ELECTRIC POWER SYSTEM SECURITY ASSESSMENT D. Cirio1, G. Demartini1, M. Salvetti1, S. Massucco2, A. Morini2, F. Silvestro2 1 CESI – Centro Elettrotecnico Sperimentale Italiano S.p.A. Via Rubattino 54, I – 20134 Milano, Italy – Phone: +39-02-21255896; fax: +39-02-21255843 e-mail: demartini@cesi.it 2 Department of Electrical Engineering, University of Genova Via Opera Pia 11/A, I – 16145 Genova, Italy – Phone: +39-010-3532.718; fax: +39-010-3532.700 e-mail: massucco@epsl.die.unige.it Dynamic Security Assessment (DSA) has become a major issue in power system operation because of increased stress sources. It presents demanding requirements especially in the context of on-line applications to support the control centre operator. Simulation is the basic investigation tool, though it needs to be integrated by proper functions to retrieve useful information and possibly control indications. Two examples of such on-line DSA platforms are presented, the former based on the simulator used to study the Italian system, the latter resulting from a European project called OMASES. These efforts show that effective DSA support systems for on-line operator use have become at hand.