  This paper develops a comprehensive framework of Area Angle Monitoring (AAM)
to monitor the stress of bulk power transfer across an area of a power
transmission system in real-time. Area angle is calculated from synchrophasor
measurements to provide alert to system operators if the area angle exceeds
pre-defined thresholds. This paper proposes general methods to identify these
warning and emergency thresholds, and tests a mitigation strategy to relieve
the area stress when the area angle exceeds the threshold. In order to handle
the limited coverage of synchrophasor measurements, this paper proposes methods
to estimate phase angles for boundary buses without synchrophasor measurements,
which extends the application of AAM. AAM is verified for a power transmission
area in the Western Electricity Coordinating Council system with both simulated
data and synchrophasor measurements recorded from real events. A utility
deployment to test the framework for monitoring area angle with live-stream and
recorded synchrophasor data is described.
