Effects of Different Voltage Sags on Three-Phase Transformers

This paper studies the effects of different types of voltage sags on three-phase transformers by means of computer simulation. The study shows that sags can produce transformer saturation during voltage recovery process. The saturation produces transformer inrush current which might be harmful in some cases. The influences of sag parameters (initial point-on-wave, duration and depth) have been analyzed in this paper. The simulation results show that current peak has a periodical dependence on sag duration and a linear dependence on sag depth. The highest peak currents are obtained for specific initial point-on-wave when the transformer supplied by different types of voltage sag.