptions and myths

Aluminum conductors are sufficiently robust. All wires of overhead power lines are aluminum. They have a long-standing reputation for reliable service.

However, in the 60-70-ies of the last century had an opinion about the problems with the aluminum wiring in homes and apartments, in particular, possible overheating of the compounds. Careful study of this issue, for example, In Canada, show, that aluminum wires are not special in this sense: if mishandled, any wires can overheat. Moreover, hundreds of thousands of houses and apartments all over the world continue to work aluminum wires. Another thing, in 60-70 years no one imagined, that houses and apartments will be so "stuffed" with electrical appliances: the cross-sections of aluminum wires could be laid and thicker.

Aluminum Electrical Conductors

The very good electrical properties of aluminum have made it an obvious choice for applications in the electrical industry., especially in power distribution, where it is used almost exclusively for overhead power lines and busbars. The first major aluminum transmission line was completed in 1898 year in the USA: a three-phase line with a length of 46 miles for Standard Electric Company of California from Blue Lakes to Stockton.

Later, its use became much more common., when it was discovered that it was possible to reinforce the cable (usually from an alloy 1350) galvanized steel wire, which increased spans without too much sag. Although this product is still in use, high strength (alloy 6061) all-aluminum stranded cables are currently preferred for some lines, because higher line tension can be achieved, what can be applied to increase the distance between supports or, alternatively, to reduce their height [2] (Fig. 2).


Fig. 2 – The use of aluminum wires in the US and Canada [3]

Electrical uses of aluminium extrusion

Street and road lighting poles

Extruded aluminum poles have advantages over, for example, steel posts, due to their lower weight, less strength-weight ratio, good appearance, long-term corrosion resistance, low maintenance costs, as well as more secure, particularly when applying special safety grounds. When this column runs into a high speed car, this foundation collapses and allows the post to move with the car. This reduces the power-hitting of the vehicle and the extent of damage to the driver and passengers. This base so "cleverly" designed, it is destroyed by hitting the pole, but withstands wind loads on post.

busbars

For all types of tire extruded aluminum used there, where it allows space for their placement, as they, first of all, much cheaper, and they are also much easier to bend (Fig. 3).


Fig. 3 – Aluminium bus bars

Electrical connector bodies

Cable lugs and sleeves made of extruded aluminum pipes have strength advantages over analogs made of steel or copper, conductivity, the cost, corrosion resistance and ease of machining (Fig. 4).


Fig, 4 – Electrical connector bodies

The channels for cable

The channels for cable increasingly used of extruded aluminum, instead of steel or plastic,, because they provide sufficient strength, are lightweight, have a high resistance to corrosion, are non-magnetic and flame retardant (Fig. 5).


Fig. 5 – An electrical chanel

Built-in electric substations

Preferably aluminum profiles, for example, galvanized steel, due to minimal maintenance, strength, corrosion resistance, low weight (especially when mounted in the field and at height). Aluminum profiles and sheets are easy to trim and drill right "place", and most importantly, they should not be painted for protection against corrosion.

Distribution traverse electric poles

Distribution traverses of electrical poles (those, which are horizontal) extruded aluminum ensure the necessary strength, but they weigh a little and do not require any maintenance.

Radiators-comb

Extruded aluminum fins for heat dissipation ("combs") are highly efficient due to their high thermal conductivity, low weight, low cost. The main advantage of aluminum – ability to be pressed into many very thin ribs (Fig. 6).


Fig. 6 – An aluminium heat sink

Outer conductor of CATV cable

The outer conductor of the coaxial TV cable often is not made from copper pipe, and from cheaper aluminum. The technology for producing such a cable is shown in Figure 5.

Fig. 7 – The manufacturing steps of outer conductor of CATV cable

 

Sources:

  1. P. Pollak / ET 2008.
  2. TALAT 1501
  3. Stabiloy, Aluminum or copper? /Alex Mak – Alcan – 2008