Elimination of three-phase transformer inrush current through core forced magnetization and simultaneous closing

The inrush current occurs during transformer energization due to flux saturation in the core. Controlled switching connects transformer to power grid in proper phase angle derived from core remanent fluxes. The DC forced magnetization prior to transformer energization is one of simultaneous closing strategy methods. Active intervention to the transformer remanent flux was realized as a DC power supply with current splitter and automated disconnection circuit. Inrush currents were measured in dependency on switch on angle. Resulting current maps determine the range of switch on angles in which the current does not exceed the limits. This angle range restricts the choice of synchronous switch closing time scatter. This paper shows the results of a research on possible closing time scatter dependency both on forced pre-magnetizing current and on transformer working flux for star, grounded star and delta winding connections.