  In order to identify the extent to which results from topological graph
models are useful for modeling vulnerability in electricity infrastructure, we
measure the susceptibility of power networks to random failures and directed
attacks using three measures of vulnerability: characteristic path lengths,
connectivity loss and blackout sizes. The first two are purely topological
metrics. The blackout size calculation results from a model of cascading
failure in power networks. Testing the response of 40 areas within the Eastern
US power grid and a standard IEEE test case to a variety of attack/failure
vectors indicates that directed attacks result in larger failures using all
three vulnerability measures, but the attack vectors that appear to cause the
most damage depend on the measure chosen. While our topological and power grid
model results show some trends that are similar, there is only a mild
correlation between the vulnerability measures for individual simulations. We
conclude that evaluating vulnerability in power networks using purely
topological metrics can be misleading.
