Incorporating health constraints in reliability evaluation of subtransmission systems

The conventional reliability indices of a sub-transmission system are used for assessing the severity of system failures in future reliability predictions as well as for assessing the past system performance. These indices are generally based on probabilistic methods and include basic load point indices and system performance indices. In spite of the fact that these probabilistic indices are well established and their evaluation techniques are well developed, many power utilities are continuing to use deterministic methods to assess the reliabilities of their systems. The reluctance by a power system planner to accept probabilistic methods in their present form dictates a need to create a bridge between the deterministic methods and the existing probabilistic techniques. This can be achieved by using a well-being framework which links the existing deterministic criteria with a probabilistic method which responds to the actual factors that influence the adequacy of the sub-transmission systems. This paper illustrates an extension of the conventional probabilistic approach utilized in the sub-transmission system in the form of health and margin indices that provide system planners with measures of system well-being in addition to more conventional risk indices. The concept proposed in the paper can be utilized to assess the adequacy of subtransmission systems, as shown by application to a test system