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The Evolution / Revolution of Overhead Conductors… and why it matters

By Randy Hurst

Brief Background:

In the early 1900's Aluminum Conductor Steel Reinforced (ACSR) conductor was developed to replace copper wires, due to the war effort when copper was needed for munitions. In the 1970's growing demand for electricity inspired the development of higher capacity Aluminum Conductor Steel Reinforced (ACSS) conductor. The ACSS conductor became known as the first "High-Temperature, Low-Sag" (HTLS) conductor. The design used the same steel core as ACSR (with improved galvanized coatings) and fully annealed aluminum so it could operate at higher temperatures and allow the delivery of more electric energy. While fully annealed aluminum is slightly more conductive than non-annealed aluminum, it is somewhat weaker, so overall conductor strength was slightly decreased. In the 1990's a number of conductor manufacturers began using higher strength steel to make up the difference. Comparative data can be found in the chart below.

Something New:

In the early 2000's, a handful of manufacturers introduced composite core conductors such as Aluminum Conductor Composite Reinforced (ACCR)1 and Aluminum Conductor Composite Core (ACCC)2. The ACCR conductor replaced the steel core wires with aluminum wires reinforced with ceramic fibers. The improved conductivity of the core compared to steel and ability to operate at higher temperatures due to the utilization of anneal-resistant aluminum-zirconium alloy, enabled the ACCR conductor to carry twice the twice the current of ACSR conductors, with decreased thermal sag.
While ACSS conductors (and other HTLS conductors shown in the adjacent sag graph) can also carry twice the current of ACSR conductors, the coefficient of thermal expansion of various conductor cores differs and, in some cases, could cause the conductor to sag below safe clearances at higher temperatures depending upon structure height, initial tension and so forth.

Read full article in the Overhead and Underground T&D Special Edition 2021

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