Comparison of vulnerability and reliability analysis of technical infrastructures

The society depends on reliable and robust services provided by technical infrastructures for its function. The impact of large-scale outages due to the inherent vulnerabilities of technical infrastructures has been demonstrated, for example, by the power outage in the U.S. in 2003 and the power outages in Sweden due to the storms Gudrun in January 2005 and Per in January 2007. Two of the main approaches for gaining knowledge required for understanding and improving technical infrastructures are reliability analysis and vulnerability analysis. Reliability refers to the ability of a system to perform its intended function. Vulnerability, on the other hand, refers to the ability of a system to withstand strains. These two approaches have similarities but also some differences with respect to what type of information they generate about the system. In the present paper these two approaches are compared in the context of technical infrastructures, and analyses are carried out for an electric power system. A version of the IEEE RTS96 reliability test system is studied with the purpose of highlighting the similarities and differences between the two approaches. The conclusion is that both vulnerability and reliability based approaches are very useful for both prevention and emergency preparedness planning, however providing different input to such decision-making.