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

This paper describes the effects of symmetrical voltage sags on three-phase three-legged transformers. The transformer model includes saturation and is based on experimental parameters. It has been implemented in PSpice. Voltage recovery after a voltage sag can produce 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, namely depth, duration, and initial point-on-wave are studied. A result that must be emphasized is the periodical influence of the sag duration.