Impact of protection system reliability on power system reliability: A new minimal cutset approach

In order to capture the effect of dependent failures that could arise due to the various transmission protection system response scenarios on power system reliability, complex Markov models or fault trees combined with event trees are typically employed in the predictive reliability studies. A unique approach utilizing minimal cutsets (MC) and the approximate methods of system reliability evaluation, dispensing with the assumption of perfect protection and control, was recently postulated to obtain various power system reliability indices. The approach was basic in that it was applicable to single circuit meshed transmission systems, where only MCs up to a maximum order of two could be handled. However, the parallel structure of transmission lines in multi-circuit meshed transmission systems, in addition to resulting in possible higher order critical transmission line MCs, creates unique topological dependencies among the backup protection system coordination schemes. In this paper, a comprehensive MC approach to capture the impact of protection system reliability on power system reliability is presented, covering all such consequent dependencies. An illustrative sample case study is used to explain the salient features of the proposed methodology.