Generalized equal-area criterion: a method for on-line transient stability analysis

The method of generalized equal-area criterion (GEAC) for transient stability analysis of power systems and its recent generalization to cover a wider range of faults are explained. The method is based on an exact mathematical transformation of the time-invariant dynamical equations of an n-machine system into an equivalent single-machine-infinite-bus (SMIB) system equation with time-varying parameters. Further approximations are made to assign appropriate constant values to the SMIB parameters, thus enabling the use of a modified version of the well-known equal-area criterion. An approximate stability index is then defined to yield the degree of stability/instability. GEAC and time simulation results showed excellent agreement in the majority of cases; in the worst case the difference did not exceed 7%. Some tests results are presented. Potential applications of the GEAC method for online transient stability assessment are discussed