Impact of Imperfect Repairs and Diagnostic Coverage on the Reliability of Multi-Channel IEC-61850 Substation Communication Network

The reliability evaluation of IEC-61850 based Substation Communication Network (SCN) is often achieved by using combinatorial methods such as Reliability Block Diagram (RBD) because it is considered to be conceptually simple and easy to apply. These methods, however, assume that all system faults can be identified and fully repaired; which is not practically achievable. As a result, the methods overstate the performance of the system during its useful life. System diagnostic coverage is one of the critical factors that necessitate consideration during the evaluation of system reliability when SCN interface with IEC-61508 based Safety Related System (SRS) in power distribution centres. In this article, the impact and significance of quality of repairs comprising repair efficiency and diagnostic coverage on the reliability of the system are investigated using Markov and symbolic dynamics based on linear dynamical systems. The originality of the research is in the utilisation of transition probability matrix and its eigenvalues to analyse the effectiveness of repair efficiency and the dynamical behaviour of the system under varying levels of repair efficiency and system diagnostic coverage. The results indicate that the magnitudes of the eigenvalues can be used to optimally select the individual factors in order to attain the desired reliability and availability of IEC-61850 based SCN, this aspect is characterised the spectral gap on the complex plane. The results also indicate that the effectiveness of the repair efficiency factors is dependent on the level of system diagnostic coverage, wherein high impact is noticeable at low system diagnostic factors.