Microcontroller-based switch for three-phase transformer inrush current minimization

This paper presents a novel method for the minimization of three-phase transformer inrush current in the case of sustained switching-on operations. First, a simple mathematical model of the three-phase transformer was derived taking the residual flux and the switching-on instant into consideration. A table of optimum switching-on instants corresponding to different residual fluxes was constructed for a specified three-phase transformer. Based on an 8031 microcontroller a controlled-switch was built using the mentioned table. Experimental results using the controlled-switch were obtained and compared with others found by direct switching-on which gave good results.