Wide-Area Assessment of Aperiodic Small Signal Rotor Angle Stability in Real-Time

This paper presents the details of a new real-time stability assessment method. The method assesses a particular mechanism of stability: each generator´s capability to generate sufficient steady state electromechanical torque. The lack of sufficient steady state torque causes aperiodic increase in rotor angle and a loss of synchronism, referred to as aperiodic small signal instability. The paper provides the theoretical background of the method and an analytical assessment criterion. Furthermore, a mathematical mapping of the generators´ operating points that enables informative visualization of multiple operating points is derived in the paper. Finally, results from time-domain simulation of instability scenarios in the Nordic32 test system are presented and results used for testing the assessment method. The results illustrate the method´s capability to efficiently identify the location of the emerging problem and to quantify margins to stability boundary.