A method to compute reactive power margins with respect to voltage collapse

A method of computing the reactive power margin-i.e. the difference between the maximum reactive load and the corresponding base case value-for a given set of load buses of a power system is proposed. This margin is aimed at assessing the system robustness with respect to voltage collapse. The corresponding collapse point is directly obtained as the solution of an optimization problem with the load increase as the objective, the nonoptimized loads as equality constraints, and the generator reactive limits as inequality constraints. The CRIC electrical decoupling yields a voltage-only problem. The latter is solved using the Newton approach and a procedure is given to deal with the inequality constraints efficiently. A simple illustrative example and simulation results obtained on the Belgian 520-bus, 41-generator system are given.>