The article considers the issue of designing power transformers for power supply of AC railway 25 kV. The authors propose to consider a single-phase-two-phase nature of the load of these transformers. The proposed non-standard version of the distribution of power phases of the transformer, based on the measured three-phase transformers types TDNZhD and TRDNZhD. Their estimated parameters show that the proposed approach in the development of transformers, allows to achieve higher energy efficiency compared to existing solutions. The use of transformers TDNZhD and TRDNZhD on traction substations of alternating current makes it possible to reduce the cost of acquisition and maintenance of transformer equipment.