ComEd developed a methodology for evaluating the reliability of transm
ission system protection schemes in 1995. Two approaches were develope
d; one focused on component reliability data, and the other on compone
nt operating history. The second approach has been put into practice.
Review of disturbances identified protection schemes and lines that ar
e less reliable than others, thus permitting a focused program of main
tenance and replacements. The reliability method is described, along w
ith sample data and results.