Probabilistic Design of Transmission Line Structures

Abstract

For many years, electric transmission line structures in the U.S. have been designed in accordance with the minimum load and strength requirements given in the National Electrical Safety Code (NESC). Transmission line designers have recognized certain deficiencies in the NESC and usually specify increased design loading requirements based on conditions in local service areas. This practice has led to a lack of uniformity in design criteria for transmission line structures in the U.S. and points to the need for a uniform design approach based on probabilistic concepts. A load and resistance factor design format is recommended in which the design factors are probability‐based. The design point method for reliability analysis is reviewed and a computer program which applies this method to transmission line structures is described. A calibration example is presented which illustrates the use of this program for establishing the level of reliability in an existing structure and the corresponding design factors. It is concluded that the methodology is quite suitable for application to transmission line structures and that sufficient data are available for determining the required design factors.