It was early learned that the electrical resistivity of aluminum is markedly increased by impurities; electrical conductor grade (EC) metal, containing approximately 99.5% Al, was established for most conductor uses. At present, aluminum producers offer EC with a minimum of 99.6% Al and conductivity of 62.0% IACS on a volume basis, although ASTM specifications permit 99.45% Al minimum and 61.0% conductivity. EC wire has a tensile strength range of (83-200 MPa), depending on temper.
Transmission Conductor
All-aluminum stranded conductors, although having the advantage of light weight, had to be strung with large sags, because of their low yield strength compared to stranded copper.
Experiments were conducted with several alloys of aluminum, and with combinations of aluminum with other metals, to obtain higher mechanical strength combined with suitable electrical characteristics.
Aluminized and aluminum-clad core wires recently have been employed to reinforce aluminum conductors. For many years, it was believed that a superior acsr could be produced if the zinc coating of the steel wire were replaced with aluminum, in 1957, hot-dipped aluminum-coated (aluminized) steel wire was produced as an acceptable core wire for acsr. The excellent resistance to atmospheric corrosion of aluminized wire resulted in its acceptance for service in coastal and severely corrosive industrial atmospheres. Aluminized steel core wire is covered by ASTM B 341.
Another method of covering steel wire incorporates an aluminum cladding that is about 10% of the composite diameter, representing approximately 25% of the total cross section, bonded to a high-strength steel core. It is utilized as a highly corrosion-resistant core for acsr, and as an overhead ground wire for transmission and distribution lines.
In recent years, both heat treatable alloy 6201-T81 (0.7% Si, 0.75% Mg) and non-heat-treatable 5005-H19 (0.8% Mg) have been employed as stranded aluminum conductors for transmission and distribution lines. Material selection involves comparing the estimated installed cost of these and other conductors with expected service requirements, considering current-carrying capacity, thermal overload characteristics, line electric-energy losses, and atmospheric exposure characteristics.
Distribution Conductor
The use of aluminum conductors for urban distribution has increased rapidly since World War II, stimulated by the change in the aluminum-copper price relationship. Aluminum has over twice the conductivity of copper on a weight basis, and aluminum conductor is used for virtually all overhead subtransmission and distribution lines.
For many years, predating even the introduction of acsr, weatherproof distribution conductors were covered with cotton braid and impregnated with asphalt. After World War II, the cotton braided coverings were displaced by neoprene and, later, by polyethylene. In addition to excellent weathering characteristics, neoprene and (especially) polyethylene have high electrical insulating properties.
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Utilizing these properties, multiplex cable, a new secondary and service-drop multiple conductor, was developed. These cables are either duplex, triplex, or quadruplex, consisting of one, two or three insulated conductors wrapped around a bare aluminum or acsr neutral. The bare neutral act as the messenger, supporting the entire cable when strung is an aerial line.
The aluminum alloys employed for conductor accessories, including drawn, extruded, and cast products, vary with the specific application and with the preferences of the individual manufacturer. However, the alloys are generally selected to provide suitable conductivity, high resistance to atmospheric corrosion, galvanic compatibility with conductor grade (EC) aluminum, and satisfactory mechanical properties. Typical suitable alloys are 6061-TG for wrought forms and 356-T6 for castings.
Aluminum clamps, frequently 356-T6, are preferred to other metals for supporting stranded aluminum conductors. They eliminate heating and power waste from hysteresis losses that occur in ferrous materials. Because the use of dissimilar metals is avoided, the possibility of galvanic corrosion is minimized. The body and keeper components of suspension clamps and dead-end clamps are aluminum castings or forgings.
Aluminum armor rods are spiraled around the conductors at points of support. They provide some vibration damping and reinforce the conductors against the effect of vibration. Two general types of armor rods are available. One is straight rods that are applied by winding them on the conductor with special wrenches. The other is pre-formed during manufacture, and usually can be worked into place on the conductor by hand. The pre-formed type is generally easier to install; however, the straight rods applied with wrenches have considerably better damping characteristics.
GLOSSARY
Acceptor impurity An impurity added to a semiconductor substance with one valency electron less per atom than the semiconductor.
Cable Either a stranded conductor (single-conductor cable) or a combination of conductors insulated from one another (multiple-conductor cable). Small cable sizes are called stranded wire or cords.
