The aim of the bachelor‘s thesis is to project and then realize models of transformer in Matlab/Simulink program. These proposed procedures show the relation between original transformer and its spare connections. The first part of bachelor‘s thesis is oriented to theory of transformers which defines basic parametres and relations between them in transformer. Later in this part we try to describe cross-over from basic transformer model to the spare connection which is needed in realization of model in Simulink. The second part of bachelor‘;s thesis is oriented to theoretical description of vector transformation. It describes some basic relations of general transformation, currents transformation and voltage in certain connections. The third...