Finding a Zipf distribution and cascading propagation metric in utility line outage data

Observed transmission line outage data is grouped into successive generations of events. The empirical distribution of the number of generations in the cascades follows a Zipf distribution that implies the increasing propagation as cascades progress. The slope of the Zipf distribution gives a System Event Propagation Slope Index (SEPSI). This new metric quantifies the cascade propagation, varies as expected, and determines the probabilities of small, medium, and large cascades.