  When there is a fault, the protection system automatically removes one or
more transmission lines on a fast time scale of less than one minute. The
outaged lines form a pattern in the transmission network. We extract these
patterns from utility outage data, determine some key statistics of these
patterns, and then show how to generate new patterns consistent with these
statistics. The generated patterns provide a new and easily feasible way to
model the overall effect of the protection system at the scale of a large
transmission system. This new generative modeling of protection is expected to
contribute to simulations of disturbances in large grids so that they can
better quantify the risk of blackouts. Analysis of the pattern sizes suggests
an index that describes how much outages spread in the transmission network at
the fast timescale.
