An accurate evaluation of the energy losses is a crucial factor for every device dealing with high currents. This thesis investigates the power dissipation of water-cooled High Power Rectifiers, which require an accurate knowledge to optimize the mechanical structure, choose the correct materials, properly model and design the cooling system and finally fulfill customers’ efficiency requirements. The analysis explores different methodologies, ranging from model simulations to physical measurements. Their advantages and drawbacks are compared using multiple criteria to decide which is the most reasonable approach to employ. Due to the uncertainty of the available measurement methods, paired with the required efforts for an appropriate test setup, physical measurements were disqualified for this work.