This paper discusses some complex regimes of electric network with various interchange power. Results of modeling of power grids are presented. Questions of modeling of generators, transformers and power lines are considered. The object of this research is generalized criterion. That criterion based on various damper properties of power grids models. Study contains qualitative assessment of damper moments. Generalized criteria based on simplified mathematical models of synchronous machines. These criteria allow detecting stability range of power settings. Research contains a lot of solutions of differential equations and root values are presented graphically in order to monitor the system state. Electromechanical transients are described linearized differential equation system in different power settings.