Linear and nonlinear methods for contingency analysis in on-line voltage security assessments

The strategy of using an effective scheme to screen out a large number of stable contingencies and to apply detailed simulation programs only to potentially unstable contingencies is well recognized. This strategy is implemented in on-line voltage security assessment (VSA). This paper presents a hybrid of linear, quadratic and nonlinear methods for on-line VSA. Linear methods are fast but may not be sufficiently accurate while nonlinear methods are accurate but may not be sufficiently fast. To meet the demands of speed and accuracy for online application, the hybrid of three methods for performing screening, ranking and detailed analysis is thus developed and applied to the CAISO system with promising results.