Aluminium-conductor steel-reinforced cable

Aluminium conductor steel-reinforced cable (ACSR) is a type of high-capacity, high-strength stranded conductor typically used in overhead power lines. The outer strands are high-purity aluminium, chosen for its excellent conductivity, low weight and low cost. The center strand is steel for additional strength to help support the weight of the conductor. Steel is higher strength than aluminium which allows for increased mechanical tension to be applied on the conductor. Steel also has lower elastic and inelastic deformation (permanent elongation) due to mechanical loading (e.g. wind and ice) as well as a lower coefficient of thermal expansion under current loading. These properties allow ACSR to sag significantly less than all-aluminium conductors. Per the International Electrotechnical Commission (IEC) and The CSA Group (formerly the Canadian Standards Association or CSA) naming convention, ACSR is designated A1/S1A.

The aluminium alloy and temper used for the outer strands in the United States and Canada is normally 1350-H19 and elsewhere is 1370-H19, each with 99.5+% aluminium content. The temper of the aluminium is defined by the aluminium version’s suffix, which in the case of H19 is extra hard. To extend the service life of the steel strands used for the conductor core they are normally galvanized, or coated with another material to prevent corrosion. The diameters of the strands used for both the aluminum and steel strands vary for different ACSR conductors.

ACSR cable still depends on the tensile strength of the aluminium; it is only reinforced by the steel. Because of this, its continuous operating temperature is limited to 75 °C (167 °F), the temperature at which aluminium begins to anneal and soften over time. Cable which relies entirely on the steel for strength, and so can be used at temperatures up to 250 °C (480 °F), is called aluminium-conductor steel-supported (ACSS).

The standard steel core used for ACSR is galvanized steel, but zinc-5% aluminium mischmetal alloy coated steel (sometimes called by the trade-names Bezinal or Galfan) and aluminium clad steel (sometimes called by the trade-name Alumoweld) are also available. Higher strength steel may also be used.

In the United States the most commonly used steel is designated GA2 for galvanized steel (G) with class A zinc coating thickness (A) and regular strength (2). Class C zinc coatings are thicker than class A and provide increased corrosion protection at the expense of reduced tensile strength. A regular strength galvanized steel core with Class C coating thickness would be designated GC2. Higher strength grades of steel are designated high-strength (3), extra-high-strength (4), and ultra-high-strength (5). An ultra-high-strength galvanized steel core with class A coating thickness would be designated GA5. The use of higher strength steel cores increases the tensile strength of the conductor allowing for higher tensions which results in lower sag.

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