The task of thesis is a detailed description of the modeling power transformer. By using Clark's transformation, the model is transferred from the three-phase system (ABC) in a two-phase (quiet) system (α-β). Simulating a short circuit and idling was conducted to test the correctness of transformers. Once established the correct operation of the transformer, simulations of failures in some parts of the power transformer. A short circuit is simulated in different parts (beginning, middle and end) of secondary windings which is divided into segments (two, three and four). Increasing the number of segments, a decrease of current and voltage is occured due to reduced windings per segment. In the model of secondary is inserted parallel line and modeled threephase short circuit at the beginning, middle and end of the line. Simulations have determined Ferranti effect that occurs because under loaded line.