  With the growing number of severe system disturbances and blackouts around
the world, controlled system separation is becoming an increasingly important
system integrity protection scheme (SIPS) to save the electric power system
from a complete or partial disintegration. A successful controlled splitting
approach should at least tackle the following two well-known and interrelated
problems: "when to split?" and "where to split?". Multiple previous
publications consider these problems separately, and even those pursuing a
combined approach propose solutions with limited applicability. In this paper,
we are proposing a novel PMU-based detector of loss of synchronism that
utilizes generator rotor angles and speeds to promptly detect rotor angle
instabilities over a wide area. Moreover, we are showing how our loss of
synchronism detection principle can be coupled with the known controlled
splitting techniques to form an integrated defense scheme against unintentional
loss of synchronism. The performance of this wide-area SIPS is demonstrated on
the IEEE 39-bus test power system for various types of unstable conditions.
