Impacts of electromechanical oscillations on the operation of the Itaipu 50Hz interconnected power system

Argentina was completed, enabling energy exchange between the two countries and connecting the Itaipu 50Hz generators to the Argentine generators.

This interconnection was only made possible after addressing potential risks associated with interconnected operation, such as collapses due to the shutdown of simple transmission elements (N-1), potential uneven distribution of generation between generators resulting from different adjustments to control parameters, and uncontrollable power oscillations (unstable, with negative damping).

These risks were mitigated by putting into service the Itaipu 50Hz power system stabilizers [12], and by designing, testing, and implementing a wide-area monitoring, protection, and control system based on synchronized phasor measurements (WAMPAC – Wide Area Monitoring

Protection and Control), named Esquema de Controle Contra Contingências na ANDE –

ECCANDE [3]. However, although all these actions were essential to enable the stable operation of the interconnected system, episodes of electromechanical oscillations were observed over the following two years. Some of these episodes were related to the system's condition, others to the exhaustion of control capacity, and others even to operational actions by real-time teams.

In the context where large disturbances as the 28 April 2025 Iberian Peninsula blackout, strongly motivate the power system engineers’ community to cooperate to enhance its capabilities to share the experience in identification, research, and actions to mitigate power system oscillations, this article describes the situations experienced, seeking to illustrate the challenges existing in the operation of electrical systems associated with the oscillatory nature of power systems, their potential origins, implications, aspects of their treatment, risk to realtime operation, operational uncertainties, impacts of their lack of containment, actions for a posteriori treatment, and restoration actions.

In addition, contemporary technologies that can assist real-time teams in identifying and treating risk conditions in marginal situations during real-time operation are cited, to promote discussions about the scenario in which, if model uncertainties become significant, how the operation can ensure the healthy operation of electrical systems based on real-time monitoring and actions.

This article also mentions the potential of online modal analysis tools, applied to ParaguayanArgentinean Power System, which can be used to indicate the existence of power oscillations in real-time teams. Simulation tools that utilize operational data to identify operational limits in relation to electromechanical oscillations and recommend redispatch actions for each case are also mentioned.

These aspects are components of the proposed work, which seeks to present practical cases where electromechanical oscillations have affected the operation of the electrical system in question and to discuss potential tools and their feasibility in assisting operations teams in realtime.