In this paper, electrome-chanical wave oscillation propagation is modeled, and its impact on different power system protective relays, such as overcurrent, distance, and out-of-step relays is studied. They can cause adverse effect on power system protective relays. Specially designed relaying devices are often employed to detect and isolate harmful SSO. Abstract: Power swings and loss of synchronism are complex events which occur during severe system disturbances. Many protection functions may respond during such events, but not always in an intended, expected, or coordinated manner. Most microprocessor relays track system frequency to calculate the. Role of Measurement-based Tools to Mitigate Sub - synchronous Oscillations Conclusions Overview Introductions 3 Introduction • Sub-synchronous oscillations (SSOs) refer to the oscillations that occur at frequencies below the system's fundamental frequency (50/60 Hz). • SSOs do not involve coherent.