Soft reliability assessment of existing transmission lines

This paper introduces a method for “soft” reliability assessment of existing transmission lines. The method relates the design safety factors of existing lines to the failure probability in the presence of structural deterioration. Cognitive uncertainty inherent in the visual inspection and assessment of existing lines is included using a fuzzy strength condition rating function. This fuzzy strength function is obtained by combining the condition ratings of the major components of the line using a fuzzy weighted average technique. In this method the probability of failure is derived as a function of the cumulative distribution of the standardized safety margin and expanded in terms of the cumulants using Edgeworth´s series and the Tchebycheff-Hermite polynomials. A numerical example is presented