A power system oscillation detection device is provided for use in an electric power system. A plurality of sample signals are acquired from the electrical power system via a plurality of intelligent electronic devices (IEDs) in communication with the power system. The power system oscillation detection device includes a real-time modal analysis module, a real-time mode identification module, and real-time decision and control logic. The real-time modal analysis module calculates modes of at least one of the signals, each mode including mode information. The real-time mode identification module together with the real-time decision and control logic determines, from the mode information, whether there is an undesirable oscillation in the electric power system and activates a remedial action.