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The change in the loading margin to voltage collapse when line outages occur is estimated. First a nose curve is computed by continuation to obtain a nominal loading margin. Then linear and quadratic sensitivities of the loading margin to each contingency are computed and used to estimate the resulting change in the loading margin. The method is tested on a critical area of a 1390 bus system and all the line outages of the IEEE 118 bus system. The results show the effective ranking of contingencies and the very fast computation of the linear estimates.
Greene et al. (Fri,) studied this question.