The Effects of Scheduled Outages in Transmission System Reliability Evaluation

For several components in the power transmission system, the probability distributions of the scheduled outage durations were found to be significantly different from the conventionally assumed exponential, Weibull, or log-normal distributions. Based on statistical data, a unique distribution was obtained for these durations. New equations were derived for the frequency and mean duration of the system failures due to coincident forced and scheduled outages. Computations for a sample system show that the application of a Markov model with the implied assumption of exponentially distributed scheduled down times may lead to significant errors in the system reliability indices.