Probabilistic Assessment of Voltage Stability in composite generation and transmission systems

Several papers have recognized the effect of uncertainties in system parameters on voltage stability analysis through probabilistic methods. In these papers, the unstable states are identified by the unsolvability of the power flow equations or the violation in the Voltage Stability Margin (VSM) minimum limit. However, voltage stability problems may also be associated with the loss of voltage controllability, when a voltage control action has the effect contrary to the expected and usual one. The main aim of this paper is to include unstable states caused by unsolvability and voltage controllability loss in the Voltage Stability Probabilistic Assessment (VSPA). The proposed method to include these two mechanisms in the VSPA is based on the combination of three techniques: the Monte Carlo Simulation Method (MCSM), the nonlinear Optimal Power Flow (OPF) and the D´ Matrix Method (DMM), for the voltage stability assessment. The results demonstrate that the voltage controllability loss is an important mechanism in VSPA.