Number and propagation of line outages in cascading events in electric power transmission systems

Large blackouts typically involve the cascading outage of transmission lines. We estimate from observed utility data how transmission line outages propagate, and obtain parameters of a branching process model of the propagation. We show that the branching process model is consistent with the utility data by using it to estimate the distribution of the total number of lines outages and showing that this closely matches the distribution of the total number of line outages observed in the utility data. The branching process model and the measured propagation can then be applied to predict the distribution of total number of outages for a given number of initial failures. We study how the total number of lines outages depends on the amounts of propagation as the cascade progresses. The analysis gives a new way to quantify the effect of cascading failure from standard utility data about automatic line outages.