Effects of voltage sags on three-phase three-legged transformers

This paper describes the influence of voltage sags on three-phase three-legged transformers. The model includes saturation, and it is based on experimental parameters. It has been implemented in PSpice. Voltage recovery after the voltage sag causes transformer saturation. This saturation produces an inrush current similar to that of the transformer energizing. The variables that influence the peak value of the inrush current are studied: depth, duration and initial point-on-wave. The most important variable is sag duration, which has a periodical influence.