A model for circuit unavailability

A model for the distributions of total unavailability during a given time interval and the number of unavailability events during a given time interval for a circuit is derived. The model can be used to determine the probability that circuit unavailability objectives will be met. Two applications of the model are illustrated. To apply the model in specific contexts, it is required to describe the unavailability characteristics of each circuit component by specifying its mean time to failure and the mean and variance of its repair time distribution. Although the model was derived assuming exponentially distributed interfailure times and lognormally distributed repair times, it would be a straightforward modification to repeat the derivation with other classes of distributions