  Sustained oscillations observed in power systems can damage equipment,
degrade the power quality and increase the risks of cascading blackouts. There
are several mechanisms that can give rise to oscillations, each requiring
different countermeasure to suppress or eliminate the oscillation. This work
develops mathematical framework for analysis of sustained oscillations and
identifies statistical signatures of each mechanism, based on which a novel
oscillation diagnosis method is developed via real-time processing of phasor
measurement units (PMUs) data. Case studies show that the proposed method can
accurately identify the exact mechanism for sustained oscillation, and
meanwhile provide insightful information to locate the oscillation sources.
