Patent ID: 8310106

Claim:
A magnetizing inrush current suppression method for a three-phase transformer having primary windings Y-connected and secondary windings or tertiary windings any of which are Δ-connected, the transformer being connected to a three-phase power supply via circuit breakers coupled with each of three phases to interrupt power supplying to the transformer, the method comprising the steps of: calculating steady-state magnetic flux for each of the three phases of the transformer by integrating each phase-voltage or phase-to-phase voltage of the three phases on the primary, the secondary, or the tertiary windings side obtained when AC voltage is applied in a steady state to the three phases of the transformer; calculating polarity and magnitude of residual magnetic flux for each of the three phases of the transformer after the circuit breakers shuts off the transformer; detecting voltage-phase for each of the three phases of the transformer and determining a region in which polarity of the steady-state magnetic flux coincides with polarity of the residual magnetic flux; and causing the circuit breakers to close simultaneously in an area where the region of each of the three phases overlaps with each other, thereby suppressing a magnetizing inrush current occurring at the start of energizing of the three-phase transformer.