Reactive Power Considerations in Automatic Contingency Selection

On-line steady-state security analysis requires the evaluation of the effects of a large number of possible contingencies on a power system. Almost all contingency analysis programs have had to rely on a list of selected contingencies to be studied. The brute force approach of testing all contingencies every time an evaluation of the system performance is needed, becomes prohibitive due to its computational burden. A particularly attractive technique is to utilize a fast, approximate method to select the few contingencies that actually affect the security of the power system and then analyze only these cases in more detail. The contingency ranking and selection methods presented in the literature have all ranked outage cases on the basis of transmission line overloads. This limits the usefulness of these technqiues as contingencies that cause only voltage problems are totally overlooked. This paper shows that there is little correlation between the contingencies that produce line overloads and those that result in unacceptable voltage profiles, further establishing the need for a contingency selection method that is also voltage sensitive. Such a method, using the first iteration of an AC power flow, is presented. It is shown that the method meets both the speed and accuracy requirements for on-line use.