This work describes the power transformer as an element of electric power networks, presents the models of the two-winding transformer, three winding transformer, and autotransformer, and determines the replacement model for calculating the power flows of a 35/10 kV distribution transformer. Each chapter of the work corresponds to a specific topic of the given task. The second chapter shows the general mode of operation of the transformer, the transfer of energ y from the primary to the secondary winding. The transformer uses a sinusoidal voltage because DC is connected to the primary transformer, more precisely a constant voltage will create an inva riably magnetic field. The third chapter describes the historical development of transformers, the location of transforme rs, the basic parts of transformers that are necessary for the operation of transformers, divided tra nsformers according to the number of phases, and the method of cooling. Transformer compoun ds are shown, as well as ways of marking transformers. The short-circuit and idle motion is shown in chapter four. The short-circuit and idle motion determine the parameters needed to make a transformer model. Transformer models and models for power flow calculation have been developed. In the fifth chapter, the calculation of power flows on a specific distribution transformer was performed. Based on them, it is possible to conclude that the parameters in a distribution transformer with and without a transverse branch are identical and that the transverse branch in a distribution transformer can be neglected.