Energy-Based Reinterpretation of Equal Area Criterion for Generator Instability Assessment via Local Rotational Speed and Voltage Frequency Measurements

To apply the physical concept of stability embedded in the equal area criterion (EAC) to large-scale power systems, this study proposes a measurement-based reinterpretation of the EAC from an energy perspective in the time domain. Based on this approach, a system for assessing generator instability is developed. The study reinterprets the primary state variables in the angle domain, which define the accelerating and decelerating areas in the EAC, by converting them into measurable quantities in the time domain, enabling direct measurement of accelerating and decelerating energy. The proposed method determines the accumulated accelerating energy and the decelerating energy released to the power system after fault clearance by measuring the generator's terminal voltage and mechanical rotational speed. An algorithm for generator instability assessment in large-scale power systems using this measurement-based EAC is implemented, taking into account practical aspects for constructing an instability assessment system. The effectiveness of this energy-based reinterpretation is validated in multi-machine power systems through simulations on the IEEE 39-bus and IEEE 118-bus systems modeled in MATLAB/Simulink to assess its practical applicability. Time-domain simulations of various fault scenarios are conducted to analyze the performance of the proposed algorithm in assessing instability. Furthermore, a comparative analysis with previous studies evaluates the performance and practicality of the proposed method for application in multi-machine power systems.