Low Bus Voltage and Ill-Conditioned Network Situations in a Composite System Adequacy Evaluation

The adequacy assessment of bulk power systems generally involves solution of a network configuration under different outage events. Various solution techniques, depending upon the adequacy criteria employed and the intent behind the studies are available in order to analyze the adequacy of a power system. Transportation models [1,2] D.C. load flow and A.C. load flow solutions [3,14,5] are the most commonly used techniques. The transportation model approach and the D.C. load flow techniques do not take into account bus voltage violations and generating unit VAr limit violations in a network. In order to include these considerations, it is therefore necessary to employ an A.C. load flow technique to evaluate the adequacy of the system. A.C. load flow techniques are computationally more expensive and require larger storage than approximate techniques. A drawback of an A.C. load flow technique is the possible non-convergent situation for a network. Under these circumstances, it is not possible to calculate adequacy indices for the system. This paper clearly illustrates these non-convergent situations in two test systems on which adequacy studies were conducted. A heuristic approximate technique to handle these non-convergent or ill-conditioned network situations is also presented and illustrated by application to the two test systems.