TWO-PHASE CONNECTIONSTWO-PHASE CONNECTIONS77. Transformers connected to four-wire two-phase circuits are shown in Fig. 5.48. As a rule, two-phase primary lines are four-wire as shown, and to such a four-wire line the transformers are connected to each of the side circuits, as if each side circuit were a single-phase circuit not having any connection with the other. The total load should be so divided between the phases that the loads on each will be as nearly equal as possible. Each transformer should be designed for line voltage and will carry line current. Each transformer should have a kilovolt-ampere capacity equal to one-half of the kilovolt-ampere load that is served by the two transformers.
Terrell Croft; Frederic P. Hartwell; Wilford I. Summers: American Electricians' Handbook, Sixteenth Edition. TWO-PHASE CONNECTIONS, Chapter (McGraw-Hill Professional, 2013), AccessEngineering