Contingency cut-off criteria in transmission system adequacy assessment

It is necessary when performing transmission-system adequacy assessment to include high-level outage contingencies in the calculation of adequacy indices for relatively large power networks. This requirement results in a large computation time as the total number of outage contingencies to be examined becomes very large. The computation time can, however, be reduced by employing suitable contingency cut-off criteria. Various contingency cut-off criteria are presently utilised to limit the number of contingencies to be considered. Contingencies beyond a particular level can be excluded from the studies or a subset of the total contingencies can be examined from a ranked list created using an approximate but fast technique. An additional method is proposed in this paper, in which a relatively small number of contingencies are selected using an appropriate criterion and subjected to exhaustive analysis using the fast decoupled AC load flow method. The approach has been found to be more efficient than the other two procedures.The selection method is based on the implementation of the DC load-flow-based ranking method proposed in Reference 1 and provides more accurate adequacy indices. The procedure has been tested on various power systems and found to provide quick, satisfactory results. In the paper, application of the method and its comparison with other methods are illustrated using the IEEE reliability test system (RTS).