  This paper describes an adaptive method to reduce a nonlinear power system
model for fast and accurate transient stability simulation. It presents an
approach to analyze and rank participation factors of each system state
variable into dominant system modes excited by a disturbance so as to determine
which regions or generators can be reduced without impacting the accuracy of
simulation for a study area. In this approach, the generator models located in
an external area with large participation factors are nonlinearly reduced and
the rest of the generators will be linearized. The simulation results confirm
that the assessment of the level of interaction between generators and system
modes by participation factors is effective in enhancing the accuracy and speed
of power system models. The proposed method is applied to the Northeastern
Power Coordinating Council region system with 48-machine, 140-bus power system
model and the results are compared with two cases including fully linearized
model reduction and model reduction using the rotor angle deviation criteria.
