Contingency ranking for voltage collapse via sensitivities from a single nose curve

The change in the loading margin to voltage collapse when line outages occu r is estimated. First a nose curve is computed by continuation to obtain a nominal loading margin. Then linear and quadratic sensitivities of the load ing margin to each contingency are computed and used to estimate the result ing change in the loading margin. The method is tested on a critical area o f a 1390 bus system and all the line outages of the IEEE 118 bus system. Th e results show the effective ranking of contingencies and the very fast com putation of the linear estimates.