Abstract: Primary and secondary windings of each transformer in a three-phase system each form a pair of independent windings, the first winding of each of the primary and secondary pairs formed on the iron core of one of the transformers and the second winding of each of the primary and secondary pairs formed on the iron core of the transformer adjacent thereto are connected in series to each other. These serially connected windings are regarded as one phase winding respectively, and they are connected to each other in either a delta connection or a Y connection. A variation in the voltage phase caused by a change in the load current of one of the system outputs has an influence not only on the phase of the voltage at that output but also on the phase of the voltages on the outputs adjacent thereto and consequently enables the deviation in the phase difference between the output phase voltages due to loss of balance of the load to be decreased to about one half.