PURPOSE: To ensure the little applied voltage of a shunt reactor and the low magnetic flux density of a core, by dividing an exciting winding into two portions, and by connecting the shunt reactor to the earthing side.

CONSTITUTION: In a tap change-over transformer when loading for operating two tap changers 6A, 6B in parallel, a winding is divided into two portions of exciting windings 11A, 11B, and a shunt reactor 10 is connected to the earthing side. Thus, circulating current is limited by the leakage impedance of the exciting windings even if a core of the shunt reactor 10 is saturated and the impedance of the shunt reactor becomes zero. This means that circulating current is within the operation limit of tap change-over even if the core is saturated, thus eliminating the need for the control of the magnetic flux density of the core at low values. And the ground insulation of the windings can be lowered because a terminal of the shunt reactor is directly earthed, and layer insulation can also be reduced because other phase shunt reactor windings can also be earthed.