Reliability evaluation of substation control systems

A technique to assess the reliability of substation control systems (SCSs) is demonstrated. The technique was developed as part of an ongoing project with National Grid Co. (NGC) that aims at quantitatively evaluating the merit of different approaches to substation control. Event trees are used to model the interdependency between the multiple functions (switch gear control, synchronising indications, feeder autoreclosure, interlocking etc) present in a modem SCS. The event trees reflect the operating policies used by NGC in its transmission substations, but the applicability of the technique is not constrained by this. Hardware models of the computational equipment used in the SCS complement the functional models. The reliability indices chosen for this type of system and the reliability data used are discussed. The application of the technique is illustrated by an example and a sensitivity analysis is performed on the results.