  Once critical substations are compromised, attack agents can coordinate among
their peers to plot for maximizing disruption using local control devices. For
defenders, it is critical to enumerate and identify all digital relays to
determine the systemic risks. Any combination of disruptive switching via the
compromised relays can result in misoperation or immediate effect to the
system. The resulting consequence of these attack's initial events would
possibly incur cascading failure to a grid. This paper quantifies the
criticality of substation protective relays with the combination of the outage
level and its corresponding severity risk index. The proposed hypothesized
outages are based on the type of protective relaying, bus configuration of a
substation, and commonly implemented relaying schemes, such as bus
differential, directional overcurrent, and distance relays, are studied. This
preliminary work also provides three approaches of determination in
probabilities for sensitivity analysis. The proposed risk indices are evaluated
using IEEE test systems.
