This program investigates the system dynamic responses and stability limits of a power system before, during, and after system changes or disturbances. It models the dynamic characteristics of a power system, implements the user-defined events and actions, solves the system network equation and machine differential equations interactively to find out system and machine responses in time domain. These responses can be used to determine the system transient behavior, make stability assessment, set protective device settings, and apply the necessary remedy or enhancement to improve the system stability.