This Master's thesis focuses on analysing and reducing AC losses in high-frequency electrical machines designed for use in electrified aircraft. The research involves finite element modelling (FEM) of a megawatt-range propulsion motor, with particular emphasis placed on accurately calculating AC losses in the stator windings. These calculations take into account the physical properties of the conductor materials when operating at high frequencies. Additionally, an analytical model through a Matlab code mirroring the losses in the single slot model of the machine has been implemented, achieving minimum error in comparison to the FEM simulations and confirming the reliability of the developed code.