Failure Probabilities of Existing Overhead Shield Wires

The objective of this paper is to introduce analytical models for accurate prediction of failure probabilities of existing shield wires and to recommend a time window for wire replacement at an acceptable failure threshold. Ductile and strength tests results and failures records of shield wires were examined to determine the trend of wires deteriorations as they age. Since most of failures occurred due to ice accretion during winter storms and wire deteriorations due to corrosion; an ice accretion model and corrosion models were used to predicts wire tensions and wire deteriorations during service life. To calculate the probability of failures, the strength and cross section area were assumed to be random variables modeled using normal distributions. The wire tensions due to ice accretions were calculated from the last 50 years of recorded winter storms. Anderson-Darling goodness of fit test was used to determine the best statistical model to fit the maximum annual wire tensions. The Gumbel distribution passes the test and was found to give stable results over wide range of tested conditions. Limit state function was developed and a computer program was written to determine the failure probabilities of shield wires using Rackwitz-Fiessler algorithm.