High-voltage direct current (HVDC) grids are viable for expanding the existing grids. The development of DC transmission corridors by multiple manufacturers requires practical DC-DC converters to create multi-terminal HVDC grids. Unlike their low- and medium-voltage counterparts, these DC-DC converters face special challenges, including physical constraints and high costs, despite having no fixed operating frequency restrictions. This paper investigates power loss behavior of a 1 GW, 500 kV bipolar isolated DC-DC converter through theoretical analysis and simulation results for HVDC interconnections. The research aims to identify suitable operating frequencies which optimize converter efficiency and compactness through individual loss assessments of converter and transformer components. For accurate core loss calculations, finite element analysis (FEM) is performed using ANSYS and combined with MATLAB for detailed converter loss analysis. The results will provide fundamental principles for the design of high-power DCDC converters in HVDC grid interconnections.