Risk and Vulnerability Analysis of Large Scale Technical Infrastructures - Electrical Distribution Systems

Abstract: The thesis treats the subject of risk and vulnerability analysis of large-scale
technical infrastructures. In particular the focus is on the development of
methods for vulnerability analysis of electrical distribution systems. The
methods and the concepts behind them should nevertheless also be seen as
applicable to other technical infrastructures.
Robust and reliable technical infrastructures are a prerequisite for modern
society. If they fail to deliver their services, severe consequences arise. Two
major crises in Sweden regarding the supply of electricity have clearly showed
the magnitude of the consequences on society and its dependency on a
reliable electricity supply and the emergency response necessary to return to
normal. Furthermore, most technical infrastructures depend on a reliable
power supply for their proper functioning. The power supply in turn relies on
some of these for its proper operation and control. There is a need for
methods aimed at assessing the vulnerability of the interconnected
infrastructures the society depends upon.
In the thesis two approaches, or methods, of assessing the vulnerability of
technical infrastructures are presented: global vulnerability analysis and
critical components. The applicability of the methods was tested by empirical
studies of three electrical distribution systems in Sweden. The result from the
global vulnerability analysis clearly shows that distribution systems are highly
vulnerable to some type of perturbations. The results from the analysis of
critical components show that the methods can be used for finding and
ranking components that are critical for the system and that they render a
very feasible way to test the system for N-k contingencies.
The design approach of the methods was to use a network model and a
corresponding physical model of the electrical distribution system. The
network model contains the topological information. The physical model
describes the behavior of the network. Performance measures have been
developed to describe the consequences of perturbation to the network. The
studies indicate that these measures are relevant for describing vulnerability of
an electrical distribution system and in finding its critical components. The
design approach of the methods constitutes an important step towards
vulnerability analysis of interdependent infrastructures.
The results from applying the methods can be useful for emergency
mitigation and preparedness planning. The results can further be visualized in
the form of geographical vulnerability maps. These maps can facilitate the
discussions between persons working in different fields.