Transmission system protection: a reliability study

ComEd developed a methodology for evaluating the reliability of transmission system protection schemes in 1995. Two approaches were developed: one focused on component reliability data; and the other on component operating history. The second approach has been put into practice. A review of transmission system disturbances identified protection schemes and lines that are less reliable than others, thus permitting a focused program of maintenance and replacements. The reliability method is described, along with sample data and results.