Circular mil The area of a circle having a diameter of 1 mil. The standard unit of measurement of wire cross-sectional area. One circular mil equals.7854 square mils.
Circular-mil-foot A unit of volume of a conductor having a cross-sectional area of 1 circular mil and a length of 1 foot.
Coercive force The magnetizing force needed to demagnetize completely a piece of magnetized material.
Conductance The ability of a material to conduct or carry an electric current. It is the reciprocal of the resistance of the material. The symbol for conductance is G, and the property is measured in reciprocal ohms (W-1).
Conduction band The band of quantized energy levels (higher than the energy levels of the valency band) into which an electron can be raised by thermal vibration of a crystalline lattice.
Conductivity The disposition (a property) of a conducting material by which it conducts electricity. It is the reciprocal of the resistivity, i.e. conductivity= 1/resistivity. The symbol for conductivity is (the Greek letter kappa).
Conductor A body made of a material which readily allows an electric current to flow through it.
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Donor impurity An impurity added to a semiconductor substance with one valency electron more per atom than the semiconductor.
Doping The process of adding a very small quantity of an impurity to a semiconductor to obtain a particular electrical characteristic.
Ductile Easily drawn out-as to form filaments or wires.
Electric flux density The amount of electric flux passing through one square metre of material.
Electric flux A measure of the electrostatic field between two charged plates; measured in coulombs.
Electromagnet A current-carrying coil with an iron core.
Electromagnetic induction The production of an e.m.f. in a circuit, arising from a change in the amount of magnetic flux linking the circuit.
Electron A negative charge carrier, and a constituent part of every atom.
Extrinsic semiconductor A type of semiconductor in which the electrical properties depend upon the presence of an impurity in the basic semiconductor material.
Ferromagnetic material A material which can be strongly magnetized in the direction of an applied magnetizing force.
Forbidden band/zone The zone between the valency and conduction bands. It represents energy levels that cannot be occupied by electrons.
Free electron An electron in a crystal which is free to move under the influence of an electric field.
Hall coefficient The potential difference developed by the Hall effect is proportional to the flux density of the magnetic field, to the current density, and to the width of the conductor.
Hall effect The development of a potential difference between the sides of a conductor (through which an electric current flows) when a magnetic field is applied to the conductor.
Hard magnetic material A material which retains much of its magnetism after the magnetizing force has been removed.
Hole When an electron is raised from the valency band to the conduction band of energy levels, the absence of the electron creates a hole in the valency structure of a crystalline solid.
Insulation The prevention of the passage of an electric current, or heat, by the use of non-conducting material.
Insulator An object made of material which is a nonconductor; the term is particularly used of any object or device, which prevents a flow of electric current.
Intrinsic semiconductor A type of semiconductor in which the electrical properties are characteristic of the pure substance.
Magnetic circuit An interconnected set of ferromagnetic branches in which a magnetic flux is established.
Magnetic domain A group of atoms in a ferromagnetic material which form a localized magnetic field system.
Magnetic field intensity The m.m.f. per unit length of a magnetic circuit; symbol H; measured in ampere-turns per metre or amperes per metre.
Magnetic flux A measure of the magnetic field produced by a permanent magnet or electromagnet, symbol ; measured in webers (Wb).
Magnetic flux density The amount of magnetic flux passing through an area of 1 m2; symbol B, measured in tesla (T).
Magnetic saturation The state of a ferromagnetic material when all its domains are aligned in one direction.
Magnetizing force An alternative name for magnetic field intensity.
Magnetomotive force The force which produces a magnetic flux;
(m.m.f.) symbol F, measured in ampere-turns or amperes.
Majority carriers The type of current carrier (electrons or holes) that carries most of the electric current in a semiconductor.
Mil-foot A unit of measurement for conductors. (Diameter of 1 mil, 1 foot in length.)
Minority carriers The carriers that are not majority carriers in a semiconductor.
n-type semiconductor A type of semiconductor in which most of the current is carried by electrons (rather than holes).
Permanent magnet A piece of ferromagnetic material which has been permanently magnetized.
Permeability The ratio of the magnetic flux density (B) in a material to the magnetic field intensity (H) needed to produce it. Also known as the absolute permeability of the material. Symbol , measured in henrys per metre (H/m).
