Generator Small-Signal Stability Test Procedure (IEEE 112-2017 Appendix B)

Small-signal stability refers to a power system’s ability to maintain synchronism following infinitesimal disturbances, such as minor load or generation fluctuations. The IEEE 112-2017 Appendix B procedure provides a field-test framework to empirically identify key linearized generator model parameters—particularly those associated with the rotor swing equation and excitation system interactions—that are otherwise difficult to estimate accurately from nameplate data or manufacturer models. The test involves applying controlled, low-amplitude, multi-frequency perturbations (typically via temporary modulation of the automatic voltage regulator (AVR) reference or mechanical input) while measuring synchronized phasor quantities (e.g., terminal voltage, current, rotor angle, speed deviation) using high-fidelity PMUs or calibrated transducers. Data are processed using spectral analysis (e.g., FFT, Prony analysis) or time-domain system identification (e.g., subspace methods) to extract eigenvalues, damping ratios, and mode shapes of dominant electromechanical modes. Crucially, the procedure mandates strict adherence to operating point stabilization, signal-to-noise ratio requirements (>20 dB), and coherence validation between input perturbation and output responses to ensure identifiability and repeatability. Results directly inform the tuning and validation of Type Synchronous Machine (GENROU, GENSAL, etc.) and Excitation System (IEEE ST1A, EXAC1, etc.) models in industry-standard simulation tools like PSS/E, PSSE, or PSCAD.