Use of Transmission Line Outage History for Probabilistic Transmission Risk Assessment

Probabilistic transmission planning and risk assessment has been used for several decades. One key component is the use of historical outage data to compute failure rates of individual transmission lines which are used in the modeling of a transmission system. The most common approach used to calculate transmission line outage probabilities is the assumption of a Poisson distribution of outages in a unit time period, with an Exponential distribution of time between failures. This paper provides a discussion of some factors which influence reliability. It compares two commonly used statistical failure distributions, the Exponential and Weibull applied to a large sample of outage history from individual transmission circuits of US systems.