Effect of Voltage Sag on Transformers Inrush Current

In this paper, the inrush current due to symmetrical and unsymmetrical voltage sag is studied analytically and in details and considering the fault removal in all three phases simultaneously. This summarization leads to the determinationof analytical phrasesof magnetic flux and inrush current, after the voltage sag. The dependence of the inrush current to type, depth, duration and the initial point of the sagare determined. These phrases describe the behavior of three phase transformers during the voltage recovery after the voltagesag and anapproximate value for inrush current peak will be obtained analytically. These values can be useful in power system studies such as relays synchronization, transformers tension and etc.