  Knowledge of power grid's topology during cascading failure is an essential
element of centralized blackout prevention control, given that multiple islands
are typically formed, as a cascade progresses. Moreover, academic research on
interdependency between cyber and physical layers of the grid indicate that
power failure during a cascade may lead to outages in communication networks,
which progressively reduce the observable areas. These challenge the current
literature on line outage detection, which assumes that the grid remains as a
single connected component. We propose a new approach to eliminate that
assumption. Following an islanding event, first the buses forming that
connected components are identified and then further line outages within the
individual islands are detected. In addition to the power system measurements,
observable breaker statuses are integrated as constraints in our topology
identification algorithm. The impact of error propagation on the estimation
process as reliance on previous estimates keeps growing during cascade is also
studied. Finally, the estimated admittance matrix is used in preventive control
of cascading failure, creating a closed-loop system. The impact of such an
interlinked estimation and control on that total load served is studied for the
first time. Simulations in IEEE-118 bus system and 2,383-bus Polish network
demonstrate the effectiveness of our approach.
