Aluminium-conductor steel-reinforced cable
Steel is of higher strength than aluminium which allows for increased mechanical tension to be applied on the conductor.
To extend the service life of the steel strands used for the conductor core they are normally galvanized, or coated with zinc to prevent corrosion.
Aluminium-clad steel offers increased corrosion protection and conductivity at the expense of reduced tensile strength.
The present day CSA standards for overhead electrical conductor do not yet officially recognize the ASTM equivalent GA4 or GA5 grades.
The present day CSA standards do not yet officially recognize the ASTM "M" family of zinc alloy coating material.
Canadian utilities are using conductors built with the higher strength steels with the "M" zinc alloy coating.
Some South American countries specify left-hand lay for the outer conductor layer on their ACSR, so those are wound differently than those used in the USA.
ACSR conductors are available in numerous specific sizes, with single or multiple center steel wires and generally larger quantities of aluminium strands.
Manufacturers of ACSR typically provide ampacity tables for a defined set of assumptions.
The skin effect decreases the cross sectional area in which the current travels through the conductor as AC frequency increases.
The skin effect benefits the design, as it causes the current to be concentrated towards the low-resistivity aluminum on the outside of the conductor.
To illustrate the impact of the skin effect, the American Society for Testing and Materials (ASTM) standard includes the conductivity of the steel core when calculating the DC and AC resistance of the conductor, but the IEC and CSA Group standards do not.
Hysteresis losses in ACSR are undesirable and can be minimized by using an even number of aluminium layers in the conductor.
Due to the cancelling effect of the magnetic field from the opposing lay (right-hand and left-hand) conductors for two aluminium layers there is significantly less hysteresis loss in the steel core than there would be for one or three aluminium layers where the magnetic field does not cancel out.
The hysteresis effect is negligible on ACSR conductors with even numbers of aluminium layers and so it is not considered in these cases.
For ACSR conductors with an odd number of aluminium layers however, a magnetization factor is used to accurately calculate the AC resistance.
All standard ACSR conductors smaller than Partridge (135.2 mm2 {266.8 kcmil} 26/7 Aluminium/Steel) have only one layer due to their small diameters so the hysteresis losses cannot be avoided.
Variations of standard (sometimes called traditional or conventional) ACSR are used in some cases due to the special properties they offer which provide sufficient advantage to justify their added expense.
Special conductors may be more economic, offer increased reliability, or provide a unique solution to an otherwise difficult, of impossible, design problem.
Also in the 1980s, Bonneville Power Administration (BPA) introduced TW designs where the size of the steel core was increased to maintain the same Aluminium/Steel ratio.
It is a concentric-lay stranded, self-damping conductor designed to control wind induced (Aeolian-type) vibration in overhead transmission lines by internal damping.
The use of trapezoidal strands also results in reduced conductor diameter for a given AC resistance per mile.
Annealing the aluminium strands reduces the composite conductor strength, but after installation, permanent elongation of the aluminium strands results in a much larger percentage of the conductor tension being carried in the steel core than is true for standard ACSR.
The major advantages of ACSS are: The major disadvantages of ACSS are: Twisted pair (TP) conductor (sometimes called by the trade-names T-2 or VR) has the two sub-conductors twisted (usually with a left-hand lay) about one another generally with a lay length of approximately three meters (nine feet).
The temperature of the splice is kept lower by having a larger cross-sectional area and thus less electrical resistance than the conductor.
As the conductor ages the color becomes dull gray due to the oxidation reaction of the aluminium strands.
In high pollution environments, the color may turn almost black after many years of exposure to the elements and chemicals.
These types of coatings have the ability to potentially increase the current rating of the ACSR conductor.
For the same amount of amperage, the temperature of the same conductor will be lower due to the better heat dissipation of the higher emissivity coating.
