A Probability Method for Transmission and Distribution Outage Calculations

This paper shows how probability arithmetic can be applied to the historic failure rates of components to calculate the expected outage frequencies and durations at any point in an electric system. Calculations reveal the portions of time that a number of items will be subjected to simultaneous occurrences. In turn, these can be related to simultaneous conditions that must prevail for power to flow in series and parallel combinations of system components. These principles are demonstrated by samples that employ equipment outage rates developed for the author's company. It is possible actually to verify the method by comparing the calculations with actual experience.