ACSR

Aluminum conductor steel-reinforced cable (ACSR) is a type of high-capacity, high-strength stranded cable typically used in overhead power lines. The outer strands are high-purity aluminum, chosen for its good conductivity, low weight and low cost. The center strand is of steel for additional strength that is required to help support the weight of the cable without stretching the aluminum due to its ductility. Steel is higher strength than aluminum which allows for increased mechanical tension to be applied on the cable. This gives the cable an overall high tensile strength. 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-aluminum conductors. The higher resistance of the steel core is of no consequence to the transmission of electricity since it is located far below the skin depth where essentially no AC current flows.