The energy transformer is a key element in any electrical network, and is an indispensable part of electricity transmission. The energy transformer consists of his core, on which the low-voltage and the high-voltage windings of the are wound. A boiler, which usually contains special oil that cools the transformer elements, is in charge of keeping the system at working temperature. Conductive isolators or bushings are responsible for preventing a short circuit at the transformer connections. The energy transformer works on the principle of electromagnetic induction and transmits alternating current from the primary to the secondary coil. The current and voltage of the primary and secondary winding depend on the ratio of the number of turns of their windings. The energy transfer in an autotransformer is completely different, namely it transfers energy directly, and the ratio of input and output voltage is the ratio of the common and the whole winding. Electrical transformer models allow us to make certain mathematical safety calculations before the transformer is connected to the network. In this way, it is known what is expected in normal operating conditions, as well as in the event of a short circuit. Since in practice one socket is not used for a three-winding transformer, and the autotransformer can be reduced to a two-winding one, electrical models of a two-winding transformer are used for all calculations. Out of the electrical models of the two-winding transformer, the T model is the most accurate because it shows the impedances of the transformer where they are in reality. The Π and Γ electrical models are less accurate than the T model, but the Γ model is therefore used more because of its simplicity. When special accuracy is not required, only the longitudinal branch of the transformer is used, i.e. the so-called I electrical model.