Bare overhead conductors of the Aluminium Conductor Steel Reinforced (ACSR) type, conforming to AS 3607, are widely used in New Zealand. Many of these conductors have been in service for 40 to 50 years in comparison with an anticipated life span of 50 to 75 years. Current replacement strategies are based on the removal and analysis of representative samples of the lines. The samples are selected by experienced lines maintenance staff to give a cross section of environmental conditions, and the laboratory analysis is designed to give a prediction of the range of remaining life for the lines. The life prediction is based on qualitative and quantitative models for assessing the extent of deterioration of the conductor and for estimating the rate of damage accumulation at the time of removal of the samples. The rate of damage accumulation is compared to a pre-determined allowed level of damage accumulation to determine the remaining time to reach end of life. This paper outlines the methodologies used in the development of the models and the contribution of different degradation processes to the damage accumulation kinetics.
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