Prediction of Overhead Sag Using Cigre Elastic and Plastic Analytical Models and their Validation by Experimental Measurement on Overhead Line

Thermal Engineering

Over 80% of existing overhead transmission lines have been strung using Aluminum Steel Reinforced (ACSR) type conductors, which are used for voltage ratings upto 1200 kV. An important parameter characterizing the overhead lines is the conductor sag as it determines the safe electrical clearances mandated as per various codes & specifications. Therefore, it is important that accurate models for prediction of sag of overhead conductors be available as a function of conductor temperature. In light of this, CIGRE has developed two linear and one non-linear models for predicting the conductor sag. The two linear models include the “Linear Elastic (LE)” and the “Simplified Plastic Elongation (SPE)” models. In both these models, the elastic modulus and coefficient of thermal elongation are computed for the complete conductor using appropriate methodologies and values of individual elastic modulus and coefficient of thermal expansion of steel core and surrounding Aluminium are not considered separately. In the third “Experimental Plastic Elongation (EPE)” model, the behavior of the steel core and Aluminium sheath are modeled separately by actual experimental measurements (for computing the elastic moduli) and computation (for coefficient of thermal expansion). Further, in this model the stress strain behavior is represented by a polynomial type equation. The central objective of the present work is to undertake experimental measurements of conductor sag as a function of temperature of an actual overhead line in the state of Gujarat and validation of the measurements with “linear elastic” and “linear plastic” sag prediction models of CIGRE

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