Aluminium material and its alloys used in electrical engineering.

Aluminium Meterial and its alloy used in electrical engineering

Introduction

Aluminium material has been used for many years as a conductive material in almost all branches of industry. Electrical engineering . Besides pure aluminum, several of its alloys are also excellent conductors, combining structural resistance and quite acceptable conductivity.

Aluminium material is used everywhere in the electricity industry. Motors wind up with it, high voltage lines are built with it, and the drop from the power line to your home’s circuit breaker is likely aluminium.

The material is lighter than copper ( about a third of the density ) and therefore easier to handle; it’s also cheaper .

Another advantage is that its price is not subject to large fluctuations like copper. The price of copper around the world rose sharply in the 1960s and 1970s. This led to many examples of aluminum being used in situations where copper was previously the norm.

In a few applications, for example domestic With regard to the wiring and transformer sheets identified below, aluminum has been found to be less suitable than expected, so by the end of the 90s copper reverted to normal and that the use of aluminum tended to be limited to the applications for which it is used. Clearly superior.

There are two groups of UK standard specifications for aluminum:

1.     An aluminum coating for electrical purposes , which relates to high purity aluminum with emphasis on electrical properties, and

2.     The second concerns aluminium for Electrical engineering .

Aluminum for electrical use covers conductivity qualities between 55% and 61% International Annealed Copper Standard ( IACS ) and includes pure aluminum.

The relevant UK standards are as follows:

·         BS 215 Part 1: ( IEC 207 ) Stranded aluminum conductors for overhead transmission.

·         BS 215 Part 2: ( IEC 209 ) Aluminum conductors, steel reinforced, intended for overhead transmission.

·         BS 2627. Forged aluminum for electrical purposes – wire.

·         BS 2897. Forged aluminum for electrical purposes – strip with drawn or rolled edges.

·         BS 2898. Wrought aluminum for electrical purposes – extruded bars, tubes and round sections.

·         BS 3242. (IEC 208) Stranded aluminum alloy conductors for overhead power transmission.

·         BS 3988. Forged aluminum for electrical engineering – solid conductors for insulated cables.

·         BS 6360. Specifications for conductors in insulated cables and cords.

This specification group includes grade 1350 ( formerly 1E ) pure aluminum with a conductivity of 61% IACS and grade 6101A ( formerly 91E ) which is a heat treatable alloy with an average strength and a conductivity of 55% IACS.

Aluminum for general engineering use includes grades with conductivity as low as 30% IACS , but with high structural strength, up to 60% of that of steel , with more emphasis on mechanical properties .

This is covered by the following UK standards:

·         BS 1471 Wrought aluminum and aluminum alloys – drawn tube.

·         BS 1472 Wrought aluminum and aluminum alloys – forgings and forgings.

·         BS 1473 Wrought aluminum and aluminum alloys – stock of rivets, bolts and screws.

·         BS 1474 Wrought aluminum and aluminum alloys – bars, extruded round tubes and profiles.

·         BS 1475 Wrought Aluminum and Aluminum Alloys – Wire.

·         BS 1490 Aluminum ingots and castings ( based on but not identical to ISO 3522 ).

·         BS EN 485 Aluminum and aluminum alloys – sheets, strip and sheets.

This specification group includes grade 1050A ( formerly 1B ) with conductivity 61.6 IACS, grade 1080A ( formerly 1A ) also with conductivity 61.6 IACS, and grade 1200 ( formerly 1C ) with conductivity 59, 5% IACS. These grades are generally used in sheet form, up to 10mm thick, or plate, over 10mm .

Further information on grades and specifications of aluminum can be obtained from the Aluminum Federation.

Aluminum applications

Busbars

Aluminum has been used in busbars for over 60 years and from 1960 on it is increasingly used in a variety of busbar applications due to its light weight and durability .

Tubular aluminium is used exclusively for 275 kv and 400 kv network substation bars (Gas Insulated Transmission Line – GIL) and is increasingly used at 132 kv for the renovation and upgrading of substations, aluminium material is also using in Electrical Engineering.