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p-type semiconductor A type of semiconductor in which most of the current is carried by holes (rather than electrons).
Resistivity The disposition (a property) of a conducting material by which it resists the flow of electric current. It is defined as the resistance of a metre cube at 0C, and is a constant for a given material at a stated temperature. The symbol for resistivity is r.
Semiconductor junction A junction between an n-type semiconductor and a p-type semiconductor, a diode has one p-n junction, and a junction transistor has two p-n junctions.
Semiconductor A substance with conducting properties intermediate between those of a conductor and an insulator.
Soft magnetic material A magnetic material which easily loses its magnetism; its coercive force is low
Square mil The area of a square, the sides of which are each equal to 1 mil. One square mil is equal to 1.2732 circular mils.
Stranded conductor A conductor composed of a group of wires. The wires in a stranded conductor are usually twisted together and not insulated from each other.
Superconductivity The resistivity of all metals and alloys decreases as the temperature is lowered, and tends to become zero at the absolute zero of temperature.
Superconductor A metal, alloy, or object, that exhibits superconductivity.
Temperature coefficient The amount of increase in the resistance of a 1-
of resistance ohm sample of a conductor per each degree of rise in temperature above 0C.
Unit size The standards adopted to make comparisons between things of like value (for example, the unit size for conductors is the mil-foot).
Valency band The band of quantized energy levels which can be occupied by an electron when in a valency orbital in a crystalline solid.
THE LIST OF CHEMICAL ELEMENTS*
Ag argentum [a:'dʒentəm] = silver ['sılvə]
Al aluminium [ælju'mınıəm]
Ar argon [':gɔn]
As arsenic ['a:s(ə)nık]
Au aurum ['ɔ:rəm] = gold [gould]
boron ['bɔ:rɔn]
Ba barium ['be(ə)rıəm]
Be beryllium [bə'rılıəm]
Bi bismuth ['bızməθ]
Br bromine ['broumi:n]
carbon ['ka:bən]
Ca calcium ['kælsıəm]
cerium ['sı(ə)rıəm]
Cd cadmium ['kædmıəm]
Cl chlorine ['klɔ:ri:n]
Co cobalt ['koubɔ:lt]
Cr chromium ['kroumıəm]
Cs caesium ['si:zıəm]
Cu copper ['kɔpə]
F fluorine ['flu(ə)ri:n]
Fe ferrum ['ferəm] = iron ['aıən]
Ga gallium ['gælıəm]
Ge germanium [dʒə:'meınıəm]
H hydrogen ['haıdrədʒən]
He helium ['hi:lıəm]
Hg hydrargyrum [haı'dra:dʒırəm] = mercury ['mə:kjurı]
I iodine ['aıədi:n]
Ir iridium [ı'rıdıəm]
kalium ['keılıəm] = potassium [pə'tæsıəm]
Li lithium ['lıθıəm]
Mg magnesium [mæg'ni:zıəm]
Mn manganese [mæŋgə'ni:z]
Mo molybdenum [mə'lıbdənəm]
N nitrogen ['naıtrədʒ(ə)n]
Na natrium ['neıtrıəm] = sodium ['soudıəm]
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Ne neon ['ni:ɔn]
Ni nickel ['nık(ə)l]
oxygen ['ɔksidʒ(ə)n]
P phosphorus ['fɔsf(ə)rəs]
Pb plumbum ['plΛmbəm] = lead [led]
Pt platinum ['plætınəm]
Pu plutonium [plu:'tounıəm]
Ra radium ['reıdıəm]
Rb rubidium [ru:'bıdıəm]
S sulphur ['sΛlfə]
Sb antimony ['æntımənı]
Sc scandium ['skændıəm]
Se selenium [sı'li:nıəm]
Si silicone ['sılıkoun]
Sn stannum ['stænəm] = tin [tın]
Sr strontium ['strɔntıəm]
tellurium [tə'l(j)u(ə)rıəm]
Th thorium ['θɔ:rıəm]
Ti titanium [t(a)ı'teınıəm]
U uranium [ju'reınıəm]
W wolfram ['wulfrəm] = tungsten ['tΛŋstən]
Zn zinc [zıŋk]
Zr zirconium [zə:'kounıəm]
Tapescripts
Unit I
