Probabilistic Relational Models for assessment of reliability of active distribution management systems

This paper presents the use of Probabilistic Relational Models (PRM) for reliability analysis of control systems for active distribution grids. The approach is based on two key concepts; first, it addresses both the reliability of primary system components and the supporting secondary, ICT-based systems. Secondly, the use of PRMs enables representation of architecture of the ICT systems, including for instance redundancy of hardware and allocation of software functions to several hardware devices. This later aspect is important, since allocation of software across different hardware platforms is a feature enabled by for instance the IEC 61850 standard. The increasing number of software dependent systems for controlling and supervising the power grid enhances the risk of software-caused failures. Thus, for reliable operation it is of high importance to not only concern primary component, but also the software and hardware of the secondary systems controlling it. A variety of methods exist for reliability analysis of secondary systems, however few address the issue of failing software together with failing primary components. The paper presents the underlying theory for Probabilistic Relational Models, and presents the steps necessary to use the technique. The paper is concluded with an example of application of the approach.