Effect of Aluminum Compression on ACSR Conductor Sags at High Operating Temperaturesby Parvez Rashid, P.E.,
Document Type: Proceeding Paper
Part of: Electrical Transmission in a New Age
Deregulation and restructuring are sweeping the electric utility industry in the United States. As a result, many utility engineers are analyzing, re-rating, and upgrading their most critical transmission circuits in order to maximize their usefulness while ensuring that safe clearances are maintained under all operating conditions. Recent tests have indicated that ACSR conductors, the type most frequently used on transmission lines, exhibit greater sags at high operating temperatures than the old assumptions and methods for predicting sags had indicated. The most important source of error in calculating high operating temperature sags in ACSR conductors appears to be the phenomenon of aluminum strand compression, or simply aluminum compression. This phenomenon is caused by the differences in the coefficient of thermal elongation and modulus of elasticity between the aluminum strands and steel core wires. Most sag/tension programs used today are computerized versions of graphic methods developed in the 1930s. They assume that there is no mechanical interaction between the steel core and the aluminum strands above a specified (knee point) temperature, i.e. they assume no aluminum compression. If the aluminum wires go into compression, the stress in the steel core and the conductor sag will be increased. This paper discusses the effects of conductor composition, span length, and conductor tension in the prediction of high temperature sags in ACSR conductors under the old assumption of no aluminum compression and the newer approaches involving compression in the aluminum strands.
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