Impact of electromechanical wave oscillations propagation on protection schemes

• Electromechanical oscillations occur in the system following fault, generator outage, etc.
• Propagation speed of electromechanical waves is much slower than electromagnetic ones.
• Protection devices might be affected due to propagation of electromechanical disturbances through their terminals.
• In most cases, relays’ settings can be modified to avoid mis-operations.

Major disturbances in power system can take place after power system elements such as generators, loads, or transmission lines are suddenly disconnected. Such disturbances can create so called “electromechanical wave oscillations” waves which propagate through transmission lines at much lower speed than speed of light. They can cause adverse effect on power system protective relays. In this paper, electromechanical 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. Modified protection schemes are presented for each protective device to avoid their malfunction under effects of electromechanical wave oscillations. The electromechanical model adopted in this study considers the dynamics of generator mechanical shaft as well as conversion of mechanical power to electrical. Simulations used for testing of the improved protection solutions are carried out in MATLAB considering 64-bus generator ring system and IEEE 118-bus system.