Aluminium and Its Alloy Used in Electrical Engineering

Subject: Aluminium and its Alloys used in Electrical Engineering

From: EEP - Electrical Engineering Portal ([email protected])

To: [email protected];

Date: Monday, November 5, 2012 10:05 PM

Technical articles receive 8,338 electrical engineers worldwide. Email not displaying correctly?View it in your browser.

Published on Nov 04, 2012 10:36 pm by Edvard | Subscribe to Monthly Download Updates

Recommended - Calculation of Touch Voltage & Ground CurrentForward this article to your colleagues

Print http://us.mg1.mail.yahoo.com/dc/launch?.gx=1&.rand=88mniifk1e4hg&re...

1 of 6 11/15/2012 10:27 AM

Aluminium and its Alloys used in Electrical Engineering (photo by Daniel Richert @ Flickr)

Introduction

Aluminium has been used for many years as a conductor material in almost all branches of electrical

engineering. In addition to the pure aluminium, several its alloys are also excellent conductors, combining

structural strength with an quite acceptable conductivity.

Aluminum is used everywhere in the electrical industry. Motors are wound with it, high voltage lines are

made with it, and the drop from the power line to your house’s circuit breaker box is probably aluminum.

The material is lighter than copper (about one third the density) and therefore easier to handle; it is also

cheaper.

Another advantage is that its price is not subject to wide fluctuations as is copper. There was a sharp

increase in the price of copper worldwide in the 1960s and 1970s. This led to many instances of aluminium

being used in situations where copper had previously been the norm.

In a few applications, for example domestic wiring and transformer foil-windings identified below, aluminium

proved to be less suitable than was initially hoped, so that in the late 1990s there has been some return to

copper and the use of aluminium has tended to be restricted to those applications for which it is clearly

superior.

There are two groups of British Standard Specifications for aluminium:


2 of 6 11/15/2012 10:27 AM

One covering aluminium for electrical purposes, which relates to high purity aluminium with emphasis

on electrical properties, and

1.

The second concerning aluminium for general engineering.2.

Aluminium for electrical purposes covers grades with conductivities between 55% and 61% International

Annealed Copper Standard (IACS) and includes pure aluminium.

The following are the relevant British Standards:

BS 215 Part 1: (IEC 207) Aluminium stranded conductors for overhead power transmission purposes.

BS 215 Part 2: (IEC 209) Aluminium conductors, steel-reinforced for overhead power transmission

purposes.

BS 2627. Wrought aluminium for electrical purposes – wire.

BS 2897. Wrought aluminium for electrical purposes – strip with drawn or rolled edges.

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

BS 3242. (IEC 208) Aluminium alloy stranded conductors for overhead power transmission.

BS 3988. Wrought aluminium for electrical purposes – solid conductors for insulated cables.

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

This group of specifications include grade 1350 (formerly 1E) pure aluminium with a conductivity of 61%

IACS and grade 6101A (formerly 91E) which is a heat treatable alloy with moderate strength and a

conductivity of 55% IACS.

Aluminium for general engineering uses includes grades with conductivities as low as 30% IACS, but with

high structural strength, up to 60% of that of steel, with greater emphasis on mechanical properties.

This is covered by the following British Standards:

BS 1471 Wrought aluminium and aluminium alloys – drawn tube.

BS 1472 Wrought aluminium and aluminium alloys – forging stock and forgings.

BS 1473 Wrought aluminium and aluminium alloys – rivet, bolt and screw stock.

BS 1474 Wrought aluminium and aluminium alloys – bars, extruded round tube and sections.

BS 1475 Wrought aluminium and aluminium alloys – wire.

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

BS EN 485 Aluminium and aluminium alloys – sheet, strip and plate.

This group of specifications includes grade 1050A (formerly 1B) with a conductivity of 61.6 IACS, grade

1080A (formerly 1A) also with a conductivity of 61.6 IACS, and grade 1200 (formerly 1C) with a conductivity

of 59.5% IACS. These grades are generally used in sheet form, up to 10mm thick, or plate, over 10mm

thick.

Further information on aluminium grades and specifications can be obtained from the Aluminium Federation.

Aluminium ApplicationsBusbars

Aluminium has been used for busbars for more than 60 years and from 1960 onwards is increasingly being

used for a whole range of busbar applications due to its light weight and durability.

Tubular aluminium is used exclusively for grid substation busbars at 275kV and 400kV (Gas-Insulated


3 of 6 11/15/2012 10:27 AM

Transmission Line – GIL) and is increasingly being used at 132kV for substation refurbishments and

redevelopments.

Aluminium is used in large industrial plants such as smelters and electrochemical plants because of the

availability of large sections of cast bars (up to 600mm × 150mm). Aluminium is also used in switchgear and

rising main systems because of its lighter weight compared with copper.

A major problem with aluminium is the rapidity with which it oxidizes when the surface is prepared for bolted

jointing. Much research was carried out by the former CEGB into the problem especially with the heavy

currents which arise between a generator and its associated step-up transformer. This resulted in significant

improvements in jointing techniques.

