Studies, simulations, and tests carried out to damp electromechanical oscillations are described. The solution was to install Power System Stabilizer (PSS) in 4 generator of 118 MW each one, located in one hydraulic plant. This plant is connected to “Sistema Eléctrico Patagónico Interconectado (SEPI)” trough a double 330 kV transmission line, with its far end connected to one aluminum plant with two 160 MW series of 200 electrolytic cells each one. Studies began with whole system data base validation, included the aluminum plant dynamic load model. Modal analysis and temporal simulation of event that excite dominant electromechanical oscillation mode were done. PSS tuning parameters were found, and the reciprocal influences between PSS and turbine governor were minimized. PSS commissioning test were carried out, and the results are compared with previous studies, showing a good agreement.Este trabajo también fue presentado en la I Conferencia Internacional del Área Andina del IEEE (IEEE-ANDESCON) (Isla Margarita, Venezuela, septiembre de 1999).Instituto de Investigaciones Tecnológicas para Redes y Equipos Eléctricos (IITREE
