PURPOSE: To conduct a single-phase three-wire system power distribution in which 200V class voltage is used as 400V class voltage accurately by a method wherein, to one end and other end of a second unit secondary winding, the other end of a second secondary winding and one end of a first secondary winding are connected.

CONSTITUTION: Terminals are led out from the mid-point (the point where the number of turns of a winding will be divided into two equal parts) of a first and a second secondary windings Cu2 and Cw2 respectively, and these terminals are connected to external terminals U2n and W2n respectively. Also, one end (ua) of the first secondary winding Cu2 and its other end (ue) are connected to external terminals U2 and U2e respectively, and the one end (wa) and (we) of the second secondary winding Cw2 are connected to external terminals W2 and W2e respectively. Besides, one end Va1 and other end Ve1 of the first unit secondary winding Cv21 are connected to external terminals V21 and V21e, and one end Va2 and other end Ve2 of the second unit secondary winding Cv22 are connected to external terminals V22 and V22e respectively. As a result, the voltage of E2 (400V class) and 1/2E2 (200V class voltage) can be obtained.