Bolted joints in aluminium busbars which are subject to frequent dismantling are frequently electroplated

using silver or tin.

Cable

Aluminium is extensively employed as the conductors over 16mm2 cross-sectional area for power cables

up to 66kV. Aluminium is not normally found in domestic wiring installations because of the specialized

jointing and termination techniques needed to ensure longevity of trouble-free service.

Overhead lines

The a.c.s.r. (aluminium conductor steel reinforced) overhead line conductors are used worldwide for power

distribution systems.

A.c.a.r. (aluminium conductor aluminium alloy wire reinforced) have increasingly been used since 1960

because of the elimination of the risk of bi-metallic corrosion and improved conductivity for a given cross-

section. A.c.a.r. catenary conductors for supporting the contact wire are also finding favour with railway

authorities for overhead electrification schemes because of their lower weight and the reduced risk of theft in

comparison with copper.

Motors

Cage rotors for induction motors often employ aluminium bars. Casings are also made from the material as

are fans used for motor cooling purposes.

Foil windings

Aluminium is the norm for the windings of capacitors from the smallest types used in lighting fittings to

large power capacitors.

Foil windings are suitable for some transformers, reactors and solenoids. Foil thicknesses range from 0.040

mm to 1.20 mm in 34 steps. A better space factor than for a wire wound copper coil is obtained, the

aluminium conductor occupying some 90% of the space as against 60% for copper wire.

Heating and cooling are aided by the better space factor and the smaller amount of insulation needed for

foil wound coils. Rapid radial heat transfer ensures an even temperature gradient.

The disadvantage of aluminium is its poorer mechanical strength, particularly from the viewpoint of


4 of 6 11/15/2012 10:27 AM

making winding end connections.

The tendency, therefore has been to turn to the use of copper foil for air insulated low voltage windings.

Aluminium foil is, however, almost exclusively used for the HV windings of cast resin insulated

transformers as it has a thermal expansion coefficient closer to that of the resin encapsulation material than

does copper which thus reduces the thermal stresses arising under load.

Constants and physical properties of very high purity aluminium

Description ValueAtomic number 13

Atomic volume 10cm3/g-atomAtomic weight 26.98Valency 3Crystal structure fccInteratomic distance (co-ordination number 12) 2.68 kXHeat of combustion 200 k cal/g-atomLatent heat of fusion 94.6 cal/gMelting point 660.2 °CBoiling point 2480 °C

Vapour pressure at 1200°C 1 × 10-2 mm HgMean specific heat (0–100°C) 0.219 cal/g°CThermal conductivity (0–100°C) 0.57 cal/cm s°C

Temperature coefficient of linear expansion (0–100°C) 23.5 × 10-6 per °CElectrical resistivity at 20°C 2.69 microhm cm

Temperature coefficient of resistance (0–100°C) 4.2 × 10-3 per °C

Electrochemical equivalent 3.348 × 10-1 g/Ah

Density at 20°C 2.6898 g/cm3

Modulus of elasticity 68.3 kN/mm2

Modulus of torsion 25.5 kN/mm2

Poisson’s ratio 0.34

Heating elements

Aluminium foil heating elements have been developed but are not widely used at present. Applications

include foil film wallpaper, curing concrete and possibly soil warming.

Heatsinks

High thermal conductivity of aluminium and ease of extruding or casting into solid or hollow shapes with

integral fins makes the material ideal for heatsinks.

Semiconductor devices and transformer tanks illustrate the wide diversity of applications in this field. Its light

weight makes it ideal for pole-mounted transformer tanks and it has the added advantage that the material

does not react with transformer oil to form a sludge.


5 of 6 11/15/2012 10:27 AM

Resource: Newnes Electrical Pocket Book – E.A. Reeves; Martin J. Heathcote

(get this book at Amazon)

Jump to original technical article at EEP - Aluminium and its Alloys used in Electrical Engineering

Category & Tags: Energy and Power, aluminium, aluminium alloys, conductivity, copper, electrical

engineering, electrical purposes, wrought aluminium

Subscribe to Monthly Download Updates

Recently published technical articles:

Application of Circuit Breakers in IT Networks

Motors for Hazardous Areas

Transformer Differential Protection Principles

Application of 4-pole Switchgear Devices

Smart and Safe Protective Shutdown with Selectivity

Transformers Are Never Silent

Short Overview of LV Cable Terminations

Industrial Applications of Brushless Servomotor

Corrosion Types Encountered With Power Cables

Share with your friends!

Copyright © 2012 EEP - Electrical Engineering Portal, All rights reserved.You're receiving this newsletter because you opted in at our website EEP forreceiving technical articles.Our mailing address is:EEP - Electrical Engineering PortalMurska 10Belgrade 11000Serbia

Add us to your address book

unsubscribe from this list | update subscription preferences


6 of 6 11/15/2012 10:27 AM

Aluminium and Its Alloy Used in Electrical Engineering

Documents

Transcript of Aluminium and Its Alloy Used in Electrical Engineering