PURPOSE: To prevent the overheat of a terminal section by connecting each two-winding output of the first phase of a transformer and each two-winding output of a third phase in the same polarity and the output circuit of a second phase in reverse polarity.

CONSTITUTION: Currents fed from the second secondary winding of the R phase of a transformer are represented by I2. Currents supplied from the secondary winding of an S phase are represented by I3. Consequently, the values of currents I2 and currents I3 are equalized, and the currents I2 and I3 have phase difference at 180°. As a result, the vectorial sum I23 of the current values of both currents flowing through a terminal is equalized to the currents I2, and the currents I3. Likewise, a current value flowing through a terminal 3d is also equalized to current values supplied from each secondary winding of the transformer. Accordingly, currents are reduced, and there is no possibility that a specified terminal is burnt.