Analytical calculation and stochastic assessment of voltage sags

In this paper, analytical expressions for the calculation of voltage sag magnitude due to faults at every point of a meshed or radial power network are derived. Balanced and unbalanced faults are considered and the effect of power transformers is taken into account. The following methods for stochastic assessment of voltage sag magnitude are compared using these expressions: the method of critical distances, method of fault positions, and Monte Carlo method. The minimum required number of fault positions and iterations assumed by the two methods in order to achieve results of acceptable accuracy are determined.