Formulas for both earth return and internal impedances of submarine HVDC cables have been provided in past studies; however, they are based on simplifying hypotheses, e.g. considering 2D geometries, treating armor layers as coaxial tubular conductors, and neglecting the proximity effect. In this paper, a Finite Element analysis investigates the effects of the deviations of realistic geometries and configurations of submarine HVDC cables from idealized ones. In particular, the impact of the twisting of armor wires on internal impedances and the proximity effect in multiple cable configurations on earth return impedance are analyzed.