Maximize use of existing route: new conductor designs offer improved properties for increasing current-carrying capacity

摘要

Although aluminum conductor was used for overhead transmission as early as 1898, its widespread use did not occur until the 1940s, when copper was designated as a vital war material and was no longer available for use by electric utilities. To obtain the desired strength required for transmission lines, the lightweight aluminum was combined with the high tensile strength of steel in the development of aluminum conductor steel reinforced (ACSR). Today, most overhead transmission lines use this conductor construction, which consists of stranded hard-drawn aluminum wires over a stranded core of high-strength steel. On a continuous basis, ACSR usually can be operated at temperatures up to 100℃ (212°F) and, for limited time emergencies, at temperatures as high as 125℃ (257°F) without any significant change in the conductor's physical properties related to a reduction in tensile strength because of annealing of aluminum. These temperature limits constrain the thermal rating of a typical 230-kV line, strung with 795 kcmil ACSR "Drake" conductor, to about 400 MVA, corresponding to a current of 1000 A.