The idea of the thesis is to design and simulate a single-pole short circuit on a triplex of a double line using ATPDesigner on a given network. The second chapter provides a general description of ATPDesigner and describes individual elements (generator, transformer, busbar, double line, excitation regulator, and electrical network) as well as the method of defining and managing these elements, accompanied by visual displays (print screen). The third part of the thesis describes an example of a single-phase and three-phase short circuit at the end of a line in a network offered in ATPDesigner, and simulations were performed on it, the results of which are shown in the pictures. The fourth chapter elaborates the target task of the thesis, the simulation of transient phenomena in the power system using ATPDesigner.