  The modeling of cascading failure in power systems is difficult because of
the many different mechanisms involved; no single model captures all of these
mechanisms. Understanding the relative importance of these different mechanisms
is an important step in choosing which mechanisms need to be modeled for
particular types of cascading failure analysis. This work presents a dynamic
simulation model of both power networks and protection systems, which can
simulate a wider variety of cascading outage mechanisms, relative to existing
quasi-steady state (QSS) models. The model allows one to test the impact of
different load models and protections on cascading outage sizes. This paper
describes each module of the developed dynamic model and demonstrates how
different mechanisms interact. In order to test the model we simulated a batch
of randomly selected $N-2$ contingencies for several different static load
configurations, and found that the distribution of blackout sizes and event
lengths from the proposed dynamic simulator correlates well with historical
trends. The results also show that load models have significant impacts on the
cascading risks. This dynamic model was also compared against a QSS model based
on the dc power flow approximations; we find that the two models largely agree,
but produce substantially different results for later stages of cascading.
