Emanuele Ciapessoni *, Luca Ferrarini **, Leonardo Ambrosi ** The Sixth World Energy System Conference Torino, 10-12 Luglio 2006 * CESI RICERCA * * POLITECNICO DI MILANO This paper addresses the problem of risk analysis of protection systems and protection scheme of transmission grid. According to IEC 61508, a hybrid model has been developed supporting the analysis of protection systems. The use of analytic models in risk analysis of the elements of system protection scheme allows evaluating the security level associated to different protection strategies and supports the identification of specific ICT criticalities. In this paper we pursue this approach by advocating the application of risk analysis techniques in the life cycle of protection system and protection scheme of the transmission grid. In particular, the goal is here to obtain a quantitative model in order to evaluate and compare protection systems and protection strategies able to improve the overall reliability of a system. Yu and Singh (Yu and Singh, 2004) followed this approach trying to define a simulation-based method to quantitatively evaluate hybrid stochastic models of power systems. That model was based on stationary continuous models (the so called “load flow model”), and discrete part is a logic model of the operating modes of a suitable combination of more physical components. The work extends that approach in these facts: – instead only stationary continuous models, dynamic models are used (DAEs) – a full modular approach has been adopted, implemented into an object-oriented hybrid dynamic simulator (Modelica/Dymola): any model of the system can be rewritten with more or with less detail without changing anything else of the system , provided that its physical interface is not changed of course; – the discrete parts have been greatly improved, by separating components – each discrete model of the physical component has a higher number of states, associated to physical phenomena and not to modes of operation.