Aluminum is used in large industrial plants such as foundries and electrochemical plants due to the availability of large sections of cast iron bars (up to 600mm × 150mm). Aluminum is also used in main switchgear and mounting systems due to its lighter weight compared to copper.

One of the major problems with aluminum is how quickly it oxidizes when the surface is prepared for the bolted connection. The former CEGB did a lot of research into the problem, especially with the large currents generated between a generator and its associated step-up transformer. This has resulted in significant improvements in assembly techniques.

Bolted joints in aluminum bars that require frequent disassembly are often galvanized using silver or tin.

Cable

Aluminum material is widely used as a conductor over 16mm 2 cross section for power cables up to 66 kv . Aluminum is not normally found in household wiring installations due to the specialized splicing and termination techniques required to ensure longevity of trouble-free service.

Overhead lines

The ACSR aluminium material conductor steel reinforced ) conductors of overhead lines are used worldwide for power distribution systems.

A car. ( Aluminium Conductor Reinforced Aluminium Alloy Wire ) have been increasingly used since 1960 due to the elimination of the risk of bi-metallic corrosion and improved conductivity for a given cross section. A car. Catenary conductors intended to support the contact wire are also highly valued by railway authorities for overhead electrification systems due to their reduced weight and reduced risk of theft compared to copper.

Engines

Cage rotors for induction motors often use aluminium material bars. The crankcases are also made from the material, as are the fans used for engine cooling.

Sheet windings

Aluminium is the standard for capacitor windings of the smallest types used in lighting fixtures with large power capacitors .

Sheet windings are suitable for some transformers, reactors and solenoids. Sheet thicknesses range from 0.040mm to 1.20mm in 34 steps . A better bulk factor is obtained than for a copper coil with wound wire, the aluminum conductor taking up about 90% of the space against 60% for the copper wire.

Heating and cooling are aided by the best space factor and the least amount of insulation required for the foil wound coils. The rapid radial heat transfer ensures a uniform temperature gradient.

The disadvantage of aluminum is its lower mechanical strength , especially from the point of view of making winding end connections .

The tendency has therefore been to resort to copper foil for low voltage air insulated windings.

Aluminium foil is however almost exclusively used for HV windings of resin insulated transformers, its coefficient of thermal expansion being closer to that of the resin encapsulating material than that of copper, which reduces thermal stresses due to the load. .

Constants and physical properties of very high purity aluminum

The descriptionValue
Atomic number13
Atomic volume10cm 3 / g-atom
Atomic weight26.98
Valence3
Crystal structureFcc
Interatomic distance (coordination number 12)2.68 kx
Combustion heat200 kcal / atom-g
Latent heat of fusion94.6 cal / g
Fusion point660.2 ° C
Boiling point2480 ° C
Vapor pressure at 1200 ° C1 × 10 -2 mm Hg
Average specific heat (0–100 ° C)0.219 cal / g ° C
Thermal conductivity (0–100 ° C)0.57 cal / cm s ° C
Temperature coefficient of linear expansion (0–100 ° C)23.5 × 10 -6 per ° C
Electrical resistivity at 20 ° C2.69 microhm cm
Temperature coefficient of resistance (0–100 ° C)4.2 × 10 -3 per ° C
Electrochemical equivalent3.348 × 10 -1 g / Ah
Density at 20 ° C2.6898 g / cm 3
Elasticity module68.3 kn / mm 2
Torsion modulus25.5 kn / mm 2
Poisson coefficient0.34

Heating elements

Aluminium material foil heating elements have been developed but are not widely used today. Applications include aluminum foil wallpaper , curing concrete and possibly warming the floor .

Radiators

Aluminum’s high thermal conductivity and the ease of extruding or casting into solid or hollow shapes with integrated fins make it an ideal material for heat sinks.

Semiconductor devices and transformer tanks illustrate the wide variety of applications in this field. Its light weight makes it ideal for pole mounted transformer tanks and has the added benefit that the material does not react with transformer oil to form slurry.

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