Formal Reliability Analysis of Protective Relays in Power Distribution Systems

Relays are widely used in power distribution systems to isolate their faulty components and thus avoid disruption of power and damaging expensive equipment. The reliability of relay-based protection of power distribution systems is of utmost importance and is judged by first constructing Markovian models of individual modules and then analyzing these models analytically or using simulation. However, due to their inherent limitations, simulations and analytical methods cannot ascertain accurate results and are not scalable, respectively. To overcome these limitations, we propose a modular approach for developing Markovian models of relay-based protected components and then analyzing the reliability of the overall power distribution system by executing its individual modules in parallel using the PRISM probabilistic model checker. The paper presents a foundational model for a relay-based protected component that can be incrementally updated to represent more advanced behaviors, such as self-checking, routine test and continuous monitoring. Moreover, the paper provides a set of reliability assessment properties of power distribution systems that can be formally verified by PRISM. For illustration purposes, we present the analysis of a typical power distribution substation.