Reliability Evaluation of Communication-Constrained Protection Systems using Stochastic-flow Network Models

In smart grids, even the substation-located local protection schemes are built on communication networks. By relaying, the transmission performance of information flow may have a major influence on decision-making actions, and the general binary-state description of each component cannot indicate the deterioration degree of the information performance. This paper introduces the stochastic-flow network (SFN) to model flow-limited protection systems, and makes comprehensive improvement to form a practicable reliability assessment approach. The proposed model focuses on the multi-state of constrained capacities passing through critical components and the flow demand at the protective relays. The analysis method is established on classifying components multi-states by Markov chain principle, defining the availability and reliability of the protection system under a SFN model, and using the improved depth-first search to get all lower boundary points for demand level d, then fulfilling the reliability index calculation via valid states and corresponding probability distribution. Finally, according to the current protection arrangement in intelligent substations, six typical protective structures are developed into the SFN models. The reliability assessment and especially the key influence factors to relaying performance are presented.