This thesis presents the analysis and calculation of a gas turbine in a closed cycle. During the analysis of the gas turbine, all known upgrades were carried out, including a regenerator, an intercooler, an additional heat exchanger and combinations of all mentioned upgrades. During the operation of the turbine in a closed cycle, the operating parameters of the entire system were observed with different working media such as: helium (He), carbon dioxide (CO2), argon (Ar) and nitrogen (N), maintaining a constant mass flow of the working medium. Some parts of the closed process gas turbine crucial for its operation are described, as well as a description of the working media used to test the operating parameters. The upgrade of the gas turbine itself was carried out in such a way that each part was first installed separately, and then combinations of upgrades were carried out. The application of the regenerator proved to be one of the most important upgrades of the gas turbine, which has numerous benefits such as the reduction of the required heat supplied to the system by fuel, reducing heat exchanger surface area and it significantly improves the thermal efficiency of the process due to the utilization of heat that is not managed to use in the turbine. Likewise, the plant with additional heat supply and regenerator showed a high degree of usefulness. Although it had almost the largest increase in the supplied heat compared to the basic process, precisely because of the installation of the regenerator, it turned out to be a more economical solution than the case with intercooling in combination with the regenerator. The plant with a combination of all upgrades and nitrogen as the working medium proved to be the most useful. On the other hand, a plant with helium as a working medium, although it turned out to be less economical in terms of thermal utilization than a plant with nitrogen, developed several times higher power than any plant with another working medium discussed in this paper.