  In the event of large disturbances, the practice of controlled islanding is
used as a last resort to prevent cascading outages. The application of the
strategy at the right time is crucial to maintaining system security. A
controlled islanding strategy may be deployed efficiently at the right time by
predicting the time of uncontrolled system splitting. The purpose of this study
is to predict the appropriate islanding time to prevent catastrophic blackout
and uncontrolled islanding based on existing relationships between coherent
generator groups. A new instability index is derived from the proximity of
inter-area oscillations to power splitting indices. Power splitting indices are
derived using synchronization coefficients, which recognize the conditions in
the system that warrant controlled islanding. The critical values of indices
are calculated in offline mode using simulation data from IEEE 39-Buses, and
their online performance is evaluated following a controlled islanding
strategy. Through the introduction of these indices, system degradation can be
effectively evaluated, and blackouts can be predicted early and prevented by
controlled islanding at the right time.
