Patent ID: 8217536

Claim:
A magnetizing inrush current suppression device for a three-phase transformer having primary windings Y-connected or Δ-connected and secondary windings and 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 the three phases to interrupt power supplying to the transformer, the magnetizing inrush current suppression device comprising: a first calculation part which is connected to the three phases of the power supply and calculates phase-to-phase steady-state magnetic flux of the three-phases of the power supply; a second calculation part which is connected to the three phases in the primary windings side of the transformer and calculates phase-to-phase residual magnetic flux of the three phases in the primary windings side of the transformer when the circuit breakers interrupt the transformer; a voltage-phase detection part which is connected to the first and second calculation parts and detects a voltage-phase at which polarity and magnitude of the phase-to-phase steady-state magnetic flux coincide with those of the phase-to-phase residual magnetic flux; and a closing control part which is connected to the voltage phase detection part and the circuit breakers and firstly causes the circuit breakers coupled with two of the three phases to close at the voltage phase detected by the phase detection part, and then causes the circuit breaker coupled with remaining one-phase to close, thereby suppressing a magnetizing inrush current occurring at start of energizing of the three-phase transformer.