Power System Response to a Large Disturbance: Energy Associated with System Separation

Formulating the power system equations with respect to the system's inertial center, it is shown that a large disturbance tends to pull each generator from the rest of the generators, forming a two-machine equivalent. The energy associated with this equivalent is related to the energy function for individual machines, previously developed by the authors. Parameters of the two-machine equivalent are derived for any generator versus the rest of the system. Based on the two-machine equivalent concept, transient stability assessment of a multimachine power system is made, and a criterion for identifying the machines likely to separate from the system (by loss of synchronism) and the energy associated with this separation is developed. The criterion is applied successfully to a 17-generator power system.