Abstract
Blackouts in the power system are rare events that can have large consequences for society. Successful preparation and prevention of such events calls for models capable of predicting their occurrence. The simultaneous outage of multiple components is of special interest in an N-l secure transmission grid. Spatio-temporal correlation in probability of failure for components can cause blackouts to occur more often than anticipated. This paper demonstrates a new method of calculating time-series of component unavailability due to external threats based on historical data. The time-series of unavailability can be used to predict the expected occurrence of contingencies throughout the year. A test case is presented where an hourly time series of wind dependent failure probabilities and historical outage durations of transmission lines are combined to illustrate the proposed method. The results show that the simultaneous unavailability of multiple transmission lines may be significantly larger than estimated using traditional reliability analysis.