State extension in adequacy evaluation of composite power systems—concept and algorithm

Abstract

The number of possible system contingency states can be extremely large for practical composite generation and transmission systems. It is therefore not feasible or even possible to investigate all the contingencies in adequacy evaluation of composite power systems. Only those system states which are credible or usually given as up to certain contingency level are investigated in practical calculations. Although the probabilities of the ignored high level system contingency states are individually very small, the total value can be significant as the number of these high level system states is very large, especially for large size composite systems. This paper presents a state extension algorithm, which effectively includes the effects of high level contingencies without increasing the computational effort. The algorithm can, therefore, effectively and efficiently provide improved estimates of the adequacy indices. The accuracy improvement applies to the basic failure probability, frequency and duration (F&D) indices, determined for both the overall system and the individual load points. The technique also provides exact error estimates for the three adequacy indices. The concepts associated with the technique are developed and illustrated using simple networks. A numerical example is presented in the paper to illustrate the effectiveness of the proposed algorithm.